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length header suddenly has wrong value when use read int32?

I wrote a tcp listener to receive a sequence of images from single client , this is the code of server :
new Thread(() =>
{
while (true)
{
displayingFrame.Start(); // another thread to display images
Socket socket = listener.AcceptSocket();
TcpClient client = new TcpClient();
client.Client = socket;
Debug.WriteLine("Connection accepted.");
var childSocketThread = new Thread(() =>
{
NetworkStream ns = client.GetStream();
BinaryReader br = new BinaryReader(ns);
while (true)
{
using (MemoryStream ms = new MemoryStream())
{
int length = br.ReadInt32();
Debug.WriteLine("length : " + length);
byte[] buf = new byte[1024];
int totalReaded = 0;
int readed = 0;
while (totalReaded < length)
{
readed = br.Read(buf, 0, buf.Length);
ms.Write(buf, 0, readed);
totalReaded += readed;
}
byte[] frame = ms.ToArray();
this.frames.Enqueue(frame);
Debug.WriteLine("frame enqueued with length " + frame.Length);
}
}
});
childSocketThread.Start();
}
}).Start();
it receive frames very well but suddenly br.ReadInt32(); returns a very big length so br.Read(buf, 0, buf.Length); takes a very long time writing to memory stream and it writes a wrong data inside frame .
this is the client :
TcpClient client = new TcpClient();
client.Connect(new IPEndPoint(IPAddress.Loopback, 20000));
NetworkStream ns = client.GetStream();
BinaryWriter bw = new BinaryWriter(ns);
while ( true )
{
byte[] frame = Screenshot();
bw.Write(frame.Length);
Console.WriteLine("a frame length has flushed : " + frame.Length);
bw.Write(frame);
Console.WriteLine("a frame itself has flushed");
}
Console.ReadKey();
and here the debug info :

If you check the hex value you're getting - 1196314761 - you'll get 0x474E5089 and finally convert to ASCII you will get GNP\x89 which gives us the known magic value \x89PNG that is the marker of PNG file. You're actually reading the content of your screenshot as the length.
Make sure that you're code for reading the data does not read too much from the previous frame. I think you code for reading the data does not include the fact that you might get content of 2 frames in one .Read but then later you just don't care if you have too much data. You only check if it's not less than length.

TCPListener File Transfer

I have a little complication i encounter.
I may not be expert in TCP Connections but i hope someone here would help me.
This is my Client Code:
void Connect(String server, String message)
{
try
{
Int32 port = 8968;
TcpClient client = new TcpClient(server, port);
Byte[] data = File.ReadAllBytes(curSelectedFile);
NetworkStream stream = client.GetStream();
Byte[] fileData = File.ReadAllBytes(curSelectedFile);
Byte[] msgData = Encoding.ASCII.GetBytes("SendFile");
Byte[] sendData = new byte[fileData.Length + msgData.Length];
// Copy data to send package.
msgData.CopyTo(sendData, 0);
fileData.CopyTo(sendData, 4);
// Send the message to the connected TcpServer.
stream.Write(data, 0, data.Length);
Console.WriteLine("Sent: {0}", message);
// Receive the TcpServer.response.
// Buffer to store the response bytes.
data = new Byte[256];
// String to store the response ASCII representation.
String responseData = String.Empty;
// Read the first batch of the TcpServer response bytes.
Int32 bytes = stream.Read(data, 0, data.Length);
responseData = System.Text.Encoding.ASCII.GetString(data, 0, bytes);
Console.WriteLine("Received: {0}", responseData);
// Close everything.
stream.Close();
client.Close();
}
catch (ArgumentNullException e)
{
Console.WriteLine("ArgumentNullException: {0}", e);
}
catch (SocketException e)
{
Console.WriteLine("SocketException: {0}", e);
}
Console.WriteLine("\n Press Enter to continue...");
Console.Read();
}
This is my server one:
// Listen loop.
while(true)
{
using (TcpClient tcpClient = myListener.AcceptTcpClient())
{
Console.WriteLine("[Server] Acceptam client.");
using (NetworkStream networkStream = tcpClient.GetStream())
{
// Buffer for reading data
Byte[] bytes = new Byte[1024];
var data = new List<byte>();
int length;
while ((length = networkStream.Read(bytes, 0, bytes.Length)) != 0)
{
var copy = new byte[length];
Array.Copy(bytes, 0, copy, 0, length);
data.AddRange(copy);
}
// Incercam sa vedem ce doreste clientul.
string msg = Encoding.ASCII.GetString(data[0], 0, length);
if(msg.StartsWith("SendFile"))
{
using (Stream stream = new FileStream(#"C:\test.mp3", FileMode.Create, FileAccess.ReadWrite))
{
BinaryFormatter binaryFormatter = new BinaryFormatter();
networkStream.Position = 4;
binaryFormatter.Serialize(networkStream, data.ToArray());
}
}
}
}
}
What i'm trying to do here:
- I want the client to send a Message.. like "SaveFile" & after this string to be the filedata.
- The server should read the client message, and to process stuff according to the Client sentstring, before doing something with the file.
I believe that i don't know how to do it.
May i have an example on how to send/receive and read certain strings from the beggining of the file? How i can put them in the byte array and how to read it... It's quite overwhelming..
PS: The current Server Code is reading the data and CAN write as i coded it, without losing any packages. But also he's writing the aditional packets i sent before i converted the bytes of the file.

