Monoxide-Versioning

Versioning caching layer for the Monoxide ReST server.

This module is intended as a rapid-polling via ReST system where a serve record can be either the same version as before or mismatched. In the former case this module returns only a truncated version of the record (containing only _id + __v) rather than the whole record.

This module operates as a middleware layer which performs two actions:

• Checks if an incoming request contains a version string (by default ?__v=<SOMETHING>). If it does it only returns a new version of the document if the version requested is older than the server one.
• Inserts itself as a late-call middleware layer item which updates its own cache.

var app = express();
var port = 8181;
app.use(expressLogger);
app.use(bodyParser.json());
app.set('log.indent', '      ');
 
// Add middleware as an express chain
app.get('/api/users/:id', monoxideVersioning(), monoxide.express.get('users'));

Any request to /api/users/1234 can take an optional __v query parameter. If this matches a truncated version of the document is returned (containing only _id + __v). If the version mismatches the entire document is returned.

API

This module exposes a single function-factory which is designed to slot into the ExpressJS middleware chain. It accepts the following options:

Option	Type	Description
idField	function	Function used to obtain the ID from the express req object. This defaults to using req.params.id
versionField	function	Function used to obtain the requested version from the express req object. This defaults to using req.query.__v
assumeVersion	number	What value to assume when no version is explicitly passed. Set this to undefined to always return the full payload
hasher	function	Function that should return a string hash of what we need to hash against. This is usually the query + params of req
hashGet	function	Hash getting function to be called as (hash, cb). Defaults to the internal in-memory storage
hashSet	function	Hash setting function to be called as (hash, expire, cb). Defaults to the internal in-memory storage
hashRemove	function	Hash removal function to be called as (hash, cb). Defaults to the internal in-memory storage
hashClean	function	Hash cleaning function to be called as (cb). Defaults to the internal in-memory storage
hashExpire	number	The time in milliseconds a hash should expire. Defaults to 1 hour
versionedResponse	function	Function which should respond to Express if a hashed version is detected
model	string or function	The name of the current model to query against in options.invalidates. If this is a function it is run ONCE when the factory is invoked and its response used in all future calls. Defaults to a function which tries to match the model against /api/<MODEL>/:id
invalidates	function	Function which should determine if an incoming request invalidates the cache. Called as (req, res, id, version, cb). Defaults to pulling the record by its ID and checking its version if options.model is specified, otherwise uses req.method != 'GET'