问题:

I am trying to connect to a socket.io socket in R using the R function socketConnection(). However, although I am able to set up the socket properly, I am not able to read data from it into R.

The javascript code I use to set up the server is:

var app = require('http').createServer(handler) var io = require('socket.io')(app); var fs = require('fs');  app.listen(8005);  function handler (req, res) {   fs.readFile(__dirname + '/index.html',   function (err, data) {     if (err) {       res.writeHead(500);       return res.end('Error loading index.html');     }      res.writeHead(200);     res.end(data);   }); }  io.on('connection', function (socket) {   setInterval(function() {     socket.emit('update', "test")   }, 1000); });

The code for index.html is:

<script src="/socket.io/socket.io.js"></script> <script>   var socket = io('http://localhost:8005');   socket.on('update', function (data) {     console.log(data);   }); </script>

I am able to verify that the socket is indeed working by going to localhost:8005 in my web browser and opening up the Developer's Console, where I can see "test" being logged. However, when I try to connect to the socket in R by:

sock <- socketConnection("localhost", 8005, blocking = FALSE, open = "r") readLines(sock)

Every time I run readLines(sock) I get an empty character vector back. I have also confirmed I can read from other sockets in R by executing the following and indeed getting a response from readLines(sock):

sock <- socketConnection("rstudio.com", 6789, blocking = FALSE, open = "r") readLines(sock)

Any help would be greatly appreciated. Thanks!

UPDATE (2015-09-01):

Thanks to the excellent help from Aaron Dufour, I was able to adapt this net server demo to stream data into R. The javascript code I used for the server was

var net = require('net');  var server = net.createServer(function(socket) {     setInterval(function() {         socket.write('Test\r\n');         socket.pipe(socket);     }, 1000) });  server.listen(1337, '127.0.0.1');

And the R code was:

sock <- socketConnection("localhost", 1337, open = "r") readLines(sock) close(sock)

I did get the following warning warning: possible EventEmitter memory leak detected. 11 end listeners added. Use emitter.setMaxListeners() to increase limit. sometimes on the server side when I ran readLines(socket)

Also, when I ran close(socket) in R the server crashed and I get the following error: Error: This socket has been ended by the other party

With additional research, I think both the warning and error are preventable.

回答1:

As I've described here, the socket.io protocol is much more than a WebSocket. Just opening a WebSocket to it won't work.

But socketConnection appears to not even be a WebSocket, but rather a raw socket. You're getting nothing back because the server is talking HTTP and you haven't finished sending an HTTP request.

You probably need a socket.io library for R, or to switch away from socket.io on the server.

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