networkStream.Position = 4; isn't legal, because NetworkStream is not seekable.
I would discourage you from mixing text and binary data, just because of the complication it makes in the application protocol. But if you really want to do that, you should use BinaryWriter and BinaryReader, because it can write strings to a stream which can then be read later without consuming the bytes after the string.
Then you can do something like this...
In the client:
BinaryWriter writer = new BinaryWriter(networkStream);
writer.Write("SendFile");
writer.Write(fileData.Length);
writer.Write(fileData);
In the server:
BinaryReader reader = new BinaryReader(networkStream);
switch (reader.ReadString())
{
case "SendFile":
{
int length = reader.ReadInt32();
byte[] fileData = reader.ReadBytes(length);
// ... then do whatever with fileData, like write to a file
break;
}
}
The BinaryWriter/Reader implementation of the length-counted string is non-standard, so if you wanted to interact with any other non-.NET code using this technique, it would be more complicated because you have to replicate/reimplement the non-standard length-counting logic yourself.
IMHO a better approach is to encode commands as fixed-length data, e.g. an 8-, 16-, or 32-bit value, which is just some integer that specifies the command. Then you can list your commands in the code as an enum type, casting to/from the network stream for the I/O. This would be more portable, easier to implement on non-.NET platforms.

C# sockets: can't read after writing to socket

In my client/server application my client wiil communicate with the server for 2 functions: the client will either request data from the server or it will send data so the server will save it. I'm using one socket for both methods, and the method to be used is defined by the first byte sent. If the first byte is "1" it is requesting data. If it is "2", it will send data (data bytes are sent after the "2" byte). It works perfectly for sending data. But when I'm requesting data it works, as long as I don't read the socket stream in the client. It's like if I make the client read data after sending data, the server will have no data to read, and it just crashes when trying to read the data.
Here is my server code:
private const int BufferSize = 1024;
NetworkStream netstream = null;
byte[] RecData = new byte[BufferSize];
int RecBytes;
try {
netstream = clientSocket.GetStream();
int totalrecbytes = 0;
using (MemoryStream ms = new MemoryStream()) {
//When I get here, there is no data to read
while ((RecBytes = netstream.Read(RecData, 0, RecData.Length)) > 0) {
ms.Write(RecData, 0, RecBytes);
totalrecbytes += RecBytes;
}
byte[] bytes = ms.ToArray();
byte b = bytes[0];
switch (b) {
case 1:
//Here I gather data and put it in "stream" variable
byte[] SendingBuffer = null;
int NoOfPackets = Convert.ToInt32(Math.Ceiling(Convert.ToDouble(stream.Length) / Convert.ToDouble(BufferSize)));
int TotalLength = (int)stream.Length, CurrentPacketLength, counter = 0;
for (int i = 0; i < NoOfPackets; i++) {
if (TotalLength > BufferSize) {
