Trac JSON RPC Issue - Using jQuery AJAX with PHP proxy

Ok this is a tricky one, but I think I'm missing something really simple here.

Goal

I'm trying to create an interface to Trac from another domain using the XmlRpcPlugin's JSON interface to the Trac API. I'm using a PHP server-side script as a proxy because of Javascript's Same Origin Policy.

Status

The proxy appears to be (mostly) working because I do get a response back from Trac in the jQuery-driven interface. However, I always get this response:

{
  "error": {
    "message": "JsonProtocolException details : No JSON object could be decoded",
    "code": -32700,
    "name": "JSONRPCError"
  },
  "result": null,
  "id": null
}

These are the two entries in my Trac log that correspond with every request:

2012-03-05 11:37:55,943 Trac[json_rpc] ERROR: RPC(json) decode error
Traceback (most recent call last):
  File "/usr/local/lib/python2.6/dist-packages/TracXMLRPC-1.1.2_r11148-py2.6.egg/tracrpc/json_rpc.py", line 148, in parse_rpc_request
    data = json.load(req, cls=TracRpcJSONDecoder)
  File "/usr/lib/python2.6/json/__init__.py", line 267, in load
    parse_constant=parse_constant, **kw)
  File "/usr/lib/python2.6/json/__init__.py", line 318, in loads
    return cls(encoding=encoding, **kw).decode(s)
  File "/usr/local/lib/python2.6/dist-packages/TracXMLRPC-1.1.2_r11148-py2.6.egg/tracrpc/json_rpc.py", line 99, in decode
    obj = json.JSONDecoder.decode(self, obj, *args, **kwargs)
  File "/usr/lib/python2.6/json/decoder.py", line 319, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python2.6/json/decoder.py", line 338, in raw_decode
    raise ValueError("No JSON object could be decoded")
ValueError: No JSON object could be decoded

2012-03-05 11:37:55,943 Trac[web_ui] ERROR: RPC(JSON-RPC) Error
Traceback (most recent call last):
  File "/usr/local/lib/python2.6/dist-packages/TracXMLRPC-1.1.2_r11148-py2.6.egg/tracrpc/web_ui.py", line 143, in _rpc_process
    rpcreq = req.rpc = protocol.parse_rpc_request(req, content_type)
  File "/usr/local/lib/python2.6/dist-packages/TracXMLRPC-1.1.2_r11148-py2.6.egg/tracrpc/json_rpc.py", line 162, in parse_rpc_request
    raise JsonProtocolException(e, -32700)
JsonProtocolException: No JSON object could be decoded

Code

My jQuery code:

$.ajax({
    url: "/ajax/trac_proxy.php",
    dataType: "json",
    data: {"method": "system.listMethods", "id": 1},
    timeout: 5000,
    type: 'POST',
    success: function(data, status, XHR){
        alert(JSON.stringify(data));
    }
});

My PHP script (/ajax/trac_proxy.php - shortened for clarity):

<?php
    $cparams = array(
        'http' => array(
            'method' => 'POST',
            'ignore_errors' => true,
            'content' => http_build_query($_POST),
            'header' => "Authorization: Basic " . base64_encode($username . ':' . $password) . "\r\n"
                      . "Content-Type: application/json\r\n"
        )
    );
    $context = stream_context_create($cparams);
    $fp = fopen('https://mytracdomain.com/login/jsonrpc', 'rb', false, $context);
    echo stream_get_contents($fp);
?>

Debugging Results

To see what PHP is getting/doing, I changed /ajax/trac_proxy.php to this:

$cparams = array(
    'http' => array(
        'content' => http_build_query($_POST),
        'method' => 'POST',
        'ignore_errors' => true,
        'header' => "Authorization: Basic " . base64_encode($username . ':' . $password) . "\r\n"
                  . "Content-Type: application/json\r\n"
    )
);

var_dump($_POST);
var_dump(http_build_query($_POST));
var_dump($cparams);

This is what I get back:

array(2) {
  ["method"]=>
  string(18) "system.listMethods"
  ["id"]=>
  string(1) "1"
}

string(30) "method=system.listMethods&id=1"

array(1) {
  ["http"]=>
  array(4) {
    ["content"]=>
    string(30) "method=system.listMethods&id=1"
    ["method"]=>
    string(4) "POST"
    ["ignore_errors"]=>
    bool(true)
    ["header"]=>
    string(79) "Authorization: Basic <REMOVED>
Content-Type: application/json
"
  }
}

Environment

Trac: Trac 0.11.7
Python: Python 2.6
Web server: Apache 2.2.14
OS: Ubuntu 10.04

What am I doing wrong?

Solution

Figured it out.

The problem was the content param in $cparams.

http_build_query() returns a URL query string. What the JSON-RPC plugin was expecting was a JSON string (imagine that), which json_encode() handily provides.

Changing this:

$cparams = array(
    'http' => array(
        'content' => http_build_query($_POST),
        'method' => 'POST',
        'ignore_errors' => true,
        'header' => "Authorization: Basic " . base64_encode($username . ':' . $password) . "\r\n"
                  . "Content-Type: application/json\r\n"
    )
);

To this:

$cparams = array(
    'http' => array(
        'content' => json_encode($_POST),
        'method' => 'POST',
        'ignore_errors' => true,
        'header' => "Authorization: Basic " . base64_encode($username . ':' . $password) . "\r\n"
                  . "Content-Type: application/json\r\n"
    )
);

Fixed it.