Add --force-adb-forward

Add a command-line option to force "adb forward", without attempting
"adb reverse" first.

This is especially useful for using SSH tunnels without enabling remote
port forwarding.

README.md

@@ -289,6 +289,22 @@ From another terminal:
 scrcpy
 ```
 
+To avoid enabling remote port forwarding, you could force a forward connection
+instead (notice the `-L` instead of `-R`):
+
+```bash
+adb kill-server    # kill the local adb server on 5037
+ssh -CN -L5037:localhost:5037 -L27183:localhost:27183 your_remote_computer
+# keep this open
+```
+
+From another terminal:
+
+```bash
+scrcpy --force-adb-forwrad
+```
+
+
 Like for wireless connections, it may be useful to reduce quality:
 
 ```

app/scrcpy.1

@@ -52,6 +52,10 @@ The list of possible display ids can be listed by "adb shell dumpsys display"
 
 Default is 0.
 
+.TP
+.B \-\-force\-adb\-forward
+Do not attempt to use "adb reverse" to connect to the device.
+
 .TP
 .B \-f, \-\-fullscreen
 Start in fullscreen.

app/src/cli.c

@@ -54,6 +54,10 @@ scrcpy_print_usage(const char *arg0) {
         "\n"
         "        Default is 0.\n"
         "\n"
+        "    --force-adb-forward\n"
+        "        Do not attempt to use \"adb reverse\" to connect to the\n"
+        "        the device.\n"
+        "\n"
         "    -f, --fullscreen\n"
         "        Start in fullscreen.\n"
         "\n"
@@ -516,6 +520,7 @@ guess_record_format(const char *filename) {
 #define OPT_RENDER_DRIVER          1016
 #define OPT_NO_MIPMAPS             1017
 #define OPT_CODEC_OPTIONS          1018
+#define OPT_FORCE_ADB_FORWARD      1019
 
 bool
 scrcpy_parse_args(struct scrcpy_cli_args *args, int argc, char *argv[]) {
@@ -525,6 +530,8 @@ scrcpy_parse_args(struct scrcpy_cli_args *args, int argc, char *argv[]) {
         {"codec-options",          required_argument, NULL, OPT_CODEC_OPTIONS},
         {"crop",                   required_argument, NULL, OPT_CROP},
         {"display",                required_argument, NULL, OPT_DISPLAY_ID},
+        {"force-adb-forward",      no_argument,       NULL,
+                                                  OPT_FORCE_ADB_FORWARD},
         {"fullscreen",             no_argument,       NULL, 'f'},
         {"help",                   no_argument,       NULL, 'h'},
         {"lock-video-orientation", required_argument, NULL,
@@ -701,6 +708,9 @@ scrcpy_parse_args(struct scrcpy_cli_args *args, int argc, char *argv[]) {
             case OPT_CODEC_OPTIONS:
                 opts->codec_options = optarg;
                 break;
+            case OPT_FORCE_ADB_FORWARD:
+                opts->force_adb_forward = true;
+                break;
             default:
                 // getopt prints the error message on stderr
                 return false;

app/src/scrcpy.c

@@ -305,6 +305,7 @@ scrcpy(const struct scrcpy_options *options) {
         .show_touches = options->show_touches,
         .stay_awake = options->stay_awake,
         .codec_options = options->codec_options,
+        .force_adb_forward = options->force_adb_forward,
     };
     if (!server_start(&server, options->serial, &params)) {
         return false;

app/src/scrcpy.h

@@ -42,6 +42,7 @@ struct scrcpy_options {
     bool window_borderless;
     bool mipmaps;
     bool stay_awake;
+    bool force_adb_forward;
 };
 
 #define SCRCPY_OPTIONS_DEFAULT { \
@@ -79,6 +80,7 @@ struct scrcpy_options {
     .window_borderless = false, \
     .mipmaps = true, \
     .stay_awake = false, \
+    .force_adb_forward = false, \
 }
 
 bool

app/src/server.c

@@ -217,15 +217,20 @@ enable_tunnel_forward_any_port(struct server *server,
 }
 
 static bool
-enable_tunnel_any_port(struct server *server, struct port_range port_range) {
-    if (enable_tunnel_reverse_any_port(server, port_range)) {
-        return true;
+enable_tunnel_any_port(struct server *server, struct port_range port_range,
+                       bool force_adb_forward) {
+    if (!force_adb_forward) {
+        // Attempt to use "adb reverse"
+        if (enable_tunnel_reverse_any_port(server, port_range)) {
+            return true;
+        }
+
+        // if "adb reverse" does not work (e.g. over "adb connect"), it
+        // fallbacks to "adb forward", so the app socket is the client
+
+        LOGW("'adb reverse' failed, fallback to 'adb forward'");
     }
 
-    // if "adb reverse" does not work (e.g. over "adb connect"), it fallbacks to
-    // "adb forward", so the app socket is the client
-
-    LOGW("'adb reverse' failed, fallback to 'adb forward'");
     return enable_tunnel_forward_any_port(server, port_range);
 }
 
@@ -384,7 +389,8 @@ server_start(struct server *server, const char *serial,
         goto error1;
     }
 
-    if (!enable_tunnel_any_port(server, params->port_range)) {
+    if (!enable_tunnel_any_port(server, params->port_range,
+                                params->force_adb_forward)) {
         goto error1;
     }
 

app/src/server.h

@@ -56,6 +56,7 @@ struct server_params {
     uint16_t display_id;
     bool show_touches;
     bool stay_awake;
+    bool force_adb_forward;
 };
 
 // init default values