Add minimal WebSocket server implementation for evhttp (libevent#1322)

This adds few functions to use evhttp-based webserver to handle incoming
WebSockets connections. We've tried to use both libevent and libwebsockets in
our application, but found that we need to have different ports at the same
time to handle standard HTTP and WebSockets traffic. This change can help to
stick only with libevent library.

Implementation was inspired by modified Libevent source code in ipush project
[1].

  [1]: https://github.com/sqfasd/ipush/tree/master/deps/libevent-2.0.21-stable

Also, WebSocket-based chat server was added as a sample.

CMakeLists.txt

@@ -820,6 +820,7 @@ set(HDR_PRIVATE
     util-internal.h
     openssl-compat.h
     evconfig-private.h
+    sha1.h
     compat/sys/queue.h)
 
 set(HDR_COMPAT
@@ -854,6 +855,7 @@ set(HDR_PUBLIC
     include/event2/tag_compat.h
     include/event2/thread.h
     include/event2/util.h
+    include/event2/ws.h
     include/event2/visibility.h
     ${PROJECT_BINARY_DIR}/include/event2/event-config.h)
 
@@ -966,8 +968,12 @@ set(SRC_EXTRA
     event_tagging.c
     http.c
     evdns.c
+    ws.c
+    sha1.c
     evrpc.c)
 
+set_source_files_properties(sha1.c PROPERTIES COMPILE_FLAGS
+    -D${CMAKE_C_BYTE_ORDER}=1)
 add_definitions(-DHAVE_CONFIG_H)
 
 # We use BEFORE here so we don't accidentally look in system directories
@@ -1134,6 +1140,7 @@ if (NOT EVENT__DISABLE_SAMPLES)
 
     set(SAMPLES_WOPT
         dns-example
+        ws-chat-server
         http-server
     )
     foreach (SAMPLE ${SAMPLES_WOPT})
@@ -1217,6 +1224,7 @@ if (NOT EVENT__DISABLE_TESTS)
                  test/regress_et.c
                  test/regress_finalize.c
                  test/regress_http.c
+                 test/regress_http.h
                  test/regress_listener.c
                  test/regress_main.c
                  test/regress_minheap.c
@@ -1225,6 +1233,8 @@ if (NOT EVENT__DISABLE_TESTS)
                  test/regress_testutils.h
                  test/regress_util.c
                  test/regress_watch.c
+                 test/regress_ws.c
+                 test/regress_ws.h
                  test/tinytest.c)
 
             if (WIN32)

Doxyfile

@@ -81,6 +81,7 @@ INPUT                  = \
         $(SRCDIR)/include/event2/tag.h \
         $(SRCDIR)/include/event2/tag_compat.h \
         $(SRCDIR)/include/event2/thread.h \
+        $(SRCDIR)/include/event2/ws.h  \
         $(SRCDIR)/include/event2/util.h  \
         $(SRCDIR)/include/event2/watch.h
 

Makefile.am

@@ -259,6 +259,8 @@ EXTRAS_SRC =					\
 	evdns.c					\
 	event_tagging.c				\
 	evrpc.c					\
+	sha1.c					\
+	ws.c					\
 	http.c
 
 if BUILD_WITH_NO_UNDEFINED
@@ -338,6 +340,7 @@ noinst_HEADERS +=				\
 	util-internal.h				\
 	openssl-compat.h			\
 	mbedtls-compat.h			\
+	sha1.h						\
 	ssl-compat.h			    \
 	wepoll.h
 

configure.ac

@@ -857,6 +857,8 @@ AC_SUBST([LIBEVENT_GC_SECTIONS])
 
 AM_CONDITIONAL([INSTALL_LIBEVENT], [test "$enable_libevent_install" = "yes"])
 
+AC_C_BIGENDIAN([CFLAGS="$CFLAGS -DBIG_ENDIAN"], [CFLAGS="$CFLAGS -DLITTLE_ENDIAN"])
+
 dnl Doxygen support
 DX_HTML_FEATURE(ON)
 DX_MAN_FEATURE(OFF)

http-internal.h

@@ -124,6 +124,9 @@ struct evhttp_cb {
 /* both the http server as well as the rpc system need to queue connections */
 TAILQ_HEAD(evconq, evhttp_connection);
 
+/* WebSockets connections */
+TAILQ_HEAD(evwsq, evws_connection);
+
 /* each bound socket is stored in one of these */
 struct evhttp_bound_socket {
 	TAILQ_ENTRY(evhttp_bound_socket) next;
@@ -151,8 +154,10 @@ struct evhttp {
 
 	TAILQ_HEAD(httpcbq, evhttp_cb) callbacks;
 
-	/* All live connections on this host. */
+	/* All live HTTP connections on this host. */
 	struct evconq connections;
+	/* All live WebSockets sessions on this host. */
+	struct evwsq ws_sessions;
 	int connection_max;
 	int connection_cnt;
 
@@ -221,6 +226,8 @@ void evhttp_start_write_(struct evhttp_connection *);
 void evhttp_response_code_(struct evhttp_request *, int, const char *);
 void evhttp_send_page_(struct evhttp_request *, struct evbuffer *);
 
+struct bufferevent * evhttp_start_ws_(struct evhttp_request *req);
+
 /* [] has been stripped */
 #define _EVHTTP_URI_HOST_HAS_BRACKETS 0x02
 

http.c

@@ -107,6 +107,7 @@
 #include "event2/http_struct.h"
 #include "event2/http_compat.h"
 #include "event2/util.h"
+#include "event2/ws.h"
 #include "event2/listener.h"
 #include "log-internal.h"
 #include "util-internal.h"
@@ -3191,6 +3192,31 @@ evhttp_send_reply_chunk_with_cb(struct evhttp_request *req, struct evbuffer *dat
 	evhttp_write_buffer(evcon, cb, arg);
 }
 