CurrentPacketLength = BufferSize;
TotalLength = TotalLength - CurrentPacketLength;
}
else
CurrentPacketLength = TotalLength;
SendingBuffer = new byte[CurrentPacketLength];
stream.Read(SendingBuffer, 0, CurrentPacketLength);
netstream.Write(SendingBuffer, 0, (int)SendingBuffer.Length);
}
netstream.Flush();
}
catch (Exception e) {
Console.WriteLine("EXCEPTION:\n" + e.ToString());
}
break;
case 2:
//Code to read data
break;
}
}
netstream.Close()
clientSocket.Close();
And here is my client code:
using (System.Net.Sockets.TcpClient clientSocket = new System.Net.Sockets.TcpClient()) {
string returnData = "";
IAsyncResult ar = clientSocket.BeginConnect("127.0.0.1", 8080, null, null);
System.Threading.WaitHandle wh = ar.AsyncWaitHandle;
try {
if (!ar.AsyncWaitHandle.WaitOne(TimeSpan.FromSeconds(5), false)) {
clientSocket.Close();
Console.WriteLine("Timeout");
return;
}
System.Net.Sockets.NetworkStream serverStream = clientSocket.GetStream();
byte b = 1;
byte[] outStream = { b };
serverStream.Write(outStream, 0, outStream.Length);
serverStream.Flush();
//If I comment following lines, the server can read sent data, but server can't otherwise
byte[] RecData = new byte[1024];
int RecBytes;
int totalrecbytes = 0;
MemoryStream MS = new MemoryStream();
while ((RecBytes = serverStream.Read(RecData, 0, RecData.Length)) > 0) {
MS.Write(RecData, 0, RecBytes);
totalrecbytes += RecBytes;
}
serverStream.Close();
clientSocket.Close();
clientSocket.EndConnect(ar);
}
catch (Exception ex) {
Console.WriteLine("Exceção: " + ex.ToString());
}
finally {
wh.Close();
}
}
So, how can I send data to server and read the response? (I tried even putting the thread to sleep after sending data, with no luck.)
Thanks in advance.
EDIT:
With some debug messages I discovered that the server do read the "1" byte that was sent, but somehow it gets stuck inside the while loop, like, the server just stops there, no more loops and it does not leave the while loop. I saw that after writing "loop" in console inside the while loop, and writing read bytes also in console. It wrote "loop" once, and the read byte.

This code worries me:
//When I get here, there is no data to read
while ((RecBytes = netstream.Read(RecData, 0, RecData.Length)) > 0) {
ms.Write(RecData, 0, RecBytes);
totalrecbytes += RecBytes;
}
You are reading until the client closes the connection (or shuts down sending, which you don't do). But the client only closes when the server has replied. The server reply will never come. It is a deadlock.
Solution: Read a single byte to determine the requests command (b).
Unrelated to the question, your "packetised" sending (NoOfPackets, ...) does not seem to serve any purpose. Just use Stream.Copy to write. TCP does not have packets.
An even better solution would be to abandon your custom TCP protocol and use an HTTP library. All these concerns just go away. There are various smaller problems with your code that are very typical to see in TCP code.

Transfer bitmap from C# server program over TcpClient to Java Socket gets corrupted

