Streams were introduced with PHP 4.3.0 as a way of generalizing file, network, data compression, and other operations which share a common set of functions and uses. In its simplest definition, a stream is a resource object which exhibits streamable behavior. That is, it can be read from or written to in a linear fashion, and may be able to fseek() to an arbitrary locations within the stream.
A wrapper is additional code which tells the stream how to handle specific protocols/encodings. For example, the http wrapper knows how to translate a URL into an HTTP/1.0 request for a file on a remote server. There are many wrappers built into PHP by default (See Appendix L), and additional, custom wrappers may be added either within a PHP script using stream_wrapper_register(), or directly from an extension using the API Reference in Chapter 59. Because any variety of wrapper may be added to PHP, there is no set limit on what can be done with them. To access the list of currently registered wrappers, use stream_get_wrappers().
A stream is referenced as: scheme://target
scheme(string) - The name of the wrapper to be used. Examples include: file, http, https, ftp, ftps, compress.zlib, compress.bz2, and php. See Appendix L for a list of PHP builtin wrappers. If no wrapper is specified, the function default is used (typically file://).
target - Depends on the wrapper used. For filesystem related streams this is typically a path and filename of the desired file. For network related streams this is typically a hostname, often with a path appended. Again, see Appendix L for a description of targets for builtin streams.
A filter is a final piece of code which may perform operations on data as it is being read from or written to a stream. Any number of filters may be stacked onto a stream. Custom filters can be defined in a PHP script using stream_filter_register() or in an extension using the API Reference in Chapter 59. To access the list of currently registered filters, use stream_get_filters().
A context is a set of parameters and wrapper specific options which modify or enhance the behavior of a stream. Contexts are created using stream_context_create() and can be passed to most filesystem related stream creation functions (i.e. fopen(), file(), file_get_contents(), etc...).
Options can be specified when calling stream_context_create(), or later using stream_context_set_option(). A list of wrapper specific options can be found with the list of built-in wrappers (See Appendix L).
In addition, parameters may be set on a context using stream_context_set_params(). Currently the only context parameter supported by PHP is notification. The value of this parameter must be the name of a function to be called when an event occurs on a stream. The notification function called during an event should accept the following six parameters:void my_notifier ( int notification_code, int severity, string message, int message_code, int bytes_transferred, int bytes_max)
notification_code and severity are numerical values which correspond to the STREAM_NOTIFY_* constants listed below. If a descriptive message is available from the stream, message and message_code will be populated with the appropriate values. The meaning of these values is dependent on the specific wrapper in use. bytes_transferred and bytes_max will be populated when applicable.
Streams are an integral part of PHP as of version 4.3.0. No steps are required to enable them.
User designed wrappers can be registered via stream_wrapper_register(), using the class definition shown on that manual page.
class php_user_filter is predefined and is an abstract baseclass for use with user defined filters. See the manual page for stream_filter_register() for details on implementing user defined filters.
The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.
|STREAM_FILTER_READ *||Used with stream_filter_append() and stream_filter_prepend() to indicate that the specified filter should only be applied when reading|
|STREAM_FILTER_WRITE *||Used with stream_filter_append() and stream_filter_prepend() to indicate that the specified filter should only be applied when writing|
|STREAM_FILTER_ALL *||This constant is equivalent to STREAM_FILTER_READ | STREAM_FILTER_WRITE|
|PSFS_PASS_ON *||Return Code indicating that the userspace filter returned buckets in $out.|
|PSFS_FEED_ME *||Return Code indicating that the userspace filter did not return buckets in $out (i.e. No data available).|
|PSFS_ERR_FATAL *||Return Code indicating that the userspace filter encountered an unrecoverable error (i.e. Invalid data received).|
|STREAM_USE_PATH||Flag indicating if the stream used the include path.|
|STREAM_REPORT_ERRORS||Flag indicating if the wrapper is responsible for raising errors using trigger_error() during opening of the stream. If this flag is not set, you should not raise any errors.|
|STREAM_CLIENT_ASYNC_CONNECT *||Open client socket asynchronously. Used with stream_socket_client().|
|STREAM_CLIENT_PERSISTENT *||Client socket opened with stream_socket_client() should remain persistent between page loads.|
|STREAM_SERVER_BIND *||Tells a stream created with stream_socket_server() to bind to the specified target. Server sockets should always include this flag.|
|STREAM_SERVER_LISTEN *||Tells a stream created with stream_socket_server() and bound using the STREAM_SERVER_BIND flag to start listening on the socket. Connection-orientated transports (such as TCP) must use this flag, otherwise the server socket will not be enabled. Using this flag for connect-less transports (such as UDP) is an error.|
|STREAM_NOTIFY_RESOLVE *||A remote address required for this stream has been resolved, or the resolution failed. See severity for an indication of which happened.|
|STREAM_NOTIFY_CONNECT||A connection with an external resource has been established.|
|STREAM_NOTIFY_AUTH_REQUIRED||Additional authorization is required to access the specified resource. Typical issued with severity level of STREAM_NOTIFY_SEVERITY_ERR.|
|STREAM_NOTIFY_MIME_TYPE_IS||The mime-type of resource has been identified, refer to message for a description of the discovered type.|
|STREAM_NOTIFY_FILE_SIZE_IS||The size of the resource has been discovered.|
|STREAM_NOTIFY_REDIRECTED||The external resource has redirected the stream to an alternate location. Refer to message.|
|STREAM_NOTIFY_PROGRESS||Indicates current progress of the stream transfer in bytes_transferred and possibly bytes_max as well.|
|STREAM_NOTIFY_COMPLETED *||There is no more data available on the stream.|
|STREAM_NOTIFY_FAILURE||A generic error occurred on the stream, consult message and message_code for details.|
|STREAM_NOTIFY_AUTH_RESULT||Authorization has been completed (with or without success).|
|STREAM_NOTIFY_SEVERITY_INFO||Normal, non-error related, notification.|
|STREAM_NOTIFY_SEVERITY_WARN||Non critical error condition. Processing may continue.|
|STREAM_NOTIFY_SEVERITY_ERR||A critical error occurred. Processing cannot continue.|
Note: The constants marked with * are just available in PHP 5.
As with any file or socket related function, an operation on a stream may fail for a variety of normal reasons (i.e.: Unable to connect to remote host, file not found, etc...). A stream related call may also fail because the desired stream is not registered on the running system. See the array returned by stream_get_wrappers() for a list of streams supported by your installation of PHP. As with most PHP internal functions if a failure occurs an E_WARNING message will be generated describing the nature of the error.
Example 1. Using file_get_contents() to retrieve data from multiple sources
Example 2. Making a POST request to an https server
Example 3. Writing data to a compressed file