Question

UPDATED THANKS TO ANSWERS:

Can someone point out the difference between:

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $api_root);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, "xml"); // tried http_build_query also
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true); // Added this, still no good
return curl_exec($ch);  // returns false

and:

$curl = "curl -X POST -d 'xml' {$api_root}";
return `$curl`;  // returns expected xml from server

AND/OR

More generally, are there any good breakdowns out there for conversion/reference between php’s libcurl default values/headers and those of curl on the command line?

I know this is almost a dupe of curl CLI to curl PHP and CLI CURL -> PHP CURL but I’m hoping for something more definitive.

Answer 1

curl_exec returns true or false by default. You need to specify CURLOPT_RETURNTRANSFER:

curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

Since curl_exec is returning false (not NULL as indicated in the original question), try using curl_error() to determine why it’s returning false.

TFM (read it): curl_exec(), curl_setopt()

Edit for posterity’s sake:

The OP discovered that an SSL issue was the hindrance. The both libcurl (as called through PHP) and the curl command-line do SSL peer verification for every transaction, unless the user explicitly disables it.

The likely scenario is that the shell environment is using a different CA bundle than PHP’s libcurl implementation. To remedy this, set CURLOPT_CAINFO to be the same as the shell’s CURL_CA_BUNDLE environment variable and then peer verification should work.

@OP: I’d be curious to know if the above suggestion is confirmed working in your case, or if there is something else different with the SSL configuration.