Server program C#
private TcpListener serverSocket;
..
init:
serverSocket = new TcpListener(ipAddress, port_number);
when new connection request found:
TcpClient clientSock = default(TcpClient);
clientSock = serverSocket.AcceptTcpClient();
NetworkStream networkStream = clientSocket.GetStream();
String FileName = requested binary data file name from client
Byte[] sendBytes = null;
if (File.Exists(pkgName))
{
//load file contents
sendBytes = File.ReadAllBytes(pkgName);
}
if (sendBytes != null)
{
networkStream.Write(sendBytes, 0, sendBytes.Length); //sendBytes.Length = 1001883;
networkStream.Flush();
}
...
Java Android code: client
InetAddress serverAddr = InetAddress.getByName(serverIp);
Log.d("SideloadManager", "C: Connecting...");
Socket socket = new Socket(serverAddr, serverPort);
InputStream inFromServer = socket.getInputStream();
DataInputStream in = new DataInputStream(inFromServer);
FileOutputStream outStream = new FileOutputStream("...\recieved.bmp");
int size = 1001883; //same size from server
byte[] buf = new byte[size];
in.read(buf);
outStream.write(buf, 0, buf.length);
outStream.flush();
outStream.close();
received.bmp is of same size as on server 1001883 bytes. But its contents gets corrupted. After debugging i have seen that:
on C# program byte array is [ 149, 145, 10, .....]
on Java program byte array is: [ -105, -101, 10, .....] this is due to signed byte in java
What am i missing to receive correct bitmap?
SOLVED as below:
Replace:
int size = 1001883; //same size from server
byte[] buf = new byte[size];
in.read(buf);
outStream.write(buf, 0, buf.length);
with this:
int len=-1;
byte[] buf = new byte[1024];
while ((len = in.read(buf, 0, buf.length)) > 0) {
outStream.write(buf, 0, len);
}
solved the issue :)

The data is transferred correctly because 149 and -105 have the same binary representation as bytes. The more likely problem is that you're not reading all of the data that was sent in the java side.
The read method returns the number of bytes that have been read, and -1 when the end of the stream has been reached. You need a loop to read the entire file:
int bytesRead;
while ((bytesRead = in.read(buf)) != -1) {
outStream.write(buf, 0, bytesRead);
}

create a "listener" for an incoming socket stream that will contain a byte[] array

I'm creating a socket server that needs to continuously listen for incoming messages from the connected clients. Those messages will be sent in a byte[] array. I had the server working great with a StreamReader but StreamReader only works with textual represenations of the data being sent...not byte[] arrays.
Here's what I had:
StreamReader reader = new StreamReader(Client.GetStream());
string line = "";
while (true)
{
line = reader.ReadLine();
if (!string.IsNullOrEmpty(line))
{
parentForm.ApplyText(line + "\r\n");
SocketServer.SendBroadcast(line);
}
}
I need to now convert that into a raw stream somehow that will convert the stream contents into a byte[] array but I can't seem to get a handle on it.
I tried this:
while (true)
{
var bytes = default(byte[]);
using (var memstream = new MemoryStream())
{
var buffer = new byte[512];
var bytesRead = default(int);
while ((bytesRead = reader.BaseStream.Read(buffer, 0, buffer.Length)) > 0)
memstream.Write(buffer, 0, bytesRead);
bytes = memstream.ToArray();
}
//parentForm.ApplyText(bytes.Length + "\r\n");
}
but as you might guess, the while(true) loop doesn't quite work how I need it to. Can anyone help me with some code adjustment to make this work as I need it to. It needs to continuously listen for incoming messages, then when a message is received, it needs to do something with that message (the byte[] array) then go back to listening again.
TIA

I guess "listening continuously" is not task of reader its a task of listener. I ran into same problem when i was writing server using TcpListener. I am not sure what you want to do but i am posting solution for your "listening continuous" and reading into byte[] problem. I guess this code might help you:
TcpListener t = new TcpListener(IPAddress.Loopback, _port);
t.Start();
Console.WriteLine("Server is started and waiting for client\n\n");
byte[] buff = new byte[255];
NetworkStream stream;
TcpClient client;
while(true)
{
client = t.AcceptTcpClient();
if (!client.Connected)
return;
stream = client.GetStream();
while ((stream.Read(buff, 0, buff.Length)) != 0)
{
break;
}
if (0 != buff.Length)
break;
}

There's no need to convert anything. GetStream() returns a NetworkStream. See the sample Microsoft includes in the NetworkStream.Read Method. All you have to do is replace the myCompleteMessage.AppendFormat("{0}", Encoding.ASCII.GetString(myReadBuffer, 0, numberOfBytesRead)); line with an appropriate storage mechanism.