adb: implement "adb reverse <local> <remote>"

This implements the logical opposite of 'adb forward', i.e.
the ability to reverse network connections from the device
to the host.

This feature is very useful for testing various programs
running on an Android device without root or poking at the
host's routing table.

Options and parameters are exactly the same as those for
'adb forward', except that the direction is reversed.

Examples:

  adb reverse tcp:5000 tcp:6000
    connections to localhost:5000 on the device will be
    forwarded to localhost:6000 on the host.

  adb reverse --no-rebind tcp:5000 tcp:6000
    same as above, but fails if the socket is already
    bound through a previous 'adb reverse tcp:5000 ...'
    command.

  adb reverse --list
    list all active reversed connections for the target
    device. Note: there is no command to list all
    reversed connections for all devices at once.

  adb reverse --remove tcp:5000
    remove any reversed connection on the device from
    localhost:5000

  adb reverse --remove-all
    remove all reversed connections form the current
    device.

Reversed connections are tied to a transport, in other
words, they disappear as soon as a device is disconnected.

Simple testing protocol:

  adb forward tcp:5000 tcp:6000
  adb reverse tcp:6000 tcp:7000
  nc -l localhost 7000

in another terminal:
  echo "Hello" | nc localhost 5000

Will print "Hello" on the first terminal.

Change-Id: I761af790cdb06829b68430afa4145a919fa0e6d5

5 files changed, 198 insertions, 101 deletions

diff --git a/adb/SERVICES.TXT b/adb/SERVICES.TXT
index 7f85dc3..63000f2 100644
--- a/adb/SERVICES.TXT
+++ b/adb/SERVICES.TXT
@@ -240,3 +240,20 @@ sync:
     This starts the file synchronisation service, used to implement "adb push"
     and "adb pull". Since this service is pretty complex, it will be detailed
     in a companion document named SYNC.TXT
+
+reverse:<forward-command>
+    This implements the 'adb reverse' feature, i.e. the ability to reverse
+    socket connections from a device to the host. <forward-command> is one
+    of the forwarding commands that are described above, as in:
+
+      list-forward
+      forward:<local>;<remote>
+      forward:norebind:<local>;<remote>
+      killforward-all
+      killforward:<local>
+
+    Note that in this case, <local> corresponds to the socket on the device
+    and <remote> corresponds to the socket on the host.
+
+    The output of reverse:list-forward is the same as host:list-forward
+    except that <serial> will be just 'host'.
diff --git a/adb/adb.c b/adb/adb.c
index 0e41b34..8c1f005 100644
--- a/adb/adb.c
+++ b/adb/adb.c
@@ -318,7 +318,18 @@ static size_t fill_connect_data(char *buf, size_t bufsize)
 #endif
 }
 
-static void send_msg_with_okay(int fd, char* msg, size_t msglen) {
+#if !ADB_HOST
+static void send_msg_with_header(int fd, const char* msg, size_t msglen) {
+    char header[5];
+    if (msglen > 0xffff)
+        msglen = 0xffff;
+    snprintf(header, sizeof(header), "%04x", (unsigned)msglen);
+    writex(fd, header, 4);
+    writex(fd, msg, msglen);
+}
+#endif
+
+static void send_msg_with_okay(int fd, const char* msg, size_t msglen) {
     char header[9];
     if (msglen > 0xffff)
         msglen = 0xffff;
@@ -1428,6 +1439,120 @@ int adb_main(int is_daemon, int server_port)
     return 0;
 }
 
