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Android TCP Socket InputStrem Intermittent Read or too Slow

I need to implement a TCP comunication between an IoT device(custom) and an Android App.
For the Wifi device we have a Server Socket, while in Android i have an AsyncTask as a Client Socket. Both the device and the smarthone are connected to the same network.
Here is the Android Client Socket code for the initialization/socket-read and socket-write:
Variables:
static public Socket nsocket; //Network Socket
static public DataInputStream nis; //Network Input Stream
static private OutputStream nos; //Network Output Stream
AsyncTask method doInBackgroud:
#Override
protected Boolean doInBackground(Void... params) { //This runs on a different thread
boolean result = false;
try {
//Init/Create Socket
SocketInit(IP, PORT);
// Socket Manager
SocketUpdate();
} catch (IOException e) {
e.printStackTrace();
Log.i("AsyncTask", "doInBackground: IOException");
clearCmdInStack();
MainActivity.SocketDisconnectAndNetworkTaskRestart();
result = true;
} catch (Exception e) {
e.printStackTrace();
Log.i("AsyncTask", "doInBackground: Exception");
result = true;
} finally {
try {
SocketDisconnect();
} catch (IOException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
Log.i("AsyncTask", "doInBackground: Finished");
}
return result;
}
Socket Initializzation:
public void SocketInit(String ip, int port) throws IOException {
InetAddress addr = InetAddress.getByName(ip);
SocketAddress sockaddr = new InetSocketAddress(addr, port);
nsocket = new Socket();
nsocket.setReuseAddress(false);
nsocket.setTcpNoDelay(true);
nsocket.setKeepAlive(true);
nsocket.setSoTimeout(0);
nsocket.connect(sockaddr, 0);
StartInputStream();
StartOutputStream();
}
Read from Socket:
private void SocketUpdate() throws IOException, ClassNotFoundException {
int read = 0;
// If connected Start read
if (socketSingleton.isSocketConnected()) {
// Print "Connected!" to UI
setPublishType(Publish.CONNECTED);
publishProgress();
if(mConnectingProgressDialog != null)
mConnectingProgressDialog.dismiss(); //End Connecting Progress Dialog Bar
//Set Communications Up
setCommunicationsUp(true);
Log.i("AsyncTask", "doInBackground: Socket created, streams assigned");
Log.i("AsyncTask", "doInBackground: Waiting for inital data...");
byte[] buffer = new byte[3];
do{
nis.readFully(buffer, 0, 3);
setPublishType(Publish.READ);
publishProgress(buffer);
}while(!isCancelled());
SocketDisconnect();
}
}
Streams init:
public void StartInputStream() throws IOException{
nis = new DataInputStream(nsocket.getInputStream());
}
public void StartOutputStream() throws IOException{
nos = nsocket.getOutputStream();
}
Read and Write methods:
public int Read(byte[] b, int off, int len) throws IOException{
return nis.read(b, off, len); //This is blocking
}
public void Write(byte b[]) throws IOException {
nos.write(b);
nos.flush();
}
public boolean sendDataToNetwork(final String cmd)
{
if (isSocketConnected())
{
Log.i("AsyncTask", "SendDataToNetwork: Writing message to socket");
new Thread(new Runnable()
{
public void run()
{
try
{
Write(cmd.getBytes());
}
catch (Exception e)
{
e.printStackTrace();
Log.i("AsyncTask", "SendDataToNetwork: Message send failed. Caught an exception");
}
}
}).start();
return true;
}
Log.i("AsyncTask", "SendDataToNetwork: Cannot send message. Socket is closed");
return false;
}
The application is very simple, the android app sends a command(via sendDataToNetwork method) to the IoT device and the latter sends back an "ACK" Command string.
The problem
The problem is that while the IoT device always receives the command, the smartphone rarely gets the ACK back. Sometimes i get something like "ACKACKACKACK". By debugging the IoT device i'm sure that it successfully sends back the ACK, so the problem lies in the InputStream read() method which doesn't retrieve the string right away.
Is there a way to empty the InputStream buffer right away, so that i get an "ACK" string back from the IoT device every time i send a command?
Update
I've updated the socket config so that there are no more buffer limitations and i've replaced read() method with readFully. It greatly improved, but still make some mistakes. For istance one out of 2-3 times no ack is received and i get 2 ack the next turn. Is this perhaps the computational limit of the IoT device? Or is there still margin for a better approach?

the problem lies in the InputStream read() method which doesn't empty the buffer right away.
I don't know what 'empty the buffer' means here, but InputStream.read() is specified to return as soon as even one byte has been transferred.
Is there a way to empty the InputStream buffer right away, so that i get an "ACK" string back from the IoT device every time i send a command?
The actual problem is that you could be reading more than one ACK at a time. And there are others.
If you're trying to read exactly three bytes, you should be using DataInputStream.readFully() with a byte array of three bytes.
This will also get rid of the need for the following array copy.
You should not mess with the socket buffer sizes except to increase them. 20 and 700 are both ridiculously small values, and will not be the actual values used, as the platform can adjust the value supplied. Your claim that this improved things isn't credible.
You should not spin-loop while available() is zero. This is literally a waste of time. Your comment says you are blocked in the following read call. You aren't, although you should be. You are spinning here. Remove this.

