Document remote ADB server in README

Refs #2807 <https://github.com/Genymobile/scrcpy/pull/2807>

README.md

@@ -412,12 +412,47 @@ autoadb scrcpy -s '{}'
 
 [AutoAdb]: https://github.com/rom1v/autoadb
 
-#### SSH tunnel
+#### Tunnels
 
 To connect to a remote device, it is possible to connect a local `adb` client to
 a remote `adb` server (provided they use the same version of the _adb_
 protocol).
 
+##### Remote ADB server
+
+To connect to a remote ADB server, make the server listen on all interfaces:
+
+```bash
+adb kill-server
+adb -a nodaemon server start
+# keep this open
+```
+
+**Warning: all communications between clients and ADB server are unencrypted.**
+
+Suppose that this server is accessible at 192.168.1.2. Then, from another
+terminal, run scrcpy:
+
+```bash
+export ADB_SERVER_SOCKET=tcp:192.168.1.2:5037
+scrcpy --tunnel-host=192.168.1.2
+```
+
+By default, scrcpy uses the local port used for `adb forward` tunnel
+establishment (typically `27183`, see `--port`). It is also possible to force a
+different tunnel port (it may be useful in more complex situations, when more
+redirections are involved):
+
+```
+scrcpy --tunnel-port=1234
+```
+
+
+##### SSH tunnel
+
+To communicate with a remote ADB server securely, it is preferable to use a SSH
+tunnel.
+
 First, make sure the ADB server is running on the remote computer:
 
 ```bash

app/meson.build

@@ -199,6 +199,7 @@ if get_option('buildtype') == 'debug'
             'tests/test_cli.c',
             'src/cli.c',
             'src/options.c',
+            'src/util/net.c',
             'src/util/str.c',
             'src/util/strbuf.c',
             'src/util/term.c',

app/scrcpy.1

@@ -203,6 +203,18 @@ Enable "show touches" on start, restore the initial value on exit.
 
 It only shows physical touches (not clicks from scrcpy).
 
+.TP
+.BI "\-\-tunnel\-host " ip
+Set the IP address of the adb tunnel to reach the scrcpy server. This option automatically enables --force-adb-forward.
+
+Default is localhost.
+
+.TP
+.BI "\-\-tunnel\-port " port
+Set the TCP port of the adb tunnel to reach the scrcpy server. This option automatically enables --force-adb-forward.
+
+Default is 0 (not forced): the local port used for establishing the tunnel will be used.
+
 .TP
 .BI "\-\-v4l2-sink " /dev/videoN
 Output to v4l2loopback device.

app/src/cli.c

@@ -9,6 +9,7 @@
 
 #include "options.h"
 #include "util/log.h"
+#include "util/net.h"
 #include "util/str.h"
 #include "util/strbuf.h"
 #include "util/term.h"
@@ -46,6 +47,8 @@
 #define OPT_V4L2_SINK              1027
 #define OPT_DISPLAY_BUFFER         1028
 #define OPT_V4L2_BUFFER            1029
+#define OPT_TUNNEL_HOST            1030
+#define OPT_TUNNEL_PORT            1031
 
 struct sc_option {
     char shortopt;
@@ -330,6 +333,25 @@ static const struct sc_option options[] = {
                 "on exit.\n"
                 "It only shows physical touches (not clicks from scrcpy).",
     },
+    {
+        .longopt_id = OPT_TUNNEL_HOST,
+        .longopt = "tunnel-host",
+        .argdesc = "ip",
+        .text = "Set the IP address of the adb tunnel to reach the scrcpy "
+                "server. This option automatically enables "
+                "--force-adb-forward.\n"
+                "Default is localhost.",
+    },
+    {
+        .longopt_id = OPT_TUNNEL_PORT,
+        .longopt = "tunnel-port",
+        .argdesc = "port",
+        .text = "Set the TCP port of the adb tunnel to reach the scrcpy "