+// Try to handle a network forwarding request.
+// This returns 1 on success, 0 on failure, and -1 to indicate this is not
+// a forwarding-related request.
+int handle_forward_request(const char* service, transport_type ttype, char* serial, int reply_fd)
+{
+    if (!strcmp(service, "list-forward")) {
+        // Create the list of forward redirections.
+        int buffer_size = format_listeners(NULL, 0);
+        // Add one byte for the trailing zero.
+        char* buffer = malloc(buffer_size + 1);
+        if (buffer == NULL) {
+            sendfailmsg(reply_fd, "not enough memory");
+            return 1;
+        }
+        (void) format_listeners(buffer, buffer_size + 1);
+#if ADB_HOST
+        send_msg_with_okay(reply_fd, buffer, buffer_size);
+#else
+        send_msg_with_header(reply_fd, buffer, buffer_size);
+#endif
+        free(buffer);
+        return 1;
+    }
+
+    if (!strcmp(service, "killforward-all")) {
+        remove_all_listeners();
+#if ADB_HOST
+        /* On the host: 1st OKAY is connect, 2nd OKAY is status */
+        adb_write(reply_fd, "OKAY", 4);
+#endif
+        adb_write(reply_fd, "OKAY", 4);
+        return 1;
+    }
+
+    if (!strncmp(service, "forward:",8) ||
+        !strncmp(service, "killforward:",12)) {
+        char *local, *remote, *err;
+        int r;
+        atransport *transport;
+
+        int createForward = strncmp(service, "kill", 4);
+        int no_rebind = 0;
+
+        local = strchr(service, ':') + 1;
+
+        // Handle forward:norebind:<local>... here
+        if (createForward && !strncmp(local, "norebind:", 9)) {
+            no_rebind = 1;
+            local = strchr(local, ':') + 1;
+        }
+
+        remote = strchr(local,';');
+
+        if (createForward) {
+            // Check forward: parameter format: '<local>;<remote>'
+            if(remote == 0) {
+                sendfailmsg(reply_fd, "malformed forward spec");
+                return 1;
+            }
+
+            *remote++ = 0;
+            if((local[0] == 0) || (remote[0] == 0) || (remote[0] == '*')) {
+                sendfailmsg(reply_fd, "malformed forward spec");
+                return 1;
+            }
+        } else {
+            // Check killforward: parameter format: '<local>'
+            if (local[0] == 0) {
+                sendfailmsg(reply_fd, "malformed forward spec");
+                return 1;
+            }
+        }
+
+        transport = acquire_one_transport(CS_ANY, ttype, serial, &err);
+        if (!transport) {
+            sendfailmsg(reply_fd, err);
+            return 1;
+        }
+
+        if (createForward) {
+            r = install_listener(local, remote, transport, no_rebind);
+        } else {
+            r = remove_listener(local, transport);
+        }
+        if(r == 0) {
+#if ADB_HOST
+            /* On the host: 1st OKAY is connect, 2nd OKAY is status */
+            writex(reply_fd, "OKAY", 4);
+#endif
+            writex(reply_fd, "OKAY", 4);
+            return 1;
+        }
+
+        if (createForward) {
+            const char* message;
+            switch (r) {
+              case INSTALL_STATUS_CANNOT_BIND:
+                message = "cannot bind to socket";
+                break;
+              case INSTALL_STATUS_CANNOT_REBIND:
+                message = "cannot rebind existing socket";
+                break;
+              default:
+                message = "internal error";
+            }
+            sendfailmsg(reply_fd, message);
+        } else {
+            sendfailmsg(reply_fd, "cannot remove listener");
+        }
+        return 1;
+    }
+    return 0;
+}
+
 int handle_host_request(char *service, transport_type ttype, char* serial, int reply_fd, asocket *s)
 {
     atransport *transport = NULL;
@@ -1548,97 +1673,9 @@ int handle_host_request(char *service, transport_type ttype, char* serial, int r
     }
 #endif // ADB_HOST
 
