Client handshake returns error message "Transport unknown"

I was trying to initialize a handshake, following the specs I’ve found at LearnBoost/socket.io-spec. Sometime I found that it has to be done with a POST request, sometime with GET. I’ve tried both of them and they both returned the same error:

GET http://acme.local:3700/socket.io/1
or
POST http://acme.local:3700/socket.io/1

{ “code”: 0, “message”: “Transport unknown” }

[akkunchoi]

I’ve encountered same error on socket.io v1.1.0.

I added a follow line at server side script, then I fixed this problem. io.set('transports', ["websocket", "polling"]);

Errors I encountered:

• GET /socket.io returns Transport unknown.
• DEBUG=* node-dev app.js prints a lot of unknown transport polling.

I refer http://stackoverflow.com/questions/23962047/socket-io-v1-0-x-unknown-transport-polling

[afshinm]

I fixed this problem by adding this setting to my socket.io server:

var socket = io({
  transports: [
    'websocket', 
    'flashsocket', 
    'htmlfile', 
    'xhr-polling', 
    'jsonp-polling', 
    'polling'
  ]
});

read more here: http://stackoverflow.com/a/24244413/375966