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Node.js server for my online Paco Sako single-page distributed web app
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README.md

README

This is the REST API server for the online Paco Ŝako chess variation front-end provided by the paco-sako package. The server stores game data in a SQLite3 database and exposes interfaces for immediate queries, long-polling, and POST updates. The listening port is configurable and HTTPS is supported with a certificate file.

Invocation

node ./server.js [PORT]

or

npm start [PORT]

or

npm install --global git+https://jessemcdonald.info/gogs/nybble/paco_sako.git

paco-sako-server [PORT]

Environment Variables

OPENSHIFT_NODEJS_PORT, VCAP_APP_PORT, or PORT

If any of these variables are defined then the first one encountered determines the listening port, overriding any port specified on the command line. The default port is 8765 if no environment variable is defined and no port is given on the command line.

HTTPS_KEY and HTTPS_CERT

If the HTTPS_KEY environment variable is defined then the server operates in HTTPS mode using the key found in the file named by HTTPS_KEY and the certificate found in the file named by HTTPS_CERT. If HTTPS_KEY is set then HTTPS_CERT is also required.

JSON Schema

Most APIs either accept or return a JSON "game data" object with some or all of the following fields:

  • gameId: String. Sixteen hexadecimal characters. The randomly-generated code which uniquely identifies a game.

  • lightName: String. The name of the player controlling the light pieces.

  • darkName: String. The name of the player controlling the dark pieces.

  • moves: Integer. The number of partial or completed turns in the current game. Also the number of times the light player has started a move. (The use of the name moves rather than turns is a historical artifact.)

  • status: String. A short string which describes the current state of the game, for example the current player if the game is ongoing or the winner otherwise. This string appears in the game selection list.

  • timestamp: Integer. The UTC time in milliseconds of the most recent move. Typically the same as the timestamp metadata for the last move in board.past, or the time when the metadata was most recently updated if there are no moves. The timestamp can decrease, for example in response to a player undoing a move.

  • board: Object. An arbitrary JSON object provided by the front-end to describe the current state of the game. The object is not validated by the server at present but it typically includes two fields, past and future, which are arrays of objects respectively representing the moves completed thus far and (in reverse order) any moves which were undone, to support the redo operation. This object is stored in the database as a JSON-encoded string.

  • modified: Integer. The modification time of the record as determined by the server. This is normally a UTC time in milliseconds but the server adjusts the value to ensure that updates have modification times which are strictly greater than any modification times previously stored in the database.

The "metadata" fields are all the fields listed above except board. The board field is potentially large and consequently is omitted from the responses for certain APIs.

Fields which are either NULL or equal to an empty string are not included in game objects returned from the REST APIs.

The following data is stored in the database but not included in any REST API:

  • added: The value of the modified field at the point where the game record was first inserted into the database.

REST APIs

GET /api/games

Returns the list of active games. A game is considered "active" if the timestamp field indicates that either the game was started or the last move was played within the past two weeks according to the server's clock. The successful JSON response consists of two fields, games which is an array of game objects in descending order by their timestamp fields, and modified which is the maximum value of the modified fields of all of the games in the games array, or zero if the array is empty. The objects in the games array include all of the game object fields described above except the board field.

GET /api/games/poll/:afterTime

Parameters:

  • afterTime: Integer. Any record with a modified field less than or equal to this value is excluded from the results.

Equivalent to the GET /api/games API with two exceptions. First, it excludes games with older modified times from the results. Second, if there are no results which match this criteria then the server waits up to one minute for the situation to change before responding with a 204 status code. It is expected that the client will respond to a 204 status by repeating the request. If a game is updated during the waiting period then the server will respond immediately with the new information.

The afterTime parameter will normally match the modified field from the most recent successful response to either GET /api/games or GET /api/games/poll/:afterTime.

GET /api/game/:gameId

Parameters:

  • gameId: String. Identifies the game object to be returned.

On success this API returns the complete game object for the given gameId, which must be a 16-character hexadecimal string. If there is no record matching the given gameId then a 404 status code is returned.

GET /api/meta/:gameId

This API is identical to GET /api/game/:gameId except that the board field is omitted from the response.

GET /api/game/:gameId/poll/:afterTime

Parameters:

  • gameId: String. Identifies the game object to be returned.

  • afterTime: Integer. The response must be a game object with a modified field strictly greater than this value.

Equivalent to the GET /api/game/:gameId API except that if there is no record with a matching gameId or the record has a modified field less than or equal to the afterTime parameter then the server waits up to one minute for the situation to change before responding with a 204 status code. It is expected that the client will respond to a 204 status by repeating the request. If the game is created or updated during the waiting period then the server will respond immediately with the new information. Unlike the non-polling version, this API does not return a 404 status code when the gameId does not exist.

The afterTime parameter will normally match the modified field from the most recent successful response to either GET /api/game/:gameId or GET /api/game/:gameId/poll/:afterTime.

GET /api/meta/:gameId/poll/:afterTime

This API is identical to GET /api/game/:gameId/poll/:afterTime except that the board field is omitted from the response.

POST /api/game/:gameId

Parameters:

  • gameId: String. Identifies the game object to be updated.

The JSON-encoded request body for this API should consist of a subset of a game object which includes the modified field and at least one other field to be updated. The modified field in the request must match the current version of the record in the database for the update to be successful, if such a record exists; this serves as a form of locking to prevent race conditions between multiple clients updating the same game record. The modified field of the new version of the record on success will be determined by the server. If there is no existing version of the record then value of the modified field in the request is not used; however, the field is still required. It is recommended that a modified value of zero be used when initializing a new game since this value is guaranteed not to match any existing game record.

A 400 status will be returned if the request body does not follow the expected schema. If the modified field does not match the modified field in the database and the value of any other field in the request does not match the current version of the data in the database then a 409 response is returned with a message string field describing the error and the modified field from the current version of the record in the database. Otherwise the POST request succeeds with a status code of 200 and the response body consists of a success field with the value true and the modified field of the new version of the record.

POST /api/meta/:gameId

This is an alias for the POST /api/game/:gameId API. Either API can be used to update any field, including board.

Static Files

If a directory named public exists in the current directory then the contents of the public directory are served as static files for any request which does not match one of the REST APIs listed above. This allows this package to serve as a standalone server for both the REST APIs and any client-side resources.