Use current adb port (if any) for --tcpip

If the current adb port is not 5555 (typically 0 because it is not in
TCP/IP mode), --tcpip automatically executes (among other commands):

    adb tcpip 5555

In case adb was already listening on another port, this command forced
to listen on 5555, and the connection should still succeed.

But this reconfiguration might be inconvenient for the user. If adb is
already in TCP/IP mode, use the current enabled port without
reconfiguration.

Fixes #3591 <https://github.com/Genymobile/scrcpy/issues/3591>

app/src/server.c

@@ -19,6 +19,8 @@
 #define SC_SERVER_PATH_DEFAULT PREFIX "/share/scrcpy/" SC_SERVER_FILENAME
 #define SC_DEVICE_SERVER_PATH "/data/local/tmp/scrcpy-server.jar"
 
+#define SC_ADB_PORT_DEFAULT 5555
+
 static char *
 get_server_path(void) {
 #ifdef __WINDOWS__
@@ -513,27 +515,36 @@ sc_server_on_terminated(void *userdata) {
     LOGD("Server terminated");
 }
 
-static bool
-is_tcpip_mode_enabled(struct sc_server *server, const char *serial) {
+static uint16_t
+get_adb_tcp_port(struct sc_server *server, const char *serial) {
     struct sc_intr *intr = &server->intr;
 
     char *current_port =
         sc_adb_getprop(intr, serial, "service.adb.tcp.port", SC_ADB_SILENT);
     if (!current_port) {
-        return false;
+        return 0;
     }
 
-    // Is the device is listening on TCP on port 5555?
-    bool enabled = !strcmp("5555", current_port);
+    long value;
+    bool ok = sc_str_parse_integer(current_port, &value);
     free(current_port);
-    return enabled;
+    if (!ok) {
+        return 0;
+    }
+
+    if (value < 0 || value > 0xFFFF) {
+        return 0;
+    }
+
+    return value;
 }
 
 static bool
 wait_tcpip_mode_enabled(struct sc_server *server, const char *serial,
-                        unsigned attempts, sc_tick delay) {
-    if (is_tcpip_mode_enabled(server, serial)) {
-        LOGI("TCP/IP mode enabled");
+                        uint16_t expected_port, unsigned attempts,
+                        sc_tick delay) {
+    uint16_t adb_port = get_adb_tcp_port(server, serial);
+    if (adb_port == expected_port) {
         return true;
     }
 
@@ -547,28 +558,23 @@ wait_tcpip_mode_enabled(struct sc_server *server, const char *serial,
             return false;
         }
 
-        if (is_tcpip_mode_enabled(server, serial)) {
-            LOGI("TCP/IP mode enabled");
+        adb_port = get_adb_tcp_port(server, serial);
+        if (adb_port == expected_port) {
             return true;
         }
     } while (--attempts);
     return false;
 }
 
-char *
-append_port_5555(const char *ip) {
-    size_t len = strlen(ip);
-
-    // sizeof counts the final '\0'
-    char *ip_port = malloc(len + sizeof(":5555"));
-    if (!ip_port) {
+static char *
+append_port(const char *ip, uint16_t port) {
+    char *ip_port;
+    int ret = asprintf(&ip_port, "%s:%" PRIu16, ip, port);
+    if (ret == -1) {
         LOG_OOM();
         return NULL;
     }
 
-    memcpy(ip_port, ip, len);
-    memcpy(ip_port + len, ":5555", sizeof(":5555"));
-
     return ip_port;
 }
 
@@ -586,34 +592,36 @@ sc_server_switch_to_tcpip(struct sc_server *server, const char *serial) {
         return NULL;
     }
 
-    char *ip_port = append_port_5555(ip);
-    free(ip);
-    if (!ip_port) {
-        return NULL;
-    }
+    uint16_t adb_port = get_adb_tcp_port(server, serial);
+    if (adb_port) {
+        LOGI("TCP/IP mode already enabled on port %" PRIu16, adb_port);
+    } else {
+        LOGI("Enabling TCP/IP mode on port " SC_STR(SC_ADB_PORT_DEFAULT) "...");
 
-    bool tcp_mode = is_tcpip_mode_enabled(server, serial);
-
-    if (!tcp_mode) {
-        bool ok = sc_adb_tcpip(intr, serial, 5555, SC_ADB_NO_STDOUT);
+        bool ok = sc_adb_tcpip(intr, serial, SC_ADB_PORT_DEFAULT,
+                               SC_ADB_NO_STDOUT);
         if (!ok) {
             LOGE("Could not restart adbd in TCP/IP mode");
-            goto error;
+            free(ip);
+            return NULL;
         }
 
         unsigned attempts = 40;
         sc_tick delay = SC_TICK_FROM_MS(250);
-        ok = wait_tcpip_mode_enabled(server, serial, attempts, delay);
+        ok = wait_tcpip_mode_enabled(server, serial, SC_ADB_PORT_DEFAULT,
+                                     attempts, delay);
         if (!ok) {
-            goto error;
+            free(ip);
+            return NULL;
         }
+
+        adb_port = SC_ADB_PORT_DEFAULT;
+        LOGI("TCP/IP mode enabled on port " SC_STR(SC_ADB_PORT_DEFAULT));
     }
 
+    char *ip_port = append_port(ip, adb_port);
+    free(ip);
     return ip_port;
-
-error:
-    free(ip_port);
-    return NULL;
 }
 
 static bool
@@ -640,7 +648,8 @@ sc_server_configure_tcpip_known_address(struct sc_server *server,
                                         const char *addr) {
     // Append ":5555" if no port is present
     bool contains_port = strchr(addr, ':');
-    char *ip_port = contains_port ? strdup(addr) : append_port_5555(addr);
+    char *ip_port = contains_port ? strdup(addr)
+                                  : append_port(addr, SC_ADB_PORT_DEFAULT);
     if (!ip_port) {
         LOG_OOM();
         return false;