+struct bufferevent *
+evhttp_start_ws_(struct evhttp_request *req)
+{
+	struct evhttp_connection *evcon = req->evcon;
+	struct bufferevent *bufev;
+
+	evhttp_response_code_(req, HTTP_SWITCH_PROTOCOLS, "Switching Protocols");
+
+	if (req->evcon == NULL)
+		return NULL;
+
+	evhttp_make_header(req->evcon, req);
+	evhttp_write_buffer(req->evcon, NULL, NULL);
+
+	TAILQ_REMOVE(&evcon->requests, req, next);
+
+	bufev = evcon->bufev;
+	evcon->bufev = NULL;
+	evcon->closecb = NULL;
+
+	evhttp_request_free(req);
+	evhttp_connection_free(evcon);
+	return bufev;
+}
+
 void
 evhttp_send_reply_chunk(struct evhttp_request *req, struct evbuffer *databuf)
 {
@@ -3961,6 +3987,7 @@ evhttp_new_object(void)
 	TAILQ_INIT(&http->sockets);
 	TAILQ_INIT(&http->callbacks);
 	TAILQ_INIT(&http->connections);
+	TAILQ_INIT(&http->ws_sessions);
 	TAILQ_INIT(&http->virtualhosts);
 	TAILQ_INIT(&http->aliases);
 
@@ -4005,6 +4032,7 @@ evhttp_free(struct evhttp* http)
 {
 	struct evhttp_cb *http_cb;
 	struct evhttp_connection *evcon;
+	struct evws_connection *evws;
 	struct evhttp_bound_socket *bound;
 	struct evhttp* vhost;
 	struct evhttp_server_alias *alias;
@@ -4023,6 +4051,10 @@ evhttp_free(struct evhttp* http)
 		evhttp_connection_free(evcon);
 	}
 
+	while ((evws = TAILQ_FIRST(&http->ws_sessions)) != NULL) {
+		evws_connection_free(evws);
+	}
+
 	while ((http_cb = TAILQ_FIRST(&http->callbacks)) != NULL) {
 		TAILQ_REMOVE(&http->callbacks, http_cb, next);
 		mm_free(http_cb->what);

include/event2/ws.h

@@ -0,0 +1,58 @@
+#ifndef EVENT2_WS_H_INCLUDED_
+#define EVENT2_WS_H_INCLUDED_
+
+struct evws_connection;
+
+#define WS_CR_NONE 0
+#define WS_CR_NORMAL 1000
+#define WS_CR_PROTO_ERR 1002
+#define WS_CR_DATA_TOO_BIG 1009
+
+#define WS_TEXT_FRAME 0x1
+#define WS_BINARY_FRAME 0x2
+
+typedef void (*ws_on_msg_cb)(
+	struct evws_connection *, int type, const unsigned char *, size_t, void *);
+typedef void (*ws_on_close_cb)(struct evws_connection *, void *);
+
+/** Opens new WebSocket session from HTTP request.
+  @param req a request object
+  @param cb the callback function that gets invoked on receiving message
+  with len bytes length. In case of receiving text messages user is responsible
+  to make a string with terminating \0 (with copying-out data) or use text data
+  other way in which \0 is not required
+  @param arg an additional context argument for the callback
+  @return a pointer to a newly initialized WebSocket connection or NULL
+	on error
+  @see evws_close()
+ */
+EVENT2_EXPORT_SYMBOL
+struct evws_connection *evws_new_session(
+	struct evhttp_request *req, ws_on_msg_cb, void *arg);
+
+/** Sends data over WebSocket connection */
+EVENT2_EXPORT_SYMBOL
+void evws_send(
+	struct evws_connection *evws, const char *packet_str, size_t str_len);
+
+/** Closes a WebSocket connection with reason code */
+EVENT2_EXPORT_SYMBOL
+void evws_close(struct evws_connection *evws, uint16_t reason);
+
+/** Sets a callback for connection close. */
+EVENT2_EXPORT_SYMBOL
+void evws_connection_set_closecb(
+	struct evws_connection *evws, ws_on_close_cb, void *);
+
+/** Frees a WebSocket connection */
+EVENT2_EXPORT_SYMBOL
+void evws_connection_free(struct evws_connection *evws);
+
+/**
+ * Return the bufferevent that an evws_connection is using.
+ */
+EVENT2_EXPORT_SYMBOL
+struct bufferevent *evws_connection_get_bufferevent(
+	struct evws_connection *evws);
+
+#endif

include/include.am

@@ -31,6 +31,7 @@ EVENT2_EXPORT = \
 	include/event2/tag_compat.h \
 	include/event2/thread.h \
 	include/event2/util.h \
+	include/event2/ws.h \
 	include/event2/visibility.h
 
 if OPENSSL

sample/include.am

@@ -12,6 +12,7 @@ SAMPLES = \
 	sample/http-connect				\
 	sample/signal-test				\
 	sample/time-test				\
+	sample/ws-chat-server				\
 	sample/watch-timing
 
 if OPENSSL
@@ -74,3 +75,6 @@ sample_http_connect_SOURCES = sample/http-connect.c
 sample_http_connect_LDADD = $(LIBEVENT_GC_SECTIONS) libevent.la
 sample_watch_timing_SOURCES = sample/watch-timing.c
 sample_watch_timing_LDADD = $(LIBEVENT_GC_SECTIONS) libevent.la -lm
+sample_ws_chat_server_SOURCES = sample/ws-chat-server.c
+sample_ws_chat_server_LDADD = $(LIBEVENT_GC_SECTIONS) libevent.la -lm
+EXTRA_DIST+=sample/ws-chat.html