# src/connection.js

    // @flow

    import assert from 'assert';
    import bs58 from 'bs58';
    import {parse as urlParse, format as urlFormat} from 'url';
    import fetch from 'node-fetch';
    import jayson from 'jayson/lib/client/browser';
    import {struct} from 'superstruct';
    import {Client as RpcWebSocketClient} from 'rpc-websockets';

    import {NonceAccount} from './nonce-account';
    import {PublicKey} from './publickey';
    import {MS_PER_SLOT} from './timing';
    import {Transaction} from './transaction';
    import {Message} from './message';
    import {sleep} from './util/sleep';
    import {toBuffer} from './util/to-buffer';
    import type {Blockhash} from './blockhash';
    import type {FeeCalculator} from './fee-calculator';
    import type {Account} from './account';
    import type {TransactionSignature} from './transaction';

    export const BLOCKHASH_CACHE_TIMEOUT_MS = 30 * 1000;

    type RpcRequest = (methodName: string, args: Array<any>) => any;

    type TokenAccountsFilter =
      | {|
          mint: PublicKey,
        |}
      | {|
          programId: PublicKey,
        |};

    /**
     * Extra contextual information for RPC responses
     *
     * @typedef {Object} Context
     * @property {number} slot
     */
    type Context = {
      slot: number,
    };

    /**
     * Options for sending transactions
     *
     * @typedef {Object} SendOptions
     * @property {boolean | undefined} skipPreflight disable transaction verification step
     */
    export type SendOptions = {
      skipPreflight?: boolean,
    };

    /**
     * Options for confirming transactions
     *
     * @typedef {Object} ConfirmOptions
     * @property {boolean | undefined} skipPreflight disable transaction verification step
     * @property {number | undefined} confirmations desired number of cluster confirmations
     */
    export type ConfirmOptions = {
      skipPreflight?: boolean,
      confirmations?: number,
    };

    /**
     * Options for getConfirmedSignaturesForAddress2
     *
     * @typedef {Object} ConfirmedSignaturesForAddress2Options
     * @property {TransactionSignature | undefined} before start searching backwards from this transaction signature.
     *               If not provided the search starts from the highest max confirmed block.
     * @property {number | undefined} limit maximum transaction signatures to return (between 1 and 1,000, default: 1,000).
     *
     */
    export type ConfirmedSignaturesForAddress2Options = {
      before?: TransactionSignature,
      limit?: number,
    };

    /**
     * RPC Response with extra contextual information
     *
     * @typedef {Object} RpcResponseAndContext
     * @property {Context} context
     * @property {T} value response
     */
    type RpcResponseAndContext<T> = {
      context: Context,
      value: T,
    };

    /**
     * @private
     */
    function jsonRpcResultAndContext(resultDescription: any) {
      return jsonRpcResult({
        context: struct({
          slot: 'number',
        }),
        value: resultDescription,
      });
    }

    /**
     * @private
     */
    function jsonRpcResult(resultDescription: any) {
      const jsonRpcVersion = struct.literal('2.0');
      return struct.union([
        struct({
          jsonrpc: jsonRpcVersion,
          id: 'string',
          error: 'any',
        }),
        struct({
          jsonrpc: jsonRpcVersion,
          id: 'string',
          error: 'null?',
          result: resultDescription,
        }),
      ]);
    }

    /**
     * @private
     */
    function notificationResultAndContext(resultDescription: any) {
      return struct({
        context: struct({
          slot: 'number',
        }),
        value: resultDescription,
      });
    }

    /**
     * The level of commitment desired when querying state
     * <pre>
     *   'max':    Query the most recent block which has been finalized by the cluster
     *   'recent': Query the most recent block which has reached 1 confirmation by the connected node
     *   'root':   Query the most recent block which has been rooted by the connected node
     *   'single': Query the most recent block which has reached 1 confirmation by the cluster
     *   'singleGossip': Query the most recent block which has reached 1 confirmation according to votes seen in gossip
     * </pre>
     *
     * @typedef {'max' | 'recent' | 'root' | 'single' | 'singleGossip'} Commitment
     */
    export type Commitment = 'max' | 'recent' | 'root' | 'single' | 'singleGossip';

    /**
     * Filter for largest accounts query
     * <pre>
     *   'circulating':    Return the largest accounts that are part of the circulating supply
     *   'nonCirculating': Return the largest accounts that are not part of the circulating supply
     * </pre>
     *
     * @typedef {'circulating' | 'nonCirculating'} LargestAccountsFilter
     */
    export type LargestAccountsFilter = 'circulating' | 'nonCirculating';

    /**
     * Configuration object for changing `getLargestAccounts` query behavior
     *
     * @typedef {Object} GetLargestAccountsConfig
     * @property {Commitment|undefined} commitment The level of commitment desired
     * @property {LargestAccountsFilter|undefined} filter Filter largest accounts by whether they are part of the circulating supply
     */
    type GetLargestAccountsConfig = {
      commitment: ?Commitment,
      filter: ?LargestAccountsFilter,
    };

    /**
     * Configuration object for changing query behavior
     *
     * @typedef {Object} SignatureStatusConfig
     * @property {boolean} searchTransactionHistory enable searching status history, not needed for recent transactions
     */
    export type SignatureStatusConfig = {
      searchTransactionHistory: boolean,
    };

    /**
     * Information describing a cluster node
     *
     * @typedef {Object} ContactInfo
     * @property {string} pubkey Identity public key of the node
     * @property {string|null} gossip Gossip network address for the node
     * @property {string|null} tpu TPU network address for the node (null if not available)
     * @property {string|null} rpc JSON RPC network address for the node (null if not available)
     * @property {string|null} version Software version of the node (null if not available)
     */
    type ContactInfo = {
      pubkey: string,
      gossip: string | null,
      tpu: string | null,
      rpc: string | null,
      version: string | null,
    };

    /**
     * Information describing a vote account
     *
     * @typedef {Object} VoteAccountInfo
     * @property {string} votePubkey Public key of the vote account
     * @property {string} nodePubkey Identity public key of the node voting with this account
     * @property {number} activatedStake The stake, in lamports, delegated to this vote account and activated
     * @property {boolean} epochVoteAccount Whether the vote account is staked for this epoch
     * @property {Array<Array<number>>} epochCredits Recent epoch voting credit history for this voter
     * @property {number} commission A percentage (0-100) of rewards payout owed to the voter
     * @property {number} lastVote Most recent slot voted on by this vote account
     */
    type VoteAccountInfo = {
      votePubkey: string,
      nodePubkey: string,
      activatedStake: number,
      epochVoteAccount: boolean,
      epochCredits: Array<[number, number, number]>,
      commission: number,
      lastVote: number,
    };

    /**
     * A collection of cluster vote accounts
     *
     * @typedef {Object} VoteAccountStatus
     * @property {Array<VoteAccountInfo>} current Active vote accounts
     * @property {Array<VoteAccountInfo>} delinquent Inactive vote accounts
     */
    type VoteAccountStatus = {
      current: Array<VoteAccountInfo>,
      delinquent: Array<VoteAccountInfo>,
    };

    /**
     * Network Inflation
     * (see https://docs.solana.com/implemented-proposals/ed_overview)
     *
     * @typedef {Object} InflationGovernor
     * @property {number} foundation
     * @property {number} foundation_term
     * @property {number} initial
     * @property {number} taper
     * @property {number} terminal
     */
    type InflationGovernor = {
      foundation: number,
      foundationTerm: number,
      initial: number,
      taper: number,
      terminal: number,
    };

    const GetInflationGovernorResult = struct({
      foundation: 'number',
      foundationTerm: 'number',
      initial: 'number',
      taper: 'number',
      terminal: 'number',
    });

    /**
     * Information about the current epoch
     *
     * @typedef {Object} EpochInfo
     * @property {number} epoch
     * @property {number} slotIndex
     * @property {number} slotsInEpoch
     * @property {number} absoluteSlot
     * @property {number} blockHeight
     */
    type EpochInfo = {
      epoch: number,
      slotIndex: number,
      slotsInEpoch: number,
      absoluteSlot: number,
      blockHeight: number | null,
    };

    const GetEpochInfoResult = struct({
      epoch: 'number',
      slotIndex: 'number',
      slotsInEpoch: 'number',
      absoluteSlot: 'number',
      blockHeight: 'number?',
    });

    /**
     * Epoch schedule
     * (see https://docs.solana.com/terminology#epoch)
     *
     * @typedef {Object} EpochSchedule
     * @property {number} slotsPerEpoch The maximum number of slots in each epoch
     * @property {number} leaderScheduleSlotOffset The number of slots before beginning of an epoch to calculate a leader schedule for that epoch
     * @property {boolean} warmup Indicates whether epochs start short and grow
     * @property {number} firstNormalEpoch The first epoch with `slotsPerEpoch` slots
     * @property {number} firstNormalSlot The first slot of `firstNormalEpoch`
     */
    type EpochSchedule = {
      slotsPerEpoch: number,
      leaderScheduleSlotOffset: number,
      warmup: boolean,
      firstNormalEpoch: number,
      firstNormalSlot: number,
    };

    const GetEpochScheduleResult = struct({
      slotsPerEpoch: 'number',
      leaderScheduleSlotOffset: 'number',
      warmup: 'boolean',
      firstNormalEpoch: 'number',
      firstNormalSlot: 'number',
    });

    /**
     * Leader schedule
     * (see https://docs.solana.com/terminology#leader-schedule)
     *
     * @typedef {Object} LeaderSchedule
     */
    type LeaderSchedule = {
      [address: string]: number[],
    };

    const GetLeaderScheduleResult = struct.record([
      'string',
      struct.array(['number']),
    ]);

    /**
     * Transaction error or null
     */
    const TransactionErrorResult = struct.union(['null', 'object']);

    /**
     * Signature status for a transaction
     */
    const SignatureStatusResult = struct({err: TransactionErrorResult});

    /**
     * Version info for a node
     *
     * @typedef {Object} Version
     * @property {string} solana-core Version of solana-core
     */
    const Version = struct({
      'solana-core': 'string',
    });

    type SimulatedTransactionResponse = {
      err: TransactionError | string | null,
      logs: Array<string> | null,
    };

    const SimulatedTransactionResponseValidator = jsonRpcResultAndContext(
      struct.pick({
        err: struct.union(['null', 'object', 'string']),
        logs: struct.union(['null', struct.array(['string'])]),
      }),
    );

