How to decode/inflate a chunked gzip string? - php

Question

After making a gzip deflate request in PHP, I receive the deflated string in offset chunks, which looks like the following
Example shortened greatly to show format:
00001B4E
¾”kŒj…Øæ’ìÑ«F1ìÊ`+ƒQì¹UÜjùJƒZ\µy¡ÓUžGr‡J&=KLËÙÍ~=ÍkR
0000102F
ñÞœÞôΑüo[¾”+’Ñ8#à»0±R-4VÕ’n›êˆÍ.MCŽ…ÏÖr¿3M—èßñ°r¡\+
00000000
I'm unable to inflate that presumably because of the chunked format. I can confirm the data is not corrupt after manually removing the offsets with a Hex editor and reading the gzip archive. I'm wondering if there's a proper method to parse this chunked gzip deflated response into a readable string?
I might be able to split these offsets and join the data together in one string to call gzinflate, but it seems there must be an easier way.

Answer 1

The proper method to deflate a chunked response is roughly as follows:
initialise string to hold result
for each chunk {
check that the stated chunk length equals the string length of the chunk
append the chunk data to the result variable
}
Here's a handy PHP function to do that for you (FIXED):
function unchunk_string ($str) {
// A string to hold the result
$result = '';
// Split input by CRLF
$parts = explode("\r\n", $str);
// These vars track the current chunk
$chunkLen = 0;
$thisChunk = '';
// Loop the data
while (($part = array_shift($parts)) !== NULL) {
if ($chunkLen) {
// Add the data to the string
// Don't forget, the data might contain a literal CRLF
$thisChunk .= $part."\r\n";
if (strlen($thisChunk) == $chunkLen) {
// Chunk is complete
$result .= $thisChunk;
$chunkLen = 0;
$thisChunk = '';
} else if (strlen($thisChunk) == $chunkLen + 2) {
// Chunk is complete, remove trailing CRLF
$result .= substr($thisChunk, 0, -2);
$chunkLen = 0;
$thisChunk = '';
} else if (strlen($thisChunk) > $chunkLen) {
// Data is malformed
return FALSE;
}
} else {
// If we are not in a chunk, get length of the new one
if ($part === '') continue;
if (!$chunkLen = hexdec($part)) break;
}
}
// Return the decoded data of FALSE if it is incomplete
return ($chunkLen) ? FALSE : $result;
}

Answer 2

To decode a String use gzinflate, Zend_Http_Client lib will help to do this kind of common tasks, its wasy to use, Refer Zend_Http_Response code if you need to do it on your own

Answer 3

The solution from user #user1309276 really helped me! Received from the server a gzip-compressed json response with transfer-encoding: chunked header. None of the solutions helped. This solution works like magic for me! It just remove the first 10 bytes.
$data = json_decode(gzinflate(substr($response->getContent(), 10)), true);