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doc: Update tutorial-client.rst

This commit is contained in:
Tatsuhiro Tsujikawa 2014-05-08 00:11:36 +09:00
parent d2890dfb91
commit 48fc0c04bc
1 changed files with 9 additions and 48 deletions
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doc/sources/tutorial-client.rst
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@ -159,7 +159,6 @@ finished successfully. We first initialize nghttp2 session object in
nghttp2_session_callbacks callbacks = {0};
callbacks.send_callback = send_callback;
callbacks.before_frame_send_callback = before_frame_send_callback;
callbacks.on_frame_recv_callback = on_frame_recv_callback;
callbacks.on_data_chunk_recv_callback = on_data_chunk_recv_callback;
callbacks.on_stream_close_callback = on_stream_close_callback;
@ -213,7 +212,7 @@ request in ``submit_request()`` function::
static void submit_request(http2_session_data *session_data)
{
int rv;
int32_t stream_id;
http2_stream_data *stream_data = session_data->stream_data;
const char *uri = stream_data->uri;
const struct http_parser_url *u = stream_data->u;
@ -226,11 +225,13 @@ request in ``submit_request()`` function::
};
fprintf(stderr, "Request headers:\n");
print_headers(stderr, hdrs, ARRLEN(hdrs));
rv = nghttp2_submit_request(session_data->session, NULL,
hdrs, ARRLEN(hdrs), NULL, stream_data);
if(rv != 0) {
errx(1, "Could not submit HTTP request: %s", nghttp2_strerror(rv));
stream_id = nghttp2_submit_request(session_data->session, NULL,
hdrs, ARRLEN(hdrs), NULL, stream_data);
if(stream_id < 0) {
errx(1, "Could not submit HTTP request: %s", nghttp2_strerror(stream_id));
}
stream_data->stream_id = stream_id;
}
We build HTTP request header fields in ``hdrs`` which is an array of
@ -239,6 +240,8 @@ We build HTTP request header fields in ``hdrs`` which is an array of
we use `nghttp2_submit_request()` function. The `stream_data` is
passed in *stream_user_data* parameter. It is used in nghttp2
callbacks which we'll describe about later.
`nghttp2_submit_request()` returns the newly assigned stream ID for
this request.
The next bufferevent callback is ``readcb()``, which is invoked when
data is available to read in the bufferevent input buffer::
@ -344,48 +347,6 @@ We have already described about nghttp2 callback ``send_callback()``.
Let's describe remaining nghttp2 callbacks we setup in
``initialize_nghttp2_setup()`` function.
The `before_frame_send_callback()` function is invoked when a frame is
about to be sent::
static int before_frame_send_callback
(nghttp2_session *session, const nghttp2_frame *frame, void *user_data)
{
http2_session_data *session_data = (http2_session_data*)user_data;
http2_stream_data *stream_data;
if(frame->hd.type == NGHTTP2_HEADERS &&
frame->headers.cat == NGHTTP2_HCAT_REQUEST) {
stream_data =
(http2_stream_data*)nghttp2_session_get_stream_user_data
(session, frame->hd.stream_id);
if(stream_data == session_data->stream_data) {
stream_data->stream_id = frame->hd.stream_id;
}
}
return 0;
}
Remember that we have not get stream ID when we submit HTTP request
using `nghttp2_submit_request()`. Since nghttp2 library reorders the
request based on priority and stream ID must be monotonically
increased, the stream ID is not assigned just before transmission.
The one of the purpose of this callback is get the stream ID assigned
to the frame. First we check that the frame is HEADERS frame. Since
HEADERS has several meanings in HTTP/2, we check that it is request
HEADERS (which means that the first HEADERS frame to create a stream).
The assigned stream ID is ``frame->hd.stream_id``. Recall that we
passed ``stream_data`` in the *stream_user_data* parameter of
`nghttp2_submit_request()` function. We can get it using
`nghttp2_session_get_stream_user_data()` function. To really sure that
this HEADERS frame is the request HEADERS we have queued, we check
that ``session_data->stream_data`` and ``stream_data`` returned from
`nghttp2_session_get_stream_user_data()` are pointing the same
location. In this example program, we just only uses 1 stream, it is
unnecessary to compare them, but real applications surely deal with
multiple streams, and *stream_user_data* is very handy to identify
which HEADERS we are seeing in the callback. Therefore we just show
how to use it here.
Each request header name/value pair is emitted via
``on_header_callback`` function::