Use socketpair() to create sockets

Author: jakobrs

src/program/GameLoop.cpp

@@ -52,6 +52,7 @@
 #include <sys/stat.h> // stat
 #include <sys/wait.h> // waitpid
 // #include <X11/X.h>
+#include <sys/socket.h>
 #include <stdint.h>
 
 GameLoop::GameLoop(Context* c) : movie(MovieFile(c)), context(c)
@@ -183,20 +184,29 @@ void GameLoop::init()
     /* Remove savestates again in case we did not exist cleanly the previous time */
     remove_savestates(context);
 
-    /* Remove the file socket */
-    int err = removeSocket();
-    if (err != 0)
-        emit alertToShow(QString("Could not remove socket file /tmp/libTAS.socket: %2").arg(strerror(err)));
-
     /* Init savestate list */
     SaveStateList::init(context);
 
+    /* Create socket pair */
+    int sockets[2];
+
+    if (socketpair(AF_UNIX, SOCK_STREAM, 0, sockets) == -1) {
+        perror("Failed to create socket pair");
+        return;
+    }
+
     /* We fork here so that the child process calls the game */
     context->fork_pid = fork();
     if (context->fork_pid == 0) {
-        GameThread::launch(context);
+        close(sockets[0]);
+
+        // noreturn; calls exec
+        return GameThread::launch(context, sockets[1]);
     }
 
+    close(sockets[1]);
+    setSocket(sockets[0]);
+
     /* Compute the MD5 hash of the game binary */
     context->md5_game.clear();
     std::ostringstream cmd;
@@ -267,9 +277,6 @@ void GameLoop::init()
 
 void GameLoop::initProcessMessages()
 {
-    /* Connect to the socket between the program and the game */
-    initSocketProgram();
-
     /* Receive informations from the game */
     int message = receiveMessage();
     while (message != MSGB_END_INIT) {
@@ -739,7 +746,6 @@ void GameLoop::loopExit()
         (context->status != Context::QUITTING))) {
 
         /* We keep the movie opened and indicate the main thread to restart the game */
-
         closeSocket();
 
         /* Remove savestates because they are invalid on future instances of the game */

src/program/GameThread.cpp

@@ -32,7 +32,7 @@
 #include <unistd.h> // chdir()
 #include <fcntl.h> // O_RDWR, O_CREAT
 
-void GameThread::launch(Context *context)
+void GameThread::launch(Context *context, int sock)
 {
 #ifdef __unix__
     /* Update the LD_LIBRARY_PATH environment variable if the user set one */
@@ -120,6 +120,9 @@ void GameThread::launch(Context *context)
     /* Override timezone for determinism */
     setenv("TZ", "UTC0", 1);
 
+    /* Pass socket file descriptor to the game */
+    setenv("LIBTAS_SOCKET_FD", std::to_string(sock).c_str(), 1);
+
     /* Build the argument list to be fed to execv */
     std::list<std::string> arg_list;
 

src/program/GameThread.h

@@ -28,7 +28,7 @@ namespace GameThread {
      * Because this function eventually calls execl, it does not return.
      * So, it is called from a child process using fork().
      */
-    void launch(Context *context);
+    void launch(Context *context, int sock);
 }
 
 #endif

src/shared/sockethelpers.cpp

@@ -19,14 +19,14 @@
 
 #include "sockethelpers.h"
 #include <sys/socket.h>
-#include <sys/stat.h>
 #include <cstdlib>
 #include <unistd.h>
 #include <sys/un.h>
 #include <iostream>
 #include <vector>
 #include <mutex>
 #include <errno.h>
+#include <fcntl.h>
 
 #ifdef SOCKET_LOG
 #include "lcf.h"
@@ -35,8 +35,6 @@
 #include <iostream>
 #endif
 
-#define SOCKET_FILENAME "/tmp/libTAS.socket"
-
 #ifndef MSG_NOSIGNAL
 #define MSG_NOSIGNAL 0
 #endif
@@ -48,80 +46,20 @@ static int socket_fd = 0;
 
 static std::mutex mutex;
 
