Tutorial: HTTP/2 clientΒΆ
In this tutorial, we are going to write very primitive HTTP/2 client. The complete source code, libevent-client.c, is attached at the end of this page. It also resides in examples directory in the archive or repository.
This simple client takes 1 argument, HTTPS URI, and retrieves the resource denoted by the URI. Its synopsis is like this:
$ libevent-client HTTPS_URI
We use libevent in this tutorial to handle networking I/O. Please note that nghttp2 itself does not depend on libevent.
First we do some setup routine for libevent and OpenSSL library in function main() and run(), which is not so relevant to nghttp2 library use. The one thing you should look at is setup NPN callback. The NPN callback is used for the client to select the next application protocol over the SSL/TLS transport. In this tutorial, we use nghttp2_select_next_protocol() function to select the HTTP/2 protocol the library supports:
static int select_next_proto_cb(SSL* ssl,
unsigned char **out, unsigned char *outlen,
const unsigned char *in, unsigned int inlen,
void *arg)
{
if(nghttp2_select_next_protocol(out, outlen, in, inlen) <= 0) {
errx(1, "Server did not advertise " NGHTTP2_PROTO_VERSION_ID);
}
return SSL_TLSEXT_ERR_OK;
}
The callback is set to the SSL_CTX object using SSL_CTX_set_next_proto_select_cb() function:
static SSL_CTX* create_ssl_ctx(void)
{
SSL_CTX *ssl_ctx;
ssl_ctx = SSL_CTX_new(SSLv23_client_method());
if(!ssl_ctx) {
errx(1, "Could not create SSL/TLS context: %s",
ERR_error_string(ERR_get_error(), NULL));
}
SSL_CTX_set_options(ssl_ctx,
SSL_OP_ALL | SSL_OP_NO_SSLv2 | SSL_OP_NO_COMPRESSION |
SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION);
SSL_CTX_set_next_proto_select_cb(ssl_ctx, select_next_proto_cb, NULL);
return ssl_ctx;
}
We use http2_session_data structure to store the data related to the HTTP/2 session:
typedef struct {
nghttp2_session *session;
struct evdns_base *dnsbase;
struct bufferevent *bev;
http2_stream_data *stream_data;
} http2_session_data;
Since this program only handles 1 URI, it uses only 1 stream. We store its stream specific data in http2_stream_data structure and the stream_data points to it. The struct http2_stream_data is defined as follows:
typedef struct {
/* The NULL-terminated URI string to retreive. */
const char *uri;
/* Parsed result of the |uri| */
struct http_parser_url *u;
/* The authroity portion of the |uri|, not NULL-terminated */
char *authority;
/* The path portion of the |uri|, including query, not
NULL-terminated */
char *path;
/* The length of the |authority| */
size_t authoritylen;
/* The length of the |path| */
size_t pathlen;
/* The stream ID of this stream */
int32_t stream_id;
} http2_stream_data;
We creates and initializes these structures in create_http2_session_data() and create_http2_stream_data() respectively.
Then we call function initiate_connection() to start connecting to the remote server:
static void initiate_connection(struct event_base *evbase,
SSL_CTX *ssl_ctx,
const char *host, uint16_t port,
http2_session_data *session_data)
{
int rv;
struct bufferevent *bev;
SSL *ssl;
ssl = create_ssl(ssl_ctx);
bev = bufferevent_openssl_socket_new(evbase, -1, ssl,
BUFFEREVENT_SSL_CONNECTING,
BEV_OPT_DEFER_CALLBACKS |
BEV_OPT_CLOSE_ON_FREE);
bufferevent_setcb(bev, readcb, writecb, eventcb, session_data);
rv = bufferevent_socket_connect_hostname(bev, session_data->dnsbase,
AF_UNSPEC, host, port);
if(rv != 0) {
errx(1, "Could not connect to the remote host %s", host);
}
session_data->bev = bev;
}
We set 3 callbacks for the bufferevent: reacb, writecb and eventcb.
