IssueTracker

Summary:
Android's Socket implementation fails to detect socket closure by remote.
This basically means Android breaks every client/server TCP application
known to mankind.

I have found numerous other bug reports in various places all indicating
issues along these lines. I suspect they are all related to this
fundamental socket bug; as it breaks all applications which rely of proper
TCP socket semantics.

Test Environment:
Tested on CyanogenMod 4.2.13 and stock emulator running 1.6. Both have the
exact same broken behavior.

Setup:
Client is running on Android within a service. Service initiates connection
to server. Server accepts connection. Netstat clearly tracks connection
state. Below you can see the connection has been established.

tcp  0  0 10.0.2.15:34434        192.168.1.100:43210     ESTABLISHED

I can send a message from the client to the server. I log the socket's
state both before and after the write to the socket. Notice both the local
and remote ports match, clearly indicating this is the same socket. State
before and after are exactly as one would expect.
D/xxx(  388):   socket_: Socket[addr=/192.168.1.100,port=43210,localport=34434]
D/xxx(  388):   isConnected: true
D/xxx(  388):   isClosed: false
D/xxx(  388):   isConnected: true
D/xxx(  388):   isClosed: false

So far so good. I'll now terminate the server which will cause the TCP
connection to be reset on the client (Android). Netstat clearly tracks the
state of the socket exactly as it should. This seems to indicate it is not
a Linux kernel and/or TCP stack bug. Again, make note the local and remote
ports are identical and the state is properly indicated.

tcp  0  1 10.0.2.15:34434        192.168.1.100:43210     CLOSE_WAIT

At this point the client is unlikely to know the socket has been closed as
keep alives are not in use and the client has yet to written to the socket.
So let's fix that.

I'll now have the client write to its socket. This should immediately
result in an error as the stack absolutely knows the socket has been
closed. Once again, the socket's state both before and after the write, is
logged. Notice the local and remote ports are identical. Also notice the
socket's logged state does not change. That's BAD! Remember, the Android
device absolutely knows the socket has been closed at this point.

D/xxx(  388):   socket_: Socket[addr=/192.168.1.10,port=43210,localport=34434]
D/xxx(  388):   isConnected: true
D/xxx(  388):   isClosed: false
D/xxx(  388):   isConnected: true
D/xxx(  388):   isClosed: false

Notice the socket indicates its connected and not closed both before and
after the write. An exception is never thrown. An error is never provided.
And yet, netstat still shows:

tcp  0  1 10.0.2.15:34434        192.168.1.100:43210     CLOSE_WAIT

Clearly the socket is closed. Clearly the stack is properly tracking state.
The server is no longer running. The socket is absolutely not connected.
And yet, the socket provided by Android continues to write to a completely
broken socket and never properly reports the state change to the
application nor does it provide any type of error or exception indicating
that the write absolutely is failing.

In short, Android's socket implementation is completely broken to such a
degree, every client/server TCP application on Android is broken.