    /**
     * Metadata for a confirmed transaction on the ledger
     *
     * @typedef {Object} ConfirmedTransactionMeta
     * @property {number} fee The fee charged for processing the transaction
     * @property {Array<number>} preBalances The balances of the transaction accounts before processing
     * @property {Array<number>} postBalances The balances of the transaction accounts after processing
     * @property {object|null} err The error result of transaction processing
     */
    type ConfirmedTransactionMeta = {
      fee: number,
      preBalances: Array<number>,
      postBalances: Array<number>,
      err: TransactionError | null,
    };

    /**
     * A confirmed transaction on the ledger
     *
     * @typedef {Object} ConfirmedTransaction
     * @property {number} slot The slot during which the transaction was processed
     * @property {Transaction} transaction The details of the transaction
     * @property {ConfirmedTransactionMeta|null} meta Metadata produced from the transaction
     */
    type ConfirmedTransaction = {
      slot: number,
      transaction: Transaction,
      meta: ConfirmedTransactionMeta | null,
    };

    /**
     * A partially decoded transaction instruction
     *
     * @typedef {Object} ParsedMessageAccount
     * @property {PublicKey} pubkey Public key of the account
     * @property {PublicKey} accounts Indicates if the account signed the transaction
     * @property {string} data Raw base-58 instruction data
     */
    type PartiallyDecodedInstruction = {|
      programId: PublicKey,
      accounts: Array<PublicKey>,
      data: string,
    |};

    /**
     * A parsed transaction message account
     *
     * @typedef {Object} ParsedMessageAccount
     * @property {PublicKey} pubkey Public key of the account
     * @property {boolean} signer Indicates if the account signed the transaction
     * @property {boolean} writable Indicates if the account is writable for this transaction
     */
    type ParsedMessageAccount = {
      pubkey: PublicKey,
      signer: boolean,
      writable: boolean,
    };

    /**
     * A parsed transaction instruction
     *
     * @typedef {Object} ParsedInstruction
     * @property {string} program Name of the program for this instruction
     * @property {PublicKey} programId ID of the program for this instruction
     * @property {any} parsed Parsed instruction info
     */
    type ParsedInstruction = {|
      program: string,
      programId: PublicKey,
      parsed: any,
    |};

    /**
     * A parsed transaction message
     *
     * @typedef {Object} ParsedMessage
     * @property {Array<ParsedMessageAccount>} accountKeys Accounts used in the instructions
     * @property {Array<ParsedInstruction | PartiallyDecodedInstruction>} instructions The atomically executed instructions for the transaction
     * @property {string} recentBlockhash Recent blockhash
     */
    type ParsedMessage = {
      accountKeys: ParsedMessageAccount[],
      instructions: (ParsedInstruction | PartiallyDecodedInstruction)[],
      recentBlockhash: string,
    };

    /**
     * A parsed transaction
     *
     * @typedef {Object} ParsedTransaction
     * @property {Array<string>} signatures Signatures for the transaction
     * @property {ParsedMessage} message Message of the transaction
     */
    type ParsedTransaction = {
      signatures: Array<string>,
      message: ParsedMessage,
    };

    /**
     * A parsed and confirmed transaction on the ledger
     *
     * @typedef {Object} ParsedConfirmedTransaction
     * @property {number} slot The slot during which the transaction was processed
     * @property {ParsedTransaction} transaction The details of the transaction
     * @property {ConfirmedTransactionMeta|null} meta Metadata produced from the transaction
     */
    type ParsedConfirmedTransaction = {
      slot: number,
      transaction: ParsedTransaction,
      meta: ConfirmedTransactionMeta | null,
    };

    /**
     * A ConfirmedBlock on the ledger
     *
     * @typedef {Object} ConfirmedBlock
     * @property {Blockhash} blockhash Blockhash of this block
     * @property {Blockhash} previousBlockhash Blockhash of this block's parent
     * @property {number} parentSlot Slot index of this block's parent
     * @property {Array<object>} transactions Vector of transactions and status metas
     * @property {Array<object>} rewards Vector of block rewards
     */
    type ConfirmedBlock = {
      blockhash: Blockhash,
      previousBlockhash: Blockhash,
      parentSlot: number,
      transactions: Array<{
        transaction: Transaction,
        meta: ConfirmedTransactionMeta | null,
      }>,
      rewards: Array<{
        pubkey: string,
        lamports: number,
      }>,
    };

    function createRpcRequest(url): RpcRequest {
      const server = jayson(async (request, callback) => {
        const options = {
          method: 'POST',
          body: request,
          headers: {
            'Content-Type': 'application/json',
          },
        };

        try {
          const res = await fetch(url, options);
          const text = await res.text();
          callback(null, text);
        } catch (err) {
          callback(err);
        }
      });

      return (method, args) => {
        return new Promise((resolve, reject) => {
          server.request(method, args, (err, response) => {
            if (err) {
              reject(err);
              return;
            }
            resolve(response);
          });
        });
      };
    }

    /**
     * Expected JSON RPC response for the "getInflationGovernor" message
     */
    const GetInflationGovernorRpcResult = struct({
      jsonrpc: struct.literal('2.0'),
      id: 'string',
      error: 'any?',
      result: GetInflationGovernorResult,
    });

    /**
     * Expected JSON RPC response for the "getEpochInfo" message
     */
    const GetEpochInfoRpcResult = struct({
      jsonrpc: struct.literal('2.0'),
      id: 'string',
      error: 'any?',
      result: GetEpochInfoResult,
    });

    /**
     * Expected JSON RPC response for the "getEpochSchedule" message
     */
    const GetEpochScheduleRpcResult = struct({
      jsonrpc: struct.literal('2.0'),
      id: 'string',
      error: 'any?',
      result: GetEpochScheduleResult,
    });

    /**
     * Expected JSON RPC response for the "getLeaderSchedule" message
     */
    const GetLeaderScheduleRpcResult = jsonRpcResult(GetLeaderScheduleResult);

    /**
     * Expected JSON RPC response for the "getBalance" message
     */
    const GetBalanceAndContextRpcResult = jsonRpcResultAndContext('number?');

    /**
     * Expected JSON RPC response for the "getBlockTime" message
     */
    const GetBlockTimeRpcResult = struct({
      jsonrpc: struct.literal('2.0'),
      id: 'string',
      error: 'any?',
      result: struct.union(['null', 'number', 'undefined']),
    });

    /**
     * Expected JSON RPC response for the "minimumLedgerSlot" and "getFirstAvailableBlock" messages
     */
    const SlotRpcResult = struct({
      jsonrpc: struct.literal('2.0'),
      id: 'string',
      error: 'any?',
      result: 'number',
    });

    /**
     * Supply
     *
     * @typedef {Object} Supply
     * @property {number} total Total supply in lamports
     * @property {number} circulating Circulating supply in lamports
     * @property {number} nonCirculating Non-circulating supply in lamports
     * @property {Array<PublicKey>} nonCirculatingAccounts List of non-circulating account addresses
     */
    type Supply = {
      total: number,
      circulating: number,
      nonCirculating: number,
      nonCirculatingAccounts: Array<PublicKey>,
    };

    /**
     * Expected JSON RPC response for the "getSupply" message
     */
    const GetSupplyRpcResult = jsonRpcResultAndContext(
      struct({
        total: 'number',
        circulating: 'number',
        nonCirculating: 'number',
        nonCirculatingAccounts: struct.array(['string']),
      }),
    );

    /**
     * Token amount object which returns a token amount in different formats
     * for various client use cases.
     *
     * @typedef {Object} TokenAmount
     * @property {string} amount Raw amount of tokens as string ignoring decimals
     * @property {number} decimals Number of decimals configured for token's mint
     * @property {number} uiAmount Token account as float, accounts for decimals
     */
    type TokenAmount = {
      amount: string,
      decimals: number,
      uiAmount: number,
    };

    /**
     * Expected JSON RPC structure for token amounts
     */
    const TokenAmountResult = struct.object({
      amount: 'string',
      uiAmount: 'number',
      decimals: 'number',
    });

    /**
     * Token address and balance.
     *
     * @typedef {Object} TokenAccountBalancePair
     * @property {PublicKey} address Address of the token account
     * @property {string} amount Raw amount of tokens as string ignoring decimals
     * @property {number} decimals Number of decimals configured for token's mint
     * @property {number} uiAmount Token account as float, accounts for decimals
     */
    type TokenAccountBalancePair = {
      address: PublicKey,
      amount: string,
      decimals: number,
      uiAmount: number,
    };

    /**
     * Expected JSON RPC response for the "getTokenLargestAccounts" message
     */
    const GetTokenLargestAccountsResult = jsonRpcResultAndContext(
      struct.array([
        struct.pick({
          address: 'string',
          amount: 'string',
          uiAmount: 'number',
          decimals: 'number',
        }),
      ]),
    );

    /**
     * Expected JSON RPC response for the "getTokenAccountBalance" message
     */
    const GetTokenAccountBalance = jsonRpcResultAndContext(TokenAmountResult);

    /**
     * Expected JSON RPC response for the "getTokenSupply" message
     */
    const GetTokenSupplyRpcResult = jsonRpcResultAndContext(TokenAmountResult);

    /**
     * Expected JSON RPC response for the "getTokenAccountsByOwner" message
     */
    const GetTokenAccountsByOwner = jsonRpcResultAndContext(
      struct.array([
        struct.object({
          pubkey: 'string',
          account: struct.object({
            executable: 'boolean',
            owner: 'string',
            lamports: 'number',
            data: 'string',
            rentEpoch: 'number?',
          }),
        }),
      ]),
    );

    /**
     * Expected JSON RPC response for the "getTokenAccountsByOwner" message with parsed data
     */
    const GetParsedTokenAccountsByOwner = jsonRpcResultAndContext(
      struct.array([
        struct.object({
          pubkey: 'string',
          account: struct.object({
            executable: 'boolean',
            owner: 'string',
            lamports: 'number',
            data: struct.pick({
              program: 'string',
              parsed: 'any',
              space: 'number',
            }),
            rentEpoch: 'number?',
          }),
        }),
      ]),
    );

    /**
     * Pair of an account address and its balance
     *
     * @typedef {Object} AccountBalancePair
     * @property {PublicKey} address
     * @property {number} lamports
     */
    type AccountBalancePair = {
      address: PublicKey,
      lamports: number,
    };

    /**
     * Expected JSON RPC response for the "getLargestAccounts" message
     */
    const GetLargestAccountsRpcResult = jsonRpcResultAndContext(
      struct.array([
        struct({
          lamports: 'number',
          address: 'string',
        }),
      ]),
    );

    /**
     * Expected JSON RPC response for the "getVersion" message
     */
    const GetVersionRpcResult = struct({
      jsonrpc: struct.literal('2.0'),
      id: 'string',
      error: 'any?',
      result: Version,
    });