The eventcb() is invoked by libevent event loop when an event (e.g., connection has been established, timeout, etc) happens on the underlying network socket:
static void eventcb(struct bufferevent *bev, short events, void *ptr)
{
http2_session_data *session_data = (http2_session_data*)ptr;
if(events & BEV_EVENT_CONNECTED) {
int fd = bufferevent_getfd(bev);
int val = 1;
fprintf(stderr, "Connected\n");
setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, (char *)&val, sizeof(val));
initialize_nghttp2_session(session_data);
send_client_connection_header(session_data);
submit_request(session_data);
if(session_send(session_data) != 0) {
delete_http2_session_data(session_data);
}
return;
}
if(events & BEV_EVENT_EOF) {
warnx("Disconnected from the remote host");
} else if(events & BEV_EVENT_ERROR) {
warnx("Network error");
} else if(events & BEV_EVENT_TIMEOUT) {
warnx("Timeout");
}
delete_http2_session_data(session_data);
}
For BEV_EVENT_EOF, BEV_EVENT_ERROR and BEV_EVENT_TIMEOUT event, we just simply tear down the connection. The BEV_EVENT_CONNECTED event is invoked when SSL/TLS handshake is finished successfully. We first initialize nghttp2 session object in initialize_nghttp2_session() function:
static void initialize_nghttp2_session(http2_session_data *session_data)
{
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;
callbacks.on_header_callback = on_header_callback;
callbacks.on_begin_headers_callback = on_begin_headers_callback;
nghttp2_session_client_new(&session_data->session, &callbacks, session_data);
}
Since we are creating client, we use nghttp2_session_client_new() to initialize nghttp2 session object. We setup 7 callbacks for the nghttp2 session. We’ll explain these callbacks later.
The delete_http2_session_data() destroys session_data and frees its bufferevent, so it closes underlying connection as well. It also calls nghttp2_session_del() to delete nghttp2 session object.
We begin HTTP/2 communication by sending client connection preface, which is 24 bytes magic byte sequence (NGHTTP2_CLIENT_CONNECTION_PREFACE) and SETTINGS frame. The transmission of client connection header is done in send_client_connection_header():
static void send_client_connection_header(http2_session_data *session_data)
{
nghttp2_settings_entry iv[1] = {
{ NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS, 100 }
};
int rv;
bufferevent_write(session_data->bev,
NGHTTP2_CLIENT_CONNECTION_PREFACE,
NGHTTP2_CLIENT_CONNECTION_PREFACE_LEN);
rv = nghttp2_submit_settings(session_data->session, NGHTTP2_FLAG_NONE,
iv, ARRLEN(iv));
if(rv != 0) {
errx(1, "Could not submit SETTINGS: %s", nghttp2_strerror(rv));
}
}
Here we specify SETTINGS_MAX_CONCURRENT_STREAMS to 100, which is really not needed for this tiny example progoram, but we are demonstrating the use of SETTINGS frame. To queue the SETTINGS frame for the transmission, we use nghttp2_submit_settings(). Note that nghttp2_submit_settings() function only queues the frame and not actually send it. All nghttp2_submit_*() family functions have this property. To actually send the frame, nghttp2_session_send() is used, which is described about later.
After the transmission of client connection header, we enqueue HTTP request in submit_request() function:
static void submit_request(http2_session_data *session_data)
{
int rv;
http2_stream_data *stream_data = session_data->stream_data;
const char *uri = stream_data->uri;
const struct http_parser_url *u = stream_data->u;
nghttp2_nv hdrs[] = {
MAKE_NV2(":method", "GET"),
MAKE_NV(":scheme",
&uri[u->field_data[UF_SCHEMA].off], u->field_data[UF_SCHEMA].len),
MAKE_NV(":authority", stream_data->authority, stream_data->authoritylen),
MAKE_NV(":path", stream_data->path, stream_data->pathlen)
};
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));
}
}
We build HTTP request header fields in hdrs which is an array of nghttp2_nv. There are 4 header fields to be sent: :method, :scheme, :authority and :path. To queue this HTTP request, 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.
