Stream Contexts
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 List of Supported Protocols/Wrappers).
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:
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.
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Two important terms:
- An *option* is a protocol-specific setting, e.g. "method" (get, post, put...) if you are using HTTP or "callback function to be called when inserting a document" in MongoDB.
- A *parameter* is a settings that's common to all protocols. As of 2015 only one parameter got implemented ("notification").
While these words might look vague they are used coherently throughout the stream feature, documentation included.