    /**
     * @private
     */
    const AccountInfoResult = struct({
      executable: 'boolean',
      owner: 'string',
      lamports: 'number',
      data: 'any',
      rentEpoch: 'number?',
    });

    /**
     * @private
     */
    const ParsedAccountInfoResult = struct.object({
      executable: 'boolean',
      owner: 'string',
      lamports: 'number',
      data: struct.union([
        'string',
        struct.pick({
          program: 'string',
          parsed: 'any',
          space: 'number',
        }),
      ]),
      rentEpoch: 'number?',
    });

    /**
     * Expected JSON RPC response for the "getAccountInfo" message
     */
    const GetAccountInfoAndContextRpcResult = jsonRpcResultAndContext(
      struct.union(['null', AccountInfoResult]),
    );

    /**
     * Expected JSON RPC response for the "getAccountInfo" message with jsonParsed param
     */
    const GetParsedAccountInfoResult = jsonRpcResultAndContext(
      struct.union(['null', ParsedAccountInfoResult]),
    );

    /**
     * Expected JSON RPC response for the "getConfirmedSignaturesForAddress" message
     */
    const GetConfirmedSignaturesForAddressRpcResult = jsonRpcResult(
      struct.array(['string']),
    );

    /**
     * Expected JSON RPC response for the "getConfirmedSignaturesForAddress2" message
     */

    const GetConfirmedSignaturesForAddress2RpcResult = jsonRpcResult(
      struct.array([
        struct({
          signature: 'string',
          slot: 'number',
          err: TransactionErrorResult,
          memo: struct.union(['null', 'string']),
        }),
      ]),
    );

    /***
     * Expected JSON RPC response for the "accountNotification" message
     */
    const AccountNotificationResult = struct({
      subscription: 'number',
      result: notificationResultAndContext(AccountInfoResult),
    });

    /**
     * @private
     */
    const ProgramAccountInfoResult = struct({
      pubkey: 'string',
      account: AccountInfoResult,
    });

    /**
     * @private
     */
    const ParsedProgramAccountInfoResult = struct({
      pubkey: 'string',
      account: ParsedAccountInfoResult,
    });

    /***
     * Expected JSON RPC response for the "programNotification" message
     */
    const ProgramAccountNotificationResult = struct({
      subscription: 'number',
      result: notificationResultAndContext(ProgramAccountInfoResult),
    });

    /**
     * @private
     */
    const SlotInfoResult = struct({
      parent: 'number',
      slot: 'number',
      root: 'number',
    });

    /**
     * Expected JSON RPC response for the "slotNotification" message
     */
    const SlotNotificationResult = struct({
      subscription: 'number',
      result: SlotInfoResult,
    });

    /**
     * Expected JSON RPC response for the "signatureNotification" message
     */
    const SignatureNotificationResult = struct({
      subscription: 'number',
      result: notificationResultAndContext(SignatureStatusResult),
    });

    /**
     * Expected JSON RPC response for the "rootNotification" message
     */
    const RootNotificationResult = struct({
      subscription: 'number',
      result: 'number',
    });

    /**
     * Expected JSON RPC response for the "getProgramAccounts" message
     */
    const GetProgramAccountsRpcResult = jsonRpcResult(
      struct.array([ProgramAccountInfoResult]),
    );

    /**
     * Expected JSON RPC response for the "getProgramAccounts" message
     */
    const GetParsedProgramAccountsRpcResult = jsonRpcResult(
      struct.array([ParsedProgramAccountInfoResult]),
    );

    /**
     * Expected JSON RPC response for the "getSlot" message
     */
    const GetSlot = jsonRpcResult('number');

    /**
     * Expected JSON RPC response for the "getSlotLeader" message
     */
    const GetSlotLeader = jsonRpcResult('string');

    /**
     * Expected JSON RPC response for the "getClusterNodes" message
     */
    const GetClusterNodes = jsonRpcResult(
      struct.array([
        struct.pick({
          pubkey: 'string',
          gossip: struct.union(['null', 'string']),
          tpu: struct.union(['null', 'string']),
          rpc: struct.union(['null', 'string']),
          version: struct.union(['null', 'string']),
        }),
      ]),
    );

    /**
     * Expected JSON RPC response for the "getVoteAccounts" message
     */
    const GetVoteAccounts = jsonRpcResult(
      struct({
        current: struct.array([
          struct.pick({
            votePubkey: 'string',
            nodePubkey: 'string',
            activatedStake: 'number',
            epochVoteAccount: 'boolean',
            epochCredits: struct.array([
              struct.tuple(['number', 'number', 'number']),
            ]),
            commission: 'number',
            lastVote: 'number',
            rootSlot: 'number?',
          }),
        ]),
        delinquent: struct.array([
          struct.pick({
            votePubkey: 'string',
            nodePubkey: 'string',
            activatedStake: 'number',
            epochVoteAccount: 'boolean',
            epochCredits: struct.array([
              struct.tuple(['number', 'number', 'number']),
            ]),
            commission: 'number',
            lastVote: 'number',
            rootSlot: 'number?',
          }),
        ]),
      }),
    );

    /**
     * Expected JSON RPC response for the "getSignatureStatuses" message
     */
    const GetSignatureStatusesRpcResult = jsonRpcResultAndContext(
      struct.array([
        struct.union([
          'null',
          struct.pick({
            slot: 'number',
            confirmations: struct.union(['number', 'null']),
            err: TransactionErrorResult,
          }),
        ]),
      ]),
    );

    /**
     * Expected JSON RPC response for the "getTransactionCount" message
     */
    const GetTransactionCountRpcResult = jsonRpcResult('number');

    /**
     * Expected JSON RPC response for the "getTotalSupply" message
     */
    const GetTotalSupplyRpcResult = jsonRpcResult('number');

    /**
     * Expected JSON RPC response for the "getMinimumBalanceForRentExemption" message
     */
    const GetMinimumBalanceForRentExemptionRpcResult = jsonRpcResult('number');

    /**
     * @private
     */
    const ConfirmedTransactionResult = struct({
      signatures: struct.array(['string']),
      message: struct({
        accountKeys: struct.array(['string']),
        header: struct({
          numRequiredSignatures: 'number',
          numReadonlySignedAccounts: 'number',
          numReadonlyUnsignedAccounts: 'number',
        }),
        instructions: struct.array([
          struct({
            accounts: struct.array(['number']),
            data: 'string',
            programIdIndex: 'number',
          }),
        ]),
        recentBlockhash: 'string',
      }),
    });

    /**
     * @private
     */
    const ParsedConfirmedTransactionResult = struct({
      signatures: struct.array(['string']),
      message: struct({
        accountKeys: struct.array([
          struct({
            pubkey: 'string',
            signer: 'boolean',
            writable: 'boolean',
          }),
        ]),
        instructions: struct.array([
          struct.union([
            struct({
              accounts: struct.array(['string']),
              data: 'string',
              programId: 'string',
            }),
            struct({
              parsed: 'any',
              program: 'string',
              programId: 'string',
            }),
          ]),
        ]),
        recentBlockhash: 'string',
      }),
    });

    /**
     * @private
     */
    const ConfirmedTransactionMetaResult = struct.union([
      'null',
      struct.pick({
        err: TransactionErrorResult,
        fee: 'number',
        preBalances: struct.array(['number']),
        postBalances: struct.array(['number']),
      }),
    ]);

    /**
     * Expected JSON RPC response for the "getConfirmedBlock" message
     */
    export const GetConfirmedBlockRpcResult = jsonRpcResult(
      struct.union([
        'null',
        struct.pick({
          blockhash: 'string',
          previousBlockhash: 'string',
          parentSlot: 'number',
          transactions: struct.array([
            struct({
              transaction: ConfirmedTransactionResult,
              meta: ConfirmedTransactionMetaResult,
            }),
          ]),
          rewards: struct.union([
            'undefined',
            struct.array([
              struct({
                pubkey: 'string',
                lamports: 'number',
              }),
            ]),
          ]),
        }),
      ]),
    );

    /**
     * Expected JSON RPC response for the "getConfirmedTransaction" message
     */
    const GetConfirmedTransactionRpcResult = jsonRpcResult(
      struct.union([
        'null',
        struct.pick({
          slot: 'number',
          transaction: ConfirmedTransactionResult,
          meta: ConfirmedTransactionMetaResult,
        }),
      ]),
    );

    /**
     * Expected JSON RPC response for the "getConfirmedTransaction" message
     */
    const GetParsedConfirmedTransactionRpcResult = jsonRpcResult(
      struct.union([
        'null',
        struct.pick({
          slot: 'number',
          transaction: ParsedConfirmedTransactionResult,
          meta: ConfirmedTransactionMetaResult,
        }),
      ]),
    );

    /**
     * Expected JSON RPC response for the "getRecentBlockhash" message
     */
    const GetRecentBlockhashAndContextRpcResult = jsonRpcResultAndContext(
      struct({
        blockhash: 'string',
        feeCalculator: struct({
          lamportsPerSignature: 'number',
        }),
      }),
    );

    /**
     * Expected JSON RPC response for the "getFeeCalculatorForBlockhash" message
     */
    const GetFeeCalculatorRpcResult = jsonRpcResultAndContext(
      struct.union([
        'null',
        struct({
          feeCalculator: struct({
            lamportsPerSignature: 'number',
          }),
        }),
      ]),
    );

    /**
     * Expected JSON RPC response for the "requestAirdrop" message
     */
    const RequestAirdropRpcResult = jsonRpcResult('string');

    /**
     * Expected JSON RPC response for the "sendTransaction" message
     */
    const SendTransactionRpcResult = jsonRpcResult('string');

    /**
     * Information about the latest slot being processed by a node
     *
     * @typedef {Object} SlotInfo
     * @property {number} slot Currently processing slot
     * @property {number} parent Parent of the current slot
     * @property {number} root The root block of the current slot's fork
     */
    type SlotInfo = {
      slot: number,
      parent: number,
      root: number,
    };

    /**
     * Parsed account data
     *
     * @typedef {Object} ParsedAccountData
     * @property {string} program Name of the program that owns this account
     * @property {any} parsed Parsed account data
     * @property {number} space Space used by account data
     */
    type ParsedAccountData = {
      program: string,
      parsed: any,
      space: number,
    };

    /**
     * Information describing an account
     *
     * @typedef {Object} AccountInfo
     * @property {number} lamports Number of lamports assigned to the account
     * @property {PublicKey} owner Identifier of the program that owns the account
     * @property {T} data Optional data assigned to the account
     * @property {boolean} executable `true` if this account's data contains a loaded program
     */
    type AccountInfo<T> = {
      executable: boolean,
      owner: PublicKey,
      lamports: number,
      data: T,
    };