Android UDP server does not receive packets

I have the following code to receive UDP packets:
public class AsyncReceiveUdp2 extends AsyncTask<String, Void, Boolean> {
#Override
protected Boolean doInBackground(String... f_url) {
int udp=111;
byte[] packet = new byte[2000];
DatagramPacket dp = new DatagramPacket(packet, packet.length);
DatagramSocket ds = null;
try {
ds = new DatagramSocket(udp);
ds.receive(dp);
//...
} catch (SocketException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (ds != null) {
ds.close();
}
}
return null;
}
}
I send UDP data to computer from Android device.
Computer immediately sends response as UDP packet.
I save information to my log file on SD.
And I see, that my app stays on the line "ds.receive(dp);" and does not run after it.
I've tested on the Android device against a program on computer.
As I understand it is tricky to receive UDP packets on Emulator.
I could not do it.
Redirect does not work for me as it is described here
Another important issue is to receive all packets, that were sent to the device. Lossless. How to modify the code for that?
Please help! Thanks!

put your receive inside a while(true) loop. When you receive a packet call an if (pkg_received){break;}... or whatever you want to do...
The problem is that you are probably only be receiving one package and you are getting timeout before receiving it.
Code edited and not tested
while(true)
{
byte[] message = new byte[60*1024];
DatagramPacket recv_packet = new DatagramPacket(message, message.length);
try {
socket.receive(recv_packet);
} catch (IOException e) {
e.printStackTrace();
}
Log.d("UDP", "S: Receiving...listening on port " + recv_packet.getPort() );
String rec_str;
rec_str=new String(recv_packet.getData)
Log.d("PACKAGE LENGTH",Integer.toString(recv_packet.getLength()));
}

QTcpServer with android client unable to print or use data received from client

I am developing Client-Server application in C++ using Qt framework, but the clients can be android phones and computers(Qt client app)
Now i'm having troubles to handle Reception of data on the server side; the server is not receiving data properly.
First, I got things working nicely between the server(Qt app) and the client(Qt app) using these methods for sending and receiving:
The size of the message is kept at the beginning of the packet to help check whether the whole message is received or not.
This is the method to send message to the clients
void Server::send(const QString &message)
{
QByteArray paquet;
QDataStream out(&paquet, QIODevice::WriteOnly);
out << (quint16) 0; // just put 0 at the head of the paquet to reserve place to put the size of the message
out << message; // adding the message
out.device()->seek(0); // coming back to the head of the paquet
out << (quint16) (paquet.size() - sizeof(quint16)); // replace the 0 value by the real size
clientSocket->write(paquet); //sending...
}
This slot is called every time a single paquet is received.
void Server::dataReceived()
{
forever
{
// 1 : a packet has arrived from any client
// getting the socket of that client (recherche du QTcpSocket du client)
QTcpSocket *socket = qobject_cast<QTcpSocket *>(sender());
if (socket == 0)
return;
QDataStream in(socket);
if (dataSize == 0) // if we don't know the size of data we are suppose to receive...
{
if (socket->bytesAvailable() < (int)sizeof(quint16)) // we haven't yet receive the size of the data completly then return...
return;
in >> dataSize; // now we know the amount of data we should get
}
if (socket->bytesAvailable() < dataSize)
return;
// Here we are sure we got the whole data then we can startreadind
QString message;
in >> message;
//Processing....
dataSize = 0; // re-initialize for the coming data
}
}
This is working well when the server is talking with the Qt app Client, because the same methods are used there, and the size of quint16 will remain the same hover it doesn't work with android client, then i tried another way in which i wanted to ignore the size of the message sent, but format the message in a way such that i can know where it starts and where it ends, then with some controls i can get it however i'm stuck here, cause the data read doesn't contain anything when printed, but his size has a value(which even vary according to the amount of text the client send)!
void Server::dataReceived() // a packet is received!
{
QTcpSocket *socket = qobject_cast<QTcpSocket *>(sender());
if (socket == 0)
return;
QByteArray data= socket->readAll(); //reading all data available
QString message(data)
qDebug() << data; // this prints nothing!
qDebug() << data.size();// But this prints a non null number, wich means we got something, and that number varies according to the amount of text sent!
qDebug() << message; // this also prints notghing!
}
PS: it's not working even for the Qt app Client.
Can you help me find out what's wrong, i'm a bit confused how the tcp protocol is handling the data, and if you could and also advise me a good way for doing this.
here is the android class I made for the purpose
class QTcpSocket implements Runnable {
private String ip="";
private int port;
private Socket socket;
private PrintWriter printWriter;
private DataOutputStream dataOutputStream;
private DataInputStream dataInputStream;
public QTcpSocket(String ip, int port) {
this.ip = ip;
this.port = port;
}
public void setIp(String ip) {
this.ip = ip;
}
public String getIp() {
return this.ip;
}
public void setPort(int port) {
this.port = port;
}
public void run() {
try {
socket = new Socket(this.ip, this.port);
dataOutputStream = new DataOutputStream( socket.getOutputStream() );
dataInputStream = new DataInputStream(socket.getInputStream());
String response = dataInputStream.readUTF();
dataOutputStream.writeUTF("Hello server!");
} catch (IOException e) {
e.printStackTrace();
}
}
public void sendMessage(String message) {
try {
dataOutputStream.writeUTF(message);
}catch (IOException e) {
e.printStackTrace();
}
}
public void disconnect() {
try {
printWriter.flush();
printWriter.close();
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
public boolean isClosed() {
return socket.isClosed();
}
}

