Extract adb tunnel to a separate component

This simplifies the server code.

app/src/adb_tunnel.c

@@ -0,0 +1,192 @@
+#include "adb_tunnel.h"
+
+#include <assert.h>
+
+#include "adb.h"
+#include "util/log.h"
+#include "util/net_intr.h"
+#include "util/process_intr.h"
+
+#define SC_SOCKET_NAME "scrcpy"
+
+static bool
+enable_tunnel_reverse(struct sc_intr *intr, const char *serial,
+                      uint16_t local_port) {
+    sc_pid pid = adb_reverse(serial, SC_SOCKET_NAME, local_port);
+    return sc_process_check_success_intr(intr, pid, "adb reverse");
+}
+
+static bool
+disable_tunnel_reverse(struct sc_intr *intr, const char *serial) {
+    sc_pid pid = adb_reverse_remove(serial, SC_SOCKET_NAME);
+    return sc_process_check_success_intr(intr, pid, "adb reverse --remove");
+}
+
+static bool
+enable_tunnel_forward(struct sc_intr *intr, const char *serial,
+                      uint16_t local_port) {
+    sc_pid pid = adb_forward(serial, local_port, SC_SOCKET_NAME);
+    return sc_process_check_success_intr(intr, pid, "adb forward");
+}
+
+static bool
+disable_tunnel_forward(struct sc_intr *intr, const char *serial,
+                       uint16_t local_port) {
+    sc_pid pid = adb_forward_remove(serial, local_port);
+    return sc_process_check_success_intr(intr, pid, "adb forward --remove");
+}
+
+static bool
+listen_on_port(struct sc_intr *intr, sc_socket socket, uint16_t port) {
+    return net_listen_intr(intr, socket, IPV4_LOCALHOST, port, 1);
+}
+
+static bool
+enable_tunnel_reverse_any_port(struct sc_adb_tunnel *tunnel,
+                               struct sc_intr *intr, const char *serial,
+                               struct sc_port_range port_range) {
+    uint16_t port = port_range.first;
+    for (;;) {
+        if (!enable_tunnel_reverse(intr, 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.
+        sc_socket server_socket = net_socket();
+        if (server_socket != SC_INVALID_SOCKET) {
+            bool ok = listen_on_port(intr, server_socket, port);
+            if (ok) {
+                // success
+                tunnel->server_socket = server_socket;
+                tunnel->local_port = port;
+                tunnel->enabled = true;
+                return true;
+            }
+
+            net_close(server_socket);
+        }
+
+        if (sc_intr_is_interrupted(intr)) {
+            // Stop immediately
+            return false;
+        }
+
+        // failure, disable tunnel and try another port
+        if (!disable_tunnel_reverse(intr, 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, (uint16_t) (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 sc_adb_tunnel *tunnel,
+                               struct sc_intr *intr, const char *serial,
+                               struct sc_port_range port_range) {
+    tunnel->forward = true;
+
+    uint16_t port = port_range.first;
+    for (;;) {
+        if (enable_tunnel_forward(intr, serial, port)) {
+            // success
+            tunnel->local_port = port;
+            tunnel->enabled = true;
+            return true;
+        }
+
+        if (sc_intr_is_interrupted(intr)) {
+            // Stop immediately
+            return false;
+        }
+
+        if (port < port_range.last) {
+            LOGW("Could not forward port %" PRIu16", retrying on %" PRIu16,
+                 port, (uint16_t) (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;
+    }
+}
+
+void
+sc_adb_tunnel_init(struct sc_adb_tunnel *tunnel) {
+    tunnel->enabled = false;
+    tunnel->forward = false;
+    tunnel->server_socket = SC_INVALID_SOCKET;
+    tunnel->local_port = 0;
+}
+
+bool
+sc_adb_tunnel_open(struct sc_adb_tunnel *tunnel, struct sc_intr *intr,
+                   const char *serial, struct sc_port_range port_range,
+                   bool force_adb_forward) {
+    assert(!tunnel->enabled);
+
+    if (!force_adb_forward) {
+        // Attempt to use "adb reverse"
+        if (enable_tunnel_reverse_any_port(tunnel, intr, serial, 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(tunnel, intr, serial, port_range);
+}
+
+bool
+sc_adb_tunnel_close(struct sc_adb_tunnel *tunnel, struct sc_intr *intr,
+                    const char *serial) {
+    assert(tunnel->enabled);
+
+    bool ret;
+    if (tunnel->forward) {
+        ret = disable_tunnel_forward(intr, serial, tunnel->local_port);
+    } else {
+        ret = disable_tunnel_reverse(intr, serial);
+
+        assert(tunnel->server_socket != SC_INVALID_SOCKET);
+        if (!net_close(tunnel->server_socket)) {
+            LOGW("Could not close server socket");
+        }
+
+        // server_socket is never used anymore
+    }
+
+    // Consider tunnel disabled even if the command failed
+    tunnel->enabled = false;
+
+    return ret;
+}