The next bufferevent callback is readcb(), which is invoked when data is available to read in the bufferevent input buffer:
static void readcb(struct bufferevent *bev, void *ptr)
{
http2_session_data *session_data = (http2_session_data*)ptr;
int rv;
struct evbuffer *input = bufferevent_get_input(bev);
size_t datalen = evbuffer_get_length(input);
unsigned char *data = evbuffer_pullup(input, -1);
rv = nghttp2_session_mem_recv(session_data->session, data, datalen);
if(rv < 0) {
warnx("Fatal error: %s", nghttp2_strerror(rv));
delete_http2_session_data(session_data);
return;
}
evbuffer_drain(input, rv);
if(session_send(session_data) != 0) {
delete_http2_session_data(session_data);
return;
}
}
In this function, we feed all unprocessed, received data to nghttp2 session object using nghttp2_session_mem_recv() function. The nghttp2_session_mem_recv() processes the received data and may invoke nghttp2 callbacks and also queue frames. Since there may be pending frames, we call session_send() function to send those frames. The session_send() function is defined as follows:
static int session_send(http2_session_data *session_data)
{
int rv;
rv = nghttp2_session_send(session_data->session);
if(rv != 0) {
warnx("Fatal error: %s", nghttp2_strerror(rv));
return -1;
}
return 0;
}
The nghttp2_session_send() function serializes the frame into wire format and call nghttp2_session_callbacks.send_callback with it. We set send_callback() function to nghttp2_session_callbacks.send_callback in initialize_nghttp2_session() function described earlier. It is defined as follows:
static ssize_t send_callback(nghttp2_session *session,
const uint8_t *data, size_t length,
int flags, void *user_data)
{
http2_session_data *session_data = (http2_session_data*)user_data;
struct bufferevent *bev = session_data->bev;
bufferevent_write(bev, data, length);
return length;
}
Since we use bufferevent to abstract network I/O, we just write the data to the bufferevent object. Note that nghttp2_session_send() continues to write all frames queued so far. If we were writing the data to the non-blocking socket directly using write() system call in the nghttp2_session_callbacks.send_callback, we will surely get EAGAIN or EWOULDBLOCK since the socket has limited send buffer. If that happens, we can return NGHTTP2_ERR_WOULDBLOCK to signal the nghttp2 library to stop sending further data. But writing to the bufferevent, we have to regulate the amount data to be buffered by ourselves to avoid possible huge memory consumption. In this example client, we do not limit anything. To see how to regulate the amount of buffered data, see the send_callback() in the server tutorial.
The third bufferevent callback is writecb(), which is invoked when all data written in the bufferevent output buffer have been sent:
static void writecb(struct bufferevent *bev, void *ptr)
{
http2_session_data *session_data = (http2_session_data*)ptr;
if(nghttp2_session_want_read(session_data->session) == 0 &&
nghttp2_session_want_write(session_data->session) == 0 &&
evbuffer_get_length(bufferevent_get_output(session_data->bev)) == 0) {
delete_http2_session_data(session_data);
}
}
As described earlier, we just write off all data in send_callback(), we have no data to write in this function. All we have to do is check we have to drop connection or not. The nghttp2 session object keeps track of reception and transmission of GOAWAY frame and other error conditions as well. Using these information, nghttp2 session object will tell whether the connection should be dropped or not. More specifically, both nghttp2_session_want_read() and nghttp2_session_want_write() return 0, we have no business in the connection. But since we are using bufferevent and its deferred callback option, the bufferevent output buffer may contain the pending data when the writecb() is called. To handle this situation, we also check whether the output buffer is empty or not. If these conditions are met, we drop connection.
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:
static int on_header_callback(nghttp2_session *session,
const nghttp2_frame *frame,
const uint8_t *name, size_t namelen,
const uint8_t *value, size_t valuelen,
uint8_t flags,
void *user_data)
{
http2_session_data *session_data = (http2_session_data*)user_data;
switch(frame->hd.type) {
case NGHTTP2_HEADERS:
if(frame->headers.cat == NGHTTP2_HCAT_RESPONSE &&
session_data->stream_data->stream_id == frame->hd.stream_id) {
/* Print response headers for the initiated request. */
print_header(stderr, name, namelen, value, valuelen);
break;
}
}
return 0;
}
In this turotial, we just print the name/value pair.
