Force creation of application listening socket

If a previous mojo_shell run exited uncleanly, there may
be a unix domain socket sitting at the path that
IncomingConnectionListener wants to own and listen at.
This change destroys it, if possible, and creates a new
one.

BUG=407782
TEST=new unit test, run mojo_shell multiple times in a row with --enable-external-applications

Review URL: https://codereview.chromium.org/611833005

Cr-Commit-Position: refs/heads/master@{#297271}

mojo/shell/incoming_connection_listener_posix.cc

@@ -47,15 +47,15 @@ void IncomingConnectionListenerPosix::StartListening() {
   DCHECK(listen_thread_checker_.CalledOnValidThread());
 
   int rv = net::OK;
-  if (base::PathExists(socket_path_)) {
-    LOG(ERROR) << "Listening socket file already exists.";
-    rv = net::ERR_FILE_EXISTS;
-  } else if (!base::DirectoryExists(socket_path_.DirName())) {
+  if (!base::DirectoryExists(socket_path_.DirName())) {
     LOG(ERROR) << "Directorty for listening socket does not exist.";
     rv = net::ERR_FILE_NOT_FOUND;
   } else if (!base::PathIsWritable(socket_path_.DirName())) {
     LOG(ERROR) << "Listening socket file path is not writable.";
     rv = net::ERR_ACCESS_DENIED;
+  } else if (!base::DeleteFile(socket_path_, false)) {
+    PLOG(ERROR) << "Listening socket file exists and can't be deleted";
+    rv = net::ERR_FILE_EXISTS;
   } else {
     const std::string& socket_address = socket_path_.value();
     rv = listen_socket_.ListenWithAddressAndPort(socket_address, 0, 100);

mojo/shell/incoming_connection_listener_unittest.cc

@@ -97,15 +97,40 @@ TEST_F(IncomingConnectionListenerTest, ConnectSuccess) {
   run_loop_.Run();
 }
 
-TEST_F(IncomingConnectionListenerTest, ConnectFails_SocketFileExists) {
+TEST_F(IncomingConnectionListenerTest, ConnectSuccess_SocketFileExists) {
+  TestDelegate delegate;
+  IncomingConnectionListenerPosix listener(socket_path_, &delegate);
+
+  ASSERT_EQ(1, base::WriteFile(socket_path_, "1", 1));
+  ASSERT_TRUE(base::PathExists(socket_path_));
+  listener.StartListening();
+
+  ExternalApplicationRegistrarConnection connection(socket_path_);
+  connection.Connect(base::Bind(&OnConnect, run_loop_.QuitClosure()));
+
+  run_loop_.Run();
+}
+
+TEST_F(IncomingConnectionListenerTest, ConnectFails_SocketFileUndeletable) {
   ListeningFailsDelegate fail_delegate(net::ERR_FILE_EXISTS);
   IncomingConnectionListenerPosix listener(socket_path_, &fail_delegate);
 
+  // Create the socket file.
   ASSERT_EQ(1, base::WriteFile(socket_path_, "1", 1));
   ASSERT_TRUE(base::PathExists(socket_path_));
 
+  // Render it undeletable, but in a way that the test harness can recover
+  // later.
+  int temp_dir_perms = 0;
+  ASSERT_TRUE(base::GetPosixFilePermissions(temp_dir_.path(), &temp_dir_perms));
+  ASSERT_TRUE(
+      base::SetPosixFilePermissions(temp_dir_.path(),
+                                    base::FILE_PERMISSION_READ_BY_USER |
+                                        base::FILE_PERMISSION_WRITE_BY_USER));
   // The listener should fail to start up.
   listener.StartListening();
+
+  ASSERT_TRUE(base::SetPosixFilePermissions(temp_dir_.path(), temp_dir_perms));
 }
 
 TEST_F(IncomingConnectionListenerTest, ConnectFails_SocketDirNonexistent) {