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84 ” Rolling Y o u Own r Logic to separate individual headers must account for the ability of header values to span multiple lines as per RFC 2616 Section 2.2. As such, preg_match_all is used here to separate individual headers. See the later chapter on PCRE for more information on regular expressions. If a situation necessitates parsing data contained in URLs and query strings, check out the parse_url and parse_str functions. As with the request, it is generally desirable to parse response data into a data structure for ease of reference. T r a Encoding s f e r Before parsing the body, the headers should be checked for a few things. If a Transfer-Encoding header is present and has a value of chunked, it means that the server is sending the response back in chunks rather than all at once. The advantage to this is that the server does not have to wait until the entire response is composed before starting to return it (in order to determine and include its length in the Content-Length header), which can increase o v e r a l l server throughput. When each chunk is sent, it is preceded by a hexadecimal number to indicate the size of the chunk followed by a CRLF sequence. The end of each chunk is also denoted by a CRLF sequence. The end of the body is denoted with a chunk size of 0, which is particularly important when using a persistent connection since the client must know where one response ends and the next begins. The strstr function can be used to obtain characters in a string prior to a newline. T oconvert strings containing hexadecimal numbers to their decimal equivalents, see the hexdec function. An example of what these two might look like in action is included below. The example assumes that a request body has been written to a string.
Rolling Y o u Own r ” 85 ?> See Section 3.6.1 and Appendix 19.4.6 of RFC 2616 for more information on chunked transfer encoding. Content Encoding If the zlib extension is loaded (which can be checked using the extension_loaded function or executing php -m from command line), the client can optionally include an Accept-Encoding header with a value of gzip,deflate in its request. If the server supports content compression, it will include a Content-Encoding header in its response with a value indicating which of the two compression schemes it used on the response body before sending it. The purpose of this is to reduce the amount of data being sent to reduce bandwidth consumption and increase throughput (assuming that compression and decompression takes less time than data transfer, which is generally the case). U p o n receiving the response, the client must decompress the response using the original scheme used by the server to compress it. • Y e the s function , names are correct. One would think that gzinflate would be used to decode a body encoded using the deflate encoding scheme. Apparently this is just an oddity in the naming scheme used by the zlib library. • When the encoding scheme is gzip, a GZIP header is included in the response. gzinflate does not respond well to this. H e n c e , the header (contained in the first 10 by t e s of the body) is stripped before the body is passed to gzinflate.
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