Return to README.STREAMS CVS log

Up to [ELWIX - Embedded LightWeight unIX -] / embedaddon / php

php 5.4.3+patches

    1: An Overview of the PHP Streams abstraction
    2: ==========================================
    3: $Id: README.STREAMS,v 1.1.1.2 2012/05/29 12:34:34 misho Exp $
    4: 
    5: WARNING: some prototypes in this file are out of date.
    6: The information contained here is being integrated into
    7: the PHP manual - stay tuned...
    8: 
    9: Please send comments to: Wez Furlong <wez@thebrainroom.com>
   10: 
   11: Why Streams?
   12: ============
   13: You may have noticed a shed-load of issock parameters flying around the PHP
   14: code; we don't want them - they are ugly and cumbersome and force you to
   15: special case sockets and files every time you need to work with a "user-level"
   16: PHP file pointer.
   17: Streams take care of that and present the PHP extension coder with an ANSI
   18: stdio-alike API that looks much nicer and can be extended to support non file
   19: based data sources.
   20: 
   21: Using Streams
   22: =============
   23: Streams use a php_stream* parameter just as ANSI stdio (fread etc.) use a
   24: FILE* parameter.
   25: 
   26: The main functions are:
   27: 
   28: PHPAPI size_t php_stream_read(php_stream * stream, char * buf, size_t count);
   29: PHPAPI size_t php_stream_write(php_stream * stream, const char * buf, size_t
   30:         count);
   31: PHPAPI size_t php_stream_printf(php_stream * stream TSRMLS_DC, 
   32:         const char * fmt, ...);
   33: PHPAPI int php_stream_eof(php_stream * stream);
   34: PHPAPI int php_stream_getc(php_stream * stream);
   35: PHPAPI char *php_stream_gets(php_stream * stream, char *buf, size_t maxlen);
   36: PHPAPI int php_stream_close(php_stream * stream);
   37: PHPAPI int php_stream_flush(php_stream * stream);
   38: PHPAPI int php_stream_seek(php_stream * stream, off_t offset, int whence);
   39: PHPAPI off_t php_stream_tell(php_stream * stream);
   40: PHPAPI int php_stream_lock(php_stream * stream, int mode);
   41: 
   42: These (should) behave in the same way as the ANSI stdio functions with similar
   43: names: fread, fwrite, fprintf, feof, fgetc, fgets, fclose, fflush, fseek, ftell, flock.
   44: 
   45: Opening Streams
   46: ===============
   47: In most cases, you should use this API:
   48: 
   49: PHPAPI php_stream *php_stream_open_wrapper(char *path, char *mode,
   50:     int options, char **opened_path TSRMLS_DC);
   51: 
   52: Where:
   53:     path is the file or resource to open.
   54:     mode is the stdio compatible mode eg: "wb", "rb" etc.
   55:     options is a combination of the following values:
   56:         IGNORE_PATH  (default) - don't use include path to search for the file
   57:         USE_PATH        - use include path to search for the file
   58:         IGNORE_URL      - do not use plugin wrappers
   59:         REPORT_ERRORS   - show errors in a standard format if something
   60:                           goes wrong.
   61:         STREAM_MUST_SEEK - If you really need to be able to seek the stream
   62:                            and don't need to be able to write to the original
   63:                            file/URL, use this option to arrange for the stream
   64:                            to be copied (if needed) into a stream that can
   65:                            be seek()ed.
   66:                            
   67:     opened_path is used to return the path of the actual file opened,
   68:     but if you used STREAM_MUST_SEEK, may not be valid.  You are
   69:     responsible for efree()ing opened_path.  opened_path may be (and usually
   70:     is) NULL.
   71: 
   72: If you need to open a specific stream, or convert standard resources into
   73: streams there are a range of functions to do this defined in php_streams.h.
   74: A brief list of the most commonly used functions:
   75: 
   76: PHPAPI php_stream *php_stream_fopen_from_file(FILE *file, const char *mode);
   77:     Convert a FILE * into a stream.
   78: 
   79: PHPAPI php_stream *php_stream_fopen_tmpfile(void);
   80:     Open a FILE * with tmpfile() and convert into a stream.
   81: 
   82: PHPAPI php_stream *php_stream_fopen_temporary_file(const char *dir,
   83:     const char *pfx, char **opened_path TSRMLS_DC);
   84:     Generate a temporary file name and open it.
