Source

File: wp-includes/class-wp-http-encoding.php

public static function compatible_gzinflate( $gzData ) {

		// Compressed data might contain a full header, if so strip it for gzinflate().
		if ( "\x1f\x8b\x08" === substr( $gzData, 0, 3 ) ) {
			$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 = @gzinflate( substr( $gzData, $i, -8 ) );
			if ( false !== $decompressed ) {
				return $decompressed;
			}
		}

		// Compressed data from java.util.zip.Deflater amongst others.
		$decompressed = @gzinflate( substr( $gzData, 2 ) );
		if ( false !== $decompressed ) {
			return $decompressed;
		}

		return false;
	}