Replace in 'data' all bytes with value 0 by value 20 and print again. I think you see nothing printed because the first byte is 0. You could also replace with 'X'. Did you already replace writeUTF() by write() ?
20 is the space character. But then you also see nothing printed so better use a X char. Strings get printed until a \0 char (which indicates the end of a string) is met. Because nothing was printed i supposed one right at the beginning. So writeUTF causes that leading 0. I could only explain that if all chars had doubled. What was the first char you sent?
But now: send size-of-message first so it equals your qt client.

Why is my android receiver dropping 10-60% of UDP broadcast packets?

I have an 802.3 wired transmitter application on my computer that I've written to broadcast UDP packets every 10ms. Each broadcast packet contains a 4-byte integer value that is unique to its particular packet, which allows me to figure out on the receiver end exactly how many packets have been dropped.
I have verified that the transmitter works with Wireshark. I set up four 802.11 receivers (2 android phones and 2 laptop computers) on the same network. The laptops received 95% of the UDP broadcast packets; one phone received 89%; the other phone received 40%.
Why?
Here is part of my android receiver code:
public class NetThread extends Thread {
int[] pkt_nums;
int p;
NetThread(int[] pkt_nums)
{
this.pkt_nums = pkt_nums;
for (int i=0; i<pkt_nums.length; i++)
{
pkt_nums[i]=0;
}
p = 0;
}
#Override
public void run()
{
receiveData();
}
public void receiveData()
{
// request permission to do network operations in manifest file...done
// start the network side of things
DatagramSocket sock = null;
DatagramPacket pkt = null;
try
{
byte[] data = new byte[C.PAYLOAD_MAX];
sock = new DatagramSocket(C.NET_PORT);
sock.setSoTimeout(C.NET_SO_TIMEOUT);
pkt = new DatagramPacket(data, 0, C.PAYLOAD_MAX);
while (true)
{
Thread.sleep(0); // allow for an interrupt
try
{
sock.receive(pkt);
int length = pkt.getLength();
boolean success = writeToBuffer(pkt.getData(), length);
if (!success) break;
}
catch (InterruptedIOException e)
{
// thrown when a timeout occurs
Log.d(C.DTAG, "net: no packets yet");
}
}
Log.d(C.DTAG, "buffer is full. done receiving.");
if (sock != null) sock.close();
}
catch (InterruptedException x)
{
Log.d(C.DTAG, "net: was interrupted.");
}
catch (SocketException e)
{
Log.d(C.DTAG, "net: SocketException");
e.printStackTrace();
}
catch (IOException e)
{
Log.d(C.DTAG, "net: IOException");
e.printStackTrace();
}
if (sock != null) sock.close();
}
public boolean writeToBuffer(byte[] data, int length)
{
// each packet should have exactly 4 bytes - a number
int pkt_num = data[0] & 0x000000FF | data[1]<<8 & 0x0000FF00 | data[2]<<16 & 0x00FF0000 | data[3]<<24 & 0xFF000000;
if (p < pkt_nums.length)
{
pkt_nums[p++] = pkt_num;
return true; // success
}
else
{
return false;
}
}
}
I declare the above class in my main activity as follows:
mNetThrd = new NetThread(pkt_nums);
mNetThrd.setDaemon(true);
mNetThrd.start();
I will try boosting the thread priority now, but I have a feeling I'm doing something wrong. I need to get at least 95% of UDP broadcast packets for my application.
More details: Laptops and phones are situated next to each other, 30 ft from the router with line-of sight visibility. Laptop 1 received 95% of packets. Laptop 2 received 94%. Phone 1 received 89%. Phone 2 received 40%. Both ran the same app. Other network traffic is minimal. Dropped packets in android typically happen in groups of 20-50 at a time. 802.11 has a clean channel. Each packet contains a 4-byte payload.
Is there something drastically wrong with my receiver code or is this another issue altogether?