    /**
     * Account information identified by pubkey
     *
     * @typedef {Object} KeyedAccountInfo
     * @property {PublicKey} accountId
     * @property {AccountInfo<Buffer>} accountInfo
     */
    type KeyedAccountInfo = {
      accountId: PublicKey,
      accountInfo: AccountInfo<Buffer>,
    };

    /**
     * Callback function for account change notifications
     */
    export type AccountChangeCallback = (
      accountInfo: AccountInfo<Buffer>,
      context: Context,
    ) => void;

    /**
     * @private
     */
    type SubscriptionId = 'subscribing' | number;

    /**
     * @private
     */
    type AccountSubscriptionInfo = {
      publicKey: string, // PublicKey of the account as a base 58 string
      callback: AccountChangeCallback,
      commitment: ?Commitment,
      subscriptionId: ?SubscriptionId, // null when there's no current server subscription id
    };

    /**
     * Callback function for program account change notifications
     */
    export type ProgramAccountChangeCallback = (
      keyedAccountInfo: KeyedAccountInfo,
      context: Context,
    ) => void;

    /**
     * @private
     */
    type ProgramAccountSubscriptionInfo = {
      programId: string, // PublicKey of the program as a base 58 string
      callback: ProgramAccountChangeCallback,
      commitment: ?Commitment,
      subscriptionId: ?SubscriptionId, // null when there's no current server subscription id
    };

    /**
     * Callback function for slot change notifications
     */
    export type SlotChangeCallback = (slotInfo: SlotInfo) => void;

    /**
     * @private
     */
    type SlotSubscriptionInfo = {
      callback: SlotChangeCallback,
      subscriptionId: ?SubscriptionId, // null when there's no current server subscription id
    };

    /**
     * Callback function for signature notifications
     */
    export type SignatureResultCallback = (
      signatureResult: SignatureResult,
      context: Context,
    ) => void;

    /**
     * @private
     */
    type SignatureSubscriptionInfo = {
      signature: TransactionSignature, // TransactionSignature as a base 58 string
      callback: SignatureResultCallback,
      commitment: ?Commitment,
      subscriptionId: ?SubscriptionId, // null when there's no current server subscription id
    };

    /**
     * Callback function for root change notifications
     */
    export type RootChangeCallback = (root: number) => void;

    /**
     * @private
     */
    type RootSubscriptionInfo = {
      callback: RootChangeCallback,
      subscriptionId: ?SubscriptionId, // null when there's no current server subscription id
    };

    /**
     * Signature result
     *
     * @typedef {Object} SignatureResult
     */
    export type SignatureResult = {|
      err: TransactionError | null,
    |};

    /**
     * Transaction error
     *
     * @typedef {Object} TransactionError
     */
    export type TransactionError = {};

    /**
     * Signature status
     *
     * @typedef {Object} SignatureStatus
     * @property {number} slot when the transaction was processed
     * @property {number | null} confirmations the number of blocks that have been confirmed and voted on in the fork containing `slot` (TODO)
     * @property {TransactionError | null} err error, if any
     */
    export type SignatureStatus = {
      slot: number,
      confirmations: number | null,
      err: TransactionError | null,
    };

    /**
     * A confirmed signature with its status
     *
     * @typedef {Object} ConfirmedSignatureInfo
     * @property {string} signature the transaction signature
     * @property {number} slot when the transaction was processed
     * @property {TransactionError | null} err error, if any
     * @property {string | null} memo memo associated with the transaction, if any
     */
    export type ConfirmedSignatureInfo = {
      signature: string,
      slot: number,
      err: TransactionError | null,
      memo: string | null,
    };

    /**
     * A connection to a fullnode JSON RPC endpoint
     */
    export class Connection {
      _rpcRequest: RpcRequest;
      _rpcWebSocket: RpcWebSocketClient;
      _rpcWebSocketConnected: boolean = false;

      _commitment: ?Commitment;
      _blockhashInfo: {
        recentBlockhash: Blockhash | null,
        lastFetch: Date,
        simulatedSignatures: Array<string>,
        transactionSignatures: Array<string>,
      };
      _disableBlockhashCaching: boolean = false;
      _accountChangeSubscriptions: {[number]: AccountSubscriptionInfo} = {};
      _accountChangeSubscriptionCounter: number = 0;
      _programAccountChangeSubscriptions: {
        [number]: ProgramAccountSubscriptionInfo,
      } = {};
      _programAccountChangeSubscriptionCounter: number = 0;
      _slotSubscriptions: {
        [number]: SlotSubscriptionInfo,
      } = {};
      _slotSubscriptionCounter: number = 0;
      _signatureSubscriptions: {
        [number]: SignatureSubscriptionInfo,
      } = {};
      _signatureSubscriptionCounter: number = 0;
      _rootSubscriptions: {
        [number]: RootSubscriptionInfo,
      } = {};
      _rootSubscriptionCounter: number = 0;

      /**
       * Establish a JSON RPC connection
       *
       * @param endpoint URL to the fullnode JSON RPC endpoint
       * @param commitment optional default commitment level
       */
      constructor(endpoint: string, commitment: ?Commitment) {
        let url = urlParse(endpoint);

        this._rpcRequest = createRpcRequest(url.href);
        this._commitment = commitment;
        this._blockhashInfo = {
          recentBlockhash: null,
          lastFetch: new Date(0),
          transactionSignatures: [],
          simulatedSignatures: [],
        };

        url.protocol = url.protocol === 'https:' ? 'wss:' : 'ws:';
        url.host = '';
        if (url.port !== null) {
          url.port = String(Number(url.port) + 1);
        }
        this._rpcWebSocket = new RpcWebSocketClient(urlFormat(url), {
          autoconnect: false,
          max_reconnects: Infinity,
        });
        this._rpcWebSocket.on('open', this._wsOnOpen.bind(this));
        this._rpcWebSocket.on('error', this._wsOnError.bind(this));
        this._rpcWebSocket.on('close', this._wsOnClose.bind(this));
        this._rpcWebSocket.on(
          'accountNotification',
          this._wsOnAccountNotification.bind(this),
        );
        this._rpcWebSocket.on(
          'programNotification',
          this._wsOnProgramAccountNotification.bind(this),
        );
        this._rpcWebSocket.on(
          'slotNotification',
          this._wsOnSlotNotification.bind(this),
        );
        this._rpcWebSocket.on(
          'signatureNotification',
          this._wsOnSignatureNotification.bind(this),
        );
        this._rpcWebSocket.on(
          'rootNotification',
          this._wsOnRootNotification.bind(this),
        );
      }

      /**
       * The default commitment used for requests
       */
      get commitment(): ?Commitment {
        return this._commitment;
      }

      /**
       * Fetch the balance for the specified public key, return with context
       */
      async getBalanceAndContext(
        publicKey: PublicKey,
        commitment: ?Commitment,
      ): Promise<RpcResponseAndContext<number>> {
        const args = this._buildArgs([publicKey.toBase58()], commitment);
        const unsafeRes = await this._rpcRequest('getBalance', args);
        const res = GetBalanceAndContextRpcResult(unsafeRes);
        if (res.error) {
          throw new Error(
            'failed to get balance for ' +
              publicKey.toBase58() +
              ': ' +
              res.error.message,
          );
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Fetch the balance for the specified public key
       */
      async getBalance(
        publicKey: PublicKey,
        commitment: ?Commitment,
      ): Promise<number> {
        return await this.getBalanceAndContext(publicKey, commitment)
          .then(x => x.value)
          .catch(e => {
            throw new Error(
              'failed to get balance of account ' + publicKey.toBase58() + ': ' + e,
            );
          });
      }

      /**
       * Fetch the estimated production time of a block
       */
      async getBlockTime(slot: number): Promise<number | null> {
        const unsafeRes = await this._rpcRequest('getBlockTime', [slot]);
        const res = GetBlockTimeRpcResult(unsafeRes);
        if (res.error) {
          throw new Error(
            'failed to get block time for slot ' + slot + ': ' + res.error.message,
          );
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Fetch the lowest slot that the node has information about in its ledger.
       * This value may increase over time if the node is configured to purge older ledger data
       */
      async getMinimumLedgerSlot(): Promise<number> {
        const unsafeRes = await this._rpcRequest('minimumLedgerSlot', []);
        const res = SlotRpcResult(unsafeRes);
        if (res.error) {
          throw new Error(
            'failed to get minimum ledger slot: ' + res.error.message,
          );
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Fetch the slot of the lowest confirmed block that has not been purged from the ledger
       */
      async getFirstAvailableBlock(): Promise<number> {
        const unsafeRes = await this._rpcRequest('getFirstAvailableBlock', []);
        const res = SlotRpcResult(unsafeRes);
        if (res.error) {
          throw new Error(
            'failed to get first available block: ' + res.error.message,
          );
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Fetch information about the current supply
       */
      async getSupply(
        commitment: ?Commitment,
      ): Promise<RpcResponseAndContext<Supply>> {
        const args = this._buildArgs([], commitment);
        const unsafeRes = await this._rpcRequest('getSupply', args);
        const res = GetSupplyRpcResult(unsafeRes);
        if (res.error) {
          throw new Error('failed to get supply: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        res.result.value.nonCirculatingAccounts = res.result.value.nonCirculatingAccounts.map(
          account => new PublicKey(account),
        );
        return res.result;
      }

