Use random name for device socket

For the initial connection between the device and the computer, an adb
tunnel is established (with "adb reverse" or "adb forward").

The device-side of the tunnel is a local socket having the hard-coded
name "scrcpy". This may cause issues when several scrcpy instances are
started in a few seconds for the same device, since they will try to
bind the same name.

To avoid conflicts, make the client generate a random UID, and append
this UID to the local socket name ("scrcpy_01234567").

app/src/adb/adb_tunnel.c

@@ -7,8 +7,6 @@
 #include "util/net_intr.h"
 #include "util/process_intr.h"
 
-#define SC_SOCKET_NAME "scrcpy"
-
 static bool
 listen_on_port(struct sc_intr *intr, sc_socket socket, uint16_t port) {
     return net_listen_intr(intr, socket, IPV4_LOCALHOST, port, 1);
@@ -17,10 +15,11 @@ listen_on_port(struct sc_intr *intr, sc_socket socket, uint16_t port) {
 static bool
 enable_tunnel_reverse_any_port(struct sc_adb_tunnel *tunnel,
                                struct sc_intr *intr, const char *serial,
+                               const char *device_socket_name,
                                struct sc_port_range port_range) {
     uint16_t port = port_range.first;
     for (;;) {
-        if (!sc_adb_reverse(intr, serial, SC_SOCKET_NAME, port,
+        if (!sc_adb_reverse(intr, serial, device_socket_name, port,
                             SC_ADB_NO_STDOUT)) {
             // the command itself failed, it will fail on any port
             return false;
@@ -52,7 +51,7 @@ enable_tunnel_reverse_any_port(struct sc_adb_tunnel *tunnel,
         }
 
         // failure, disable tunnel and try another port
-        if (!sc_adb_reverse_remove(intr, serial, SC_SOCKET_NAME,
+        if (!sc_adb_reverse_remove(intr, serial, device_socket_name,
                                 SC_ADB_NO_STDOUT)) {
             LOGW("Could not remove reverse tunnel on port %" PRIu16, port);
         }
@@ -78,12 +77,13 @@ enable_tunnel_reverse_any_port(struct sc_adb_tunnel *tunnel,
 static bool
 enable_tunnel_forward_any_port(struct sc_adb_tunnel *tunnel,
                                struct sc_intr *intr, const char *serial,
+                               const char *device_socket_name,
                                struct sc_port_range port_range) {
     tunnel->forward = true;
 
     uint16_t port = port_range.first;
     for (;;) {
-        if (sc_adb_forward(intr, serial, port, SC_SOCKET_NAME,
+        if (sc_adb_forward(intr, serial, port, device_socket_name,
                            SC_ADB_NO_STDOUT)) {
             // success
             tunnel->local_port = port;
@@ -123,13 +123,14 @@ sc_adb_tunnel_init(struct sc_adb_tunnel *tunnel) {
 
 bool
 sc_adb_tunnel_open(struct sc_adb_tunnel *tunnel, struct sc_intr *intr,
-                   const char *serial, struct sc_port_range port_range,
-                   bool force_adb_forward) {
+                   const char *serial, const char *device_socket_name,
+                   struct sc_port_range port_range, bool force_adb_forward) {
     assert(!tunnel->enabled);
 
     if (!force_adb_forward) {
         // Attempt to use "adb reverse"
-        if (enable_tunnel_reverse_any_port(tunnel, intr, serial, port_range)) {
+        if (enable_tunnel_reverse_any_port(tunnel, intr, serial,
+                                           device_socket_name, port_range)) {
             return true;
         }
 
@@ -139,12 +140,13 @@ sc_adb_tunnel_open(struct sc_adb_tunnel *tunnel, struct sc_intr *intr,
         LOGW("'adb reverse' failed, fallback to 'adb forward'");
     }
 
-    return enable_tunnel_forward_any_port(tunnel, intr, serial, port_range);
+    return enable_tunnel_forward_any_port(tunnel, intr, serial,
+                                          device_socket_name, port_range);
 }
 
 bool
 sc_adb_tunnel_close(struct sc_adb_tunnel *tunnel, struct sc_intr *intr,
-                    const char *serial) {
+                    const char *serial, const char *device_socket_name) {
     assert(tunnel->enabled);
 
     bool ret;
@@ -152,7 +154,7 @@ sc_adb_tunnel_close(struct sc_adb_tunnel *tunnel, struct sc_intr *intr,
         ret = sc_adb_forward_remove(intr, serial, tunnel->local_port,
                                     SC_ADB_NO_STDOUT);
     } else {
-        ret = sc_adb_reverse_remove(intr, serial, SC_SOCKET_NAME,
+        ret = sc_adb_reverse_remove(intr, serial, device_socket_name,
                                     SC_ADB_NO_STDOUT);
 
         assert(tunnel->server_socket != SC_SOCKET_NONE);

app/src/adb/adb_tunnel.h

@@ -34,14 +34,14 @@ sc_adb_tunnel_init(struct sc_adb_tunnel *tunnel);
  */
 bool
 sc_adb_tunnel_open(struct sc_adb_tunnel *tunnel, struct sc_intr *intr,
-                   const char *serial, struct sc_port_range port_range,
-                   bool force_adb_forward);
+                   const char *serial, const char *device_socket_name,
+                   struct sc_port_range port_range, bool force_adb_forward);
 