commumicating between windows app and android app

I'm sorry if this is a very general question but I don't know where to start so I'm looking for ideas.
I have a windows app (music score editing) and I'm currently porting it to Andriod which is coming along well.
I would like to add the feature than documents created in the windows app can be sent to the users android tablet. I was wondering, how would I write some kind of listener on Android that the windows side could open a socket or something to and send data across to it, assuming both are on the same local network.
thanks

I think sending files directly over a local network isn't the best approach. You are prone to many user complaints that the sharing isn't working.. and this will mostly be due to their own network configuration issues.
Why not use a service like DropBox to implement file sharing?
Services like DropBox offer simple API that can be used in apps in order to save files into a remote folder, and read files from a remote folder.
This way, users will not have to be in the same network at all.. and most of the heavy-lifting of implementing file sharing will be done by a service that is focused around that.
Addition:
If you don't want to require an account for a separate service like DropBox, consider this approach: Implement a very simple DropBox-like service on your own web server. Make a simple script that will allow users to upload a file to your server anonymously via HTTP. After upload, they will receive a 5 digit id for this file, or some other link they could share. When using this id or link from the 2nd app, the file could be downloaded (again via HTTP). If you delete files automatically from the server after a few hours, you will not run out of space.
You can implement such a service with about 20 lines of PHP code. And the required apps code is extremely simple (since it only relies on HTTP). If you're worried about the costs of a web server, you can get one from about $5/month or even use a free service like Google App Engine (free if your bandwidth+space requirements are low).
Code example for the file upload. Downloading should be simple enough to do alone. Regarding the periodical file delete - the obvious approach is cron but I think it's easy to manage without it. Whenever you accept a new upload (in the PHP script), go over all the downloads and delete old ones.

