Source

File: wp-includes/class-requests.php

public static function compatible_gzinflate($gzData) {
		// Compressed data might contain a full zlib header, if so strip it for
		// gzinflate()
		if (substr($gzData, 0, 3) == "\x1f\x8b\x08") {
			$i = 10;
			$flg = ord(substr($gzData, 3, 1));
			if ($flg > 0) {
				if ($flg & 4) {
					list($xlen) = unpack('v', substr($gzData, $i, 2));
					$i = $i + 2 + $xlen;
				}
				if ($flg & 8) {
					$i = strpos($gzData, "\0", $i) + 1;
				}
				if ($flg & 16) {
					$i = strpos($gzData, "\0", $i) + 1;
				}
				if ($flg & 2) {
					$i = $i + 2;
				}
			}
			$decompressed = self::compatible_gzinflate(substr($gzData, $i));
			if (false !== $decompressed) {
				return $decompressed;
			}
		}

		// If the data is Huffman Encoded, we must first strip the leading 2
		// byte Huffman marker for gzinflate()
		// The response is Huffman coded by many compressors such as
		// java.util.zip.Deflater, Ruby’s Zlib::Deflate, and .NET's
		// System.IO.Compression.DeflateStream.
		//
		// See https://decompres.blogspot.com/ for a quick explanation of this
		// data type
		$huffman_encoded = false;

		// low nibble of first byte should be 0x08
		list(, $first_nibble)    = unpack('h', $gzData);

		// First 2 bytes should be divisible by 0x1F
		list(, $first_two_bytes) = unpack('n', $gzData);

		if (0x08 == $first_nibble && 0 == ($first_two_bytes % 0x1F)) {
			$huffman_encoded = true;
		}

		if ($huffman_encoded) {
			if (false !== ($decompressed = @gzinflate(substr($gzData, 2)))) {
				return $decompressed;
			}
		}

		if ("\x50\x4b\x03\x04" == substr($gzData, 0, 4)) {
			// ZIP file format header
			// Offset 6: 2 bytes, General-purpose field
			// Offset 26: 2 bytes, filename length
			// Offset 28: 2 bytes, optional field length
			// Offset 30: Filename field, followed by optional field, followed
			// immediately by data
			list(, $general_purpose_flag) = unpack('v', substr($gzData, 6, 2));

			// If the file has been compressed on the fly, 0x08 bit is set of
			// the general purpose field. We can use this to differentiate
			// between a compressed document, and a ZIP file
			$zip_compressed_on_the_fly = (0x08 == (0x08 & $general_purpose_flag));

			if (!$zip_compressed_on_the_fly) {
				// Don't attempt to decode a compressed zip file
				return $gzData;
			}

			// Determine the first byte of data, based on the above ZIP header
			// offsets:
			$first_file_start = array_sum(unpack('v2', substr($gzData, 26, 4)));
			if (false !== ($decompressed = @gzinflate(substr($gzData, 30 + $first_file_start)))) {
				return $decompressed;
			}
			return false;
		}

		// Finally fall back to straight gzinflate
		if (false !== ($decompressed = @gzinflate($gzData))) {
			return $decompressed;
		}

		// Fallback for all above failing, not expected, but included for
		// debugging and preventing regressions and to track stats
		if (false !== ($decompressed = @gzinflate(substr($gzData, 2)))) {
			return $decompressed;
		}

		return false;
	}