tube/server/index.js

Experimental Resource Loader implementing using Server Sent Events

var async = require('async'),
    debug = require('debug')('tube'),
    fs = require('fs'),
    path = require('path'),
    http = require('http'),
    fstream = require('fstream'),
    Manifest = require('../src/manifest'),
    reLineBreak = /\r?\n/g,
    defaultAssetPath = path.resolve(path.dirname(module.parent.filename), 'assets');
    
function loadManifest(req, opts, callback) {
    var manifestLocation = opts.manifest || defaultAssetPath,
        manifest = new Manifest();
    
    console.log(req.url);

    // stat the manifest
    fs.stat(manifestLocation, function(err, stats) {
        if (err) return callback(err);
        
        // if we have a directory, then load the files from the directory
        if (stats.isDirectory()) {
            fstream.Reader({ path: manifestLocation })
                .on('child', function(file) {
                    if (file.type === 'File') {
                        manifest.add({
                            path: file.path, 
                            size: file.size
                        });
                    }
                })
                .on('end', function() {
                    callback(null, manifest);
                });
        }
        else {
            return callback();
        }
    });
}

function loadManifestContent(manifest, callback) {
    async.map(manifest.files, fs.readFile, function(err, results) {
        if (err) return callback(err);
        
        // iterate through the results and update the manifest resources
        results.forEach(function(buffer, index) {
            manifest.resources[index].data = buffer.toString();
        });
                
        callback(null, manifest);
    });
}

function reportError(err, res) {
    res.write('event: exception\n');
    res.write('data: ' + err.message + '\n\n');
    return res.end();
}

function supplyAsset(res, separator) {
    // ensure we have a separator (default to 0x214B - ⅋)
    separator = separator || String.fromCharCode(0x214B);
    
    return function(resource, callback) {
        debug('attempting to load asset: ' + resource.path);
        fs.readFile(resource.path, 'utf8', function(err, data) {
            if (err) return callback(err);
            
            res.write('event: resource\n');
            res.write('data: ' + JSON.stringify({
                data: data.split(reLineBreak).join(separator)
            }) + '\n\n');
        });
    };
}

module.exports = function(opts) {
    // ensure we have opts
    opts = opts || {};
    
    return function(req, res) {
        loadManifest(req, opts, function(err, manifest) {
            if (err) {
                debug('received error: ' + err);
            }
            
            req.once('end', function() {
                console.log('request aborted');
                res.end();
            });
            
            // if we hit an error, then provide a 204 which tells the EventSource to stop 
            // attempting to reconnect
            // see: http://www.w3.org/TR/eventsource/#processing-model
            res.writeHead(err ? 204 : 200, {
                "content-type":"text/event-stream", 
                "Cache-Control":"no-cache", 
                "Connection":"keep-alive"
            });

            if (err) return reportError(err, res);
            
            async.forEach(manifest.resources, supplyAsset(res, opts.separator), function(err) {
                return reportError(err, res);
                
                res.write('event: done\n\n');
                res.end();
            });
        });
    };
};