# 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 {DEFAULT_TICKS_PER_SLOT, NUM_TICKS_PER_SECOND} from './timing';
    import {Transaction} from './transaction';
    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';

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

    /**
     * Extra contextual information for RPC responses
     *
     * @typedef {Object} Context
     * @property {number} slot
     */
    type Context = {
      slot: 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
     *   'max':    Query the most recent block which has reached max voter lockout
     *   'recent': Query the most recent block
     *
     * @typedef {'max' | 'recent'} Commitment
     */
    export type Commitment = 'max' | 'recent';

    /**
     * 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} gossip Gossip network address for the node
     * @property {string} 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)
     */
    type ContactInfo = {
      pubkey: string,
      gossip: string,
      tpu: string | null,
      rpc: 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 parameters
     * (see https://docs.solana.com/implemented-proposals/ed_overview)
     *
     * @typedef {Object} Inflation
     * @property {number} foundation
     * @property {number} foundation_term
     * @property {number} initial
     * @property {number} storage
     * @property {number} taper
     * @property {number} terminal
     */
    const GetInflationResult = struct({
      foundation: 'number',
      foundationTerm: 'number',
      initial: 'number',
      storage: 'number',
      taper: 'number',
      terminal: 'number',
    });

    /**
     * EpochInfo parameters
     * (see https://docs.solana.com/terminology#epoch)
     *
     * @typedef {Object} EpochInfo
     * @property {number} epoch
     * @property {number} slotIndex
     * @property {number} slotsInEpoch
     * @property {number} absoluteSlot
     */
    const GetEpochInfoResult = struct({
      epoch: 'number',
      slotIndex: 'number',
      slotsInEpoch: 'number',
      absoluteSlot: 'number',
    });

    /**
     * EpochSchedule parameters
     * (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`
     */
    const GetEpochScheduleResult = struct({
      slotsPerEpoch: 'number',
      leaderScheduleSlotOffset: 'number',
      warmup: 'boolean',
      firstNormalEpoch: 'number',
      firstNormalSlot: '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',
    });

    /**
     * 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 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 "getInflation" message
     */
    const GetInflationRpcResult = struct({
      jsonrpc: struct.literal('2.0'),
      id: 'string',
      error: 'any?',
      result: GetInflationResult,
    });

    /**
     * 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 "getBalance" message
     */
    const GetBalanceAndContextRpcResult = jsonRpcResultAndContext('number?');

    /**
     * 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: 'string',
      rentEpoch: 'number?',
    });

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

    /**
     * @private
     */
    const GetConfirmedSignaturesForAddressRpcResult = jsonRpcResult(
      struct.array(['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,
    });

    /***
     * 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 "confirmTransaction" message
     */
    const ConfirmTransactionAndContextRpcResult = jsonRpcResultAndContext(
      'boolean',
    );

    /**
     * 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({
          pubkey: 'string',
          gossip: 'string',
          tpu: struct.union(['null', 'string']),
          rpc: struct.union(['null', 'string']),
        }),
      ]),
    );

    /**
     * Expected JSON RPC response for the "getVoteAccounts" message
     */
    const GetVoteAccounts = jsonRpcResult(
      struct({
        current: struct.array([
          struct({
            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({
            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.union([
            struct.array(['number']),
            struct({
              accounts: struct.array(['number']),
              data: 'string',
              programIdIndex: 'number',
            }),
          ]),
        ]),
        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({
          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({
          slot: 'number',
          transaction: ConfirmedTransactionResult,
          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 "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,
    };

    /**
     * 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 {?Buffer} data Optional data assigned to the account
     * @property {boolean} executable `true` if this account's data contains a loaded program
     */
    type AccountInfo = {
      executable: boolean,
      owner: PublicKey,
      lamports: number,
      data: Buffer,
    };