   85: 
   86: There are some network enabled relatives in php_network.h:
   87: 
   88: PHPAPI php_stream *php_stream_sock_open_from_socket(int socket, int persistent);
   89:     Convert a socket into a stream.
   90: 
   91: PHPAPI php_stream *php_stream_sock_open_host(const char *host, unsigned short port,
   92: 		int socktype, int timeout, int persistent);
   93:     Open a connection to a host and return a stream.
   94: 
   95: PHPAPI php_stream *php_stream_sock_open_unix(const char *path, int persistent,
   96:     struct timeval *timeout);
   97:     Open a UNIX domain socket.
   98:    
   99: 
  100: Stream Utilities
  101: ================
  102: 
  103: If you need to copy some data from one stream to another, you will be please
  104: to know that the streams API provides a standard way to do this:
  105: 
  106: PHPAPI size_t php_stream_copy_to_stream(php_stream *src,
  107:     php_stream *dest, size_t maxlen);
  108: 
  109: If you want to copy all remaining data from the src stream, pass
  110: PHP_STREAM_COPY_ALL as the maxlen parameter, otherwise maxlen indicates the
  111: number of bytes to copy.
  112: This function will try to use mmap where available to make the copying more
  113: efficient.
  114: 
  115: If you want to read the contents of a stream into an allocated memory buffer,
  116: you should use:
  117: 
  118: PHPAPI size_t php_stream_copy_to_mem(php_stream *src, char **buf,
  119:     size_t maxlen, int persistent);
  120: 
  121: This function will set buf to the address of the buffer that it allocated,
  122: which will be maxlen bytes in length, or will be the entire length of the
  123: data remaining on the stream if you set maxlen to PHP_STREAM_COPY_ALL.
  124: The buffer is allocated using pemalloc(); you need to call pefree() to
  125: release the memory when you are done.
  126: As with copy_to_stream, this function will try use mmap where it can.
  127: 
  128: If you have an existing stream and need to be able to seek() it, you
  129: can use this function to copy the contents into a new stream that can
  130: be seek()ed:
  131: 
  132: PHPAPI int php_stream_make_seekable(php_stream *origstream, php_stream **newstream);
  133: 
  134: It returns one of the following values:
  135: #define PHP_STREAM_UNCHANGED	0 /* orig stream was seekable anyway */
  136: #define PHP_STREAM_RELEASED		1 /* newstream should be used; origstream is no longer valid */
  137: #define PHP_STREAM_FAILED		2 /* an error occurred while attempting conversion */
  138: #define PHP_STREAM_CRITICAL		3 /* an error occurred; origstream is in an unknown state; you should close origstream */
  139: 
  140: make_seekable will always set newstream to be the stream that is valid
  141: if the function succeeds.
  142: When you have finished, remember to close the stream.
  143: 
  144: NOTE: If you only need to seek forward, there is no need to call this
  145: function, as the php_stream_seek can emulate forward seeking when the
  146: whence parameter is SEEK_CUR.
  147: 
  148: NOTE: Writing to the stream may not affect the original source, so it
  149: only makes sense to use this for read-only use.
  150: 
  151: NOTE: If the origstream is network based, this function will block
  152: until the whole contents have been downloaded.
  153: 
  154: NOTE: Never call this function with an origstream that is referenced
  155: as a resource! It will close the origstream on success, and this
  156: can lead to a crash when the resource is later used/released.
  157: 
  158: NOTE: If you are opening a stream and need it to be seekable, use the
  159: STREAM_MUST_SEEK option to php_stream_open_wrapper();
  160: 
  161: PHPAPI int php_stream_supports_lock(php_stream * stream);
  162: 
  163: This function will return either 1 (success) or 0 (failure) indicating whether or
  164: not a lock can be set on this stream. Typically you can only set locks on stdio streams.
  165: 
  166: Casting Streams
  167: ===============
  168: What if your extension needs to access the FILE* of a user level file pointer?
  169: You need to "cast" the stream into a FILE*, and this is how you do it:
  170: 
  171: FILE * fp;
  172: php_stream * stream; /* already opened */
  173: 
  174: if (php_stream_cast(stream, PHP_STREAM_AS_STDIO, (void*)&fp, REPORT_ERRORS) == FAILURE)    {
  175:     RETURN_FALSE;
  176: }
  177: 
  178: The prototype is:
  179: 
  180: PHPAPI int php_stream_cast(php_stream * stream, int castas, void ** ret, int
  181:         show_err);
  182: 
  183: The show_err parameter, if non-zero, will cause the function to display an
  184: appropriate error message of type E_WARNING if the cast fails.
