Accept port range

Accept a range of ports to listen to, so that it does not fail if
another instance of scrcpy is currently starting.

The range can be passed via the command line:

    scrcpy -p 27183:27186
    scrcpy -p 27183  # implicitly 27183:27183, as before

The default is 27183:27199.

Closes #951 <https://github.com/Genymobile/scrcpy/issues/951>

app/meson.build

@@ -96,9 +96,10 @@ conf.set_quoted('PREFIX', get_option('prefix'))
 # directory as the executable)
 conf.set('PORTABLE', get_option('portable'))
 
-# the default client TCP port for the "adb reverse" tunnel
+# the default client TCP port range for the "adb reverse" tunnel
 # overridden by option --port
-conf.set('DEFAULT_LOCAL_PORT', '27183')
+conf.set('DEFAULT_LOCAL_PORT_RANGE_FIRST', '27183')
+conf.set('DEFAULT_LOCAL_PORT_RANGE_LAST', '27199')
 
 # the default max video size for both dimensions, in pixels
 # overridden by option --max-size

app/scrcpy.1

@@ -60,10 +60,10 @@ Disable device control (mirror the device in read\-only).
 Do not display device (only when screen recording is enabled).
 
 .TP
-.BI "\-p, \-\-port " port
-Set the TCP port the client listens on.
+.BI "\-p, \-\-port " port[:port]
+Set the TCP port (range) used by the client to listen.
 
-Default is 27183.
+Default is 27183:27199.
 
 .TP
 .B \-\-prefer\-text

app/src/cli.c

@@ -58,9 +58,9 @@ scrcpy_print_usage(const char *arg0) {
         "        Do not display device (only when screen recording is\n"
         "        enabled).\n"
         "\n"
-        "    -p, --port port\n"
-        "        Set the TCP port the client listens on.\n"
-        "        Default is %d.\n"
+        "    -p, --port port[:port]\n"
+        "        Set the TCP port (range) used by the client to listen.\n"
+        "        Default is %d:%d.\n"
         "\n"
         "    --prefer-text\n"
         "        Inject alpha characters and space as text events instead of\n"
@@ -193,7 +193,7 @@ scrcpy_print_usage(const char *arg0) {
         arg0,
         DEFAULT_BIT_RATE,
         DEFAULT_MAX_SIZE, DEFAULT_MAX_SIZE ? "" : " (unlimited)",
-        DEFAULT_LOCAL_PORT);
+        DEFAULT_LOCAL_PORT_RANGE_FIRST, DEFAULT_LOCAL_PORT_RANGE_LAST);
 }
 
 static bool
@@ -221,6 +221,27 @@ parse_integer_arg(const char *s, long *out, bool accept_suffix, long min,
     return true;
 }
 
+static size_t
+parse_integers_arg(const char *s, size_t max_items, long *out, long min,
+                   long max, const char *name) {
+    size_t count = parse_integers(s, ':', max_items, out);
+    if (!count) {
+        LOGE("Could not parse %s: %s", name, s);
+        return 0;
+    }
+
+    for (size_t i = 0; i < count; ++i) {
+        long value = out[i];
+        if (value < min || value > max) {
+            LOGE("Could not parse %s: value (%ld) out-of-range (%ld; %ld)",
+                 name, value, min, max);
+            return 0;
+        }
+    }
+
+    return count;
+}
+
 static bool
 parse_bit_rate(const char *s, uint32_t *bit_rate) {
     long value;
@@ -286,14 +307,30 @@ parse_window_dimension(const char *s, uint16_t *dimension) {
 }
 
 static bool
-parse_port(const char *s, uint16_t *port) {
-    long value;
-    bool ok = parse_integer_arg(s, &value, false, 0, 0xFFFF, "port");
-    if (!ok) {
+parse_port_range(const char *s, struct port_range *port_range) {
+    long values[2];
+    size_t count = parse_integers_arg(s, 2, values, 0, 0xFFFF, "port");
+    if (!count) {
         return false;
     }
 
-    *port = (uint16_t) value;
+    uint16_t v0 = (uint16_t) values[0];
+    if (count == 1) {
+        port_range->first = v0;
+        port_range->last = v0;
+        return true;
+    }
+
+    assert(count == 2);
+    uint16_t v1 = (uint16_t) values[1];
+    if (v0 < v1) {
+        port_range->first = v0;
+        port_range->last = v1;
+    } else {
+        port_range->first = v1;
+        port_range->last = v0;
+    }
+
     return true;
 }
 