+                "server. This option automatically enables "
+                "--force-adb-forward.\n"
+                "Default is 0 (not forced): the local port used for "
+                "establishing the tunnel will be used.",
+    },
 #ifdef HAVE_V4L2
     {
         .longopt_id = OPT_V4L2_SINK,
@@ -1127,6 +1149,21 @@ parse_record_format(const char *optarg, enum sc_record_format *format) {
     return false;
 }
 
+static bool
+parse_ip(const char *optarg, uint32_t *ipv4) {
+    return net_parse_ipv4(optarg, ipv4);
+}
+
+static bool
+parse_port(const char *optarg, uint16_t *port) {
+    long value;
+    if (!parse_integer_arg(optarg, &value, false, 0, 0xFFFF, "port")) {
+        return false;
+    }
+    *port = (uint16_t) value;
+    return true;
+}
+
 static enum sc_record_format
 guess_record_format(const char *filename) {
     size_t len = strlen(filename);
@@ -1199,6 +1236,16 @@ parse_args_with_getopt(struct scrcpy_cli_args *args, int argc, char *argv[],
                     return false;
                 }
                 break;
+            case OPT_TUNNEL_HOST:
+                if (!parse_ip(optarg, &opts->tunnel_host)) {
+                    return false;
+                }
+                break;
+            case OPT_TUNNEL_PORT:
+                if (!parse_port(optarg, &opts->tunnel_port)) {
+                    return false;
+                }
+                break;
             case 'n':
                 opts->control = false;
                 break;
@@ -1358,6 +1405,12 @@ parse_args_with_getopt(struct scrcpy_cli_args *args, int argc, char *argv[],
     }
 #endif
 
+    if ((opts->tunnel_host || opts->tunnel_port) && !opts->force_adb_forward) {
+        LOGI("Tunnel host/port is set, "
+             "--force-adb-forward automatically enabled.");
+        opts->force_adb_forward = true;
+    }
+
     int index = optind;
     if (index < argc) {
         LOGE("Unexpected additional argument: %s", argv[index]);

app/src/options.c

@@ -19,6 +19,8 @@ const struct scrcpy_options scrcpy_options_default = {
         .first = DEFAULT_LOCAL_PORT_RANGE_FIRST,
         .last = DEFAULT_LOCAL_PORT_RANGE_LAST,
     },
+    .tunnel_host = 0,
+    .tunnel_port = 0,
     .shortcut_mods = {
         .data = {SC_MOD_LALT, SC_MOD_LSUPER},
         .count = 2,

app/src/options.h

@@ -77,6 +77,8 @@ struct scrcpy_options {
     enum sc_record_format record_format;
     enum sc_keyboard_input_mode keyboard_input_mode;
     struct sc_port_range port_range;
+    uint32_t tunnel_host;
+    uint16_t tunnel_port;
     struct sc_shortcut_mods shortcut_mods;
     uint16_t max_size;
     uint32_t bit_rate;

app/src/scrcpy.c

@@ -345,6 +345,8 @@ scrcpy(struct scrcpy_options *options) {
         .log_level = options->log_level,
         .crop = options->crop,
         .port_range = options->port_range,
+        .tunnel_host = options->tunnel_host,
+        .tunnel_port = options->tunnel_port,
         .max_size = options->max_size,
         .bit_rate = options->bit_rate,
         .max_fps = options->max_fps,

app/src/server.c

@@ -202,8 +202,9 @@ execute_server(struct sc_server *server,
 }
 
 static bool
-connect_and_read_byte(struct sc_intr *intr, sc_socket socket, uint16_t port) {
-    bool ok = net_connect_intr(intr, socket, IPV4_LOCALHOST, port);
+connect_and_read_byte(struct sc_intr *intr, sc_socket socket,
+                      uint32_t tunnel_host, uint16_t tunnel_port) {
