adb: fix adb client running out of sockets on Windows
Background
==========
On Windows, if you run "adb shell exit" in a loop in two windows,
eventually the adb client will be unable to connect to the adb server. I
think connect() is returning WSAEADDRINUSE: "Only one usage of each
socket address (protocol/network address/port) is normally permitted.
(10048)". The Windows System Event Log may also show Event 4227, Tcpip.
Netstat output is filled with:
# for the adb server
TCP 127.0.0.1:5037 127.0.0.1:65523 TIME_WAIT
# for the adb client
TCP 127.0.0.1:65523 127.0.0.1:5037 TIME_WAIT
The error probably means that the client is running out of free
address:port pairs.
The first netstat line is unavoidable, but the second line exists
because the adb client is not waiting for orderly/graceful shutdown of
the socket, and that is apparently required on Windows to get rid of the
second line. For more info, see
https://github.com/CompareAndSwap/SocketCloseTest .
This is exacerbated by the fact that "adb shell exit" makes 4 socket
connections to the adb server: 1) host:version, 2) host:features, 3)
host:version (again), 4) shell:exit. Also exacerbating is the fact that
the adb protocol is length-prefixed so the client typically does not
have to 'read() until zero' which effectively waits for orderly/graceful
shutdown.
The Fix
=======
Introduce a function, ReadOrderlyShutdown(), that should be called in
the adb client to wait for the server to close its socket, before
closing the client socket.
I reviewed all code where the adb client makes a connection to the adb
server and added ReadOrderlyShutdown() when it made sense. I wasn't able
to add it to the following:
* interactive_shell: this doesn't matter because this is interactive and
thus can't be run fast enough to use up ports.
* adb sideload: I couldn't get enough test coverage and I don't think
this is being called frequently enough to be a problem.
* send_shell_command, backup, adb_connect_command, adb shell, adb
exec-out, install_multiple_app, adb_send_emulator_command: These
already wait for server socket shutdown since they already call
recv() until zero.
* restore, adb exec-in: protocol design can't have the server close
first.
* adb start-server: no fd is actually returned
* create_local_service_socket, local_connect_arbitrary_ports,
connect_device: probably called rarely enough not to be a problem.
Also in this change
===================
* Clarify comments in when adb_shutdown() is called before exit().
* add some missing adb_close() in adb sideload.
* Fixup error handling and comments in adb_send_emulator_command().
* Make SyncConnection::SendQuit return a success boolean.
* Add unittest for adb emu kill command. This gets code coverage over
this very careful piece of code.
Change-Id: Iad0b1336f5b74186af2cd35f7ea827d0fa77a17c
Signed-off-by: Spencer Low <CompareAndSwap@gmail.com>
diff --git a/adb/adb_io.h b/adb/adb_io.h
index 9c3b2a5..aa550af 100644
--- a/adb/adb_io.h
+++ b/adb/adb_io.h
@@ -41,6 +41,24 @@
// If this function fails, the contents of buf are undefined.
bool ReadFdExactly(int fd, void* buf, size_t len);
+// Given a client socket, wait for orderly/graceful shutdown. Call this:
+//
+// * Before closing a client socket.
+// * Only when no more data is expected to come in.
+// * Only when the server is not waiting for data from the client (because then
+// the client and server will deadlock waiting for each other).
+// * Only when the server is expected to close its socket right now.
+// * Don't call shutdown(SHUT_WR) before calling this because that will shutdown
+// the client socket early, defeating the purpose of calling this.
+//
+// Waiting for orderly/graceful shutdown of the server socket will cause the
+// server socket to close before the client socket. That prevents the client
+// socket from staying in TIME_WAIT which eventually causes subsequent
+// connect()s from the client to fail with WSAEADDRINUSE on Windows.
+// Returns true if it is sure that orderly/graceful shutdown has occurred with
+// no additional data read from the server.
+bool ReadOrderlyShutdown(int fd);
+
// Writes exactly len bytes from buf to fd.
//
// Returns false if there is an error or if the fd was closed before the write