      /**
       * Fetch the current supply of a token mint
       */
      async getTokenSupply(
        tokenMintAddress: PublicKey,
        commitment: ?Commitment,
      ): Promise<RpcResponseAndContext<TokenAmount>> {
        const args = this._buildArgs([tokenMintAddress.toBase58()], commitment);
        const unsafeRes = await this._rpcRequest('getTokenSupply', args);
        const res = GetTokenSupplyRpcResult(unsafeRes);
        if (res.error) {
          throw new Error('failed to get token supply: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Fetch the current balance of a token account
       */
      async getTokenAccountBalance(
        tokenAddress: PublicKey,
        commitment: ?Commitment,
      ): Promise<RpcResponseAndContext<TokenAmount>> {
        const args = this._buildArgs([tokenAddress.toBase58()], commitment);
        const unsafeRes = await this._rpcRequest('getTokenAccountBalance', args);
        const res = GetTokenAccountBalance(unsafeRes);
        if (res.error) {
          throw new Error(
            'failed to get token account balance: ' + res.error.message,
          );
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Fetch all the token accounts owned by the specified account
       *
       * @return {Promise<RpcResponseAndContext<Array<{pubkey: PublicKey, account: AccountInfo<Buffer>}>>>}
       */
      async getTokenAccountsByOwner(
        ownerAddress: PublicKey,
        filter: TokenAccountsFilter,
        commitment: ?Commitment,
      ): Promise<
        RpcResponseAndContext<
          Array<{pubkey: PublicKey, account: AccountInfo<Buffer>}>,
        >,
      > {
        let _args = [ownerAddress.toBase58()];
        if (filter.mint) {
          _args.push({mint: filter.mint.toBase58()});
        } else {
          _args.push({programId: filter.programId.toBase58()});
        }

        const args = this._buildArgs(_args, commitment, 'binary64');
        const unsafeRes = await this._rpcRequest('getTokenAccountsByOwner', args);
        const res = GetTokenAccountsByOwner(unsafeRes);
        if (res.error) {
          throw new Error(
            'failed to get token accounts owned by account ' +
              ownerAddress.toBase58() +
              ': ' +
              res.error.message,
          );
        }

        const {result} = res;
        const {context, value} = result;
        assert(typeof result !== 'undefined');

        return {
          context,
          value: value.map(result => ({
            pubkey: new PublicKey(result.pubkey),
            account: {
              executable: result.account.executable,
              owner: new PublicKey(result.account.owner),
              lamports: result.account.lamports,
              data: Buffer.from(result.account.data, 'base64'),
            },
          })),
        };
      }

      /**
       * Fetch parsed token accounts owned by the specified account
       *
       * @return {Promise<RpcResponseAndContext<Array<{pubkey: PublicKey, account: AccountInfo<ParsedAccountData>}>>>}
       */
      async getParsedTokenAccountsByOwner(
        ownerAddress: PublicKey,
        filter: TokenAccountsFilter,
        commitment: ?Commitment,
      ): Promise<
        RpcResponseAndContext<
          Array<{pubkey: PublicKey, account: AccountInfo<ParsedAccountData>}>,
        >,
      > {
        let _args = [ownerAddress.toBase58()];
        if (filter.mint) {
          _args.push({mint: filter.mint.toBase58()});
        } else {
          _args.push({programId: filter.programId.toBase58()});
        }

        const args = this._buildArgs(_args, commitment, 'jsonParsed');
        const unsafeRes = await this._rpcRequest('getTokenAccountsByOwner', args);
        const res = GetParsedTokenAccountsByOwner(unsafeRes);
        if (res.error) {
          throw new Error(
            'failed to get token accounts owned by account ' +
              ownerAddress.toBase58() +
              ': ' +
              res.error.message,
          );
        }

        const {result} = res;
        const {context, value} = result;
        assert(typeof result !== 'undefined');

        return {
          context,
          value: value.map(result => ({
            pubkey: new PublicKey(result.pubkey),
            account: {
              executable: result.account.executable,
              owner: new PublicKey(result.account.owner),
              lamports: result.account.lamports,
              data: result.account.data,
            },
          })),
        };
      }

      /**
       * Fetch the 20 largest accounts with their current balances
       */
      async getLargestAccounts(
        config: ?GetLargestAccountsConfig,
      ): Promise<RpcResponseAndContext<Array<AccountBalancePair>>> {
        const arg = {
          ...config,
          commitment: (config && config.commitment) || this.commitment,
        };
        const args = arg.filter || arg.commitment ? [arg] : [];
        const unsafeRes = await this._rpcRequest('getLargestAccounts', args);
        const res = GetLargestAccountsRpcResult(unsafeRes);
        if (res.error) {
          throw new Error('failed to get largest accounts: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        res.result.value = res.result.value.map(({address, lamports}) => ({
          address: new PublicKey(address),
          lamports,
        }));
        return res.result;
      }

      /**
       * Fetch the 20 largest token accounts with their current balances
       * for a given mint.
       */
      async getTokenLargestAccounts(
        mintAddress: PublicKey,
        commitment: ?Commitment,
      ): Promise<RpcResponseAndContext<Array<TokenAccountBalancePair>>> {
        const args = this._buildArgs([mintAddress.toBase58()], commitment);
        const unsafeRes = await this._rpcRequest('getTokenLargestAccounts', args);
        const res = GetTokenLargestAccountsResult(unsafeRes);
        if (res.error) {
          throw new Error(
            'failed to get token largest accounts: ' + res.error.message,
          );
        }
        assert(typeof res.result !== 'undefined');
        res.result.value = res.result.value.map(pair => ({
          ...pair,
          address: new PublicKey(pair.address),
        }));
        return res.result;
      }

      /**
       * Fetch all the account info for the specified public key, return with context
       */
      async getAccountInfoAndContext(
        publicKey: PublicKey,
        commitment: ?Commitment,
      ): Promise<RpcResponseAndContext<AccountInfo<Buffer> | null>> {
        const args = this._buildArgs(
          [publicKey.toBase58()],
          commitment,
          'binary64',
        );
        const unsafeRes = await this._rpcRequest('getAccountInfo', args);
        const res = GetAccountInfoAndContextRpcResult(unsafeRes);
        if (res.error) {
          throw new Error(
            'failed to get info about account ' +
              publicKey.toBase58() +
              ': ' +
              res.error.message,
          );
        }
        assert(typeof res.result !== 'undefined');

        let value = null;
        if (res.result.value) {
          const {executable, owner, lamports, data} = res.result.value;
          value = {
            executable,
            owner: new PublicKey(owner),
            lamports,
            data: Buffer.from(data, 'base64'),
          };
        }

        return {
          context: {
            slot: res.result.context.slot,
          },
          value,
        };
      }

      /**
       * Fetch parsed account info for the specified public key
       */
      async getParsedAccountInfo(
        publicKey: PublicKey,
        commitment: ?Commitment,
      ): Promise<
        RpcResponseAndContext<AccountInfo<Buffer | ParsedAccountData> | null>,
      > {
        const args = this._buildArgs(
          [publicKey.toBase58()],
          commitment,
          'jsonParsed',
        );
        const unsafeRes = await this._rpcRequest('getAccountInfo', args);
        const res = GetParsedAccountInfoResult(unsafeRes);
        if (res.error) {
          throw new Error(
            'failed to get info about account ' +
              publicKey.toBase58() +
              ': ' +
              res.error.message,
          );
        }
        assert(typeof res.result !== 'undefined');

        let value = null;
        if (res.result.value) {
          const {executable, owner, lamports, data: resultData} = res.result.value;

          let data = resultData;
          if (!data.program) {
            data = Buffer.from(data, 'base64');
          }

          value = {
            executable,
            owner: new PublicKey(owner),
            lamports,
            data,
          };
        }

        return {
          context: {
            slot: res.result.context.slot,
          },
          value,
        };
      }

      /**
       * Fetch all the account info for the specified public key
       */
      async getAccountInfo(
        publicKey: PublicKey,
        commitment: ?Commitment,
      ): Promise<AccountInfo<Buffer> | null> {
        return await this.getAccountInfoAndContext(publicKey, commitment)
          .then(x => x.value)
          .catch(e => {
            throw new Error(
              'failed to get info about account ' + publicKey.toBase58() + ': ' + e,
            );
          });
      }

      /**
       * Fetch all the accounts owned by the specified program id
       *
       * @return {Promise<Array<{pubkey: PublicKey, account: AccountInfo<Buffer>}>>}
       */
      async getProgramAccounts(
        programId: PublicKey,
        commitment: ?Commitment,
      ): Promise<Array<{pubkey: PublicKey, account: AccountInfo<Buffer>}>> {
        const args = this._buildArgs(
          [programId.toBase58()],
          commitment,
          'binary64',
        );
        const unsafeRes = await this._rpcRequest('getProgramAccounts', args);
        const res = GetProgramAccountsRpcResult(unsafeRes);
        if (res.error) {
          throw new Error(
            'failed to get accounts owned by program ' +
              programId.toBase58() +
              ': ' +
              res.error.message,
          );
        }

        const {result} = res;
        assert(typeof result !== 'undefined');

        return result.map(result => {
          return {
            pubkey: new PublicKey(result.pubkey),
            account: {
              executable: result.account.executable,
              owner: new PublicKey(result.account.owner),
              lamports: result.account.lamports,
              data: Buffer.from(result.account.data, 'base64'),
            },
          };
        });
      }

      /**
       * Fetch and parse all the accounts owned by the specified program id
       *
       * @return {Promise<Array<{pubkey: PublicKey, account: AccountInfo<Buffer | ParsedAccountData>}>>}
       */
      async getParsedProgramAccounts(
        programId: PublicKey,
        commitment: ?Commitment,
      ): Promise<
        Array<{
          pubkey: PublicKey,
          account: AccountInfo<Buffer | ParsedAccountData>,
        }>,
      > {
        const args = this._buildArgs(
          [programId.toBase58()],
          commitment,
          'jsonParsed',
        );
        const unsafeRes = await this._rpcRequest('getProgramAccounts', args);
        const res = GetParsedProgramAccountsRpcResult(unsafeRes);
        if (res.error) {
          throw new Error(
            'failed to get accounts owned by program ' +
              programId.toBase58() +
              ': ' +
              res.error.message,
          );
        }

        const {result} = res;
        assert(typeof result !== 'undefined');

        return result.map(result => {
          const resultData = result.account.data;

          let data = resultData;
          if (!data.program) {
            data = Buffer.from(data, 'base64');
          }

          return {
            pubkey: new PublicKey(result.pubkey),
            account: {
              executable: result.account.executable,
              owner: new PublicKey(result.account.owner),
              lamports: result.account.lamports,
              data,
            },
          };
        });
      }

      /**
       * Confirm the transaction identified by the specified signature
       */
      async confirmTransaction(
        signature: TransactionSignature,
        confirmations: ?number,
      ): Promise<RpcResponseAndContext<SignatureStatus | null>> {
        const start = Date.now();
        const WAIT_TIMEOUT_MS = 60 * 1000;

        let statusResponse = await this.getSignatureStatus(signature);
        for (;;) {
          const status = statusResponse.value;
          if (status) {
            // Received a status, if not an error wait for confirmation
            if (
              status.err ||
              status.confirmations === null ||
              (typeof confirmations === 'number' &&
                status.confirmations >= confirmations)
            ) {
              break;
            }
          } else if (Date.now() - start >= WAIT_TIMEOUT_MS) {
            break;
          }

