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

If the current adb port is not 5555 (typically it is 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 and listens on another port, use that port
without reconfiguration.

Fixes #3591 <#3591>

README.md

@@ -395,8 +395,8 @@ address), connect the device over USB, then run:
 scrcpy --tcpip    # without arguments
 ```
 
-It will automatically find the device IP address, enable TCP/IP mode, then
-connect to the device before starting.
+It will automatically find the device IP address and adb port, enable TCP/IP
+mode if necessary, then connect to the device before starting.
 
 ##### Manual
 

app/scrcpy.1

@@ -275,7 +275,7 @@ Configure and reconnect the device over TCP/IP.
 
 If a destination address is provided, then scrcpy connects to this address before starting. The device must listen on the given TCP port (default is 5555).
 
-If no destination address is provided, then scrcpy attempts to find the IP address of the current device (typically connected over USB), enables TCP/IP mode, then connects to this address before starting.
+If no destination address is provided, then scrcpy attempts to find the IP address and adb port of the current device (typically connected over USB), enables TCP/IP mode if necessary, then connects to this address before starting.
 
 .TP
 .B \-S, \-\-turn\-screen\-off

app/src/server.c

@@ -513,26 +513,35 @@ 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)) {
+    uint16_t adb_port = get_adb_tcp_port(server, serial);
+    if (adb_port) {
         LOGI("TCP/IP mode enabled");
         return true;
     }
@@ -547,28 +556,24 @@ wait_tcpip_mode_enabled(struct sc_server *server, const char *serial,
             return false;
         }
 
-        if (is_tcpip_mode_enabled(server, serial)) {
+        adb_port = get_adb_tcp_port(server, serial);
+        if (adb_port) {
             LOGI("TCP/IP mode enabled");
             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;
 }
 
@@ -586,15 +591,8 @@ 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;
-    }
-
-    bool tcp_mode = is_tcpip_mode_enabled(server, serial);
-
-    if (!tcp_mode) {
+    uint16_t adb_port = get_adb_tcp_port(server, serial);
+    if (!adb_port) {
         bool ok = sc_adb_tcpip(intr, serial, 5555, SC_ADB_NO_STDOUT);
         if (!ok) {
             LOGE("Could not restart adbd in TCP/IP mode");
@@ -607,12 +605,20 @@ sc_server_switch_to_tcpip(struct sc_server *server, const char *serial) {
         if (!ok) {
             goto error;
         }
+
+        adb_port = 5555;
+    }
+
+    char *ip_port = append_port(ip, adb_port);
+    free(ip);
+    if (!ip_port) {
+        return NULL;
     }
 
     return ip_port;
 
 error:
-    free(ip_port);
+    free(ip);
     return NULL;
 }
 
@@ -640,7 +646,7 @@ 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, 5555);
     if (!ip_port) {
         LOG_OOM();
         return false;