After all name/value pairs are emitted for a frame, on_frame_recv_callback function is called:
static int on_frame_recv_callback(nghttp2_session *session,
const nghttp2_frame *frame, void *user_data)
{
http2_session_data *session_data = (http2_session_data*)user_data;
switch(frame->hd.type) {
case NGHTTP2_HEADERS:
if(frame->headers.cat == NGHTTP2_HCAT_RESPONSE &&
session_data->stream_data->stream_id == frame->hd.stream_id) {
fprintf(stderr, "All headers received\n");
}
break;
}
return 0;
}
In this tutorial, we are just interested in the HTTP response HEADERS. We check te frame type and its category (it should be NGHTTP2_HCAT_RESPONSE for HTTP response HEADERS). Also check its stream ID.
The on_data_chunk_recv_callback() function is invoked when a chunk of data is received from the remote peer:
static int on_data_chunk_recv_callback(nghttp2_session *session, uint8_t flags,
int32_t stream_id,
const uint8_t *data, size_t len,
void *user_data)
{
http2_session_data *session_data = (http2_session_data*)user_data;
if(session_data->stream_data->stream_id == stream_id) {
fwrite(data, len, 1, stdout);
}
return 0;
}
In our case, a chunk of data is response body. After checking stream ID, we just write the recieved data to the stdout. Note that the output in the terminal may be corrupted if the response body contains some binary data.
The on_stream_close_callback() function is invoked when the stream is about to close:
static int on_stream_close_callback(nghttp2_session *session,
int32_t stream_id,
nghttp2_error_code error_code,
void *user_data)
{
http2_session_data *session_data = (http2_session_data*)user_data;
int rv;
if(session_data->stream_data->stream_id == stream_id) {
fprintf(stderr, "Stream %d closed with error_code=%d\n",
stream_id, error_code);
rv = nghttp2_session_terminate_session(session, NGHTTP2_NO_ERROR);
if(rv != 0) {
return NGHTTP2_ERR_CALLBACK_FAILURE;
}
}
return 0;
}
If the stream ID matches the one we initiated, it means that its stream is going to be closed. Since we have finished to get the resource we want (or the stream was reset by RST_STREAM from the remote peer), we call nghttp2_session_terminate_session() to commencing the closure of the HTTP/2 session gracefully. If you have some data associated for the stream to be closed, you may delete it here.
libevent-client.cΒΆ
/*
* nghttp2 - HTTP/2 C Library
*
* Copyright (c) 2013 Tatsuhiro Tsujikawa
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
#include <sys/types.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <err.h>
#include <signal.h>
#include <openssl/ssl.h>
#include <openssl/err.h>
#include <event.h>
#include <event2/event.h>
#include <event2/bufferevent_ssl.h>
#include <event2/dns.h>
#include <nghttp2/nghttp2.h>
#include "http-parser/http_parser.h"
#define ARRLEN(x) (sizeof(x)/sizeof(x[0]))
typedef struct {
/* The NULL-terminated URI string to retreive. */
const char *uri;
/* Parsed result of the |uri| */
struct http_parser_url *u;
/* The authroity portion of the |uri|, not NULL-terminated */
char *authority;
/* The path portion of the |uri|, including query, not
NULL-terminated */
char *path;
/* The length of the |authority| */
size_t authoritylen;
/* The length of the |path| */
size_t pathlen;
/* The stream ID of this stream */
int32_t stream_id;
} http2_stream_data;
typedef struct {
nghttp2_session *session;
struct evdns_base *dnsbase;
struct bufferevent *bev;
http2_stream_data *stream_data;
} http2_session_data;
static http2_stream_data* create_http2_stream_data(const char *uri,
struct http_parser_url *u)