          // Sleep for approximately one slot
          await sleep(MS_PER_SLOT);
          statusResponse = await this.getSignatureStatus(signature);
        }

        return statusResponse;
      }

      /**
       * Return the list of nodes that are currently participating in the cluster
       */
      async getClusterNodes(): Promise<Array<ContactInfo>> {
        const unsafeRes = await this._rpcRequest('getClusterNodes', []);

        const res = GetClusterNodes(unsafeRes);
        if (res.error) {
          throw new Error('failed to get cluster nodes: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Return the list of nodes that are currently participating in the cluster
       */
      async getVoteAccounts(commitment: ?Commitment): Promise<VoteAccountStatus> {
        const args = this._buildArgs([], commitment);
        const unsafeRes = await this._rpcRequest('getVoteAccounts', args);
        const res = GetVoteAccounts(unsafeRes);
        //const res = unsafeRes;
        if (res.error) {
          throw new Error('failed to get vote accounts: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Fetch the current slot that the node is processing
       */
      async getSlot(commitment: ?Commitment): Promise<number> {
        const args = this._buildArgs([], commitment);
        const unsafeRes = await this._rpcRequest('getSlot', args);
        const res = GetSlot(unsafeRes);
        if (res.error) {
          throw new Error('failed to get slot: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Fetch the current slot leader of the cluster
       */
      async getSlotLeader(commitment: ?Commitment): Promise<string> {
        const args = this._buildArgs([], commitment);
        const unsafeRes = await this._rpcRequest('getSlotLeader', args);
        const res = GetSlotLeader(unsafeRes);
        if (res.error) {
          throw new Error('failed to get slot leader: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Fetch the current status of a signature
       */
      async getSignatureStatus(
        signature: TransactionSignature,
        config: ?SignatureStatusConfig,
      ): Promise<RpcResponseAndContext<SignatureStatus | null>> {
        const {context, value} = await this.getSignatureStatuses(
          [signature],
          config,
        );
        assert(value.length === 1);
        return {context, value: value[0]};
      }

      /**
       * Fetch the current statuses of a batch of signatures
       */
      async getSignatureStatuses(
        signatures: Array<TransactionSignature>,
        config: ?SignatureStatusConfig,
      ): Promise<RpcResponseAndContext<Array<SignatureStatus | null>>> {
        const params = [signatures];
        if (config) {
          params.push(config);
        }
        const unsafeRes = await this._rpcRequest('getSignatureStatuses', params);
        const res = GetSignatureStatusesRpcResult(unsafeRes);
        if (res.error) {
          throw new Error('failed to get signature status: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Fetch the current transaction count of the cluster
       */
      async getTransactionCount(commitment: ?Commitment): Promise<number> {
        const args = this._buildArgs([], commitment);
        const unsafeRes = await this._rpcRequest('getTransactionCount', args);
        const res = GetTransactionCountRpcResult(unsafeRes);
        if (res.error) {
          throw new Error('failed to get transaction count: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return Number(res.result);
      }

      /**
       * Fetch the current total currency supply of the cluster in lamports
       */
      async getTotalSupply(commitment: ?Commitment): Promise<number> {
        const args = this._buildArgs([], commitment);
        const unsafeRes = await this._rpcRequest('getTotalSupply', args);
        const res = GetTotalSupplyRpcResult(unsafeRes);
        if (res.error) {
          throw new Error('faied to get total supply: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return Number(res.result);
      }

      /**
       * Fetch the cluster InflationGovernor parameters
       */
      async getInflationGovernor(
        commitment: ?Commitment,
      ): Promise<InflationGovernor> {
        const args = this._buildArgs([], commitment);
        const unsafeRes = await this._rpcRequest('getInflationGovernor', args);
        const res = GetInflationGovernorRpcResult(unsafeRes);
        if (res.error) {
          throw new Error('failed to get inflation: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return GetInflationGovernorResult(res.result);
      }

      /**
       * Fetch the Epoch Info parameters
       */
      async getEpochInfo(commitment: ?Commitment): Promise<EpochInfo> {
        const args = this._buildArgs([], commitment);
        const unsafeRes = await this._rpcRequest('getEpochInfo', args);
        const res = GetEpochInfoRpcResult(unsafeRes);
        if (res.error) {
          throw new Error('failed to get epoch info: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return GetEpochInfoResult(res.result);
      }

      /**
       * Fetch the Epoch Schedule parameters
       */
      async getEpochSchedule(): Promise<EpochSchedule> {
        const unsafeRes = await this._rpcRequest('getEpochSchedule', []);
        const res = GetEpochScheduleRpcResult(unsafeRes);
        if (res.error) {
          throw new Error('failed to get epoch schedule: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return GetEpochScheduleResult(res.result);
      }

      /**
       * Fetch the leader schedule for the current epoch
       * @return {Promise<RpcResponseAndContext<LeaderSchedule>>}
       */
      async getLeaderSchedule(): Promise<LeaderSchedule> {
        const unsafeRes = await this._rpcRequest('getLeaderSchedule', []);
        const res = GetLeaderScheduleRpcResult(unsafeRes);
        if (res.error) {
          throw new Error('failed to get leader schedule: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Fetch the minimum balance needed to exempt an account of `dataLength`
       * size from rent
       */
      async getMinimumBalanceForRentExemption(
        dataLength: number,
        commitment: ?Commitment,
      ): Promise<number> {
        const args = this._buildArgs([dataLength], commitment);
        const unsafeRes = await this._rpcRequest(
          'getMinimumBalanceForRentExemption',
          args,
        );
        const res = GetMinimumBalanceForRentExemptionRpcResult(unsafeRes);
        if (res.error) {
          console.warn('Unable to fetch minimum balance for rent exemption');
          return 0;
        }
        assert(typeof res.result !== 'undefined');
        return Number(res.result);
      }

      /**
       * Fetch a recent blockhash from the cluster, return with context
       * @return {Promise<RpcResponseAndContext<{blockhash: Blockhash, feeCalculator: FeeCalculator}>>}
       */
      async getRecentBlockhashAndContext(
        commitment: ?Commitment,
      ): Promise<
        RpcResponseAndContext<{blockhash: Blockhash, feeCalculator: FeeCalculator}>,
      > {
        const args = this._buildArgs([], commitment);
        const unsafeRes = await this._rpcRequest('getRecentBlockhash', args);

        const res = GetRecentBlockhashAndContextRpcResult(unsafeRes);
        if (res.error) {
          throw new Error('failed to get recent blockhash: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Fetch the fee calculator for a recent blockhash from the cluster, return with context
       */
      async getFeeCalculatorForBlockhash(
        blockhash: Blockhash,
        commitment: ?Commitment,
      ): Promise<RpcResponseAndContext<FeeCalculator | null>> {
        const args = this._buildArgs([blockhash], commitment);
        const unsafeRes = await this._rpcRequest(
          'getFeeCalculatorForBlockhash',
          args,
        );

        const res = GetFeeCalculatorRpcResult(unsafeRes);
        if (res.error) {
          throw new Error('failed to get fee calculator: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        const {context, value} = res.result;
        return {
          context,
          value: value && value.feeCalculator,
        };
      }

      /**
       * Fetch a recent blockhash from the cluster
       * @return {Promise<{blockhash: Blockhash, feeCalculator: FeeCalculator}>}
       */
      async getRecentBlockhash(
        commitment: ?Commitment,
      ): Promise<{blockhash: Blockhash, feeCalculator: FeeCalculator}> {
        return await this.getRecentBlockhashAndContext(commitment)
          .then(x => x.value)
          .catch(e => {
            throw new Error('failed to get recent blockhash: ' + e);
          });
      }

      /**
       * Fetch the node version
       */
      async getVersion(): Promise<Version> {
        const unsafeRes = await this._rpcRequest('getVersion', []);
        const res = GetVersionRpcResult(unsafeRes);
        if (res.error) {
          throw new Error('failed to get version: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Fetch a list of Transactions and transaction statuses from the cluster
       * for a confirmed block
       */
      async getConfirmedBlock(slot: number): Promise<ConfirmedBlock> {
        const unsafeRes = await this._rpcRequest('getConfirmedBlock', [slot]);
        const {result, error} = GetConfirmedBlockRpcResult(unsafeRes);
        if (error) {
          throw new Error('failed to get confirmed block: ' + result.error.message);
        }
        assert(typeof result !== 'undefined');
        if (!result) {
          throw new Error('Confirmed block ' + slot + ' not found');
        }
        return {
          blockhash: new PublicKey(result.blockhash).toString(),
          previousBlockhash: new PublicKey(result.previousBlockhash).toString(),
          parentSlot: result.parentSlot,
          transactions: result.transactions.map(result => {
            const {message, signatures} = result.transaction;
            return {
              transaction: Transaction.populate(new Message(message), signatures),
              meta: result.meta,
            };
          }),
          rewards: result.rewards || [],
        };
      }

      /**
       * Fetch a transaction details for a confirmed transaction
       */
      async getConfirmedTransaction(
        signature: TransactionSignature,
      ): Promise<ConfirmedTransaction | null> {
        const unsafeRes = await this._rpcRequest('getConfirmedTransaction', [
          signature,
        ]);
        const {result, error} = GetConfirmedTransactionRpcResult(unsafeRes);
        if (error) {
          throw new Error('failed to get confirmed transaction: ' + error.message);
        }
        assert(typeof result !== 'undefined');
        if (result === null) {
          return result;
        }

        const {message, signatures} = result.transaction;
        return {
          slot: result.slot,
          transaction: Transaction.populate(new Message(message), signatures),
          meta: result.meta,
        };
      }

      /**
       * Fetch parsed transaction details for a confirmed transaction
       */
      async getParsedConfirmedTransaction(
        signature: TransactionSignature,
      ): Promise<ParsedConfirmedTransaction | null> {
        const unsafeRes = await this._rpcRequest('getConfirmedTransaction', [
          signature,
          'jsonParsed',
        ]);
        const {result, error} = GetParsedConfirmedTransactionRpcResult(unsafeRes);
        if (error) {
          throw new Error('failed to get confirmed transaction: ' + error.message);
        }
        assert(typeof result !== 'undefined');
        if (result === null) return result;

        const {
          accountKeys,
          instructions,
          recentBlockhash,
        } = result.transaction.message;
        return {
          slot: result.slot,
          meta: result.meta,
          transaction: {
            signatures: result.transaction.signatures,
            message: {
              accountKeys: accountKeys.map(accountKey => ({
                pubkey: new PublicKey(accountKey.pubkey),
                signer: accountKey.signer,
                writable: accountKey.writable,
              })),
              instructions: instructions.map(ix => {
                let mapped: any = {programId: new PublicKey(ix.programId)};
                if ('accounts' in ix) {
                  mapped.accounts = ix.accounts.map(key => new PublicKey(key));
                }

                return {
                  ...ix,
                  ...mapped,
                };
              }),
              recentBlockhash,
            },
          },
        };
      }

