Something to keep in mind when creating SSL streams (using https://):

<?php
$context = context_create_stream($context_options)
$fp = fopen('https://url', 'r', false, $context);
?>

One would think - the proper way to create a stream options array, would be as follows: 

<?php
$context_options = array (
        'https' => array (
            'method' => 'POST',
            'header'=> "Content-type: application/x-www-form-urlencoded\r\n"
                . "Content-Length: " . strlen($data) . "\r\n",
            'content' => $data
            )
        );
?>

THAT IS THE WRONG WAY!!!
Take notice to the 3rd line: 'https' => array (

The CORRECT way, is as follows:

<?php
$context_options = array (
        'http' => array (
            'method' => 'POST',
            'header'=> "Content-type: application/x-www-form-urlencoded\r\n"
                . "Content-Length: " . strlen($data) . "\r\n",
            'content' => $data
            )
        );
?>

Notice, the NEW 3rd line: 'http' => array (

Now - keep this in mind - I spent several hours trying to trouble shoot my issue, when I finally stumbled upon this non-documented issue.

The complete code to post to a secure page is as follows:

<?php
$data = array ('foo' => 'bar', 'bar' => 'baz');
$data = http_build_query($data);

$context_options = array (
        'http' => array (
            'method' => 'POST',
            'header'=> "Content-type: application/x-www-form-urlencoded\r\n"
                . "Content-Length: " . strlen($data) . "\r\n",
            'content' => $data
            )
        );

$context = context_create_stream($context_options)
$fp = fopen('https://url', 'r', false, $context);
?>

I big NOTE that i hope will help some one. Something that is not mentioned in the documentation, is that when php is compiled --with-curlwrappers,

So, instead of:

<?php
$opts = array(
  'http'=>array(
    'method'=>"GET",
    'header'=>"Accept-language: en\r\n" .
              "Cookie: foo=bar\r\n"
  )
);

$context = stream_context_create($opts);
?>

You would setup the header this way: 

<?php
$opts = array(
  'http'=>array(
    'method'=>"GET",
    'header'=>array("Accept-language: en",
                           "Cookie: foo=bar",
                           "Custom-Header: value")
  )
);

$context = stream_context_create($opts);
?>

This will work.

Hi,you can create an array of parameters(what it's called a stream context),which can be transmitted each time you read or write a stream through a socket.In the below example:

$opts =array('http'=>arra('method'=>"GET",
'header'=>"Accept-language:en\r\n"."Cookie: foo=bar\r\n");

What you're actually doing is create a set of parameters(the protocol to be used,the request method,additional http headers and a cookie) which will be used each time you open a socket connection to request www.example.com.This saves a lot of time if you want to use these parameters (called a stream context) whenever you include them when making a request to www.example.com,instead of having to specify them over and over again.
Using the previous example,say you want to create a stream context,which sends a "Content-Type" http header and utilize it when making a request to www.example.com.Take a look:

$opts = array('http'=>array('method'=>"GET",
'header'=>"Content-Type: text/xml; charset=utf-8");

$context = stream_context_create($opts);
$fp = fopen('http://www.example.com','r',false,$context);
fpassthru($fp);
fclose($fp);

Now,when you make a request to www.example.com,the above http header will be included within the socket and transmitted to the server.Best of luck for you friends,Hossein

I spent a good five hours trying to figure this out, so hopefully it will save someone else some time.

When you are trying to download a file via ftp through an HTTP proxy note that the following will not be enough:
<?php
$opts = array('ftp' => array(
    'proxy' => 'tcp://vbinprst10:8080',
    'request_fulluri'=>true,
    'header' => array(
        "Proxy-Authorization: Basic $auth"
        )
    )
);
$context = stream_context_create($opts);
$s = file_get_contents("ftp://anonymous:[email protected]",false,$context);
?>

Your proxy will respond that authentication is required. You may scratch your head and think "but I'm providing authentication!"

The issue is that the 'header' value is only applicable to http connections. So to authenticate on a proxy, you first have to pull a file from HTTP, before the context is valid for using on FTP.
<?php
$opts = array('ftp' => array(
    'proxy' => 'tcp://vbinprst10:8080',
    'request_fulluri'=>true,
    'header' => array(
        "Proxy-Authorization: Basic $auth"
        )
    ),
    'http' => array(
    'proxy' => 'tcp://vbinprst10:8080',
    'request_fulluri'=>true,
    'header' => array(
        "Proxy-Authorization: Basic $auth"
        )
    )
);
$context = stream_context_create($opts);
$s = file_get_contents("http://www.example.com",false,$context);
$s = file_get_contents("ftp://anonymous:[email protected]",false,$context);
?>

It's a bit roundabout, but it works. Note that the 'header' val in the ftp array is redundant, but I kept it in anyway.

In addition to the context options mentioned above (appendix N), lower down context options for sockets can be found in appendix P - http://www.php.net/manual/en/transports.php

When using the https protocol you'll have to make sure to set the right context options to use the full "power" of the ssl/tls encryption.

<?php
$url = 'https://secure.example.com/test/1';
$contextOptions = array(
    'ssl' => array(
        'verify_peer'   => true,
        'cafile'        => __DIR__ . '/cacert.pem',
        'verify_depth'  => 5,
        'CN_match'      => 'secure.example.com'
    )
);
$sslContext = stream_context_create($contextOptions);
$result = file_get_contents($url, NULL, $sslContext);
?>

More information about those context options can be found at http://php.net/manual/en/context.ssl.php

I found the following code worked for me for POSTing some binary data to a remote server. I am putting it here since I could not find a quick solution to this by 'googling' or looking through this documentation. 

Disclaimer:  I have no idea if this a 'good' solution, since I'm new to PHP, but it may just suit your needs as it did mine.  I am assuming bad things will happen with very large files since the entire file is read into $fileContents. 

I am using PHP 5.2.8.

   $fileHandle = fopen("someImage.jpg", "rb");
   $fileContents = stream_get_contents($fileHandle);
   fclose($fileHandle);

   $params = array(
      'http' => array
      (
          'method' => 'POST',
          'header'=>"Content-Type: multipart/form-data\r\n",
          'content' => $fileContents
      )
   );
   $url = "http://somesite.somecompany.com?someParam=someValue";
   $ctx = stream_context_create($params);
   $fp = fopen($url, 'rb', false, $ctx);

   $response = stream_get_contents($fp);

Don't try to re-use the ressource returned by stream_context_create. It seems not to work when connecting to different domains using https.

In some cases, set a header option as an array, and not a string, depending on server configuration.

<?php
$opts = array(
  'http'=> array(
    'method'=>   "GET",
    'header'=>    array( "Cookie: foo="bar"l ),
    'user_agent'=>    $_SERVER['HTTP_USER_AGENT']
  )
);
?>

Connection via Proxy

<?php

$opts = array('http' => array('proxy' => 'tcp://127.0.0.1:8080', 'request_fulluri' => true));
$context = stream_context_create($opts);

$data = file_get_contents('http://www.php.net', false, $context);

echo $data;

?>

Here's a very simple way to do posts easily without need of cURL or writing an http request by hand using the tcp:// wrapper.  I like using contexts just because of their ubiquity and the lack of an optional library such as cURL (though one of the more popular libraries).

<?php

$options = array(
  'http'=>array(
    'method'=>"POST",
    'header'=>
      "Accept-language: en\r\n".
      "Content-type: application/x-www-form-urlencoded\r\n",
    'content'=>http_build_query(array('foo'=>'bar'))
));

$context = stream_context_create($options);

fopen('http://www.example.com/',false,$context);

?>