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| -rw-r--r-- | doc/src/guide/streams.asciidoc | 60 |
1 files changed, 59 insertions, 1 deletions
diff --git a/doc/src/guide/streams.asciidoc b/doc/src/guide/streams.asciidoc index dc38a52..841a971 100644 --- a/doc/src/guide/streams.asciidoc +++ b/doc/src/guide/streams.asciidoc @@ -1,7 +1,65 @@ [[streams]] == Streams -Placeholder chapter. +A stream is the set of messages that form an HTTP +request/response pair. +The term stream comes from HTTP/2. In Cowboy, it is +also used when talking about HTTP/1.1 or HTTP/1.0. +It should not be confused with streaming the request +or response body. +All versions of HTTP allow clients to initiate +streams. HTTP/2 is the only one also allowing servers, +through its server push feature. Both client and +server-initiated streams go through the same process +in Cowboy. +=== Stream handlers + +Stream handlers must implement five different callbacks. +Four of them are directly related; one is special. + +All callbacks receives the stream ID as first argument. + +Most of them can return a list of commands to be executed +by Cowboy. When callbacks are chained, it is possible to +intercept and modify these commands. This can be useful +for modifying responses for example. + +The `init/3` callback is invoked when a new request +comes in. It receives the Req object and the protocol options +for this listener. + +The `data/4` callback is invoked when data from the request +body is received. It receives both this data and a flag +indicating whether more is to be expected. + +The `info/3` callback is invoked when an Erlang message is +received for this stream. They will typically be messages +sent by the request process. + +Finally the `terminate/3` callback is invoked with the +terminate reason for the stream. The return value is ignored. +Note that as with all terminate callbacks in Erlang, there +is no strong guarantee that it will be called. + +The special callback `early_error/5` is called when an error +occurs before the request headers were fully received and +Cowboy is sending a response. It receives the partial Req +object, the error reason, the protocol options and the response +Cowboy will send. This response must be returned, possibly +modified. + +=== Built-in handlers + +Cowboy comes with two handlers. + +`cowboy_stream_h` is the default stream handler. +It is the core of much of the functionality of Cowboy. +All chains of stream handlers should call it last. + +`cowboy_compress_h` will automatically compress +responses when possible. It is not enabled by default. +It is a good example for writing your own handlers +that will modify responses. |