      /**
       * Fetch a list of all the confirmed signatures for transactions involving an address
       * within a specified slot range. Max range allowed is 10,000 slots.
       *
       * @param address queried address
       * @param startSlot start slot, inclusive
       * @param endSlot end slot, inclusive
       */
      async getConfirmedSignaturesForAddress(
        address: PublicKey,
        startSlot: number,
        endSlot: number,
      ): Promise<Array<TransactionSignature>> {
        const unsafeRes = await this._rpcRequest(
          'getConfirmedSignaturesForAddress',
          [address.toBase58(), startSlot, endSlot],
        );
        const result = GetConfirmedSignaturesForAddressRpcResult(unsafeRes);
        if (result.error) {
          throw new Error(
            'failed to get confirmed signatures for address: ' +
              result.error.message,
          );
        }
        assert(typeof result.result !== 'undefined');
        return result.result;
      }

      /**
       * Returns confirmed signatures for transactions involving an
       * address backwards in time from the provided signature or most recent confirmed block
       *
       *
       * @param address queried address
       * @param options
       */
      async getConfirmedSignaturesForAddress2(
        address: PublicKey,
        options: ?ConfirmedSignaturesForAddress2Options,
      ): Promise<Array<ConfirmedSignatureInfo>> {
        const unsafeRes = await this._rpcRequest(
          'getConfirmedSignaturesForAddress2',
          [address.toBase58(), options],
        );
        const result = GetConfirmedSignaturesForAddress2RpcResult(unsafeRes);
        if (result.error) {
          throw new Error(
            'failed to get confirmed signatures for address: ' +
              result.error.message,
          );
        }
        assert(typeof result.result !== 'undefined');
        return result.result;
      }

      /**
       * Fetch the contents of a Nonce account from the cluster, return with context
       */
      async getNonceAndContext(
        nonceAccount: PublicKey,
        commitment: ?Commitment,
      ): Promise<RpcResponseAndContext<NonceAccount | null>> {
        const {context, value: accountInfo} = await this.getAccountInfoAndContext(
          nonceAccount,
          commitment,
        );

        let value = null;
        if (accountInfo !== null) {
          value = NonceAccount.fromAccountData(accountInfo.data);
        }

        return {
          context,
          value,
        };
      }

      /**
       * Fetch the contents of a Nonce account from the cluster
       */
      async getNonce(
        nonceAccount: PublicKey,
        commitment: ?Commitment,
      ): Promise<NonceAccount | null> {
        return await this.getNonceAndContext(nonceAccount, commitment)
          .then(x => x.value)
          .catch(e => {
            throw new Error(
              'failed to get nonce for account ' +
                nonceAccount.toBase58() +
                ': ' +
                e,
            );
          });
      }

      /**
       * Request an allocation of lamports to the specified account
       */
      async requestAirdrop(
        to: PublicKey,
        amount: number,
      ): Promise<TransactionSignature> {
        const unsafeRes = await this._rpcRequest('requestAirdrop', [
          to.toBase58(),
          amount,
        ]);
        const res = RequestAirdropRpcResult(unsafeRes);
        if (res.error) {
          throw new Error(
            'airdrop to ' + to.toBase58() + ' failed: ' + res.error.message,
          );
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      async _recentBlockhash(disableCache: boolean): Promise<Blockhash> {
        if (!disableCache) {
          // Attempt to use a recent blockhash for up to 30 seconds
          const expired =
            Date.now() - this._blockhashInfo.lastFetch >=
            BLOCKHASH_CACHE_TIMEOUT_MS;
          if (this._blockhashInfo.recentBlockhash !== null && !expired) {
            return this._blockhashInfo.recentBlockhash;
          }
        }

        return await this._pollNewBlockhash();
      }

      async _pollNewBlockhash(): Promise<Blockhash> {
        const startTime = Date.now();
        for (let i = 0; i < 50; i++) {
          const {blockhash} = await this.getRecentBlockhash('max');

          if (this._blockhashInfo.recentBlockhash != blockhash) {
            this._blockhashInfo = {
              recentBlockhash: blockhash,
              lastFetch: new Date(),
              transactionSignatures: [],
              simulatedSignatures: [],
            };
            return blockhash;
          }

          // Sleep for approximately half a slot
          await sleep(MS_PER_SLOT / 2);
        }

        throw new Error(
          `Unable to obtain a new blockhash after ${Date.now() - startTime}ms`,
        );
      }

      /**
       * Simulate a transaction
       */
      async simulateTransaction(
        transaction: Transaction,
        signers?: Array<Account>,
      ): Promise<RpcResponseAndContext<SimulatedTransactionResponse>> {
        if (transaction.nonceInfo && signers) {
          transaction.sign(...signers);
        } else {
          let disableCache = this._disableBlockhashCaching;
          for (;;) {
            transaction.recentBlockhash = await this._recentBlockhash(disableCache);

            if (!signers) break;

            transaction.sign(...signers);
            if (!transaction.signature) {
              throw new Error('!signature'); // should never happen
            }

            // If the signature of this transaction has not been seen before with the
            // current recentBlockhash, all done.
            const signature = transaction.signature.toString('base64');
            if (
              !this._blockhashInfo.simulatedSignatures.includes(signature) &&
              !this._blockhashInfo.transactionSignatures.includes(signature)
            ) {
              this._blockhashInfo.simulatedSignatures.push(signature);
              break;
            } else {
              disableCache = true;
            }
          }
        }

        const signData = transaction.serializeMessage();
        const wireTransaction = transaction._serialize(signData);
        const encodedTransaction = bs58.encode(wireTransaction);
        const args = [encodedTransaction];

        if (signers) {
          args.push({sigVerify: true});
        }

        const unsafeRes = await this._rpcRequest('simulateTransaction', args);
        const res = SimulatedTransactionResponseValidator(unsafeRes);
        if (res.error) {
          throw new Error('failed to simulate transaction: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        assert(res.result);
        return res.result;
      }

      /**
       * Sign and send a transaction
       */
      async sendTransaction(
        transaction: Transaction,
        signers: Array<Account>,
        options?: SendOptions,
      ): Promise<TransactionSignature> {
        if (transaction.nonceInfo) {
          transaction.sign(...signers);
        } else {
          let disableCache = this._disableBlockhashCaching;
          for (;;) {
            transaction.recentBlockhash = await this._recentBlockhash(disableCache);
            transaction.sign(...signers);
            if (!transaction.signature) {
              throw new Error('!signature'); // should never happen
            }

            // If the signature of this transaction has not been seen before with the
            // current recentBlockhash, all done.
            const signature = transaction.signature.toString('base64');
            if (!this._blockhashInfo.transactionSignatures.includes(signature)) {
              this._blockhashInfo.transactionSignatures.push(signature);
              break;
            } else {
              disableCache = true;
            }
          }
        }

        const wireTransaction = transaction.serialize();
        return await this.sendRawTransaction(wireTransaction, options);
      }

      /**
       * @private
       */
      async validatorExit(): Promise<boolean> {
        const unsafeRes = await this._rpcRequest('validatorExit', []);
        const res = jsonRpcResult('boolean')(unsafeRes);
        if (res.error) {
          throw new Error('validator exit failed: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Send a transaction that has already been signed and serialized into the
       * wire format
       */
      async sendRawTransaction(
        rawTransaction: Buffer | Uint8Array | Array<number>,
        options: ?SendOptions,
      ): Promise<TransactionSignature> {
        const encodedTransaction = bs58.encode(toBuffer(rawTransaction));
        const result = await this.sendEncodedTransaction(
          encodedTransaction,
          options,
        );
        return result;
      }

      /**
       * Send a transaction that has already been signed, serialized into the
       * wire format, and encoded as a base58 string
       */
      async sendEncodedTransaction(
        encodedTransaction: string,
        options: ?SendOptions,
      ): Promise<TransactionSignature> {
        const args = [encodedTransaction];
        const skipPreflight = options && options.skipPreflight;
        if (skipPreflight) args.push({skipPreflight});
        const unsafeRes = await this._rpcRequest('sendTransaction', args);
        const res = SendTransactionRpcResult(unsafeRes);
        if (res.error) {
          throw new Error('failed to send transaction: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        assert(res.result);
        return res.result;
      }

      /**
       * @private
       */
      _wsOnOpen() {
        this._rpcWebSocketConnected = true;
        this._updateSubscriptions();
      }

      /**
       * @private
       */
      _wsOnError(err: Error) {
        console.error('ws error:', err.message);
      }

      /**
       * @private
       */
      _wsOnClose() {
        this._rpcWebSocketConnected = false;
        this._resetSubscriptions();
      }

      /**
       * @private
       */
      async _subscribe<SubInfo: {subscriptionId: ?SubscriptionId}, RpcArgs>(
        sub: SubInfo,
        rpcMethod: string,
        rpcArgs: RpcArgs,
      ) {
        if (sub.subscriptionId == null) {
          sub.subscriptionId = 'subscribing';
          try {
            const id = await this._rpcWebSocket.call(rpcMethod, rpcArgs);
            if (sub.subscriptionId === 'subscribing') {
              // eslint-disable-next-line require-atomic-updates
              sub.subscriptionId = id;
            }
          } catch (err) {
            if (sub.subscriptionId === 'subscribing') {
              // eslint-disable-next-line require-atomic-updates
              sub.subscriptionId = null;
            }
            console.error(`${rpcMethod} error for argument`, rpcArgs, err.message);
          }
        }
      }

      /**
       * @private
       */
      async _unsubscribe<SubInfo: {subscriptionId: ?SubscriptionId}>(
        sub: SubInfo,
        rpcMethod: string,
      ) {
        const subscriptionId = sub.subscriptionId;
        if (subscriptionId != null && typeof subscriptionId != 'string') {
          const unsubscribeId: number = subscriptionId;
          try {
            await this._rpcWebSocket.call(rpcMethod, [unsubscribeId]);
          } catch (err) {
            console.error(`${rpcMethod} error:`, err.message);
          }
        }
      }

      /**
       * @private
       */
      _resetSubscriptions() {
        (Object.values(this._accountChangeSubscriptions): any).forEach(
          s => (s.subscriptionId = null),
        );
        (Object.values(this._programAccountChangeSubscriptions): any).forEach(
          s => (s.subscriptionId = null),
        );
        (Object.values(this._signatureSubscriptions): any).forEach(
          s => (s.subscriptionId = null),
        );
        (Object.values(this._slotSubscriptions): any).forEach(
          s => (s.subscriptionId = null),
        );
        (Object.values(this._rootSubscriptions): any).forEach(
          s => (s.subscriptionId = null),
        );
      }