-    if(!strcmp(service,"list-forward")) {
-        // Create the list of forward redirections.
-        int buffer_size = format_listeners(NULL, 0);
-        // Add one byte for the trailing zero.
-        char* buffer = malloc(buffer_size+1);
-        (void) format_listeners(buffer, buffer_size+1);
-        send_msg_with_okay(reply_fd, buffer, buffer_size);
-        free(buffer);
-        return 0;
-    }
-
-    if (!strcmp(service,"killforward-all")) {
-        remove_all_listeners();
-        adb_write(reply_fd, "OKAYOKAY", 8);
-        return 0;
-    }
-
-    if(!strncmp(service,"forward:",8) ||
-       !strncmp(service,"killforward:",12)) {
-        char *local, *remote, *err;
-        int r;
-        atransport *transport;
-
-        int createForward = strncmp(service,"kill",4);
-        int no_rebind = 0;
-
-        local = strchr(service, ':') + 1;
-
-        // Handle forward:norebind:<local>... here
-        if (createForward && !strncmp(local, "norebind:", 9)) {
-            no_rebind = 1;
-            local = strchr(local, ':') + 1;
-        }
-
-        remote = strchr(local,';');
-
-        if (createForward) {
-            // Check forward: parameter format: '<local>;<remote>'
-            if(remote == 0) {
-                sendfailmsg(reply_fd, "malformed forward spec");
-                return 0;
-            }
-
-            *remote++ = 0;
-            if((local[0] == 0) || (remote[0] == 0) || (remote[0] == '*')){
-                sendfailmsg(reply_fd, "malformed forward spec");
-                return 0;
-            }
-        } else {
-            // Check killforward: parameter format: '<local>'
-            if (local[0] == 0) {
-                sendfailmsg(reply_fd, "malformed forward spec");
-                return 0;
-            }
-        }
-
-        transport = acquire_one_transport(CS_ANY, ttype, serial, &err);
-        if (!transport) {
-            sendfailmsg(reply_fd, err);
-            return 0;
-        }
-
-        if (createForward) {
-            r = install_listener(local, remote, transport, no_rebind);
-        } else {
-            r = remove_listener(local, transport);
-        }
-        if(r == 0) {
-                /* 1st OKAY is connect, 2nd OKAY is status */
-            writex(reply_fd, "OKAYOKAY", 8);
-            return 0;
-        }
-
-        if (createForward) {
-            const char* message;
-            switch (r) {
-              case INSTALL_STATUS_CANNOT_BIND:
-                message = "cannot bind to socket";
-                break;
-              case INSTALL_STATUS_CANNOT_REBIND:
-                message = "cannot rebind existing socket";
-                break;
-              default:
-                message = "internal error";
-            }
-            sendfailmsg(reply_fd, message);
-        } else {
-            sendfailmsg(reply_fd, "cannot remove listener");
-        }
-        return 0;
-    }
+    int ret = handle_forward_request(service, ttype, serial, reply_fd);
+    if (ret >= 0)
+      return ret - 1;
 
     if(!strncmp(service,"get-state",strlen("get-state"))) {
         transport = acquire_one_transport(CS_ANY, ttype, serial, NULL);
diff --git a/adb/adb.h b/adb/adb.h
index 6f5c93c..2504f99 100644
--- a/adb/adb.h
+++ b/adb/adb.h
@@ -323,6 +323,8 @@ asocket*  create_jdwp_tracker_service_socket();
 int       create_jdwp_connection_fd(int  jdwp_pid);
 #endif
 