@@ -424,7 +461,7 @@ scrcpy_parse_args(struct scrcpy_cli_args *args, int argc, char *argv[]) {
                 opts->display = false;
                 break;
             case 'p':
-                if (!parse_port(optarg, &opts->port)) {
+                if (!parse_port_range(optarg, &opts->port_range)) {
                     return false;
                 }
                 break;

app/src/common.h

@@ -27,4 +27,9 @@ struct position {
     struct point point;
 };
 
+struct port_range {
+    uint16_t first;
+    uint16_t last;
+};
+
 #endif

app/src/scrcpy.c

@@ -280,7 +280,7 @@ scrcpy(const struct scrcpy_options *options) {
     bool record = !!options->record_filename;
     struct server_params params = {
         .crop = options->crop,
-        .local_port = options->port,
+        .port_range = options->port_range,
         .max_size = options->max_size,
         .bit_rate = options->bit_rate,
         .max_fps = options->max_fps,

app/src/scrcpy.h

@@ -5,6 +5,7 @@
 #include <stdint.h>
 
 #include "config.h"
+#include "common.h"
 #include "input_manager.h"
 #include "recorder.h"
 
@@ -15,7 +16,7 @@ struct scrcpy_options {
     const char *window_title;
     const char *push_target;
     enum recorder_format record_format;
-    uint16_t port;
+    struct port_range port_range;
     uint16_t max_size;
     uint32_t bit_rate;
     uint16_t max_fps;
@@ -41,7 +42,10 @@ struct scrcpy_options {
     .window_title = NULL, \
     .push_target = NULL, \
     .record_format = RECORDER_FORMAT_AUTO, \
-    .port = DEFAULT_LOCAL_PORT, \
+    .port_range = { \
+        .first = DEFAULT_LOCAL_PORT_RANGE_FIRST, \
+        .last = DEFAULT_LOCAL_PORT_RANGE_LAST, \
+    }, \
     .max_size = DEFAULT_MAX_SIZE, \
     .bit_rate = DEFAULT_BIT_RATE, \
     .max_fps = 0, \

app/src/server.c

@@ -126,17 +126,6 @@ disable_tunnel_forward(const char *serial, uint16_t local_port) {
     return process_check_success(process, "adb forward --remove");
 }
 
-static bool
-enable_tunnel(struct server *server) {
-    if (enable_tunnel_reverse(server->serial, server->local_port)) {
-        return true;
-    }
-
-    LOGW("'adb reverse' failed, fallback to 'adb forward'");
-    server->tunnel_forward = true;
-    return enable_tunnel_forward(server->serial, server->local_port);
-}
-
 static bool
 disable_tunnel(struct server *server) {
     if (server->tunnel_forward) {
@@ -145,6 +134,100 @@ disable_tunnel(struct server *server) {
     return disable_tunnel_reverse(server->serial);
 }
 
+static socket_t
+listen_on_port(uint16_t port) {
+#define IPV4_LOCALHOST 0x7F000001
+    return net_listen(IPV4_LOCALHOST, port, 1);
+}
+
+static bool
+enable_tunnel_reverse_any_port(struct server *server,
+                               struct port_range port_range) {
+    uint16_t port = port_range.first;
+    for (;;) {
+        if (!enable_tunnel_reverse(server->serial, port)) {
+            // the command itself failed, it will fail on any port
+            return false;
+        }
+
+        // At the application level, the device part is "the server" because it
+        // serves video stream and control. However, at the network level, the
+        // client listens and the server connects to the client. That way, the
+        // client can listen before starting the server app, so there is no
+        // need to try to connect until the server socket is listening on the
+        // device.
+        server->server_socket = listen_on_port(port);
+        if (server->server_socket != INVALID_SOCKET) {
+            // success
+            server->local_port = port;
+            return true;
+        }
+
+        // failure, disable tunnel and try another port
+        if (!disable_tunnel_reverse(server->serial)) {
+            LOGW("Could not remove reverse tunnel on port %" PRIu16, port);
+        }
+
+        // check before incrementing to avoid overflow on port 65535
+        if (port < port_range.last) {
+            LOGW("Could not listen on port %" PRIu16", retrying on %" PRIu16,
+                 port, port + 1);
+            port++;
+            continue;
+        }
+
+        if (port_range.first == port_range.last) {
+            LOGE("Could not listen on port %" PRIu16, port_range.first);
+        } else {
+            LOGE("Could not listen on any port in range %" PRIu16 ":%" PRIu16,
+                 port_range.first, port_range.last);
+        }
+        return false;
+    }
+}
+
+static bool
+enable_tunnel_forward_any_port(struct server *server,
+                               struct port_range port_range) {
+    server->tunnel_forward = true;
+    uint16_t port = port_range.first;
+    for (;;) {
+        if (enable_tunnel_forward(server->serial, port)) {
+            // success
+            server->local_port = port;
+            return true;
+        }
+
+        if (port < port_range.last) {
+            LOGW("Could not forward port %" PRIu16", retrying on %" PRIu16,
+                 port, port + 1);
+            port++;
+            continue;
+        }
+
+        if (port_range.first == port_range.last) {
+            LOGE("Could not forward port %" PRIu16, port_range.first);
+        } else {
+            LOGE("Could not forward any port in range %" PRIu16 ":%" PRIu16,
+                 port_range.first, port_range.last);
+        }
+        return false;
+    }
+}
+
+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;
+    }
+
+    // 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);
+}
+
 static process_t
 execute_server(struct server *server, const struct server_params *params) {
     char max_size_string[6];
@@ -187,13 +270,6 @@ execute_server(struct server *server, const struct server_params *params) {
     return adb_execute(server->serial, cmd, sizeof(cmd) / sizeof(cmd[0]));
 }
 