i wrote a small thing so my windows app can find an instance of my android app running on the local network, here it is. this is the android code first
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Arrays;
import android.os.AsyncTask;
import android.util.Log;
public class TabSyncServer extends AsyncTask<Void, Void, Void> {
ServerSocket mServerSocket = null;
Socket mSocket = null;
DataInputStream mDataInputStream = null;
DataOutputStream mDataOutputStream = null;
#Override
protected void onPreExecute() {
try {
mServerSocket = new ServerSocket(2112);
//System.out.println("Listening :2112");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
#Override
protected Void doInBackground(Void... args) {
byte[] bytebuf = new byte[1024];
while (true) {
try {
mSocket = mServerSocket.accept();
mDataInputStream = new DataInputStream(mSocket.getInputStream());
mDataOutputStream = new DataOutputStream(mSocket.getOutputStream());
Log.d("TabSyncServer", "ip: " + mSocket.getInetAddress());
mDataInputStream.read(bytebuf);
String str = new String(bytebuf, "UTF8");
Log.d("TabSyncServer", "message: " + str);
if(str.contains("Hello Android")) {
Log.d("TabSyncServer", "sending reply");
mDataOutputStream.writeBytes("Hello Windows");
}
//
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
if (mSocket != null) {
try {
mSocket.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if (mDataInputStream != null) {
try {
mDataInputStream.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if (mDataOutputStream != null) {
try {
mDataOutputStream.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}
}
and the windows MFC code
void CMainFrame::OnBrowseMobile() {
CMobileSync* con = new CMobileSync();
CString ipaddr_base;
int my_last_digit;
if(!con->getMyIP(ipaddr_base, my_last_digit)) {
setMobilePath("Can't find local network");
return;
}
for(int i=1 ; i<98 ; i++) {
if(i==my_last_digit)
continue; // don;t check self
CString ipaddr; ipaddr.Format("%s.%d", ipaddr_base, i);
bool res = con->ConnectToHost(ipaddr);
if(res) {
res = con->SendMsg ("Hello Android");
if(res) {
TRACE1("send ok %s\n",ipaddr.GetBuffer());
#define RD_BUF_LEN 80
char buffer[RD_BUF_LEN];
if(con->ListenOnPortBlocking(buffer, RD_BUF_LEN)) {
if(strncmp(buffer, "Hello Windows", 12)==0) {
TRACE1("reply ok %s", buffer);
setMobilePath(ipaddr);
con->CloseConnection ();
return;
}
}
} else {
TRACE("send FAILED\n");
}
}
con->CloseConnection ();
}
setMobilePath("No TabTrax on local network");
}
#include "stdafx.h"
#include <winsock.h>
#include "MobileSync.h"
#define TTPORT 2112
bool CMobileSync::getMyIP(CString& ipaddr_front, int& ipaddr_lastdigit)
{
char szBuffer[1024];
#ifdef WIN32
WSADATA wsaData;
WORD wVersionRequested = MAKEWORD(2, 0);
if(::WSAStartup(wVersionRequested, &wsaData) != 0)
return false;
#endif
if(gethostname(szBuffer, sizeof(szBuffer)) == SOCKET_ERROR)
{
#ifdef WIN32
WSACleanup();
#endif
return false;
}
struct hostent *host = gethostbyname(szBuffer);
if(host == NULL)
{
#ifdef WIN32
WSACleanup();
#endif
return false;
}
//Obtain the computer's IP
unsigned char b1, b2, b3, b4;
b1 = ((struct in_addr *)(host->h_addr))->S_un.S_un_b.s_b1;
b2 = ((struct in_addr *)(host->h_addr))->S_un.S_un_b.s_b2;
b3 = ((struct in_addr *)(host->h_addr))->S_un.S_un_b.s_b3;
b4 = ((struct in_addr *)(host->h_addr))->S_un.S_un_b.s_b4;
ipaddr_front.Format("%d.%d.%d", b1, b2, b3);
ipaddr_lastdigit = b4;
#ifdef WIN32
WSACleanup();
#endif
return true;
}
//CONNECTTOHOST – Connects to a remote host
bool CMobileSync::ConnectToHost(const char* IPAddress)
{
//Start up Winsock…
WSADATA wsadata;
int error = WSAStartup(0x0202, &wsadata);
//Did something happen?
if (error)
return false;
//Did we get the right Winsock version?
if (wsadata.wVersion != 0x0202)
{
WSACleanup(); //Clean up Winsock
return false;
}
//Fill out the information needed to initialize a socket…
SOCKADDR_IN target; //Socket address information
target.sin_family = AF_INET; // address family Internet
target.sin_port = htons (TTPORT); //Port to connect on
target.sin_addr.s_addr = inet_addr (IPAddress); //Target IP
mSocket = socket (AF_INET, SOCK_STREAM, IPPROTO_TCP); //Create socket
if (mSocket == INVALID_SOCKET)
{
return false; //Couldn't create the socket
}
//Try connecting...
if (connect(mSocket, (SOCKADDR *)&target, sizeof(target)) == SOCKET_ERROR)
{
return false; //Couldn't connect
}
return true; //Success
}
//CLOSECONNECTION – shuts down the socket and closes any connection on it
void CMobileSync::CloseConnection ()
{
//Close the socket if it exists
if (mSocket)
closesocket(mSocket);
mSocket=0;
WSACleanup(); //Clean up Winsock
}
int CMobileSync::SendMsg (char* szpText, int buflen)
{
if(buflen==0)
buflen = strlen(szpText);
int ret = send(mSocket, szpText, buflen, 0);
TRACE1("CMobileSync::SendMsg sent %d bytes\n", ret);
return ret;
}
WSADATA w;
//LISTENONPORT – Listens on a specified port for incoming connections
//or data
bool CMobileSync::ListenOnPortBlocking(char* buffer, int buflen)
{
//Now we can start listening (allowing as many connections as possible to
//be made at the same time using SOMAXCONN). You could specify any
//integer value equal to or lesser than SOMAXCONN instead for custom
//purposes). The function will not //return until a connection request is
//made
// listen(s, SOMAXCONN);
memset(buffer, 0, sizeof(buffer)); //Clear the buffer
int iTimeout = 1600;
setsockopt( mSocket, SOL_SOCKET, SO_RCVTIMEO, (const char *)&iTimeout, sizeof(iTimeout));
//Put the incoming text into our buffer
int ret = recv (mSocket, buffer, buflen-1, 0);
//Don't forget to clean up with CloseConnection()!
if(ret != SOCKET_ERROR)
return true;
int err = WSAGetLastError();
return false;
}
its not tested extensively but it is running
this maybe useful to someone