  185: 
  186: castas can be one of the following values:
  187: PHP_STREAM_AS_STDIO - a stdio FILE*
  188: PHP_STREAM_AS_FD - a generic file descriptor
  189: PHP_STREAM_AS_SOCKETD - a socket descriptor
  190: 
  191: If you ask a socket stream for a FILE*, the abstraction will use fdopen to
  192: create it for you.  Be warned that doing so may cause buffered data to be lost
  193: if you mix ANSI stdio calls on the FILE* with php stream calls on the stream.
  194: 
  195: If your system has the fopencookie function, php streams can synthesize a
  196: FILE* on top of any stream, which is useful for SSL sockets, memory based
  197: streams, data base streams etc. etc.
  198: 
  199: In situations where this is not desirable, you should query the stream
  200: to see if it naturally supports FILE *.  You can use this code snippet
  201: for this purpose:
  202: 
  203:     if (php_stream_is(stream, PHP_STREAM_IS_STDIO)) {
  204:         /* can safely cast to FILE* with no adverse side effects */
  205:     }
  206: 
  207: You can use:
  208: 
  209: PHPAPI int php_stream_can_cast(php_stream * stream, int castas)
  210: 
  211: to find out if a stream can be cast, without actually performing the cast, so
  212: to check if a stream is a socket you might use:
  213: 
  214: if (php_stream_can_cast(stream, PHP_STREAM_AS_SOCKETD) == SUCCESS)  {
  215:     /* it can be a socket */
  216: }
  217: 
  218: Please note the difference between php_stream_is and php_stream_can_cast;
  219: stream_is tells you if the stream is a particular type of stream, whereas
  220: can_cast tells you if the stream can be forced into the form you request.
  221: The former doesn't change anything, while the later *might* change some
  222: state in the stream.
  223: 
  224: Stream Internals
  225: ================
  226: 
  227: There are two main structures associated with a stream - the php_stream
  228: itself, which holds some state information (and possibly a buffer) and a
  229: php_stream_ops structure, which holds the "virtual method table" for the
  230: underlying implementation.
  231: 
  232: The php_streams ops struct consists of pointers to methods that implement
  233: read, write, close, flush, seek, gets and cast operations.  Of these, an
  234: implementation need only implement write, read, close and flush.  The gets
  235: method is intended to be used for streams if there is an underlying method
  236: that can efficiently behave as fgets.  The ops struct also contains a label
  237: for the implementation that will be used when printing error messages - the
  238: stdio implementation has a label of "STDIO" for example.
  239: 
  240: The idea is that a stream implementation defines a php_stream_ops struct, and
  241: associates it with a php_stream using php_stream_alloc.
  242: 
  243: As an example, the php_stream_fopen() function looks like this:
  244: 
  245: PHPAPI php_stream * php_stream_fopen(const char * filename, const char * mode)
  246: {
  247:     FILE * fp = fopen(filename, mode);
  248:     php_stream * ret;
  249:     
  250:     if (fp) {
  251:         ret = php_stream_alloc(&php_stream_stdio_ops, fp, 0, 0, mode);
  252:         if (ret)
  253:             return ret;
  254: 
  255:         fclose(fp);
  256:     }
  257:     return NULL;
  258: }
  259: 
  260: php_stream_stdio_ops is a php_stream_ops structure that can be used to handle
  261: FILE* based streams.
  262: 
  263: A socket based stream would use code similar to that above to create a stream
  264: to be passed back to fopen_wrapper (or it's yet to be implemented successor).
  265: 
  266: The prototype for php_stream_alloc is this:
  267: 
  268: PHPAPI php_stream * php_stream_alloc(php_stream_ops * ops, void * abstract,
  269:         size_t bufsize, int persistent, const char * mode)
  270: 
  271: ops is a pointer to the implementation,
  272: abstract holds implementation specific data that is relevant to this instance
  273: of the stream,
  274: bufsize is the size of the buffer to use - if 0, then buffering at the stream
  275: level will be disabled (recommended for underlying sources that implement
  276: their own buffering - such a FILE*),
  277: persistent controls how the memory is to be allocated - persistently so that
  278: it lasts across requests, or non-persistently so that it is freed at the end
  279: of a request (it uses pemalloc),
  280: mode is the stdio-like mode of operation - php streams places no real meaning
  281: in the mode parameter, except that it checks for a 'w' in the string when
  282: attempting to write (this may change).
