PHP - Debugging Curl

I'd like to see what the post fields in the request are before I send it. (For debugging purposes).

The PHP library (class) I am using is already made (not by me), so I am trying to understand it.

As far as I can tell, it uses curl_setopt() to set different options like headers and such and then it uses curl_exec() to send the request.

Ideas on how to see what post fields are being sent?


You can enable the CURLOPT_VERBOSE option:

curl_setopt($curlhandle, CURLOPT_VERBOSE, true);

When CURLOPT_VERBOSE is set, output is written to STDERR or the file specified using CURLOPT_STDERR. The output is very informative.

You can also use tcpdump or wireshark to watch the network traffic.

You can enable the CURLOPT_VERBOSE option and log that information to a (temporary) CURLOPT_STDERR:

// CURLOPT_VERBOSE: TRUE to output verbose information. Writes output to STDERR, 
// or the file specified using CURLOPT_STDERR.
curl_setopt($handle, CURLOPT_VERBOSE, true);

$verbose = fopen('php://temp', 'w+');
curl_setopt($handle, CURLOPT_STDERR, $verbose);

You can then read it after curl has done the request:

$result = curl_exec($handle);
if ($result === FALSE) {
    printf("cUrl error (#%d): %s<br>\n", curl_errno($handle),

$verboseLog = stream_get_contents($verbose);

echo "Verbose information:\n<pre>", htmlspecialchars($verboseLog), "</pre>\n";

(I originally answered similar but more extended in a related question.)

More information like metrics about the last request is available via curl_getinfo. This information can be useful for debugging curl requests, too. A usage example, I would normally wrap that into a function:

$version = curl_version();
$metrics = <<<EOD
URL....: $url
Code...: $http_code ($redirect_count redirect(s) in $redirect_time secs)
Content: $content_type Size: $download_content_length (Own: $size_download) Filetime: $filetime
Time...: $total_time Start @ $starttransfer_time (DNS: $namelookup_time Connect: $connect_time Request: $pretransfer_time)
Speed..: Down: $speed_download (avg.) Up: $speed_upload (avg.)
Curl...: v{$version['version']}

Here is a simpler code for the same:

   curl_setopt($ch, CURLOPT_VERBOSE, 1);
   curl_setopt($ch, CURLOPT_STDERR, $fp);

where $fp is a file handle to output errors. For example:

   $fp = fopen(dirname(__FILE__).'/errorlog.txt', 'w');

( Read on )

Here is an even simplier way, by writing directly to php error output

curl_setopt($curl, CURLOPT_VERBOSE, true);
curl_setopt($curl, CURLOPT_STDERR, fopen('php://stderr', 'w'));

To just get the info of a CURL request do this:

$response = curl_exec($ch);

$info = curl_getinfo($ch);

Another (crude) option is to utilize netcat for dumping the full request:

nc -l -p 8000 -w 3 | tee curldbg.txt

And of course sending the failing request to it:

curl_setup(CURLOPT_URL, "http://localhost/testytest");

Notably that will always hang+fail, since netcat won't ever construct a valid HTTP response. It's really just for inspecting what really got sent. The better option, of course, is using a http request debugging service.

Output debug info to STDERR:

$curlHandler = curl_init();

curl_setopt_array($curlHandler, [
    CURLOPT_URL => '',

     * Specify debug option
    CURLOPT_VERBOSE => true,



Output debug info to file:

$curlHandler = curl_init();

curl_setopt_array($curlHandler, [
    CURLOPT_URL => '',

     * Specify debug option.
    CURLOPT_VERBOSE => true,

     * Specify log file.
     * Make sure that the folder is writable.
    CURLOPT_STDERR => fopen('./curl.log', 'w+'),




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