-int removeSocket(void) {
-    int ret = unlink(SOCKET_FILENAME);
-    if ((ret == -1) && (errno != ENOENT))
-        return errno;
-    return 0;
+void setSocket(int sock) {
+    socket_fd = sock;
 }
 
-bool initSocketProgram(void)
+bool initSocketGame(void)
 {
-#ifdef __unix__
-    const struct sockaddr_un addr = { AF_UNIX, SOCKET_FILENAME };
-#elif defined(__APPLE__) && defined(__MACH__)
-    const struct sockaddr_un addr = { sizeof(struct sockaddr_un), AF_UNIX, SOCKET_FILENAME };
-#endif
-    socket_fd = socket(AF_UNIX, SOCK_STREAM, 0);
+    socket_fd = std::stoi(getenv("LIBTAS_SOCKET_FD"));
 
-    struct timespec tim = {0, 500L*1000L*1000L};
-
-    const int MAX_RETRIES = 10;
-    int retry = 0;
-
-    nanosleep(&tim, NULL);
-    while (connect(socket_fd, reinterpret_cast<const struct sockaddr*>(&addr),
-                sizeof(struct sockaddr_un))) {
-        std::cout << "Attempt " << retry + 1 << ": Couldn't connect to socket." << std::endl;
-        retry++;
-        if (retry < MAX_RETRIES) {
-            nanosleep(&tim, NULL);
+    if (fcntl(socket_fd, F_GETFD) == -1) {
+        if (errno == EBADF) {
+            perror("LIBTAS_SOCKET_FD has been closed");
         } else {
-            return false;
-        }
-        tim.tv_nsec *= 1.5;
-        if (tim.tv_nsec >= 1000000000) {            
-            tim.tv_sec++;
-            tim.tv_nsec -= 1000000000;
+            perror("Unable to use game socket");
         }
-    }
-    std::cout << "Attempt " << retry + 1 << ": Connected." << std::endl;
-
-    return true;
-}
-
-bool initSocketGame(void)
-{
-    /* Check if socket file already exists. If so, it is probably because
-     * the link is already done in another process of the game.
-     * In this case, we just return immediately.
-     */
-    struct stat st;
-    int result = stat(SOCKET_FILENAME, &st);
-    if (result == 0)
-        return false;
-
-#ifdef __unix__
-    const struct sockaddr_un addr = { AF_UNIX, SOCKET_FILENAME };
-#elif defined(__APPLE__) && defined(__MACH__)
-    const struct sockaddr_un addr = { sizeof(struct sockaddr_un), AF_UNIX, SOCKET_FILENAME };
-#endif
-    const int tmp_fd = socket(AF_UNIX, SOCK_STREAM, 0);
-    if (bind(tmp_fd, reinterpret_cast<const struct sockaddr*>(&addr), sizeof(struct sockaddr_un)))
-    {
-        std::cerr << "Couldn't bind client socket." << std::endl;
-        exit(-1);
-    }
-
-    if (listen(tmp_fd, 1))
-    {
-        std::cerr << "Couldn't listen on client socket." << std::endl;
-        exit(-1);
-    }
-
-    if ((socket_fd = accept(tmp_fd, NULL, NULL)) < 0)
-    {
-        std::cerr << "Couldn't accept client connection." << std::endl;
         exit(-1);
     }
 
@@ -135,7 +73,6 @@ bool initSocketGame(void)
     }
 #endif
 
-    close(tmp_fd);
     return true;
 }
 

src/shared/sockethelpers.h

@@ -23,11 +23,8 @@
 #include <cstddef>
 #include <string>
 
-/* Remove the socket file and return error */
-int removeSocket();
-
-/* Initiate a socket connection with the game */
-bool initSocketProgram(void);
+/* Sets socket_fd */
+void setSocket(int sock);
 
 /* Initiate a socket connection with libTAS */
 bool initSocketGame(void);