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

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

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

    /**
     * @private
     */
    type AccountSubscriptionInfo = {
      publicKey: string, // PublicKey of the account as a base 58 string
      callback: AccountChangeCallback,
      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,
      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,
      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 connection to a fullnode JSON RPC endpoint
     */
    export class Connection {
      _rpcRequest: RpcRequest;
      _rpcWebSocket: RpcWebSocketClient;
      _rpcWebSocketConnected: boolean = false;

      _commitment: ?Commitment;
      _blockhashInfo: {
        recentBlockhash: Blockhash | null,
        seconds: number,
        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,
          seconds: -1,
          transactionSignatures: [],
        };

        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._argsWithCommitment([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 all the account info for the specified public key, return with context
       */
      async getAccountInfoAndContext(
        publicKey: PublicKey,
        commitment: ?Commitment,
      ): Promise<RpcResponseAndContext<AccountInfo | null>> {
        const args = this._argsWithCommitment([publicKey.toBase58()], commitment);
        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: bs58.decode(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 | 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}>>}
       */
      async getProgramAccounts(
        programId: PublicKey,
        commitment: ?Commitment,
      ): Promise<Array<{pubkey: PublicKey, account: AccountInfo}>> {
        const args = this._argsWithCommitment([programId.toBase58()], commitment);
        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: result.pubkey,
            account: {
              executable: result.account.executable,
              owner: new PublicKey(result.account.owner),
              lamports: result.account.lamports,
              data: bs58.decode(result.account.data),
            },
          };
        });
      }

      /**
       * Confirm the transaction identified by the specified signature, return with context
       */
      async confirmTransactionAndContext(
        signature: TransactionSignature,
        commitment: ?Commitment,
      ): Promise<RpcResponseAndContext<boolean>> {
        const args = this._argsWithCommitment([signature], commitment);
        const unsafeRes = await this._rpcRequest('confirmTransaction', args);
        const res = ConfirmTransactionAndContextRpcResult(unsafeRes);
        if (res.error) {
          throw new Error('failed to confirm transaction: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return res.result;
      }

      /**
       * Confirm the transaction identified by the specified signature
       */
      async confirmTransaction(
        signature: TransactionSignature,
        commitment: ?Commitment,
      ): Promise<boolean> {
        return await this.confirmTransactionAndContext(signature, commitment)
          .then(x => x.value)
          .catch(e => {
            throw new Error('failed to confirm transaction: ' + e);
          });
      }

      /**
       * 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._argsWithCommitment([], 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._argsWithCommitment([], 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._argsWithCommitment([], 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._argsWithCommitment([], 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._argsWithCommitment([], 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 Inflation parameters
       */
      async getInflation(commitment: ?Commitment): Promise<GetInflationRpcResult> {
        const args = this._argsWithCommitment([], commitment);
        const unsafeRes = await this._rpcRequest('getInflation', args);
        const res = GetInflationRpcResult(unsafeRes);
        if (res.error) {
          throw new Error('failed to get inflation: ' + res.error.message);
        }
        assert(typeof res.result !== 'undefined');
        return GetInflationResult(res.result);
      }

      /**
       * Fetch the Epoch Info parameters
       */
      async getEpochInfo(commitment: ?Commitment): Promise<GetEpochInfoRpcResult> {
        const args = this._argsWithCommitment([], 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<GetEpochScheduleRpcResult> {
        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 minimum balance needed to exempt an account of `dataLength`
       * size from rent
       */
      async getMinimumBalanceForRentExemption(
        dataLength: number,
        commitment: ?Commitment,
      ): Promise<number> {
        const args = this._argsWithCommitment([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._argsWithCommitment([], 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 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 = GetConfirmedBlockRpcResult(unsafeRes);
        if (result.error) {
          throw new Error('failed to get confirmed block: ' + result.error.message);
        }
        assert(typeof result.result !== 'undefined');
        if (!result.result) {
          throw new Error('Confirmed block ' + slot + ' not found');
        }
        return {
          blockhash: new PublicKey(result.result.blockhash).toString(),
          previousBlockhash: new PublicKey(
            result.result.previousBlockhash,
          ).toString(),
          parentSlot: result.result.parentSlot,
          transactions: result.result.transactions.map(result => {
            return {
              transaction: Transaction.fromRpcResult(result.transaction),
              meta: result.meta,
            };
          }),
          rewards: result.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;
        }

        return {
          slot: result.slot,
          transaction: Transaction.fromRpcResult(result.transaction),
          meta: result.meta,
        };
      }

