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380 lines
15 KiB
Plaintext
An Overview of the PHP Streams abstraction
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==========================================
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$Id$
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WARNING: some prototypes in this file are out of date.
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The information contained here is being integrated into
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the PHP manual - stay tuned...
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Please send comments to: Wez Furlong <wez@thebrainroom.com>
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Why Streams?
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============
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You may have noticed a shed-load of issock parameters flying around the PHP
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code; we don't want them - they are ugly and cumbersome and force you to
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special case sockets and files every time you need to work with a "user-level"
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PHP file pointer.
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Streams take care of that and present the PHP extension coder with an ANSI
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stdio-alike API that looks much nicer and can be extended to support non file
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based data sources.
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Using Streams
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=============
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Streams use a php_stream* parameter just as ANSI stdio (fread etc.) use a
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FILE* parameter.
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The main functions are:
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PHPAPI size_t php_stream_read(php_stream * stream, char * buf, size_t count);
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PHPAPI size_t php_stream_write(php_stream * stream, const char * buf, size_t
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count);
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PHPAPI size_t php_stream_printf(php_stream * stream,
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const char * fmt, ...);
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PHPAPI int php_stream_eof(php_stream * stream);
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PHPAPI int php_stream_getc(php_stream * stream);
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PHPAPI char *php_stream_gets(php_stream * stream, char *buf, size_t maxlen);
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PHPAPI int php_stream_close(php_stream * stream);
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PHPAPI int php_stream_flush(php_stream * stream);
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PHPAPI int php_stream_seek(php_stream * stream, off_t offset, int whence);
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PHPAPI off_t php_stream_tell(php_stream * stream);
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PHPAPI int php_stream_lock(php_stream * stream, int mode);
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These (should) behave in the same way as the ANSI stdio functions with similar
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names: fread, fwrite, fprintf, feof, fgetc, fgets, fclose, fflush, fseek, ftell, flock.
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Opening Streams
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===============
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In most cases, you should use this API:
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PHPAPI php_stream *php_stream_open_wrapper(const char *path, const char *mode,
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int options, char **opened_path);
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Where:
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path is the file or resource to open.
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mode is the stdio compatible mode eg: "wb", "rb" etc.
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options is a combination of the following values:
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IGNORE_PATH (default) - don't use include path to search for the file
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USE_PATH - use include path to search for the file
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IGNORE_URL - do not use plugin wrappers
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REPORT_ERRORS - show errors in a standard format if something
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goes wrong.
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STREAM_MUST_SEEK - If you really need to be able to seek the stream
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and don't need to be able to write to the original
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file/URL, use this option to arrange for the stream
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to be copied (if needed) into a stream that can
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be seek()ed.
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opened_path is used to return the path of the actual file opened,
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but if you used STREAM_MUST_SEEK, may not be valid. You are
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responsible for efree()ing opened_path. opened_path may be (and usually
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is) NULL.
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If you need to open a specific stream, or convert standard resources into
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streams there are a range of functions to do this defined in php_streams.h.
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A brief list of the most commonly used functions:
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PHPAPI php_stream *php_stream_fopen_from_file(FILE *file, const char *mode);
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Convert a FILE * into a stream.
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PHPAPI php_stream *php_stream_fopen_tmpfile(void);
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Open a FILE * with tmpfile() and convert into a stream.
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PHPAPI php_stream *php_stream_fopen_temporary_file(const char *dir,
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const char *pfx, char **opened_path);
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Generate a temporary file name and open it.
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There are some network enabled relatives in php_network.h:
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PHPAPI php_stream *php_stream_sock_open_from_socket(int socket, int persistent);
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Convert a socket into a stream.
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PHPAPI php_stream *php_stream_sock_open_host(const char *host, unsigned short port,
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int socktype, int timeout, int persistent);
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Open a connection to a host and return a stream.
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PHPAPI php_stream *php_stream_sock_open_unix(const char *path, int persistent,
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struct timeval *timeout);
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Open a UNIX domain socket.
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Stream Utilities
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================
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If you need to copy some data from one stream to another, you will be please
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to know that the streams API provides a standard way to do this:
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PHPAPI size_t php_stream_copy_to_stream(php_stream *src,
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php_stream *dest, size_t maxlen);
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If you want to copy all remaining data from the src stream, pass
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PHP_STREAM_COPY_ALL as the maxlen parameter, otherwise maxlen indicates the
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number of bytes to copy.
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This function will try to use mmap where available to make the copying more
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efficient.
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If you want to read the contents of a stream into an allocated memory buffer,
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you should use:
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PHPAPI size_t php_stream_copy_to_mem(php_stream *src, char **buf,
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size_t maxlen, int persistent);
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This function will set buf to the address of the buffer that it allocated,
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which will be maxlen bytes in length, or will be the entire length of the
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data remaining on the stream if you set maxlen to PHP_STREAM_COPY_ALL.