+    bool ok = net_connect_intr(intr, socket, tunnel_host, tunnel_port);
     if (!ok) {
         return false;
     }
@@ -220,13 +221,13 @@ connect_and_read_byte(struct sc_intr *intr, sc_socket socket, uint16_t port) {
 }
 
 static sc_socket
-connect_to_server(struct sc_server *server, uint32_t attempts, sc_tick delay) {
-    uint16_t port = server->tunnel.local_port;
+connect_to_server(struct sc_server *server, uint32_t attempts, sc_tick delay,
+                  uint32_t host, uint16_t port) {
     do {
         LOGD("Remaining connection attempts: %d", (int) attempts);
         sc_socket socket = net_socket();
         if (socket != SC_SOCKET_NONE) {
-            bool ok = connect_and_read_byte(&server->intr, socket, port);
+            bool ok = connect_and_read_byte(&server->intr, socket, host, port);
             if (ok) {
                 // it worked!
                 return socket;
@@ -352,9 +353,20 @@ sc_server_connect_to(struct sc_server *server, struct sc_server_info *info) {
             goto fail;
         }
     } else {
+        uint32_t tunnel_host = server->params.tunnel_host;
+        if (!tunnel_host) {
+            tunnel_host = IPV4_LOCALHOST;
+        }
+
+        uint16_t tunnel_port = server->params.tunnel_port;
+        if (!tunnel_port) {
+            tunnel_port = tunnel->local_port;
+        }
+
         uint32_t attempts = 100;
         sc_tick delay = SC_TICK_FROM_MS(100);
-        video_socket = connect_to_server(server, attempts, delay);
+        video_socket = connect_to_server(server, attempts, delay, tunnel_host,
+                                         tunnel_port);
         if (video_socket == SC_SOCKET_NONE) {
             goto fail;
         }
@@ -364,8 +376,8 @@ sc_server_connect_to(struct sc_server *server, struct sc_server_info *info) {
         if (control_socket == SC_SOCKET_NONE) {
             goto fail;
         }
-        bool ok = net_connect_intr(&server->intr, control_socket,
-                                   IPV4_LOCALHOST, tunnel->local_port);
+        bool ok = net_connect_intr(&server->intr, control_socket, tunnel_host,
+                                   tunnel_port);
         if (!ok) {
             goto fail;
         }

app/src/server.h

@@ -29,6 +29,8 @@ struct sc_server_params {
     const char *codec_options;
     const char *encoder_name;
     struct sc_port_range port_range;
+    uint32_t tunnel_host;
+    uint16_t tunnel_port;
     uint16_t max_size;
     uint32_t bit_rate;
     uint16_t max_fps;

app/src/util/net.c

@@ -1,3 +1,7 @@
+// For inet_pton() on Windows
+#define _WIN32_WINNT 0x0600
+#define WINVER 0x0600
+
 #include "net.h"
 
 #include <assert.h>
@@ -7,6 +11,7 @@
 #include "log.h"
 
 #ifdef __WINDOWS__
+# include <ws2tcpip.h>
   typedef int socklen_t;
   typedef SOCKET sc_raw_socket;
 #else
@@ -225,3 +230,15 @@ net_close(sc_socket socket) {
     return !close(raw_sock);
 #endif
 }
+
+bool
+net_parse_ipv4(const char *s, uint32_t *ipv4) {
+    struct in_addr addr;
+    if (!inet_pton(AF_INET, s, &addr)) {
+        LOGE("Invalid IPv4 address: %s", s);
+        return false;
+    }
+
+    *ipv4 = ntohl(addr.s_addr);
+    return true;
+}

app/src/util/net.h

@@ -68,4 +68,10 @@ net_interrupt(sc_socket socket);
 bool
 net_close(sc_socket socket);
 
+/**
+ * Parse `ip` "xxx.xxx.xxx.xxx" to an IPv4 host representation
+ */
+bool
+net_parse_ipv4(const char *ip, uint32_t *ipv4);
+
 #endif