curl_setopt_array

If you are writing a mini API for your library, and if you are doing merging of options, remember to use the union operator (+) !
So something like this will definitely fail. This is because array_merge effectively resets all the keys in the array into running numbers:
<?php
function post($url, $options = array) {
 $ch = curl_init();
 curl_setopt_array($ch, array_merge(array(
 CURLOPT_HEADER => 1,
 CURLOPT_RETURNTRANSFER => 1,
 .....
 )));
?>

Rather, this is the correct way of doing it:
<?php
function post($url, $options = array) {
 $ch = curl_init();
 curl_setopt_array($ch, array(
 CURLOPT_HEADER => 1,
 CURLOPT_RETURNTRANSFER => 1,
 .....
 ) + (array) $options);
?>

In case that you need to read SSL page content from https with curl, this function can help you:
<?php
function get_web_page( $url,$curl_data )
{
 $options = array(
 CURLOPT_RETURNTRANSFER => true, // return web page
 CURLOPT_HEADER => false, // don't return headers
 CURLOPT_FOLLOWLOCATION => true, // follow redirects
 CURLOPT_ENCODING => "", // handle all encodings
 CURLOPT_USERAGENT => "spider", // who am i
 CURLOPT_AUTOREFERER => true, // set referer on redirect
 CURLOPT_CONNECTTIMEOUT => 120, // timeout on connect
 CURLOPT_TIMEOUT => 120, // timeout on response
 CURLOPT_MAXREDIRS => 10, // stop after 10 redirects
 CURLOPT_POST => 1, // i am sending post data
 CURLOPT_POSTFIELDS => $curl_data, // this are my post vars
 CURLOPT_SSL_VERIFYHOST => 0, // don't verify ssl
 CURLOPT_SSL_VERIFYPEER => false, //
 CURLOPT_VERBOSE => 1 //
 );
 $ch = curl_init($url);
 curl_setopt_array($ch,$options);
 $content = curl_exec($ch);
 $err = curl_errno($ch);
 $errmsg = curl_error($ch) ;
 $header = curl_getinfo($ch);
 curl_close($ch);
 // $header['errno'] = $err;
 // $header['errmsg'] = $errmsg;
 // $header['content'] = $content;
 return $header;
}
$curl_data = "var1=60&var2=test";
$url = "https://www.example.com";
$response = get_web_page($url,$curl_data);
print '<pre>';
print_r($response);
?>

You might be tempted to use array_merge with arrays where CURLOPT constants are the keys, but beware.
<?php
array_merge([], [CURLOPT_FOO => "foo"], [CURLOPT_BAR => "bar"]);
?>

Since these constants are numeric, array_merge will happily reindex:
<?php
[0 => "foo", 1 => "bar"];
?>

You can use CURLOPT_HEADERFUNCTION with a callback inside an object. This makes is it easy to capture the headers for later use. For example:
<?php
class Test
{
 public $headers;
 //...
 public function exec($opts)
 {
 $this->headers = array();
 $opts[CURLOPT_HEADERFUNCTION] = array($this, '_setHeader');
 $ch = curl_init();
 curl_setopt_array($ch, $opts);
 return curl_exec($ch);
 }
 private function _setHeader($ch, $header)
 {
 $this->headers[] = $header;
 return strlen($header);
 }
 
}
$test = new Test();
$opts = array(
 //... your curl opts here
);
$data = $test->exec($opts);
print_r($test->headers);
?>

...something like that
(This works in php v. 5.1.4)

Important note: the option CURLINFO_HEADER_OUT is *ignored* by curl_setopt_array(). You *must* use curl_setopt() to set this option.
(True in PHP v7.3.27 at least)

Once upon a time I've got an error like "Problem with the SSL CA cert (path? access rights?)". Since what I was doing was pretty much an administrative task with no actual security issues involved, I decided to disallow certificate validation and this is where the most interesting stuff began.
First I did it like this and it worked:
 curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
 curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
Next I thought, "But hey, I don't want any hardcoded stuff here. Let's use it in a configurable way!". And so I did something like this:
// in configuration
$CURL_OPTIONS = array(CURLOPT_SSL_VERIFYPEER => 0, CURLOPT_SSL_VERIFYHOST => 0);
...........
// in place of two direct calls from earlier
 curl_setopt_array($ch, $CURL_OPTIONS);
And I was so happy, there was no error anymore... and do you think I was happy for a long time? If so, then you're wrong. It stopped giving an error, while it didn't start to work!
I checked the actual data but they were allright. Then I thought: "Is it the curl_setopt_array() problem? Let's make it a cycle." The way it is mentioned in this help, actually.
 foreach ($CURL_OPTIONS as $name => $value)
 {
 curl_setopt($ch, $name, $value);
 }
And... it did not work the same way as with the curl_setopt_array() call. And the data were still allright...
So, if by chance you can't set CURL options with the curl_setopt_array() call, then now you know what to do and you know it is definitely not you who is to blame.
P.S.
By the way, the configuration used was:
Linux i-ween.com 3.2.0-4-amd64 #1 SMP Debian 3.2.73-2+deb7u3 x86_64
PHP Version 5.5.17

This function does not mix with `curl_file_create` (`CURLFile` object) and `CURLOPT_POSTFIELDS`. Took me forever to figure out, but essentially I was getting an "Invalid filename" PHP warning and the files weren't being sent. I was able to correct the issue in a matter like so:
curl_setopt_array($curl, $curlOpts);
curl_setopt($curl, CURLOPT_POSTFIELDS, $postFields);
I removed the `$postFields` value from `$curlOpts` and set it separately using `curl_setopt`.

Starting in PHP 5.2.0, CURLOPT_FOLLOWLOCATION can't be set via curl_setopt_array() (or curl_setopt()) when either safe_mode is enabled or open_basedir is set. In these cases, the order of CURLOPT_* settings in the array can be important.