{
/* MAX 5 digits (max 65535) + 1 ':' + 1 NULL (because of snprintf) */
size_t extra = 7;
http2_stream_data *stream_data = malloc(sizeof(http2_stream_data));
stream_data->uri = uri;
stream_data->u = u;
stream_data->stream_id = -1;
stream_data->authoritylen = u->field_data[UF_HOST].len;
stream_data->authority = malloc(stream_data->authoritylen + extra);
memcpy(stream_data->authority,
&uri[u->field_data[UF_HOST].off], u->field_data[UF_HOST].len);
if(u->field_set & (1 << UF_PORT)) {
stream_data->authoritylen +=
snprintf(stream_data->authority + u->field_data[UF_HOST].len, extra,
":%u", u->port);
}
stream_data->pathlen = 0;
if(u->field_set & (1 << UF_PATH)) {
stream_data->pathlen = u->field_data[UF_PATH].len;
}
if(u->field_set & (1 << UF_QUERY)) {
/* +1 for '?' character */
stream_data->pathlen += u->field_data[UF_QUERY].len + 1;
}
if(stream_data->pathlen > 0) {
stream_data->path = malloc(stream_data->pathlen);
if(u->field_set & (1 << UF_PATH)) {
memcpy(stream_data->path,
&uri[u->field_data[UF_PATH].off], u->field_data[UF_PATH].len);
}
if(u->field_set & (1 << UF_QUERY)) {
memcpy(stream_data->path + u->field_data[UF_PATH].len + 1,
&uri[u->field_data[UF_QUERY].off], u->field_data[UF_QUERY].len);
}
} else {
stream_data->path = NULL;
}
return stream_data;
}
static void delete_http2_stream_data(http2_stream_data *stream_data)
{
free(stream_data->path);
free(stream_data->authority);
free(stream_data);
}
/* Initializes |session_data| */
static http2_session_data *create_http2_session_data(struct event_base *evbase)
{
http2_session_data *session_data = malloc(sizeof(http2_session_data));
memset(session_data, 0, sizeof(http2_session_data));
session_data->dnsbase = evdns_base_new(evbase, 1);
return session_data;
}
static void delete_http2_session_data(http2_session_data *session_data)
{
SSL *ssl = bufferevent_openssl_get_ssl(session_data->bev);
if(ssl) {
SSL_shutdown(ssl);
}
bufferevent_free(session_data->bev);
session_data->bev = NULL;
evdns_base_free(session_data->dnsbase, 1);
session_data->dnsbase = NULL;
nghttp2_session_del(session_data->session);
session_data->session = NULL;
if(session_data->stream_data) {
delete_http2_stream_data(session_data->stream_data);
session_data->stream_data = NULL;
}
free(session_data);
}
static void print_header(FILE *f,
const uint8_t *name, size_t namelen,
const uint8_t *value, size_t valuelen)
{
fwrite(name, namelen, 1, f);
fprintf(f, ": ");
fwrite(value, valuelen, 1, f);
fprintf(f, "\n");
}
/* Print HTTP headers to |f|. Please note that this function does not
take into account that header name and value are sequence of
octets, therefore they may contain non-printable characters. */
static void print_headers(FILE *f, nghttp2_nv *nva, size_t nvlen)
{
size_t i;
for(i = 0; i < nvlen; ++i) {
print_header(f,
nva[i].name, nva[i].namelen,
nva[i].value, nva[i].valuelen);
}
fprintf(f, "\n");
}
/* nghttp2_send_callback. Here we transmit the |data|, |length| bytes,
to the network. Because we are using libevent bufferevent, we just
write those bytes into bufferevent buffer. */
static ssize_t send_callback(nghttp2_session *session,
const uint8_t *data, size_t length,
int flags, void *user_data)
{
http2_session_data *session_data = (http2_session_data*)user_data;
struct bufferevent *bev = session_data->bev;
bufferevent_write(bev, data, length);
return length;
}
/* nghttp2_before_frame_send_callback: Called when nghttp2 library is
about to send a frame. We use this callback to get stream ID of new
stream. Since HEADERS in HTTP/2 has several roles, we check that