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The buffer is allocated using pemalloc(); you need to call pefree() to
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release the memory when you are done.
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As with copy_to_stream, this function will try use mmap where it can.
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If you have an existing stream and need to be able to seek() it, you
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can use this function to copy the contents into a new stream that can
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be seek()ed:
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PHPAPI int php_stream_make_seekable(php_stream *origstream, php_stream **newstream);
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It returns one of the following values:
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#define PHP_STREAM_UNCHANGED 0 /* orig stream was seekable anyway */
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#define PHP_STREAM_RELEASED 1 /* newstream should be used; origstream is no longer valid */
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#define PHP_STREAM_FAILED 2 /* an error occurred while attempting conversion */
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#define PHP_STREAM_CRITICAL 3 /* an error occurred; origstream is in an unknown state; you should close origstream */
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make_seekable will always set newstream to be the stream that is valid
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if the function succeeds.
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When you have finished, remember to close the stream.
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NOTE: If you only need to seek forward, there is no need to call this
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function, as the php_stream_seek can emulate forward seeking when the
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whence parameter is SEEK_CUR.
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NOTE: Writing to the stream may not affect the original source, so it
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only makes sense to use this for read-only use.
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NOTE: If the origstream is network based, this function will block
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until the whole contents have been downloaded.
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NOTE: Never call this function with an origstream that is referenced
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as a resource! It will close the origstream on success, and this
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can lead to a crash when the resource is later used/released.
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NOTE: If you are opening a stream and need it to be seekable, use the
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STREAM_MUST_SEEK option to php_stream_open_wrapper();
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PHPAPI int php_stream_supports_lock(php_stream * stream);
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This function will return either 1 (success) or 0 (failure) indicating whether or
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not a lock can be set on this stream. Typically you can only set locks on stdio streams.
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Casting Streams
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===============
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What if your extension needs to access the FILE* of a user level file pointer?
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You need to "cast" the stream into a FILE*, and this is how you do it:
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FILE * fp;
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php_stream * stream; /* already opened */
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if (php_stream_cast(stream, PHP_STREAM_AS_STDIO, (void*)&fp, REPORT_ERRORS) == FAILURE) {
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RETURN_FALSE;
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}
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The prototype is:
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PHPAPI int php_stream_cast(php_stream * stream, int castas, void ** ret, int
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show_err);
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The show_err parameter, if non-zero, will cause the function to display an
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appropriate error message of type E_WARNING if the cast fails.
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castas can be one of the following values:
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PHP_STREAM_AS_STDIO - a stdio FILE*
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PHP_STREAM_AS_FD - a generic file descriptor
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PHP_STREAM_AS_SOCKETD - a socket descriptor
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If you ask a socket stream for a FILE*, the abstraction will use fdopen to
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create it for you. Be warned that doing so may cause buffered data to be lost
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if you mix ANSI stdio calls on the FILE* with php stream calls on the stream.
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If your system has the fopencookie function, php streams can synthesize a
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FILE* on top of any stream, which is useful for SSL sockets, memory based
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streams, data base streams etc. etc.
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In situations where this is not desirable, you should query the stream
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to see if it naturally supports FILE *. You can use this code snippet
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for this purpose:
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if (php_stream_is(stream, PHP_STREAM_IS_STDIO)) {
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/* can safely cast to FILE* with no adverse side effects */
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}
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You can use:
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PHPAPI int php_stream_can_cast(php_stream * stream, int castas)
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to find out if a stream can be cast, without actually performing the cast, so
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to check if a stream is a socket you might use:
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if (php_stream_can_cast(stream, PHP_STREAM_AS_SOCKETD) == SUCCESS) {
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/* it can be a socket */
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}
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Please note the difference between php_stream_is and php_stream_can_cast;
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stream_is tells you if the stream is a particular type of stream, whereas
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can_cast tells you if the stream can be forced into the form you request.
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The former doesn't change anything, while the later *might* change some
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state in the stream.
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Stream Internals
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================
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There are two main structures associated with a stream - the php_stream
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itself, which holds some state information (and possibly a buffer) and a
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php_stream_ops structure, which holds the "virtual method table" for the
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underlying implementation.
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The php_streams ops struct consists of pointers to methods that implement
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read, write, close, flush, seek, gets and cast operations. Of these, an
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implementation need only implement write, read, close and flush. The gets
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method is intended to be used for streams if there is an underlying method
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that can efficiently behave as fgets. The ops struct also contains a label
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for the implementation that will be used when printing error messages - the
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stdio implementation has a label of "STDIO" for example.