-#define IPV4_LOCALHOST 0x7F000001
-
-static socket_t
-listen_on_port(uint16_t port) {
-    return net_listen(IPV4_LOCALHOST, port, 1);
-}
-
 static socket_t
 connect_and_read_byte(uint16_t port) {
     socket_t socket = net_connect(IPV4_LOCALHOST, port);
@@ -247,7 +323,7 @@ server_init(struct server *server) {
 bool
 server_start(struct server *server, const char *serial,
              const struct server_params *params) {
-    server->local_port = params->local_port;
+    server->port_range = params->port_range;
 
     if (serial) {
         server->serial = SDL_strdup(serial);
@@ -261,30 +337,11 @@ server_start(struct server *server, const char *serial,
         return false;
     }
 
-    if (!enable_tunnel(server)) {
+    if (!enable_tunnel_any_port(server, params->port_range)) {
         SDL_free(server->serial);
         return false;
     }
 
-    // if "adb reverse" does not work (e.g. over "adb connect"), it fallbacks to
-    // "adb forward", so the app socket is the client
-    if (!server->tunnel_forward) {
-        // At the application level, the device part is "the server" because it
-        // serves video stream and control. However, at the network level, the
-        // client listens and the server connects to the client. That way, the
-        // client can listen before starting the server app, so there is no
-        // need to try to connect until the server socket is listening on the
-        // device.
-
-        server->server_socket = listen_on_port(params->local_port);
-        if (server->server_socket == INVALID_SOCKET) {
-            LOGE("Could not listen on port %" PRIu16, params->local_port);
-            disable_tunnel(server);
-            SDL_free(server->serial);
-            return false;
-        }
-    }
-
     // server will connect to our server socket
     server->process = execute_server(server, params);
 

app/src/server.h

@@ -6,6 +6,7 @@
 
 #include "config.h"
 #include "command.h"
+#include "common.h"
 #include "util/net.h"
 
 struct server {
@@ -14,7 +15,8 @@ struct server {
     socket_t server_socket; // only used if !tunnel_forward
     socket_t video_socket;
     socket_t control_socket;
-    uint16_t local_port;
+    struct port_range port_range;
+    uint16_t local_port; // selected from port_range
     bool tunnel_enabled;
     bool tunnel_forward; // use "adb forward" instead of "adb reverse"
 };
@@ -25,6 +27,10 @@ struct server {
     .server_socket = INVALID_SOCKET, \
     .video_socket = INVALID_SOCKET, \
     .control_socket = INVALID_SOCKET, \
+    .port_range = { \
+        .first = 0, \
+        .last = 0, \
+    }, \
     .local_port = 0, \
     .tunnel_enabled = false, \
     .tunnel_forward = false, \
@@ -32,7 +38,7 @@ struct server {
 
 struct server_params {
     const char *crop;
-    uint16_t local_port;
+    struct port_range port_range;
     uint16_t max_size;
     uint32_t bit_rate;
     uint16_t max_fps;

app/src/util/str_util.c

@@ -81,6 +81,35 @@ parse_integer(const char *s, long *out) {
     return true;
 }
 