it is a HTTP request HEADERS. */
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;
}
/* nghttp2_on_header_callback: Called when nghttp2 library emits
single header name/value pair. */
static int on_header_callback(nghttp2_session *session,
const nghttp2_frame *frame,
const uint8_t *name, size_t namelen,
const uint8_t *value, size_t valuelen,
uint8_t flags,
void *user_data)
{
http2_session_data *session_data = (http2_session_data*)user_data;
switch(frame->hd.type) {
case NGHTTP2_HEADERS:
if(frame->headers.cat == NGHTTP2_HCAT_RESPONSE &&
session_data->stream_data->stream_id == frame->hd.stream_id) {
/* Print response headers for the initiated request. */
print_header(stderr, name, namelen, value, valuelen);
break;
}
}
return 0;
}
/* nghttp2_on_begin_headers_callback: Called when nghttp2 library gets
started to receive header block. */
static int on_begin_headers_callback(nghttp2_session *session,
const nghttp2_frame *frame,
void *user_data)
{
http2_session_data *session_data = (http2_session_data*)user_data;
switch(frame->hd.type) {
case NGHTTP2_HEADERS:
if(frame->headers.cat == NGHTTP2_HCAT_RESPONSE &&
session_data->stream_data->stream_id == frame->hd.stream_id) {
fprintf(stderr, "Response headers for stream ID=%d:\n",
frame->hd.stream_id);
}
break;
}
return 0;
}
/* nghttp2_on_frame_recv_callback: Called when nghttp2 library
received a complete frame from the remote peer. */
static int on_frame_recv_callback(nghttp2_session *session,
const nghttp2_frame *frame, void *user_data)
{
http2_session_data *session_data = (http2_session_data*)user_data;
switch(frame->hd.type) {
case NGHTTP2_HEADERS:
if(frame->headers.cat == NGHTTP2_HCAT_RESPONSE &&
session_data->stream_data->stream_id == frame->hd.stream_id) {
fprintf(stderr, "All headers received\n");
}
break;
}
return 0;
}
/* nghttp2_on_data_chunk_recv_callback: Called when DATA frame is
received from the remote peer. In this implementation, if the frame
is meant to the stream we initiated, print the received data in
stdout, so that the user can redirect its output to the file
easily. */
static int on_data_chunk_recv_callback(nghttp2_session *session, uint8_t flags,
int32_t stream_id,
const uint8_t *data, size_t len,
void *user_data)
{
http2_session_data *session_data = (http2_session_data*)user_data;
if(session_data->stream_data->stream_id == stream_id) {
fwrite(data, len, 1, stdout);
}
return 0;
}
/* nghttp2_on_stream_close_callback: Called when a stream is about to
closed. This example program only deals with 1 HTTP request (1
stream), if it is closed, we send GOAWAY and tear down the
session */
static int on_stream_close_callback(nghttp2_session *session,
int32_t stream_id,
nghttp2_error_code error_code,
void *user_data)
{
http2_session_data *session_data = (http2_session_data*)user_data;
int rv;
if(session_data->stream_data->stream_id == stream_id) {
fprintf(stderr, "Stream %d closed with error_code=%d\n",
stream_id, error_code);
rv = nghttp2_session_terminate_session(session, NGHTTP2_NO_ERROR);
if(rv != 0) {
return NGHTTP2_ERR_CALLBACK_FAILURE;
}
}
return 0;
}
/* NPN TLS extension client callback. We check that server advertised
the HTTP/2 protocol the nghttp2 library supports. If not, exit
the program. */
static int select_next_proto_cb(SSL* ssl,
unsigned char **out, unsigned char *outlen,
const unsigned char *in, unsigned int inlen,
void *arg)
{
if(nghttp2_select_next_protocol(out, outlen, in, inlen) <= 0) {
errx(1, "Server did not advertise " NGHTTP2_PROTO_VERSION_ID);
}
return SSL_TLSEXT_ERR_OK;
}
/* Create SSL_CTX. */
