PHP HTTP POST fails when cURL data > 1024

Question

Note: solution at the end

If I attempt to do a HTTP POST of over 1024 characters, it fails. Why? Here is a minimal example:

recipient.php:

<?php
if (strlen(file_get_contents('php://input')) > 1000
    || strlen($HTTP_RAW_POST_DATA) > 1000) {
 echo "This was a triumph.";
}
?>

sender.php:

<?php
function try_to_post($char_count) {
 $url = 'http://gpx3quaa.joyent.us/test/recipient.php';
 $post_data = str_repeat('x', $char_count);
 $c = curl_init();
 curl_setopt_array($c,
                    array(  CURLOPT_URL => $url,
                            CURLOPT_HEADER => false,
                            CURLOPT_CONNECTTIMEOUT => 999,
                            CURLOPT_RETURNTRANSFER => true,
                            CURLOPT_POST => 1,
                            CURLOPT_POSTFIELDS => $post_data
                    )
 );
 $result = curl_exec($c);
 echo "{$result}\n";
 curl_close($c);
}

for ($i=1020;$i<1030;$i++) {
 echo "Trying {$i} - ";
 try_to_post($i);
}
?>

output:

Trying 1020 - This was a triumph.
Trying 1021 - This was a triumph.
Trying 1022 - This was a triumph.
Trying 1023 - This was a triumph.
Trying 1024 - This was a triumph.
Trying 1025 - 
Trying 1026 - 
Trying 1027 - 
Trying 1028 - 
Trying 1029 - 

configuration:

PHP Version 5.2.6
libcurl/7.18.0 OpenSSL/0.9.8g zlib/1.2.3 libidn/1.8
lighttpd-1.4.19

Solution

Add the following option for cURL:

curl_setopt($ch,CURLOPT_HTTPHEADER,array("Expect:"));

The reason seems to be that any POST over 1024 character causes the "Expect: 100-continue" HTTP header to be sent, and Lighttpd 1.4.* does not support it. I found a ticket for it: http://redmine.lighttpd.net/issues/show/1017

They say it works in 1.5.

Answer 1

You can convince PHP's curl backend to stop doing the 100-continue-thing by setting an explicit request header:

curl_setopt($ch, CURLOPT_HTTPHEADER, array('Expect:'));

This way you can post a request however long you would ever want and curl will not do the dual phase post.

I've blogged about this nearly two years ago.