+int handle_forward_request(const char* service, transport_type ttype, char* serial, int reply_fd);
+
 #if !ADB_HOST
 typedef enum {
     BACKUP,
diff --git a/adb/commandline.c b/adb/commandline.c
index 241cefc..3970ab1 100644
--- a/adb/commandline.c
+++ b/adb/commandline.c
@@ -136,6 +136,19 @@ void help()
         "                                 if <local> is already forwarded\n"
         "  adb forward --remove <local> - remove a specific forward socket connection\n"
         "  adb forward --remove-all     - remove all forward socket connections\n"
+        "  adb reverse --list           - list all reverse socket connections from device\n"
+        "  adb reverse <remote> <local> - reverse socket connections\n"
+        "                                 reverse specs are one of:\n"
+        "                                   tcp:<port>\n"
+        "                                   localabstract:<unix domain socket name>\n"
+        "                                   localreserved:<unix domain socket name>\n"
+        "                                   localfilesystem:<unix domain socket name>\n"
+        "  adb reverse --norebind <remote> <local>\n"
+        "                               - same as 'adb reverse <remote> <local>' but fails\n"
+        "                                 if <remote> is already reversed.\n"
+        "  adb reverse --remove <remote>\n"
+        "                               - remove a specific reversed socket connection\n"
+        "  adb reverse --remove-all     - remove all reversed socket connections from device\n"
         "  adb jdwp                     - list PIDs of processes hosting a JDWP transport\n"
         "  adb install [-l] [-r] [-s] [--algo <algorithm name> --key <hex-encoded key> --iv <hex-encoded iv>] <file>\n"
         "                               - push this package file to the device and install it\n"
@@ -1299,8 +1312,11 @@ top:
         return 0;
     }
 
-    if(!strcmp(argv[0], "forward")) {
+    if(!strcmp(argv[0], "forward") ||
+       !strcmp(argv[0], "reverse"))
+    {
         char host_prefix[64];
+        char reverse = (char) !strcmp(argv[0], "reverse");
         char remove = 0;
         char remove_all = 0;
         char list = 0;
@@ -1329,15 +1345,19 @@ top:
         }
 
         // Determine the <host-prefix> for this command.
-        if (serial) {
-            snprintf(host_prefix, sizeof host_prefix, "host-serial:%s",
-                    serial);
-        } else if (ttype == kTransportUsb) {
-            snprintf(host_prefix, sizeof host_prefix, "host-usb");
-        } else if (ttype == kTransportLocal) {
-            snprintf(host_prefix, sizeof host_prefix, "host-local");
+        if (reverse) {
+            snprintf(host_prefix, sizeof host_prefix, "reverse");
         } else {
-            snprintf(host_prefix, sizeof host_prefix, "host");
+            if (serial) {
+                snprintf(host_prefix, sizeof host_prefix, "host-serial:%s",
+                        serial);
+            } else if (ttype == kTransportUsb) {
+                snprintf(host_prefix, sizeof host_prefix, "host-usb");
+            } else if (ttype == kTransportLocal) {
+                snprintf(host_prefix, sizeof host_prefix, "host-local");
+            } else {
+                snprintf(host_prefix, sizeof host_prefix, "host");
+            }
         }
 
         // Implement forward --list
diff --git a/adb/services.c b/adb/services.c
index 2d3423b..ebe84bb 100644
--- a/adb/services.c
+++ b/adb/services.c
@@ -154,6 +154,17 @@ cleanup:
     adb_close(fd);
 }
 
+void reverse_service(int fd, void* arg)
+{
+    const char* command = arg;
+
+    if (handle_forward_request(command, kTransportAny, NULL, fd) < 0) {
+        sendfailmsg(fd, "not a reverse forwarding command");
+    }
+    free(arg);
+    adb_close(fd);
+}
+
 #endif
 
 static int create_service_thread(void (*func)(int, void *), void *cookie)
@@ -398,6 +409,16 @@ int service_to_fd(const char *name)
         ret = create_service_thread(restart_tcp_service, (void *) (uintptr_t) port);
     } else if(!strncmp(name, "usb:", 4)) {
         ret = create_service_thread(restart_usb_service, NULL);
+    } else if (!strncmp(name, "reverse:", 8)) {
+        char* cookie = strdup(name + 8);
+        if (cookie == NULL) {
+            ret = -1;
+        } else {
+            ret = create_service_thread(reverse_service, cookie);
+            if (ret < 0) {
+                free(cookie);
+            }
+        }
 #endif
     }
     if (ret >= 0) {