      /**
       * 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;
      }

      /**
       * 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,
        commitment: ?Commitment,
      ): Promise<TransactionSignature> {
        const args = this._argsWithCommitment([to.toBase58(), amount], commitment);
        const unsafeRes = await this._rpcRequest('requestAirdrop', args);
        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;
      }

      /**
       * Sign and send a transaction
       */
      async sendTransaction(
        transaction: Transaction,
        ...signers: Array<Account>
      ): Promise<TransactionSignature> {
        if (transaction.nonceInfo) {
          transaction.sign(...signers);
        } else {
          for (;;) {
            // Attempt to use a recent blockhash for up to 30 seconds
            const seconds = new Date().getSeconds();
            if (
              this._blockhashInfo.recentBlockhash != null &&
              this._blockhashInfo.seconds < seconds + 30
            ) {
              transaction.recentBlockhash = this._blockhashInfo.recentBlockhash;
              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();
              if (!this._blockhashInfo.transactionSignatures.includes(signature)) {
                this._blockhashInfo.transactionSignatures.push(signature);
                if (this._disableBlockhashCaching) {
                  this._blockhashInfo.seconds = -1;
                }
                break;
              }
            }

            // Fetch a new blockhash
            let attempts = 0;
            const startTime = Date.now();
            for (;;) {
              const {blockhash} = await this.getRecentBlockhash();

              if (this._blockhashInfo.recentBlockhash != blockhash) {
                this._blockhashInfo = {
                  recentBlockhash: blockhash,
                  seconds: new Date().getSeconds(),
                  transactionSignatures: [],
                };
                break;
              }
              if (attempts === 50) {
                throw new Error(
                  `Unable to obtain a new blockhash after ${
                    Date.now() - startTime
                  }ms`,
                );
              }

              // Sleep for approximately half a slot
              await sleep((500 * DEFAULT_TICKS_PER_SLOT) / NUM_TICKS_PER_SECOND);

              ++attempts;
            }
          }
        }

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

      /**
       * @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>,
      ): Promise<TransactionSignature> {
        const encodedTransaction = bs58.encode(toBuffer(rawTransaction));
        const result = await this.sendEncodedTransaction(encodedTransaction);
        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,
      ): Promise<TransactionSignature> {
        const unsafeRes = await this._rpcRequest('sendTransaction', [
          encodedTransaction,
        ]);
        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', [sub.publicKey]);
        }

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

        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', [sub.signature]);
        }

        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: bs58.decode(value.data),
              },
              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
       * @return subscription id
       */
      onAccountChange(
        publicKey: PublicKey,
        callback: AccountChangeCallback,
      ): number {
        const id = ++this._accountChangeSubscriptionCounter;
        this._accountChangeSubscriptions[id] = {
          publicKey: publicKey.toBase58(),
          callback,
          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: bs58.decode(value.account.data),
                },
              },
              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
       * @return subscription id
       */
      onProgramAccountChange(
        programId: PublicKey,
        callback: ProgramAccountChangeCallback,
      ): number {
        const id = ++this._programAccountChangeSubscriptionCounter;
        this._programAccountChangeSubscriptions[id] = {
          programId: programId.toBase58(),
          callback,
          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}`);
        }
      }

      _argsWithCommitment(args: Array<any>, override: ?Commitment): Array<any> {
        const commitment = override || this._commitment;
        if (commitment) {
          args.push({commitment});
        }
        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
       * @return subscription id
       */
      onSignature(
        signature: TransactionSignature,
        callback: SignatureResultCallback,
      ): number {
        const id = ++this._signatureSubscriptionCounter;
        this._signatureSubscriptions[id] = {
          signature,
          callback,
          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}`);
        }
      }
    }