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The idea is that a stream implementation defines a php_stream_ops struct, and
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associates it with a php_stream using php_stream_alloc.
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As an example, the php_stream_fopen() function looks like this:
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PHPAPI php_stream * php_stream_fopen(const char * filename, const char * mode)
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{
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FILE * fp = fopen(filename, mode);
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php_stream * ret;
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if (fp) {
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ret = php_stream_alloc(&php_stream_stdio_ops, fp, 0, 0, mode);
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if (ret)
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return ret;
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fclose(fp);
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}
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return NULL;
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}
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php_stream_stdio_ops is a php_stream_ops structure that can be used to handle
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FILE* based streams.
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A socket based stream would use code similar to that above to create a stream
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to be passed back to fopen_wrapper (or it's yet to be implemented successor).
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The prototype for php_stream_alloc is this:
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PHPAPI php_stream * php_stream_alloc(php_stream_ops * ops, void * abstract,
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size_t bufsize, int persistent, const char * mode)
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ops is a pointer to the implementation,
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abstract holds implementation specific data that is relevant to this instance
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of the stream,
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bufsize is the size of the buffer to use - if 0, then buffering at the stream
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level will be disabled (recommended for underlying sources that implement
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their own buffering - such a FILE*),
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persistent controls how the memory is to be allocated - persistently so that
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it lasts across requests, or non-persistently so that it is freed at the end
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of a request (it uses pemalloc),
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mode is the stdio-like mode of operation - php streams places no real meaning
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in the mode parameter, except that it checks for a 'w' in the string when
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attempting to write (this may change).
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The mode parameter is passed on to fdopen/fopencookie when the stream is cast
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into a FILE*, so it should be compatible with the mode parameter of fopen().
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Writing your own stream implementation
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======================================
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!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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RULE #1: when writing your own streams: make sure you have configured PHP with
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--enable-debug.
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I've taken some great pains to hook into the Zend memory manager to help track
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down allocation problems. It will also help you spot incorrect use of the
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STREAMS_DC, STREAMS_CC and the semi-private STREAMS_REL_CC macros for function
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definitions.
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!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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RULE #2: Please use the stdio stream as a reference; it will help you
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understand the semantics of the stream operations, and it will always
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be more up to date than these docs :-)
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First, you need to figure out what data you need to associate with the
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php_stream. For example, you might need a pointer to some memory for memory
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based streams, or if you were making a stream to read data from an RDBMS like
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MySQL, you might want to store the connection and rowset handles.
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The stream has a field called abstract that you can use to hold this data.
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If you need to store more than a single field of data, define a structure to
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hold it, allocate it (use pemalloc with the persistent flag set
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appropriately), and use the abstract pointer to refer to it.
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For structured state you might have this:
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struct my_state {
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MYSQL conn;
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MYSQL_RES * result;
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};
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struct my_state * state = pemalloc(sizeof(struct my_state), persistent);
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/* initialize the connection, and run a query, using the fields in state to
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* hold the results */
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state->result = mysql_use_result(&state->conn);
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/* now allocate the stream itself */
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stream = php_stream_alloc(&my_ops, state, 0, persistent, "r");
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/* now stream->abstract == state */
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Once you have that part figured out, you can write your implementation and
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define the your own php_stream_ops struct (we called it my_ops in the above
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example).
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For example, for reading from this weird MySQL stream:
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static size_t php_mysqlop_read(php_stream * stream, char * buf, size_t count)
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{
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struct my_state * state = (struct my_state*)stream->abstract;
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if (buf == NULL && count == 0) {
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/* in this special case, php_streams is asking if we have reached the
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* end of file */
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if (... at end of file ...)
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return EOF;
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else
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return 0;
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}
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/* pull out some data from the stream and put it in buf */
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... mysql_fetch_row(state->result) ...
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/* we could do something strange, like format the data as XML here,
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and place that in the buf, but that brings in some complexities,
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such as coping with a buffer size too small to hold the data,
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so I won't even go in to how to do that here */
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}
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Implement the other operations - remember that write, read, close and flush
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are all mandatory. The rest are optional. Declare your stream ops struct:
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php_stream_ops my_ops = {
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php_mysqlop_write, php_mysqlop_read, php_mysqlop_close,
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php_mysqlop_flush, NULL, NULL, NULL,
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"Strange MySQL example"
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}
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Thats it!
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Take a look at the STDIO implementation in streams.c for more information
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about how these operations work.
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The main thing to remember is that in your close operation you need to release
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and free the resources you allocated for the abstract field. In the case of
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the example above, you need to use mysql_free_result on the rowset, close the
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connection and then use pefree to dispose of the struct you allocated.
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You may read the stream->persistent field to determine if your struct was
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allocated in persistent mode or not.
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vim:tw=78:et
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