Long polling server skeleton

node-long-poll-1.js

/**
 * Module import
 */
var express = require('express');
    
/**
 * Port the server listens on
 */
var port = 3000;

/**
 * User event map.
 * 
 * events[username] = [ event1, event2, ... ]
 */
var events = {}

/**
 * The request dispatcher
 */
var app = express.createServer();

/**
 * GET handler for retrieving events for the user.
 * The username is required and the timestamp parameter
 * is optional.
 *
 * Example: GET /?user=joe&timestamp=1296564580384
 */
app.get('/', function(req, res) {
    console.log('get');    
    res.send('get\n', 200);
    res.end();
});

/** 
 * POST handler for adding a new event for the user.
 * The user and the type parameters are required. 
 * The data object is in the body.
 */
app.post('/', function(req, res) {
    console.log('post');
    res.send('post\n', 200);
    res.end();
});

// start the server
app.listen(port);
console.log("Server started on port " + port);

node-long-poll-2.js

/**
 * Module import
 */
var express = require('express'),
    url = require('url');
    
/**
 * Port the server listens on
 */
var port = 3000;

/**
 * User event map
 * 
 * events[user] = [ event1, event2, ... ]
 */
var events = {}

/**
 * The request dispatcher
 */
var app = express.createServer();

/**
 * Returns the current time in milliseconds from 1 Jan 1970, 00:00
 */
function currentTimestamp() {
    return new Date().getTime();
}

/**
 * Helper function for logging a debug message
 *
 * @param String user    - the username
 * @param int requestId  - the request id (optional)
 * @param String message - the message
 */
function debug(user, requestId, message) {
    if (message) {
        console.log("["+user+"/"+requestId+"] " + message);        
    } else {
        console.log("["+user+"] " + requestId);                
    }
}

/**
 * Adds a new event 'type' and optional 'data' for 
 * the user. 
 *
 * @param String user - the username
 * @param String type - the event type
 * @param Object data - an optional data object
 */
function addEvent(user, type, data) {
    if (!events[user]) 
        events[user] = [];
        
    var event = {
        type : type, 
        timestamp : currentTimestamp()
    }
    if (data) 
        event.data = data;
        
    events[user].push(event);
    debug(user, "P", "added " + JSON.stringify(event));
}

/**
 * Checks for all pending requests for the user
 * if an event is available. If an event is 
 * available it is sent to the client and the 
 * connection is closed.
 *
 * @param String user - the username
 */
function notify(user) {
    debug(user, "P", "notify");
}

/**
 * GET handler for retrieving events for the user.
 * The username is required and the timestamp parameter
 * is optional.
 *
 * Example: GET /?user=joe&timestamp=1296564580384
 */
app.get('/', function(req, res) {
    var u = url.parse(req.url, true);

    if (u.query && u.query.user && events[u.query.user]) {
        var msg = "events: " + events[u.query.user].length;
        debug(u.query.user, msg);
        res.send(msg+"\n", 200);
    }
});

/** 
 * POST handler for adding a new event for the user.
 * The user and the type parameters are required. 
 * The data object is in the body.
 */
app.post('/', function(req, res) {
    var u = url.parse(req.url, true);
    
    // check for bad request
    if (!u.query || !u.query.user || !u.query.type) {
        res.send('', 400);
        return;
    }
    
    // extract the parameters
    var user = u.query.user,
        type = u.query.type,
        data = u.data;
        
    // add the event 
    addEvent(user, type, data);
    
    // notify pending requests
    notify(user);    
    
    // send 200 OK
    res.send('', 200);
});

// start the server
app.listen(port);
console.log("Server started on port " + port);

node-long-poll-3.js

/**
 * Module import
 */
var express = require('express'),
    url = require('url');
    
/**
 * Port the server listens on
 */
var port = 3000;

/**
 * User event map
 * 
 * events[user] = [ event1, event2, ... ]
 */
var events = {}

/**
 * Maximum age of events in seconds
 */
var maxAge = 60;

