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.
