# Server API


## Auspice client requests

The Auspice server handles requests to 3 API endpoints made by the Auspice client:
* `/charon/getAvailable` (returns a list of available datasets and narratives)
* `/charon/getDataset` (returns the requested dataset)
* `/charon/getNarrative` (returns the requested narrative)



### `/charon/getAvailable`

**URL query arguments:**

* `prefix` (optional) - the pathname of the requesting page in Auspice.
The `getAvailable` handler can use this to respond according appropriately.
Unused by the default Auspice handler.

**JSON Response (on success):**

```json
{
  "datasets": [
    {
      "request": "[required] The pathname of a valid dataset. \
          Will become the prefix of the getDataset request.",
      "buildUrl": "[optional] A URL to display in the sidebar representing \
          the build used to generate this analysis.",
      "secondTreeOptions": "[optional] A list of requests which should \
          appear as potential second-trees in the sidebar dropdown"
    },
    ...
  ],
  "narratives": [
    {"request": "URL of a narrative. Will become the prefix in a getNarrative request"},
    ...
  ]
}
```

Failure to return a valid JSON will result in a warning notification shown in Auspice.

### `/charon/getDataset`

**URL query arguments:**

* `prefix` (required) - the pathname of the requesting page in Auspice. Use this to determine which dataset to return.
* `type` (optional) -- if specified, then the request is for an additional file (e.g. "tip-frequencies"), not the main dataset.

**JSON Response (on success):**

The JSON response depends on the file-type being requested.

If the type is not specified, i.e. we're requesting the "main" dataset JSON then [see this JSON schema](https://github.com/nextstrain/augur/blob/master/augur/data/schema-export-v2.json).
Note that the Auspice client _cannot_ process v1 (meta / tree) JSONs -- [see below](server/api.md#importing-code-from-auspice) for how to convert these.

Alternative file type reponses are to be documented.

**Alternative responses:**

A `204` reponse will cause Auspice to show its splash page listing the available datasets & narratives.
Any other non-200 reponse behaves similarly but also displays a large "error" message indicating that the dataset was not valid.



### `/charon/getNarrative`

**URL query arguments:**

* `prefix` (required) - the pathname of the requesting page in Auspice. Use this to determine which narrative to return.
* `type` (optional) - the format of the data returned (see below for more information).
Current valid values are "json" and "md".
If no type is specified the server will use "json" as a default (for backwards compatibility reasons).
Requests to this API from the Auspice client are made with `type=md.

**Response (on success):**

The response depends on the `type` specified in the query.

If a markdown format is requested, then the narrative file is sent to the client unmodified to be parsed on the client.

If a JSON is requested then the narrative file is parsed into JSON format by the server.
For Auspice versions prior to v2.18 this was the only expected behavior.
The transformation from markdown (i.e. the narrative file itself) to JSON is via the `parseNarrativeFile()` function (see below for how this is exported from Auspice for use in other servers).
Here, roughly, is the code we use in the auspice server for this transformation:

```js
const fileContents = fs.readFileSync(pathName, 'utf8');
if (type === "json") {
  const blocks = parseNarrative(fileContents);
  res.send(JSON.stringify(blocks).replace(/</g, '\\u003c'));
}
```

> While the Auspice client (from v2.18 onwards) always requests the `type=md`, it will attempt to parse the response as JSON if markdown parsing fails, in an effort to remain backwards compatable with servers which may be using an earlier API.

---

## Supplying custom handlers to the Auspice server

The provided Auspice servers -- i.e. `auspice view` and `auspice develop` both have a `--handlers <JS>` option which allows you to define your own handlers.
The provided JavaScript file must export three functions, each of which handles one of the GET requests described above and must respond accordingly (see above for details).

| function name | arguments | API endpoint |
| ----------    | --------- | ----------  |
| getAvailable | req, res | /charon/getAvailable |
| getDataset   | req, res | /charon/getDataset |
| getNarrative | req, res | /charon/getNarrative |

For information about the `req` and `res` arguments see the express documentation for the [request object](https://expressjs.com/en/api.html#req) and [response object](https://expressjs.com/en/api.html#res), respectively.

You can see [nextstrain.org](https://nextstrain.org)'s implementation of these handlers [here](https://github.com/nextstrain/nextstrain.org/blob/master/server.js).

Here's a pseudocode example of an implementation for the `getAvailable` handler which may help understanding:

```js
const getAvailable = (req, res) => {
  try {
    /* collect available data */
    res.json(data);
  } catch (err) {
    const errorMessage = `error message to display in client`;
    console.log(errorMessage); /* printed by the server, not the client */
    return res.status(500).type("text/plain").send(errorMessage);
  }
};
```

---

## Importing code from Auspice

The servers included in Auspice contain lots of useful code which you may want to use to either write your own handlers or entire servers.
For instance, the code to convert v1 dataset JSONs to v2 JSONs (which the client requires) can be imported into your code so you don't have to reinvent the wheel!


Currently
```js
const auspice = require("auspice");
```
returns an object with two properties:

### `convertFromV1`

**Signature:**
```js
const v2json = convertFromV1({tree, meta})
```
where `tree` is the v1 tree JSON, and `meta` the v1 meta JSON.

**Returns:**

An object representing the v2 JSON [defined by this schema](https://github.com/nextstrain/augur/blob/master/augur/data/schema-export-v2.json).



### `parseNarrativeFile`

> This function is deprecated as of vXXX.
You can now send the untransformed contents of the narrative file (markdown) for client-side parsing.
See [above](#charon-getnarrative) for more details.

**Signature:**

```js
const blocks = parseNarrativeFile(fileContents);
```
where `fileContents` is a string representation of the narrative Markdown file.

**Returns:**

An array of objects, each entry representing a different narrative "block" or "page".
Each object has properties
* `__html` -- the HTML to render in the sidebar to form the narrative
* `dataset` -- the dataset associated with this block
* `query` -- the query associated with this block