static SSL_CTX* create_ssl_ctx(void)
{
SSL_CTX *ssl_ctx;
ssl_ctx = SSL_CTX_new(SSLv23_client_method());
if(!ssl_ctx) {
errx(1, "Could not create SSL/TLS context: %s",
ERR_error_string(ERR_get_error(), NULL));
}
SSL_CTX_set_options(ssl_ctx,
SSL_OP_ALL | SSL_OP_NO_SSLv2 | SSL_OP_NO_COMPRESSION |
SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION);
SSL_CTX_set_next_proto_select_cb(ssl_ctx, select_next_proto_cb, NULL);
return ssl_ctx;
}
/* Create SSL object */
static SSL* create_ssl(SSL_CTX *ssl_ctx)
{
SSL *ssl;
ssl = SSL_new(ssl_ctx);
if(!ssl) {
errx(1, "Could not create SSL/TLS session object: %s",
ERR_error_string(ERR_get_error(), NULL));
}
return ssl;
}
static void initialize_nghttp2_session(http2_session_data *session_data)
{
nghttp2_session_callbacks callbacks;
memset(&callbacks, 0, sizeof(callbacks));
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;
callbacks.on_header_callback = on_header_callback;
callbacks.on_begin_headers_callback = on_begin_headers_callback;
nghttp2_session_client_new(&session_data->session, &callbacks, session_data);
}
static void send_client_connection_header(http2_session_data *session_data)
{
nghttp2_settings_entry iv[1] = {
{ NGHTTP2_SETTINGS_MAX_CONCURRENT_STREAMS, 100 }
};
int rv;
bufferevent_write(session_data->bev,
NGHTTP2_CLIENT_CONNECTION_PREFACE,
NGHTTP2_CLIENT_CONNECTION_PREFACE_LEN);
rv = nghttp2_submit_settings(session_data->session, NGHTTP2_FLAG_NONE,
iv, ARRLEN(iv));
if(rv != 0) {
errx(1, "Could not submit SETTINGS: %s", nghttp2_strerror(rv));
}
}
#define MAKE_NV(NAME, VALUE, VALUELEN) \
{ (uint8_t*)NAME, (uint8_t*)VALUE, sizeof(NAME) - 1, VALUELEN, \
NGHTTP2_NV_FLAG_NONE }
#define MAKE_NV2(NAME, VALUE) \
{ (uint8_t*)NAME, (uint8_t*)VALUE, sizeof(NAME) - 1, sizeof(VALUE) - 1, \
NGHTTP2_NV_FLAG_NONE }
/* Send HTTP request to the remote peer */
static void submit_request(http2_session_data *session_data)
{
int rv;
http2_stream_data *stream_data = session_data->stream_data;
const char *uri = stream_data->uri;
const struct http_parser_url *u = stream_data->u;
nghttp2_nv hdrs[] = {
MAKE_NV2(":method", "GET"),
MAKE_NV(":scheme",
&uri[u->field_data[UF_SCHEMA].off], u->field_data[UF_SCHEMA].len),
MAKE_NV(":authority", stream_data->authority, stream_data->authoritylen),
MAKE_NV(":path", stream_data->path, stream_data->pathlen)
};
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));
}
}
/* Serialize the frame and send (or buffer) the data to
bufferevent. */
static int session_send(http2_session_data *session_data)
{
int rv;
rv = nghttp2_session_send(session_data->session);
if(rv != 0) {
warnx("Fatal error: %s", nghttp2_strerror(rv));
return -1;
}
return 0;
}
/* readcb for bufferevent. Here we get the data from the input buffer
of bufferevent and feed them to nghttp2 library. This may invoke
nghttp2 callbacks. It may also queues the frame in nghttp2 session
context. To send them, we call session_send() in the end. */
static void readcb(struct bufferevent *bev, void *ptr)
{
http2_session_data *session_data = (http2_session_data*)ptr;
int rv;
struct evbuffer *input = bufferevent_get_input(bev);
size_t datalen = evbuffer_get_length(input);
unsigned char *data = evbuffer_pullup(input, -1);
rv = nghttp2_session_mem_recv(session_data->session, data, datalen);
if(rv < 0) {
warnx("Fatal error: %s", nghttp2_strerror(rv));
delete_http2_session_data(session_data);
return;
}
evbuffer_drain(input, rv);
if(session_send(session_data) != 0) {
delete_http2_session_data(session_data);
return;
}
}
/* writecb for bufferevent. To greaceful shutdown after sending or
