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diff --git a/doc/source/qpack-howto.rst b/doc/source/qpack-howto.rst new file mode 100644 index 0000000..a38d285 --- /dev/null +++ b/doc/source/qpack-howto.rst @@ -0,0 +1,85 @@ +QPACK How-To +============ + +Using QPACK encoder +------------------- + +Firstly, create QPACK encoder by calling `nghttp3_qpack_encoder_new`. +It requires *hard_max_dtable_size* parameter. When in doubt, pass +4096 for this tutorial. Optionally, call +`nghttp3_qpack_encoder_set_max_dtable_capacity` to set the maximum +size of dynamic table. You can also call +`nghttp3_qpack_encoder_set_max_blocked_streams` to set the maximum +number of streams that can be blocked. + +In order to encode HTTP header fields, they must be stored in an array +of :type:`nghttp3_nv`. Then call `nghttp3_qpack_encoder_encode`. It +writes 3 buffers; *pbuf*, *rbuf*, and *ebuf*. They are a header block +prefix, request stream, and encoder stream respectively. A header +block prefix and request stream must be sent in this order to a stream +denoted by *stream_id* passed to the function. Encoder stream must be +sent to the encoder stream you setup. + +In order to read decoder stream, call +`nghttp3_qpack_encoder_read_decoder`. + +Once QPACK encoder is no longer used, call `nghttp3_qpack_encoder_del` +to free up memory allocated for it. + +Using QPACK decoder +------------------- + +`nghttp3_qpack_decoder_new` will create new QPACK decoder. It +requires *hard_max_dtable_size* and *max_blocked* parameters. When in +doubt, pass 4096 and 0 respectively for this tutorial. + +In order to read encoder stream, call +`nghttp3_qpack_decoder_read_encoder`. This might update dynamic +table, but does not emit any header fields. + +In order to read request stream, call +`nghttp3_qpack_decoder_read_request`. This is the function to emit +header fields. *sctx* stores a per-stream decoder state and must be +created by `nghttp3_qpack_stream_context_new`. It identifies a single +encoded header block in a particular request stream. *fin* must be +nonzero if and only if a passed data contains the last part of encoded +header block. + +The scope of :type:`nghttp3_qpack_stream_context` is per header block, +but `nghttp3_qpack_stream_context_reset` resets its state and can be +reused for an another header block in the same stream. In general, +you can reset it when you see that +:macro:`NGHTTP3_QPACK_DECODE_FLAG_FINAL` is set in *\*pflags*. When +:type:`nghttp3_qpack_stream_context` is no longer necessary, call +`nghttp3_qpack_stream_context_del` to free up its resource. + +`nghttp3_qpack_decoder_read_request` succeeds, *\*pflags* is assigned. +If it has :macro:`NGHTTP3_QPACK_DECODE_FLAG_EMIT` set, a header field +is emitted and stored in the buffer pointed by *nv*. If *\*pflags* +has :macro:`NGHTTP3_QPACK_DECODE_FLAG_FINAL` set, all header fields +have been successfully decoded. If *\*pflags* has +:macro:`NGHTTP3_QPACK_DECODE_FLAG_BLOCKED` set, decoding is blocked +due to required insert count, which means that more data must be read +by `nghttp3_qpack_decoder_read_encoder`. + +`nghttp3_qpack_decoder_read_request` returns the number of bytes read. +When a header field is emitted, it might read data partially. +Applciation has to call the function repeatedly by adjusting the +pointer to data and its length until the function consumes all data or +:macro:`NGHTTP3_QPACK_DECODE_FLAG_BLOCKED` is set in *\*pflags*. + +If *nv* is assigned, its :member:`nv->name <nghttp3_qpack_nv.name>` +and :member:`nv->value <nghttp3_qpack_nv.value>` are reference counted +and already incremented by 1. If application finishes processing +these values, it must call `nghttp3_rcbuf_decref(nv->name) +<nghttp3_rcbuf_decref>` and `nghttp3_rcbuf_decref(nv->value) +<nghttp3_rcbuf_decref>`. + +If an application has no interest to decode header fields for a +particular stream, call `nghttp3_qpack_decoder_cancel_stream`. + +In order to tell decoding state to an encoder, QPACK decoder has to +write decoder stream by calling `nghttp3_qpack_decoder_write_decoder`. + +Once QPACK decoder is no longer used, call `nghttp3_qpack_decoder_del` +to free up memory allocated for it. |