/**
 * Global counter for unique ids
 */
var lastRequestId = 0;

/**
 * The request dispatcher
 */
var app = express.createServer();

/**
 * Helper function for compacting an array by removing
 * all null values. 
 *
 * @param Array arr - the input array
 * @return Array A new array with all the non-null values from 'arr'
 */
function compact(arr) {
    if (!arr) return null;
    var i, data = [];
    for (i=0; i < arr.length; i++) {
        if (arr[i]) data.push(arr[i]);
    }
    return data;
}

/**
 * Returns the current time in milliseconds from 1 Jan 1970, 00:00
 */
function currentTimestamp() {
    return new Date().getTime();
}

/**
 * Helper function for logging a debug message
 *
 * @param String user    - the username
 * @param int requestId  - the request id (optional)
 * @param String message - the message
 */
function debug(user, requestId, message) {
    if (message) {
        console.log("["+user+"/"+requestId+"] " + message);        
    } else {
        console.log("["+user+"] " + requestId);                
    }
}

/**
 * Adds a new event 'type' and optional 'data' for 
 * the user. 
 *
 * @param String user - the username
 * @param String type - the event type
 * @param Object data - an optional data object
 */
function addEvent(user, type, data) {
    if (!events[user]) 
        events[user] = [];
        
    var event = {
        type : type, 
        timestamp : currentTimestamp()
    }
    if (data) 
        event.data = data;
        
    events[user].push(event);
    debug(user, "P", "added " + JSON.stringify(event));
}

/**
 * Returns the next event for the user.
 *
 * The next event is the first (oldest) event after the 
 * the 'timestamp'. If 'timestamp' is omitted the oldest 
 * event which has not expired is returned.
 *
 * The 'timestamp' parameter represents the last event
 * the caller has seen and the function returns the 
 * next event. 
 *
 * While iterating over the events the function also
 * expires events which are older than maxAge seconds.
 *
 * @param String user   - the username
 * @param int timestamp - the timestamp of the last event
 * @returns Object      - an event or null
 */
function nextEvent(user, timestamp) {
    if (!events[user]) return null;
    if (!timestamp) timestamp = 0;
    
    // - loop over the events for the user
    // - timeout events older than maxAge seconds
    // - return the oldest event with a timestamp 
    //   greater than 'timestamp'
    var event, i;
    var minTimestamp = currentTimestamp() - maxAge * 1000;
    for(i=0; i < events[user].length; i++) {
        event = events[user][i];
        
        // expire event?
        if (event.timestamp < minTimestamp) {
            debug(user, "expired " + JSON.stringify(event));
            events[user][i] = null;
            continue;
        } 
        
        // next event?
        if (event.timestamp > timestamp) {
            break;
        }
    }
    
    // compact the event array
    events[user] = compact(events[user]);
    
    // return the event
    return event;
}

/**
 * Checks for all pending requests for the user
 * if an event is available. If an event is 
 * available it is sent to the client and the 
 * connection is closed.
 *
 * @param String user - the username
 */
function notify(user) {
    debug(user, "P", "notify");
}

/**
 * Pauses the current request for the user and
 * stores the request and response object in 
 * the list of pending requests for the user
 *
 * @param String user      - the username
 * @param String timestamp - the timestamp filter of the request
 * @param Object req       - the request
 * @param Object res       - the response
 * @param int requestId    - the unique request id
 */
function pause(user, timestamp, req, res, requestId) {
    debug(user, requestId, "paused");
}

/**
 * GET handler for retrieving events for the user.
 * The username is required and the timestamp parameter
 * is optional.
 *
 * Example: GET /?user=joe&timestamp=1296564580384
 */
app.get('/', function(req, res) {
    var u = url.parse(req.url, true);
    
    // check for bad request
    if (!u.query || !u.query.user) {
        res.send(null, 400);
        return;
    }
    
    // extract the parameters
    var user = u.query.user,
        timestamp = u.query.timestamp || 0,
        requestId = lastRequestId++;
        