 /**
  * Close the tunnel
  */
 bool
 sc_adb_tunnel_close(struct sc_adb_tunnel *tunnel, struct sc_intr *intr,
-                    const char *serial);
+                    const char *serial, const char *device_socket_name);
 
 #endif

app/src/scrcpy.c

@@ -32,6 +32,7 @@
 #include "util/acksync.h"
 #include "util/log.h"
 #include "util/net.h"
+#include "util/rand.h"
 #ifdef HAVE_V4L2
 # include "v4l2_sink.h"
 #endif
@@ -265,6 +266,14 @@ sc_server_on_disconnected(struct sc_server *server, void *userdata) {
     // event
 }
 
+static uint32_t
+scrcpy_generate_uid() {
+    struct sc_rand rand;
+    sc_rand_init(&rand);
+    // Only use 31 bits to avoid issues with signed values on the Java-side
+    return sc_rand_u32(&rand) & 0x7FFFFFFF;
+}
+
 enum scrcpy_exit_code
 scrcpy(struct scrcpy_options *options) {
     static struct scrcpy scrcpy;
@@ -298,7 +307,10 @@ scrcpy(struct scrcpy_options *options) {
 
     struct sc_acksync *acksync = NULL;
 
+    uint32_t uid = scrcpy_generate_uid();
+
     struct sc_server_params params = {
+        .uid = uid,
         .req_serial = options->serial,
         .select_usb = options->select_usb,
         .select_tcpip = options->select_tcpip,

app/src/server.c

@@ -20,6 +20,7 @@
 #define SC_DEVICE_SERVER_PATH "/data/local/tmp/scrcpy-server.jar"
 
 #define SC_ADB_PORT_DEFAULT 5555
+#define SC_SOCKET_NAME_PREFIX "scrcpy_"
 
 static char *
 get_server_path(void) {
@@ -197,6 +198,7 @@ execute_server(struct sc_server *server,
         cmd[count++] = p; \
     }
 
+    ADD_PARAM("uid=%08x", params->uid);
     ADD_PARAM("log_level=%s", log_level_to_server_string(params->log_level));
     ADD_PARAM("bit_rate=%" PRIu32, params->bit_rate);
 
@@ -364,6 +366,7 @@ sc_server_init(struct sc_server *server, const struct sc_server_params *params,
     }
 
     server->serial = NULL;
+    server->device_socket_name = NULL;
     server->stopped = false;
 
     server->video_socket = SC_SOCKET_NONE;
@@ -463,7 +466,8 @@ sc_server_connect_to(struct sc_server *server, struct sc_server_info *info) {
     }
 
     // we don't need the adb tunnel anymore
-    sc_adb_tunnel_close(tunnel, &server->intr, serial);
+    sc_adb_tunnel_close(tunnel, &server->intr, serial,
+                        server->device_socket_name);
 
     // The sockets will be closed on stop if device_read_info() fails
     bool ok = device_read_info(&server->intr, video_socket, info);
@@ -494,7 +498,8 @@ fail:
 
     if (tunnel->enabled) {
         // Always leave this function with tunnel disabled
-        sc_adb_tunnel_close(tunnel, &server->intr, serial);
+        sc_adb_tunnel_close(tunnel, &server->intr, serial,
+                            server->device_socket_name);
     }
 
     return false;
@@ -764,13 +769,23 @@ run_server(void *data) {
     assert(serial);
     LOGD("Device serial: %s", serial);
 
+    int r = asprintf(&server->device_socket_name, SC_SOCKET_NAME_PREFIX "%08x",
+                     params->uid);
+    if (r == -1) {
+        LOG_OOM();
+        goto error_connection_failed;
+    }
+    assert(r == sizeof(SC_SOCKET_NAME_PREFIX) - 1 + 8);
+    assert(server->device_socket_name);
+
     ok = push_server(&server->intr, serial);
     if (!ok) {
         goto error_connection_failed;
     }
 
     ok = sc_adb_tunnel_open(&server->tunnel, &server->intr, serial,
-                            params->port_range, params->force_adb_forward);
+                            server->device_socket_name, params->port_range,
+                            params->force_adb_forward);
     if (!ok) {
         goto error_connection_failed;
     }
@@ -778,7 +793,8 @@ run_server(void *data) {
     // server will connect to our server socket
     sc_pid pid = execute_server(server, params);
     if (pid == SC_PROCESS_NONE) {
-        sc_adb_tunnel_close(&server->tunnel, &server->intr, serial);
+        sc_adb_tunnel_close(&server->tunnel, &server->intr, serial,
+                            server->device_socket_name);
         goto error_connection_failed;
     }
 
@@ -790,7 +806,8 @@ run_server(void *data) {
     if (!ok) {
         sc_process_terminate(pid);
         sc_process_wait(pid, true); // ignore exit code
-        sc_adb_tunnel_close(&server->tunnel, &server->intr, serial);
+        sc_adb_tunnel_close(&server->tunnel, &server->intr, serial,
+                            server->device_socket_name);
         goto error_connection_failed;
     }
 
