For more than one time I had to debug HTTP request or response headers and other details. To do that, I use two techniques, both based on cURL library. I explain them ahead.
Technique #1: From the command line
This is the easiest way to debug. It doesn’t require writing any actual code. Just call curl program from the command line, as usual, adding a new param: -vvv. This will enable the highest verbosity level.
$ curl -vvv http://google.com * Rebuilt URL to: http://google.com/ * Trying 2800:3f0:4001:802::200e... * Connected to google.com (2800:3f0:4001:802::200e) port 80 (#0) > GET / HTTP/1.1 > Host: google.com > User-Agent: curl/7.43.0 > Accept: */* > < HTTP/1.1 302 Found < Cache-Control: private < Content-Type: text/html; charset=UTF-8 < Location: http://www.google.com.br/?gfe_rd=cr&ei=bUG8V53JGcvK8gfp3L-YBg < Content-Length: 262 < Date: Tue, 23 Aug 2016 12:28:29 GMT < <HTML><HEAD><meta http-equiv="content-type" content="text/html;charset=utf-8"> <TITLE>302 Moved</TITLE></HEAD><BODY> <H1>302 Moved</H1> The document has moved <A HREF="http://www.google.com.br/?gfe_rd=cr&ei=bUG8V53JGcvK8gfp3L-YBg">here</A>. </BODY></HTML> * Connection #0 to host google.com left intact
As you can see in the example above, it outputs all request and response info.
It’s possible to output everything to a file, by adding > output_file.txt to the end of the command. Using our previous call:
$ curl -vvv http://google.com > output.txt
Well, one may now ask: if this is so easy, why do you have a second way to debug request? Following we’ll see why that.
Technique #2: From a PHP script
I’ve written on debugging cURL and PHP at Kettle.io Blog. Let’s say you have to send a dynamic header with the request, like a JWT authorization token. It’s not impossible to that from the command line, but it’s easier using programming. For those cases, I use the cURL PHP extension. Check out the script below.
$url = 'http://google.com';
$headers = [
'Accept' => 'application/json',
];
/*
* We're going to use the output buffer to store the debug info.
*/
ob_start();
$out = fopen('php://output', 'w');
$handler = curl_init($url);
/*
* Here we set the library verbosity and redirect the error output to the
* output buffer.
*/
curl_setopt($handler, CURLOPT_VERBOSE, true);
curl_setopt($handler, CURLOPT_STDERR, $out);
$requestHeaders = [];
foreach ($headers as $k => $v) {
$requestHeaders[] = $k . ': ' . $v;
}
curl_setopt($handler, CURLOPT_HTTPHEADER, $requestHeaders);
curl_setopt($handler, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($handler);
fclose($out);
/*
* Joining debug info and response body.
*/
$data = ob_get_clean();
$data .= PHP_EOL . $response . PHP_EOL;
echo $data;
Now, you can customize this code to add some dynamic data to a header or any other request part. After doing that, run it using the PHP program from the command line:
$ php curldebug.php
P.S.: I’m assuming that you saved the script as curldebug.php.
As we did with the curl program, it’s possible to output everything to a file. Just append the > output_file.txt to the call.
Conclusion
Debugging requests can be a lifesaver when dealing with third-party APIs and other services. Headers may contain helpful info to find what is going wrong with that weird response body.
Gustavo Straube 