CODEWITHSUNDEEP
javaandroidsocketsexceptionnetwork-programming
Steven Smith
Steven Smith

Reputation: 121

Socket connection half dropped - IOException not thrown

i read some of the answers here about this problem, but i wasn't satisfied with them, so i decided to ask it my self. So I know that there are similar questions, but since the answers don't really work for me, i asked myself.

I have an app that lets 2 users connect to each other (one works as a server, the other one as client). They will send files through that socket connection. I am using a Service with 2 threads inside, one to read, another one to send the file that the user chose.

Here is the problem : If a client closes the app by swiping it on the android menu (of the apps that are running), and then the server (the other guy) tries to send him something, in my opinion it should throw an IOException, since the other end of the socket streams is over. But it is not doing that and i don't know why. If i try to send something to someone that left, i want to show a Toast.

Edit: just noticed it always stops at the instruction out.reset();

Do any of you know why that exception is not being thrown? What could be a possible solution.

PS: It is a lite app, so to send Keep Alive messages wouldn't be a good solution. Also, it already showed the toast that i have one or two times, but then i couldn't replicate that behaviour again.

Here is my code where i wan't that to happen :

   ClientHandler tmp = connectedClients.get(key);
                    ObjectOutputStream out = tmp.getOut();
                    Socket s = tmp.getSocket();

                    if(s.isClosed()){
                        System.out.println("The socket of this client "+key + " is closed!");
                    }

                    if(s.isOutputShutdown()){
                        System.out.println("The output of this client is shutdown !");//only checks this side, the other one is the one that is shutdown
                    }
                    System.out.println("changed the culpado to : "+1);
                    createSendNotification();

                    File apkToSend;

                    for(int i=0;i<listOfApps.size();i++){
                        System.out.println("Item do be sent is : "+i);
                        HighwayGridViewAppItem tmpItem=listOfApps.get(i);
                        filePath=tmpItem.getFilePath();
                        appName=tmpItem.getAppName();
                        System.out.println("his filepath to send is : "+filePath);
                        System.out.println("his appname to send is : "+appName);


                        couldSend=false;

                        apkToSend=new File(filePath);

                        if(apkToSend.exists()){//do i reallly need this if?

                            apkToSendSize=apkToSend.length();
                            System.out.println("File size: " +apkToSendSize);

                            try{
                                out.writeObject(appName +": "+ apkToSendSize);//appName to send to have the name of the file

                                byte[] buffer = new byte [8192];
                                BufferedInputStream bis=new BufferedInputStream(new FileInputStream(apkToSend));
                                int count;
                                totalToSend =0;
                                showSendProgress();

                                while((count=bis.read(buffer))!=-1){
                                    out.write(buffer,0,count);
                                    totalToSend +=count;
                                    out.reset();
                                    System.out.println("ServerComm send thread - already sent this ammount : "+ totalToSend);
                                }
                                out.flush();
                                bis.close();

                            }
                            catch ( IOException e){

                                System.out.println("It is throwing the input output exception");

                                e.printStackTrace();

                                connectedClients.remove(key);
                                if(clients.size()<=1){

                                    h.post(new Runnable() {
                                        @Override
                                        public void run() {
                                            Toast.makeText(context, "No one is in your group.", Toast.LENGTH_SHORT).show();
                                        }
                                    });

                                    i=listOfApps.size()+1;
                                }else{

                                    System.out.println("Has more than one");
                                }

                            }

PS: When i try to send to a "closed" client, it prints a few "ServerComm send thread - already sent this ammount : "+ totalToSend" but then just stops, which is when i think it should throw the exception, but it just stops, and doesn't give any error, the app continues its life, but i NEED to give some input to the user that some problem went down.

Also, I create that Handler in the onCreate method of this service, it is being correctly created (since it is in a Service, it needs different creation) with the main looper.

Thank you guys in advance.

EDIT: Eventually, after almost 4 minutes, it throws a SocketException, but i can't wait that long.

Upvotes: 1

Views: 108

Answers (2)

Roberto Betancourt
Roberto Betancourt

Reputation: 2515

If you require an immediate disconnection detection then you would have to implement your own ping/keep alive mechanism which would normally mean sending packets and acknowledging them continuously to be able to catch an exception more reliably.

Upvotes: 0

Sean F
Sean F

Reputation: 4615

Just because Android disposes of an app does not mean that internally all of your open connections are closed, it is mostly likely you need to detect the Android event and then execute the code that explicitly closes the open socket rather than waiting for Android to take care of it eventually. Otherwise, you will have to wait for the socket to be closed by garbage collection calling the finalizer.

This post here has some details about Android events and the onDestroy method in particular: How to close Android application?

Upvotes: 0

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