      /**
       * @private
       */
      _updateSubscriptions() {
        const accountKeys = Object.keys(this._accountChangeSubscriptions).map(
          Number,
        );
        const programKeys = Object.keys(
          this._programAccountChangeSubscriptions,
        ).map(Number);
        const slotKeys = Object.keys(this._slotSubscriptions).map(Number);
        const signatureKeys = Object.keys(this._signatureSubscriptions).map(Number);
        const rootKeys = Object.keys(this._rootSubscriptions).map(Number);
        if (
          accountKeys.length === 0 &&
          programKeys.length === 0 &&
          slotKeys.length === 0 &&
          signatureKeys.length === 0 &&
          rootKeys.length === 0
        ) {
          this._rpcWebSocket.close();
          return;
        }

        if (!this._rpcWebSocketConnected) {
          this._resetSubscriptions();
          this._rpcWebSocket.connect();
          return;
        }

        for (let id of accountKeys) {
          const sub = this._accountChangeSubscriptions[id];
          this._subscribe(
            sub,
            'accountSubscribe',
            this._buildArgs([sub.publicKey], sub.commitment, 'binary64'),
          );
        }

        for (let id of programKeys) {
          const sub = this._programAccountChangeSubscriptions[id];
          this._subscribe(
            sub,
            'programSubscribe',
            this._buildArgs([sub.programId], sub.commitment, 'binary64'),
          );
        }

        for (let id of slotKeys) {
          const sub = this._slotSubscriptions[id];
          this._subscribe(sub, 'slotSubscribe', []);
        }

        for (let id of signatureKeys) {
          const sub = this._signatureSubscriptions[id];
          this._subscribe(
            sub,
            'signatureSubscribe',
            this._buildArgs([sub.signature], sub.commitment),
          );
        }

        for (let id of rootKeys) {
          const sub = this._rootSubscriptions[id];
          this._subscribe(sub, 'rootSubscribe', []);
        }
      }

      /**
       * @private
       */
      _wsOnAccountNotification(notification: Object) {
        const res = AccountNotificationResult(notification);
        if (res.error) {
          throw new Error('account notification failed: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        const keys = Object.keys(this._accountChangeSubscriptions).map(Number);
        for (let id of keys) {
          const sub = this._accountChangeSubscriptions[id];
          if (sub.subscriptionId === res.subscription) {
            const {result} = res;
            const {value, context} = result;

            sub.callback(
              {
                executable: value.executable,
                owner: new PublicKey(value.owner),
                lamports: value.lamports,
                data: Buffer.from(value.data, 'base64'),
              },
              context,
            );
            return true;
          }
        }
      }

      /**
       * Register a callback to be invoked whenever the specified account changes
       *
       * @param publicKey Public key of the account to monitor
       * @param callback Function to invoke whenever the account is changed
       * @param commitment Specify the commitment level account changes must reach before notification
       * @return subscription id
       */
      onAccountChange(
        publicKey: PublicKey,
        callback: AccountChangeCallback,
        commitment: ?Commitment,
      ): number {
        const id = ++this._accountChangeSubscriptionCounter;
        this._accountChangeSubscriptions[id] = {
          publicKey: publicKey.toBase58(),
          callback,
          commitment,
          subscriptionId: null,
        };
        this._updateSubscriptions();
        return id;
      }

      /**
       * Deregister an account notification callback
       *
       * @param id subscription id to deregister
       */
      async removeAccountChangeListener(id: number): Promise<void> {
        if (this._accountChangeSubscriptions[id]) {
          const subInfo = this._accountChangeSubscriptions[id];
          delete this._accountChangeSubscriptions[id];
          await this._unsubscribe(subInfo, 'accountUnsubscribe');
          this._updateSubscriptions();
        } else {
          throw new Error(`Unknown account change id: ${id}`);
        }
      }

      /**
       * @private
       */
      _wsOnProgramAccountNotification(notification: Object) {
        const res = ProgramAccountNotificationResult(notification);
        if (res.error) {
          throw new Error(
            'program account notification failed: ' + res.error.message,
          );
        }
        assert(typeof res.result !== 'undefined');
        const keys = Object.keys(this._programAccountChangeSubscriptions).map(
          Number,
        );
        for (let id of keys) {
          const sub = this._programAccountChangeSubscriptions[id];
          if (sub.subscriptionId === res.subscription) {
            const {result} = res;
            const {value, context} = result;

            sub.callback(
              {
                accountId: value.pubkey,
                accountInfo: {
                  executable: value.account.executable,
                  owner: new PublicKey(value.account.owner),
                  lamports: value.account.lamports,
                  data: Buffer.from(value.account.data, 'base64'),
                },
              },
              context,
            );
            return true;
          }
        }
      }

      /**
       * Register a callback to be invoked whenever accounts owned by the
       * specified program change
       *
       * @param programId Public key of the program to monitor
       * @param callback Function to invoke whenever the account is changed
       * @param commitment Specify the commitment level account changes must reach before notification
       * @return subscription id
       */
      onProgramAccountChange(
        programId: PublicKey,
        callback: ProgramAccountChangeCallback,
        commitment: ?Commitment,
      ): number {
        const id = ++this._programAccountChangeSubscriptionCounter;
        this._programAccountChangeSubscriptions[id] = {
          programId: programId.toBase58(),
          callback,
          commitment,
          subscriptionId: null,
        };
        this._updateSubscriptions();
        return id;
      }

      /**
       * Deregister an account notification callback
       *
       * @param id subscription id to deregister
       */
      async removeProgramAccountChangeListener(id: number): Promise<void> {
        if (this._programAccountChangeSubscriptions[id]) {
          const subInfo = this._programAccountChangeSubscriptions[id];
          delete this._programAccountChangeSubscriptions[id];
          await this._unsubscribe(subInfo, 'programUnsubscribe');
          this._updateSubscriptions();
        } else {
          throw new Error(`Unknown program account change id: ${id}`);
        }
      }

      /**
       * @private
       */
      _wsOnSlotNotification(notification: Object) {
        const res = SlotNotificationResult(notification);
        if (res.error) {
          throw new Error('slot notification failed: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        const {parent, slot, root} = res.result;
        const keys = Object.keys(this._slotSubscriptions).map(Number);
        for (let id of keys) {
          const sub = this._slotSubscriptions[id];
          if (sub.subscriptionId === res.subscription) {
            sub.callback({
              parent,
              slot,
              root,
            });
            return true;
          }
        }
      }

      /**
       * Register a callback to be invoked upon slot changes
       *
       * @param callback Function to invoke whenever the slot changes
       * @return subscription id
       */
      onSlotChange(callback: SlotChangeCallback): number {
        const id = ++this._slotSubscriptionCounter;
        this._slotSubscriptions[id] = {
          callback,
          subscriptionId: null,
        };
        this._updateSubscriptions();
        return id;
      }

      /**
       * Deregister a slot notification callback
       *
       * @param id subscription id to deregister
       */
      async removeSlotChangeListener(id: number): Promise<void> {
        if (this._slotSubscriptions[id]) {
          const subInfo = this._slotSubscriptions[id];
          delete this._slotSubscriptions[id];
          await this._unsubscribe(subInfo, 'slotUnsubscribe');
          this._updateSubscriptions();
        } else {
          throw new Error(`Unknown slot change id: ${id}`);
        }
      }

      _buildArgs(
        args: Array<any>,
        override: ?Commitment,
        encoding?: 'jsonParsed' | 'binary64',
      ): Array<any> {
        const commitment = override || this._commitment;
        if (commitment || encoding) {
          let options: any = {};
          if (encoding) {
            options.encoding = encoding;
          }
          if (commitment) {
            options.commitment = commitment;
          }
          args.push(options);
        }
        return args;
      }

      /**
       * @private
       */
      _wsOnSignatureNotification(notification: Object) {
        const res = SignatureNotificationResult(notification);
        if (res.error) {
          throw new Error('signature notification failed: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        const keys = Object.keys(this._signatureSubscriptions).map(Number);
        for (let id of keys) {
          const sub = this._signatureSubscriptions[id];
          if (sub.subscriptionId === res.subscription) {
            // Signatures subscriptions are auto-removed by the RPC service so
            // no need to explicitly send an unsubscribe message
            delete this._signatureSubscriptions[id];
            this._updateSubscriptions();
            sub.callback(res.result.value, res.result.context);
            return;
          }
        }
      }

      /**
       * Register a callback to be invoked upon signature updates
       *
       * @param signature Transaction signature string in base 58
       * @param callback Function to invoke on signature notifications
       * @param commitment Specify the commitment level signature must reach before notification
       * @return subscription id
       */
      onSignature(
        signature: TransactionSignature,
        callback: SignatureResultCallback,
        commitment: ?Commitment,
      ): number {
        const id = ++this._signatureSubscriptionCounter;
        this._signatureSubscriptions[id] = {
          signature,
          callback,
          commitment,
          subscriptionId: null,
        };
        this._updateSubscriptions();
        return id;
      }

      /**
       * Deregister a signature notification callback
       *
       * @param id subscription id to deregister
       */
      async removeSignatureListener(id: number): Promise<void> {
        if (this._signatureSubscriptions[id]) {
          const subInfo = this._signatureSubscriptions[id];
          delete this._signatureSubscriptions[id];
          await this._unsubscribe(subInfo, 'signatureUnsubscribe');
          this._updateSubscriptions();
        } else {
          throw new Error(`Unknown signature result id: ${id}`);
        }
      }

      /**
       * @private
       */
      _wsOnRootNotification(notification: Object) {
        const res = RootNotificationResult(notification);
        if (res.error) {
          throw new Error('root notification failed: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        const root = res.result;
        const keys = Object.keys(this._rootSubscriptions).map(Number);
        for (let id of keys) {
          const sub = this._rootSubscriptions[id];
          if (sub.subscriptionId === res.subscription) {
            sub.callback(root);
            return true;
          }
        }
      }

      /**
       * Register a callback to be invoked upon root changes
       *
       * @param callback Function to invoke whenever the root changes
       * @return subscription id
       */
      onRootChange(callback: RootChangeCallback): number {
        const id = ++this._rootSubscriptionCounter;
        this._rootSubscriptions[id] = {
          callback,
          subscriptionId: null,
        };
        this._updateSubscriptions();
        return id;
      }

      /**
       * Deregister a root notification callback
       *
       * @param id subscription id to deregister
       */
      async removeRootChangeListener(id: number): Promise<void> {
        if (this._rootSubscriptions[id]) {
          const subInfo = this._rootSubscriptions[id];
          delete this._rootSubscriptions[id];
          await this._unsubscribe(subInfo, 'rootUnsubscribe');
          this._updateSubscriptions();
        } else {
          throw new Error(`Unknown root change id: ${id}`);
        }
      }
    }