    // get the next event
    var event = nextEvent(user, timestamp);
    
    // pause the request if there is no pending event
    // or send the event
    if (!event) {
        pause(user, timestamp, req, res, requestId);
    } else {
        res.send(event);
        res.end();
        debug(user, requestId, "sent " + JSON.stringify(event));
    }
});

/** 
 * POST handler for adding a new event for the user.
 * The user and the type parameters are required. 
 * The data object is in the body.
 */
app.post('/', function(req, res) {
    var u = url.parse(req.url, true);
    
    // check for bad request
    if (!u.query || !u.query.user || !u.query.type) {
        res.send('', 400);
        return;
    }
    
    // extract the parameters
    var user = u.query.user,
        type = u.query.type,
        data = u.data;
        
    // add the event 
    addEvent(user, type, data);
    
    // notify pending requests
    notify(user);    
    
    // send 200 OK
    res.send('', 200);
});

// start the server
app.listen(port);
console.log("Server started on port " + port);

node-long-poll-4.js

/**
 * Module import
 */
var express = require('express'),
    url = require('url');
    
/**
 * Port the server listens on
 */
var port = 3000;

/**
 * User event map
 * 
 * events[user] = [ event1, event2, ... ]
 */
var events = {}

/**
 * Pending requests per user
 *
 * pending[user] : [ requestCtx1, requestCtx2, ... ]
 */
var pending = {};

/**
 * Timeout of a pending request in seconds
 */
var connectionTimeout = 60;

/**
 * Maximum age of events in seconds
 */
var maxAge = 60;

/**
 * Global counter for unique ids
 */
var lastRequestId = 0;

/**
 * The request dispatcher
 */
var app = express.createServer();

/**
 * Helper function for compacting an array by removing
 * all null values. 
 *
 * @param Array arr - the input array
 * @return Array A new array with all the non-null values from 'arr'
 */
function compact(arr) {
    if (!arr) return null;
    var i, data = [];
    for (i=0; i < arr.length; i++) {
        if (arr[i]) data.push(arr[i]);
    }
    return data;
}

/**
 * Returns the current time in milliseconds from 1 Jan 1970, 00:00
 */
function currentTimestamp() {
    return new Date().getTime();
}

/**
 * Helper function for logging a debug message
 *
 * @param String user    - the username
 * @param int requestId  - the request id (optional)
 * @param String message - the message
 */
function debug(user, requestId, message) {
    if (message) {
        console.log("["+user+"/"+requestId+"] " + message);        
    } else {
        console.log("["+user+"] " + requestId);                
    }
}

/**
 * Adds a new event 'type' and optional 'data' for 
 * the user. 
 *
 * @param String user - the username
 * @param String type - the event type
 * @param Object data - an optional data object
 */
function addEvent(user, type, data) {
    if (!events[user]) 
        events[user] = [];
        
    var event = {
        type : type, 
        timestamp : currentTimestamp()
    }
    if (data) 
        event.data = data;
        
    events[user].push(event);
    debug(user, "P", "added " + JSON.stringify(event));
}

/**
 * Returns the next event for the user.
 *
 * The next event is the first (oldest) event after the 
 * the 'timestamp'. If 'timestamp' is omitted the oldest 
 * event which has not expired is returned.
 *
 * The 'timestamp' parameter represents the last event
 * the caller has seen and the function returns the 
 * next event. 
 *
 * While iterating over the events the function also
 * expires events which are older than maxAge seconds.
 *
 * @param String user   - the username
 * @param int timestamp - the timestamp of the last event
 * @returns Object      - an event or null
 */
function nextEvent(user, timestamp) {
    if (!events[user]) return null;
    if (!timestamp) timestamp = 0;
    
    // - loop over the events for the user
    // - timeout events older than maxAge seconds
    // - return the oldest event with a timestamp 
    //   greater than 'timestamp'
    var event, i;
    var minTimestamp = currentTimestamp() - maxAge * 1000;
    for(i=0; i < events[user].length; i++) {
        event = events[user][i];
        