  283: 
  284: The mode parameter is passed on to fdopen/fopencookie when the stream is cast
  285: into a FILE*, so it should be compatible with the mode parameter of fopen().
  286: 
  287: Writing your own stream implementation
  288: ======================================
  289: 
  290: !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  291: RULE #1: when writing your own streams: make sure you have configured PHP with
  292: --enable-debug.
  293: I've taken some great pains to hook into the Zend memory manager to help track
  294: down allocation problems.  It will also help you spot incorrect use of the
  295: STREAMS_DC, STREAMS_CC and the semi-private STREAMS_REL_CC macros for function
  296: definitions.
  297: !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  298: 
  299: RULE #2: Please use the stdio stream as a reference; it will help you
  300: understand the semantics of the stream operations, and it will always
  301: be more up to date than these docs :-)
  302: 
  303: First, you need to figure out what data you need to associate with the
  304: php_stream.  For example, you might need a pointer to some memory for memory
  305: based streams, or if you were making a stream to read data from an RDBMS like
  306: MySQL, you might want to store the connection and rowset handles.
  307: 
  308: The stream has a field called abstract that you can use to hold this data.
  309: If you need to store more than a single field of data, define a structure to
  310: hold it, allocate it (use pemalloc with the persistent flag set
  311: appropriately), and use the abstract pointer to refer to it.
  312: 
  313: For structured state you might have this:
  314: 
  315: struct my_state {
  316:     MYSQL conn;
  317:     MYSQL_RES * result;
  318: };
  319: 
  320: struct my_state * state = pemalloc(sizeof(struct my_state), persistent);
  321: 
  322: /* initialize the connection, and run a query, using the fields in state to
  323:  * hold the results */
  324: 
  325: state->result = mysql_use_result(&state->conn);
  326: 
  327: /* now allocate the stream itself */
  328: stream = php_stream_alloc(&my_ops, state, 0, persistent, "r");
  329: 
  330: /* now stream->abstract == state */
  331: 
  332: Once you have that part figured out, you can write your implementation and
  333: define the your own php_stream_ops struct (we called it my_ops in the above
  334: example).
  335: 
  336: For example, for reading from this weird MySQL stream:
  337: 
  338: static size_t php_mysqlop_read(php_stream * stream, char * buf, size_t count)
  339: {
  340:     struct my_state * state = (struct my_state*)stream->abstract;
  341: 
  342:     if (buf == NULL && count == 0)  {
  343:         /* in this special case, php_streams is asking if we have reached the
  344:          * end of file */
  345:         if (... at end of file ...)
  346:             return EOF;
  347:         else
  348:             return 0;
  349:     }
  350:     
  351:     /* pull out some data from the stream and put it in buf */
  352:     ... mysql_fetch_row(state->result) ...
  353:     /* we could do something strange, like format the data as XML here,
  354:         and place that in the buf, but that brings in some complexities,
  355:         such as coping with a buffer size too small to hold the data,
  356:         so I won't even go in to how to do that here */
  357: }
  358: 
  359: Implement the other operations - remember that write, read, close and flush
  360: are all mandatory.  The rest are optional.  Declare your stream ops struct:
  361: 
  362: php_stream_ops my_ops = {
  363:     php_mysqlop_write, php_mysqlop_read, php_mysqlop_close,
  364:     php_mysqlop_flush, NULL, NULL, NULL,
  365:     "Strange MySQL example"
  366: }
  367: 
  368: Thats it!
  369: 
  370: Take a look at the STDIO implementation in streams.c for more information
  371: about how these operations work.
  372: The main thing to remember is that in your close operation you need to release
  373: and free the resources you allocated for the abstract field.  In the case of
  374: the example above, you need to use mysql_free_result on the rowset, close the
  375: connection and then use pefree to dispose of the struct you allocated.
  376: You may read the stream->persistent field to determine if your struct was
  377: allocated in persistent mode or not.
  378: 
  379: vim:tw=78:et