/*
* Vibe
* http://vibe-project.github.io/projects/vibe-protocol/
*
* Copyright 2014 The Vibe Project
* Licensed under the Apache License, Version 2.0
* http://www.apache.org/licenses/LICENSE-2.0
*/
var events = require("events");
var url = require("url");
var http = require("http");
var createHttpBaseTransport = require("./transport-http-base-transport");
http.globalAgent.maxSockets = Infinity;This function is exposed to the module’s transport module’s
createHttpLongpollTransport as a factory to create a HTTP long
polling transport. In long polling, the client performs a HTTP persistent
connection and the server ends the response with message. Then, the client
receives it and performs a request again and again.
module.exports = function(uri, options) {
var urlObj = url.parse(uri, true);URI’s protocol should be either http or https and transport param
should be longpoll.
if ((urlObj.protocol === "http:" || urlObj.protocol === "https:") && urlObj.query.transport === "longpoll") {A transport object.
var self = createHttpBaseTransport(uri, options);Any error on request-response should propagate to transport.
function onerror(error) {
self.emit("error", error);
}The current holding request.
var req;
self.connect = function() {Performs a HTTP persistent connection through GET method. The
first request’s when param should be open. In case of JSONP,
jsonp param should be true and callback param should be
provided as well.
req = http.get(uri + "&when=open")
.on("error", onerror).on("response", function(res) {Aggregates chunks to make a complete response body.
var body = "";
res.on("error", onerror).on("data", function(chunk) {
body += chunk;
})
.on("end", function() {The response body of the open request contains a result
of handshake. The handshake output is in the form of URI.
var result = url.parse(body, true).query;A newly issued id for HTTP transport. It is used to identify which HTTP transport is associated with which HTTP exchange.
self.id = result.id;Before giving a user opportunity to handle transport
through open event, polling must be started. Because,
when a user closes the transport on open event, the
active req is required.
poll();
self.emit("open");Then starts polling.
function poll() {From the second request, when param should be
poll and id param should be added.
req = http.get(uri + "&when=poll&id=" + encodeURIComponent(self.id))If the server responds to this request, determine whether the intention of response is to send event or to close by reading body.
.on("error", onerror).on("response", function(res) {
var body = "";
res.on("error", onerror).on("data", function(chunk) {
body += chunk;
})
.on("end", function() {The response’s body itself is message.
if (body) {Starts a poll request again before to
fire text event. There must be no idle
time between polling.
poll();
self.emit("text", body);Empty body indicates the server closed the
socket. Accordingly fires the close event.
} else {
self.emit("close");
}
});
});
}
});
});
};
self.abort = function() {Node.js fires a ‘socket hang up’ error if there was no response from the server by default. But, that is a normal case of close in long polling, hence removes all default error handlers.
req.removeAllListeners("error");To fire close event, registers error event handler to req.
The above response event handler is called only when response
is returned from the server so that close event is called only
once.
req.on("error", function() {
self.emit("close");
});
req.abort();
};
return self;
}
};