        // expire event?
        if (event.timestamp < minTimestamp) {
            debug(user, "expired " + JSON.stringify(event));
            events[user][i] = null;
            continue;
        } 
        
        // next event?
        if (event.timestamp > timestamp) {
            break;
        }
    }
    
    // compact the event array
    events[user] = compact(events[user]);
    
    // return the event
    return event;
}

/**
 * Checks for all pending requests for the user
 * if an event is available. If an event is 
 * available it is sent to the client and the 
 * connection is closed.
 *
 * @param String user - the username
 */
function notify(user) {
    if (!pending[user]) return;
    
    // loop over pending requests for the user
    // and respond if an event is available    
    var i, ctx, event;
    for (i=0; i < pending[user].length; i++) {
        ctx = pending[user][i];
        
        // ctx.req == null -> timeout, cleanup
        if (!ctx.req) {
            pending[user][i] = null;
            continue;
        } 

        // get next event
        event = nextEvent(user, ctx.timestamp);

        // user has event? -> respond, close and cleanup
        if (event) {
            ctx.req.resume();
            ctx.res.send(event);  
            ctx.res.end();              
            pending[user][i] = null;
            debug(user, ctx.id, "sent " + JSON.stringify(event)); 
        }
    }  
    
    // compact the list of pending requests
    pending[user] = compact(pending[user]);
}

/**
 * Pauses the current request for the user and
 * stores the request and response object in 
 * the list of pending requests for the user
 *
 * @param String user      - the username
 * @param String timestamp - the timestamp filter of the request
 * @param Object req       - the request
 * @param Object res       - the response
 * @param int requestId    - the unique request id
 */
function pause(user, timestamp, req, res, requestId) {
    if (!pending[user]) 
        pending[user] = [];

    // save the request context
    var ctx = {
        id : requestId, 
        timestamp : timestamp, 
        req : req, 
        res : res
    }; 
    pending[user].push(ctx);
    
    // configure a timeout on the request
    req.connection.setTimeout(connectionTimeout * 1000);
    req.connection.on('timeout', function(){  
        ctx.req = null;
        ctx.res = null;
        debug(user, requestId, "timeout");
    });
    
    // pause the request
    req.pause();        
    debug(user, requestId, "paused");
}

/**
 * GET handler for retrieving events for the user.
 * The username is required and the timestamp parameter
 * is optional.
 *
 * Example: GET /?user=joe&timestamp=1296564580384
 */
app.get('/', function(req, res) {
    var u = url.parse(req.url, true);
    
    // check for bad request
    if (!u.query || !u.query.user) {
        res.send(null, 400);
        return;
    }
    
    // add a close handler for the connection
    req.connection.on('close', function(){  
        debug(user, requestId, "close");
    });
    
    // extract the parameters
    var user = u.query.user,
        timestamp = u.query.timestamp || 0,
        requestId = lastRequestId++;
        
    // get the next event
    var event = nextEvent(user, timestamp);
    
    // pause the request if there is no pending event
    // or send the event
    if (!event) {
        pause(user, timestamp, req, res, requestId);
    } else {
        res.send(event);
        res.end();
        debug(user, requestId, "sent " + JSON.stringify(event));
    }
});

/** 
 * POST handler for adding a new event for the user.
 * The user and the type parameters are required. 
 * The data object is in the body.
 */
app.post('/', function(req, res) {
    var u = url.parse(req.url, true);
    
    // check for bad request
    if (!u.query || !u.query.user || !u.query.type) {
        res.send('', 400);
        return;
    }
    
    // extract the parameters
    var user = u.query.user,
        type = u.query.type,
        data = u.data;
        
    // add the event 
    addEvent(user, type, data);
    
    // notify pending requests
    notify(user);    
    
    // send 200 OK
    res.send('', 200);
});

// start the server
app.listen(port);
console.log("Server started on port " + port);