receiving GOAWAY, we check the some conditions on the nghttp2
library and output buffer of bufferevent. If it indicates we have
no business to this session, tear down the connection. */
static void writecb(struct bufferevent *bev, void *ptr)
{
http2_session_data *session_data = (http2_session_data*)ptr;
if(nghttp2_session_want_read(session_data->session) == 0 &&
nghttp2_session_want_write(session_data->session) == 0 &&
evbuffer_get_length(bufferevent_get_output(session_data->bev)) == 0) {
delete_http2_session_data(session_data);
}
}
/* eventcb for bufferevent. For the purpose of simplicity and
readability of the example program, we omitted the certificate and
peer verification. After SSL/TLS handshake is over, initialize
nghttp2 library session, and send client connection header. Then
send HTTP request. */
static void eventcb(struct bufferevent *bev, short events, void *ptr)
{
http2_session_data *session_data = (http2_session_data*)ptr;
if(events & BEV_EVENT_CONNECTED) {
int fd = bufferevent_getfd(bev);
int val = 1;
fprintf(stderr, "Connected\n");
setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, (char *)&val, sizeof(val));
initialize_nghttp2_session(session_data);
send_client_connection_header(session_data);
submit_request(session_data);
if(session_send(session_data) != 0) {
delete_http2_session_data(session_data);
}
return;
}
if(events & BEV_EVENT_EOF) {
warnx("Disconnected from the remote host");
} else if(events & BEV_EVENT_ERROR) {
warnx("Network error");
} else if(events & BEV_EVENT_TIMEOUT) {
warnx("Timeout");
}
delete_http2_session_data(session_data);
}
/* Start connecting to the remote peer |host:port| */
static void initiate_connection(struct event_base *evbase,
SSL_CTX *ssl_ctx,
const char *host, uint16_t port,
http2_session_data *session_data)
{
int rv;
struct bufferevent *bev;
SSL *ssl;
ssl = create_ssl(ssl_ctx);
bev = bufferevent_openssl_socket_new(evbase, -1, ssl,
BUFFEREVENT_SSL_CONNECTING,
BEV_OPT_DEFER_CALLBACKS |
BEV_OPT_CLOSE_ON_FREE);
bufferevent_setcb(bev, readcb, writecb, eventcb, session_data);
rv = bufferevent_socket_connect_hostname(bev, session_data->dnsbase,
AF_UNSPEC, host, port);
if(rv != 0) {
errx(1, "Could not connect to the remote host %s", host);
}
session_data->bev = bev;
}
/* Get resource denoted by the |uri|. The debug and error messages are
printed in stderr, while the response body is printed in stdout. */
static void run(const char *uri)
{
struct http_parser_url u;
char *host;
uint16_t port;
int rv;
SSL_CTX *ssl_ctx;
struct event_base *evbase;
http2_session_data *session_data;
/* Parse the |uri| and stores its components in |u| */
rv = http_parser_parse_url(uri, strlen(uri), 0, &u);
if(rv != 0) {
errx(1, "Could not parse URI %s", uri);
}
host = strndup(&uri[u.field_data[UF_HOST].off], u.field_data[UF_HOST].len);
if(!(u.field_set & (1 << UF_PORT))) {
port = 443;
} else {
port = u.port;
}
ssl_ctx = create_ssl_ctx();
evbase = event_base_new();
session_data = create_http2_session_data(evbase);
session_data->stream_data = create_http2_stream_data(uri, &u);
initiate_connection(evbase, ssl_ctx, host, port, session_data);
free(host);
host = NULL;
event_base_loop(evbase, 0);
event_base_free(evbase);
SSL_CTX_free(ssl_ctx);
}
int main(int argc, char **argv)
{
struct sigaction act;
if(argc < 2) {
fprintf(stderr, "Usage: libevent-client HTTPS_URI\n");
exit(EXIT_FAILURE);
}
memset(&act, 0, sizeof(struct sigaction));
act.sa_handler = SIG_IGN;
sigaction(SIGPIPE, &act, NULL);
SSL_load_error_strings();
SSL_library_init();
run(argv[1]);
return 0;
}