+size_t
+parse_integers(const char *s, const char sep, size_t max_items, long *out) {
+    size_t count = 0;
+    char *endptr;
+    do {
+        errno = 0;
+        long value = strtol(s, &endptr, 0);
+        if (errno == ERANGE) {
+            return 0;
+        }
+
+        if (endptr == s || (*endptr != sep && *endptr != '\0')) {
+            return 0;
+        }
+
+        out[count++] = value;
+        if (*endptr == sep) {
+            if (count >= max_items) {
+                // max items already reached, could not accept a new item
+                return 0;
+            }
+            // parse the next token during the next iteration
+            s = endptr + 1;
+        }
+    } while (*endptr != '\0');
+
+    return count;
+}
+
 bool
 parse_integer_with_suffix(const char *s, long *out) {
     char *endptr;

app/src/util/str_util.h

@@ -31,6 +31,11 @@ strquote(const char *src);
 bool
 parse_integer(const char *s, long *out);
 
+// parse s as integers separated by sep (for example '1234:2000')
+// returns the number of integers on success, 0 on failure
+size_t
+parse_integers(const char *s, const char sep, size_t max_items, long *out);
+
 // parse s as an integer into value
 // like parse_integer(), but accept 'k'/'K' (x1000) and 'm'/'M' (x1000000) as
 // suffix

app/tests/test_cli.c

@@ -50,7 +50,7 @@ static void test_options(void) {
         "--max-size", "1024",
         // "--no-control" is not compatible with "--turn-screen-off"
         // "--no-display" is not compatible with "--fulscreen"
-        "--port", "1234",
+        "--port", "1234:1236",
         "--push-target", "/sdcard/Movies",
         "--record", "file",
         "--record-format", "mkv",
@@ -78,7 +78,8 @@ static void test_options(void) {
     assert(opts->fullscreen);
     assert(opts->max_fps == 30);
     assert(opts->max_size == 1024);
-    assert(opts->port == 1234);
+    assert(opts->port_range.first == 1234);
+    assert(opts->port_range.last == 1236);
     assert(!strcmp(opts->push_target, "/sdcard/Movies"));
     assert(!strcmp(opts->record_filename, "file"));
     assert(opts->record_format == RECORDER_FORMAT_MKV);

app/tests/test_strutil.c

@@ -187,6 +187,55 @@ static void test_parse_integer(void) {
     assert(!ok); // out-of-range
 }
 
+static void test_parse_integers(void) {
+    long values[5];
+
+    size_t count = parse_integers("1234", ':', 5, values);
+    assert(count == 1);
+    assert(values[0] == 1234);
+
+    count = parse_integers("1234:5678", ':', 5, values);
+    assert(count == 2);
+    assert(values[0] == 1234);
+    assert(values[1] == 5678);
+
+    count = parse_integers("1234:5678", ':', 2, values);
+    assert(count == 2);
+    assert(values[0] == 1234);
+    assert(values[1] == 5678);
+
+    count = parse_integers("1234:-5678", ':', 2, values);
+    assert(count == 2);
+    assert(values[0] == 1234);
+    assert(values[1] == -5678);
+
+    count = parse_integers("1:2:3:4:5", ':', 5, values);
+    assert(count == 5);
+    assert(values[0] == 1);
+    assert(values[1] == 2);
+    assert(values[2] == 3);
+    assert(values[3] == 4);
+    assert(values[4] == 5);
+
+    count = parse_integers("1234:5678", ':', 1, values);
+    assert(count == 0); // max_items == 1
+
+    count = parse_integers("1:2:3:4:5", ':', 3, values);
+    assert(count == 0); // max_items == 3
+
+    count = parse_integers(":1234", ':', 5, values);
+    assert(count == 0); // invalid
+
+    count = parse_integers("1234:", ':', 5, values);
+    assert(count == 0); // invalid
+
+    count = parse_integers("1234:", ':', 1, values);
+    assert(count == 0); // invalid, even when max_items == 1
+
+    count = parse_integers("1234::5678", ':', 5, values);
+    assert(count == 0); // invalid
+}
+
 static void test_parse_integer_with_suffix(void) {
     long value;
     bool ok = parse_integer_with_suffix("1234", &value);
@@ -249,6 +298,7 @@ int main(void) {
     test_strquote();
     test_utf8_truncate();
     test_parse_integer();
+    test_parse_integers();
     test_parse_integer_with_suffix();
     return 0;
 }