@@ -884,6 +901,7 @@ sc_server_destroy(struct sc_server *server) {
     }
 
     free(server->serial);
+    free(server->device_socket_name);
     sc_server_params_destroy(&server->params);
     sc_intr_destroy(&server->intr);
     sc_cond_destroy(&server->cond_stopped);

app/src/server.h

@@ -22,6 +22,7 @@ struct sc_server_info {
 };
 
 struct sc_server_params {
+    uint32_t uid;
     const char *req_serial;
     enum sc_log_level log_level;
     const char *crop;
@@ -54,6 +55,7 @@ struct sc_server {
     // The internal allocated strings are copies owned by the server
     struct sc_server_params params;
     char *serial;
+    char *device_socket_name;
 
     sc_thread thread;
     struct sc_server_info info; // initialized once connected

server/src/main/java/com/genymobile/scrcpy/DesktopConnection.java

@@ -15,7 +15,7 @@ public final class DesktopConnection implements Closeable {
 
     private static final int DEVICE_NAME_FIELD_LENGTH = 64;
 
-    private static final String SOCKET_NAME = "scrcpy";
+    private static final String SOCKET_NAME_PREFIX = "scrcpy";
 
     private final LocalSocket videoSocket;
     private final FileDescriptor videoFd;
@@ -46,11 +46,22 @@ public final class DesktopConnection implements Closeable {
         return localSocket;
     }
 
-    public static DesktopConnection open(boolean tunnelForward, boolean control, boolean sendDummyByte) throws IOException {
+    private static String getSocketName(int uid) {
+        if (uid == -1) {
+            // If no UID is set, use "scrcpy" to simplify using scrcpy-server alone
+            return SOCKET_NAME_PREFIX;
+        }
+
+        return SOCKET_NAME_PREFIX + String.format("_%08x", uid);
+    }
+
+    public static DesktopConnection open(int uid, boolean tunnelForward, boolean control, boolean sendDummyByte) throws IOException {
+        String socketName = getSocketName(uid);
+
         LocalSocket videoSocket;
         LocalSocket controlSocket = null;
         if (tunnelForward) {
-            LocalServerSocket localServerSocket = new LocalServerSocket(SOCKET_NAME);
+            LocalServerSocket localServerSocket = new LocalServerSocket(socketName);
             try {
                 videoSocket = localServerSocket.accept();
                 if (sendDummyByte) {
@@ -69,10 +80,10 @@ public final class DesktopConnection implements Closeable {
                 localServerSocket.close();
             }
         } else {
-            videoSocket = connect(SOCKET_NAME);
+            videoSocket = connect(socketName);
             if (control) {
                 try {
-                    controlSocket = connect(SOCKET_NAME);
+                    controlSocket = connect(socketName);
                 } catch (IOException | RuntimeException e) {
                     videoSocket.close();
                     throw e;

server/src/main/java/com/genymobile/scrcpy/Options.java

@@ -6,6 +6,7 @@ import java.util.List;
 
 public class Options {
     private Ln.Level logLevel = Ln.Level.DEBUG;
+    private int uid = -1; // 31-bit non-negative value, or -1
     private int maxSize;
     private int bitRate = 8000000;
     private int maxFps;
@@ -37,6 +38,14 @@ public class Options {
         this.logLevel = logLevel;
     }
 
+    public int getUid() {
+        return uid;
+    }
+
+    public void setUid(int uid) {
+        this.uid = uid;
+    }
+
     public int getMaxSize() {
         return maxSize;
     }

server/src/main/java/com/genymobile/scrcpy/Server.java

@@ -66,11 +66,12 @@ public final class Server {
 
         Thread initThread = startInitThread(options);
 
+        int uid = options.getUid();
         boolean tunnelForward = options.isTunnelForward();
         boolean control = options.getControl();
         boolean sendDummyByte = options.getSendDummyByte();
 
-        try (DesktopConnection connection = DesktopConnection.open(tunnelForward, control, sendDummyByte)) {
+        try (DesktopConnection connection = DesktopConnection.open(uid, tunnelForward, control, sendDummyByte)) {
             if (options.getSendDeviceMeta()) {
                 Size videoSize = device.getScreenInfo().getVideoSize();
                 connection.sendDeviceMeta(Device.getDeviceName(), videoSize.getWidth(), videoSize.getHeight());
@@ -178,6 +179,13 @@ public final class Server {
             String key = arg.substring(0, equalIndex);
             String value = arg.substring(equalIndex + 1);
             switch (key) {
+                case "uid":
+                    int uid = Integer.parseInt(value, 0x10);
+                    if (uid < -1) {
+                        throw new IllegalArgumentException("uid may not be negative (except -1 for 'none'): " + uid);
+                    }
+                    options.setUid(uid);
+                    break;
                 case "log_level":
                     Ln.Level level = Ln.Level.valueOf(value.toUpperCase(Locale.ENGLISH));
                     options.setLogLevel(level);