response.js

var EventEmitter = require('events').EventEmitter;

var Response = module.exports = function (xhr) {
    this.xhr = xhr;
    this.offset = 0;
};

Response.prototype = new EventEmitter;

var capable = {
    streaming : true,
    status2 : true
};

function parseHeaders (xhr) {
    var lines = xhr.getAllResponseHeaders().split(/\r?\n/);
    var headers = {};
    for (var i = 0; i < lines.length; i++) {
        var line = lines[i];
        if (line === '') continue;
        
        var m = line.match(/^([^:]+):\s*(.*)/);
        if (m) {
            var key = m[1].toLowerCase(), value = m[2];
            
            if (headers[key] !== undefined) {
                if ((Array.isArray && Array.isArray(headers[key]))
                || headers[key] instanceof Array) {
                    headers[key].push(value);
                }
                else {
                    headers[key] = [ headers[key], value ];
                }
            }
            else {
                headers[key] = value;
            }
        }
        else {
            headers[line] = true;
        }
    }
    return headers;
}

Response.prototype.getHeader = function (key) {
    var header = this.headers[key.toLowerCase()];

    // Work around Mozilla bug #608735 [https://bugzil.la/608735], which causes
    // getAllResponseHeaders() to return {} if the response is a CORS request.
    // xhr.getHeader still works correctly.
    return header || this.xhr.getResponseHeader(key);
};

Response.prototype.handle = function () {
    var xhr = this.xhr;
    if (xhr.readyState === 2 && capable.status2) {
        try {
            this.statusCode = xhr.status;
            this.headers = parseHeaders(xhr);
        }
        catch (err) {
            capable.status2 = false;
        }
        
        if (capable.status2) {
            this.emit('ready');
        }
    }
    else if (capable.streaming && xhr.readyState === 3) {
        try {
            if (!this.statusCode) {
                this.statusCode = xhr.status;
                this.headers = parseHeaders(xhr);
                this.emit('ready');
            }
        }
        catch (err) {}
        
        try {
            this.write();
        }
        catch (err) {
            capable.streaming = false;
        }
    }
    else if (xhr.readyState === 4) {
        if (!this.statusCode) {
            this.statusCode = xhr.status;
            this.emit('ready');
        }
        this.write();
        
        if (xhr.error) {
            this.emit('error', xhr.responseText);
        }
        else this.emit('end');
    }
};

Response.prototype.write = function () {
    var xhr = this.xhr;
    if (xhr.responseText.length > this.offset) {
        this.emit('data', xhr.responseText.slice(this.offset));
        this.offset = xhr.responseText.length;
    }
};