Adds filtername to the list of filters attached to stream.
The target stream.
The filter name.
By default, stream_filter_append will attach the filter to the read filter chain if the file was opened for reading (i.e. File Mode: r, and/or +). The filter will also be attached to the write filter chain if the file was opened for writing (i.e. File Mode: w, a, and/or +). STREAM_FILTER_READ, STREAM_FILTER_WRITE, and/or STREAM_FILTER_ALL can also be passed to the read_write parameter to override this behavior.
This filter will be added with the specified params to the end of the list and will therefore be called last during stream operations. To add a filter to the beginning of the list, use stream_filter_prepend.
Returns a resource on success or false on failure. The resource can be used to refer to this filter instance during a call to stream_filter_remove.
false is returned if stream is not a resource or if filtername cannot be located.
Note:When using custom (user) filters
stream_filter_register must be called first in order to register the desired user filter to filtername.
Stream data is read from resources (both local and remote) in chunks, with any unconsumed data kept in internal buffers. When a new filter is appended to a stream, data in the internal buffers is processed through the new filter at that time. This differs from the behavior of stream_filter_prepend.
When a filter is added for read and write, two instances of the filter are created. stream_filter_append must be called twice with STREAM_FILTER_READ and STREAM_FILTER_WRITE to get both filter resources.