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Do not block on accept() if server died

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The server may die before connecting to the client. In that case, the
client was blocked indefinitely (until Ctrl+C) on accept().

To avoid the problem, close the server socket once the server process is
dead.
This commit is contained in:
Romain Vimont 2020-03-28 23:56:25 +01:00
parent d421741a83
commit a346bb80f4
2 changed files with 34 additions and 12 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

43
app/src/server.c
View file

@ -318,14 +318,12 @@ connect_to_server(uint16_t port, uint32_t attempts, uint32_t delay) {
}
static void
close_socket(socket_t *socket) {
assert(*socket != INVALID_SOCKET);
net_shutdown(*socket, SHUT_RDWR);
if (!net_close(*socket)) {
close_socket(socket_t socket) {
assert(socket != INVALID_SOCKET);
net_shutdown(socket, SHUT_RDWR);
if (!net_close(socket)) {
LOGW("Could not close socket");
return;
}
*socket = INVALID_SOCKET;
}
void
@ -337,6 +335,14 @@ static int
run_wait_server(void *data) {
struct server *server = data;
cmd_simple_wait(server->process, NULL); // ignore exit code
// no need for synchronization, server_socket is initialized before this
// thread was created
if (server->server_socket != INVALID_SOCKET
&& SDL_AtomicCAS(&server->server_socket_closed, 0, 1)) {
// On Linux, accept() is unblocked by shutdown(), but on Windows, it is
// unblocked by closesocket(). Therefore, call both (close_socket()).
close_socket(server->server_socket);
}
LOGD("Server terminated");
return 0;
}
@ -367,6 +373,12 @@ server_start(struct server *server, const char *serial,
goto error2;
}
// If the server process dies before connecting to the server socket, then
// the client will be stuck forever on accept(). To avoid the problem, we
// must be able to wake up the accept() call when the server dies. To keep
// things simple and multiplatform, just spawn a new thread waiting for the
// server process and calling shutdown()/close() on the server socket if
// necessary to wake up any accept() blocking call.
server->wait_server_thread =
SDL_CreateThread(run_wait_server, "wait-server", server);
if (!server->wait_server_thread) {
@ -383,7 +395,9 @@ server_start(struct server *server, const char *serial,
error2:
if (!server->tunnel_forward) {
close_socket(&server->server_socket);
// the wait server thread is not started, SDL_AtomicSet() is sufficient
SDL_AtomicSet(&server->server_socket_closed, 1);
close_socket(server->server_socket);
}
disable_tunnel(server);
error1:
@ -406,7 +420,11 @@ server_connect_to(struct server *server) {
}
// we don't need the server socket anymore
close_socket(&server->server_socket);
if (SDL_AtomicCAS(&server->server_socket_closed, 0, 1)) {
// close it from here
close_socket(server->server_socket);
// otherwise, it is closed by run_wait_server()
}
} else {
uint32_t attempts = 100;
uint32_t delay = 100; // ms
@ -433,14 +451,15 @@ server_connect_to(struct server *server) {
void
server_stop(struct server *server) {
if (server->server_socket != INVALID_SOCKET) {
close_socket(&server->server_socket);
if (server->server_socket != INVALID_SOCKET
&& SDL_AtomicCAS(&server->server_socket_closed, 0, 1)) {
close_socket(server->server_socket);
}
if (server->video_socket != INVALID_SOCKET) {
close_socket(&server->video_socket);
close_socket(server->video_socket);
}
if (server->control_socket != INVALID_SOCKET) {
close_socket(&server->control_socket);
close_socket(server->control_socket);
}
assert(server->process != PROCESS_NONE);

3
app/src/server.h
View file

@ -3,6 +3,7 @@
#include <stdbool.h>
#include <stdint.h>
#include <SDL2/SDL_atomic.h>
#include <SDL2/SDL_thread.h>
#include "config.h"
@ -14,6 +15,7 @@ struct server {
char *serial;
process_t process;
SDL_Thread *wait_server_thread;
SDL_atomic_t server_socket_closed;
socket_t server_socket; // only used if !tunnel_forward
socket_t video_socket;
socket_t control_socket;
@ -27,6 +29,7 @@ struct server {
.serial = NULL, \
.process = PROCESS_NONE, \
.wait_server_thread = NULL, \
.server_socket_closed = {0}, \
.server_socket = INVALID_SOCKET, \
.video_socket = INVALID_SOCKET, \
.control_socket = INVALID_SOCKET, \