Reset TCP/IP connection with a '+' prefix

When running scrcpy with --tcpip=xx.xx.xx.xx, to make sure a new working
connection is established, it was first disconnected by a call to:

    adb disconnect <addr>

However, this caused all running instances connected to that address to
be killed. Running several instances of scrcpy on the same device is now
useful with virtual displays, so change the default behavior to NOT
disconnect.

To force a reconnection, a '+' prefix can be added:

    scrcpy --tcpip=+192.168.0.x

Fixes #5562 <#5562>

app/scrcpy.1

@@ -518,13 +518,15 @@ Enable "show touches" on start, restore the initial value on exit.
 It only shows physical touches (not clicks from scrcpy).
 
 .TP
-.BI "\-\-tcpip\fR[=\fIip\fR[:\fIport\fR]]
-Configure and reconnect the device over TCP/IP.
+.BI "\-\-tcpip\fR[=[+]\fIip\fR[:\fIport\fR]]
+Configure and connect 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 and adb port of the current device (typically connected over USB), enables TCP/IP mode if necessary, then connects to this address before starting.
 
+Prefix the address with a '+' to force a reconnection.
+
 .TP
 .BI "\-\-time\-limit " seconds
 Set the maximum mirroring time, in seconds.

app/src/adb/adb.c

@@ -412,7 +412,7 @@ sc_adb_connect(struct sc_intr *intr, const char *ip_port, unsigned flags) {
 
     // "adb connect" always returns successfully (with exit code 0), even in
     // case of failure. As a workaround, check if its output starts with
-    // "connected".
+    // "connected" or "already connected".
     char buf[128];
     ssize_t r = sc_pipe_read_all_intr(intr, pid, pout, buf, sizeof(buf) - 1);
     sc_pipe_close(pout);
@@ -429,7 +429,8 @@ sc_adb_connect(struct sc_intr *intr, const char *ip_port, unsigned flags) {
     assert((size_t) r < sizeof(buf));
     buf[r] = '\0';
 
-    ok = !strncmp("connected", buf, sizeof("connected") - 1);
+    ok = !strncmp("connected", buf, sizeof("connected") - 1)
+        || !strncmp("already connected", buf, sizeof("already connected") - 1);
     if (!ok && !(flags & SC_ADB_NO_STDERR)) {
         // "adb connect" also prints errors to stdout. Since we capture it,
         // re-print the error to stderr.

app/src/cli.c

@@ -860,16 +860,17 @@ static const struct sc_option options[] = {
     {
         .longopt_id = OPT_TCPIP,
         .longopt = "tcpip",
-        .argdesc = "ip[:port]",
+        .argdesc = "[+]ip[:port]",
         .optional_arg = true,
-        .text = "Configure and reconnect the device over TCP/IP.\n"
+        .text = "Configure and connect the device over TCP/IP.\n"
                 "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).\n"
                 "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.",
+                "this address before starting.\n"
+                "Prefix the address with a '+' to force a reconnection.",
     },
     {
         .longopt_id = OPT_TIME_LIMIT,

app/src/server.c

@@ -829,11 +829,14 @@ sc_server_switch_to_tcpip(struct sc_server *server, const char *serial) {
 }
 
 static bool
-sc_server_connect_to_tcpip(struct sc_server *server, const char *ip_port) {
+sc_server_connect_to_tcpip(struct sc_server *server, const char *ip_port,
+                           bool disconnect) {
     struct sc_intr *intr = &server->intr;
 
-    // Error expected if not connected, do not report any error
-    sc_adb_disconnect(intr, ip_port, SC_ADB_SILENT);
+    if (disconnect) {
+        // Error expected if not connected, do not report any error
+        sc_adb_disconnect(intr, ip_port, SC_ADB_SILENT);
+    }
 
     LOGI("Connecting to %s...", ip_port);
 
@@ -849,7 +852,7 @@ sc_server_connect_to_tcpip(struct sc_server *server, const char *ip_port) {
 
 static bool
 sc_server_configure_tcpip_known_address(struct sc_server *server,
-                                        const char *addr) {
+                                        const char *addr, bool disconnect) {
     // Append ":5555" if no port is present
     bool contains_port = strchr(addr, ':');
     char *ip_port = contains_port ? strdup(addr)
@@ -860,7 +863,7 @@ sc_server_configure_tcpip_known_address(struct sc_server *server,
     }
 
     server->serial = ip_port;
-    return sc_server_connect_to_tcpip(server, ip_port);
+    return sc_server_connect_to_tcpip(server, ip_port, disconnect);
 }
 
 static bool
@@ -885,7 +888,7 @@ sc_server_configure_tcpip_unknown_address(struct sc_server *server,
     }
 
     server->serial = ip_port;
-    return sc_server_connect_to_tcpip(server, ip_port);
+    return sc_server_connect_to_tcpip(server, ip_port, false);
 }
 
 static void
@@ -972,7 +975,13 @@ run_server(void *data) {
             sc_adb_device_destroy(&device);
         }
     } else {
-        ok = sc_server_configure_tcpip_known_address(server, params->tcpip_dst);
+        // If the user passed a '+' (--tcpip=+ip), then disconnect first
+        const char *tcpip_dst = params->tcpip_dst;
+        bool plus = tcpip_dst[0] == '+';
+        if (plus) {
+            ++tcpip_dst;
+        }
+        ok = sc_server_configure_tcpip_known_address(server, tcpip_dst, plus);
         if (!ok) {
             goto error_connection_failed;
         }

doc/connection.md

@@ -85,6 +85,12 @@ scrcpy --tcpip=192.168.1.1       # default port is 5555
 scrcpy --tcpip=192.168.1.1:5555
 ```
 
+Prefix the address with a '+' to force a reconnection:
+
+```bash
+scrcpy --tcpip=+192.168.1.1
+```
+
 
 ### Manual