Asynchronous TCP socket connection... packets are in an undefined order

[Brian Rice]

I have a socket application that is sending and receiving packets
asynchronously. It works great except, when I receive packets that are
larger than my receive buffer which then generate several EndReceive
calls... these calls seem to be sometimes coming out of order.

For example, the following is from my log file:

Connection at 5/1/2004 11:39:14 AM
SENT> ZZZ:1:FMZZZ:ID1 234:PWAAAA:VR10 0:\0
RCVD> ZZZ:1:FMZZZ:SW2 4657:CNUS:TO480 :TX113731:DX050 12004:DEOCX OPR
RCVD> ACASHTESTSX:\0
Connection at 5/1/2004 11:39:32 AM
SENT> ZZZ:1:FMZZZ:ID1 234:PWAAAA:VR10 0:\0
RCVD> ACASHTESTSX:\0
RCVD> ZZZ:1:FMZZZ:SW2 4657:CNUS:TO480 :TX113748:DX050 12004:DEOCX OPR

Is there any way I can manage this? Or something that would prevent
this from happening?

Thanks!

- Brian

Here is my test code:

using System;
using System.Net;
using System.Net.Sock ets;

namespace UnitTest
{
/// <summary>
/// Summary description for SocketTest.
/// </summary>
public class SocketTest
{
public SocketTest()
{
}

protected Socket _socket = null;

public class SocketPacket
{
public byte[] Buffer = new Byte[100];
public Socket Socket;

public SocketPacket(So cket socket)
{
Socket = socket;
}
}

public void Stop()
{
_socket.Shutdow n(SocketShutdow n.Both);
_socket.Close() ;
}

public void Start(string ipAddress, int port)
{
// Create socket and connect

_socket = new Socket(AddressF amily.InterNetw ork,SocketType. Stream,
ProtocolType.Tc p);

IPEndPoint endPoint = new IPEndPoint(IPAd dress.Parse(ipA ddress),
port);

_socket.Connect (endPoint);

System.IO.Strea mWriter sw;
sw = System.IO.File. AppendText("C:\ \Connection.log ");
sw.WriteLine("C onnection at " + DateTime.Now.To String());
sw.Close();

// set up a bunch of receive packets
for (int i=1;i<10;i++)
{
SocketPacket packet = new SocketPacket(_s ocket);
_socket.BeginRe ceive(
packet.Buffer, 0, packet.Buffer.L ength,
SocketFlags.Non e,
new AsyncCallback(E ndReceive),
packet
);
}

// send a message
SocketPacket packet2 = new SocketPacket(_s ocket);
packet2.Buffer = System.Text.Enc oding.ASCII.Get Bytes("FOL:1:FM FOL:IDONE-FOL:PWEXIT:VR10 0:\0");
WriteBufferToLo g("SENT> ", packet2.Buffer) ;
_socket.BeginSe nd(
packet2.Buffer, 0, packet2.Buffer. Length,
SocketFlags.Non e,
new AsyncCallback(E ndSend),
packet2
);
}

public void EndSend(IAsyncR esult asyncResult)
{
SocketPacket packet = (SocketPacket)a syncResult.Asyn cState;
packet.Socket.E ndSend(asyncRes ult);
}

public void EndReceive(IAsy ncResult asyncResult)
{
// we seem to get EndReceive's while disconnecting
// is there a way to drop these before we shutdown
// so EndReceive doesn't get called?
if (_socket == null)
return;
if (!_socket.Conne cted)
return;

SocketPacket packet = (SocketPacket)a syncResult.Asyn cState;

packet.Socket.E ndSend(asyncRes ult);

WriteBufferToLo g("RCVD> ", packet.Buffer);

// put packet back on receive queue
_socket.BeginRe ceive(
packet.Buffer, 0, packet.Buffer.L ength,
SocketFlags.Non e,
new AsyncCallback(E ndReceive),
packet
);
}

public void WriteBufferToLo g(string prefix, byte[] buffer)
{
System.IO.Strea mWriter sw;
sw = System.IO.File. AppendText("C:\ \Connection.log ");
sw.WriteLine(pr efix + GetString(buffe r));
sw.Close();
}

public string GetString(byte[] buffer)
{
string result = "";

int index = 0;
while (index < buffer.Length && buffer[index] > 0)
{
char[] chars = new char[buffer.Length + 1];
System.Text.Dec oder d = System.Text.Enc oding.ASCII.Get Decoder();
int len = d.GetChars(buff er, index, buffer.Length - index, chars,
0);
string str = new System.String(c hars);

int n = str.IndexOf("\0 ");
if (n >= 0)
str = str.Substring(0 , n);

index += str.Length + 1;

if (index < buffer.Length)
result += str + @"\0";
else
result += str;
}

return result;
}
}
}

[Ivar]

Hi,

You should not send new packet before others are sent.

Currenlty you call BeginSend multiple times, you can't do this.
You must send all packets with single send, if this isn't possible, you need
to wait before first send completes and calls callback method.

"Brian Rice" <ma**@brianrice .com> wrote in message
news:dc******** *************** ***@posting.goo gle.com...

I have a socket application that is sending and receiving packets
asynchronously. It works great except, when I receive packets that are
larger than my receive buffer which then generate several EndReceive
calls... these calls seem to be sometimes coming out of order.

For example, the following is from my log file:

Connection at 5/1/2004 11:39:14 AM
SENT> ZZZ:1:FMZZZ:ID1 234:PWAAAA:VR10 0:\0
RCVD> ZZZ:1:FMZZZ:SW2 4657:CNUS:TO480 :TX113731:DX050 12004:DEOCX OPR
RCVD> ACASHTESTSX:\0
Connection at 5/1/2004 11:39:32 AM
SENT> ZZZ:1:FMZZZ:ID1 234:PWAAAA:VR10 0:\0
RCVD> ACASHTESTSX:\0
RCVD> ZZZ:1:FMZZZ:SW2 4657:CNUS:TO480 :TX113748:DX050 12004:DEOCX OPR

Is there any way I can manage this? Or something that would prevent
this from happening?

Thanks!

- Brian

Here is my test code:

using System;
using System.Net;
using System.Net.Sock ets;

namespace UnitTest
{
/// <summary>
/// Summary description for SocketTest.
/// </summary>
public class SocketTest
{
public SocketTest()
{
}

protected Socket _socket = null;

public class SocketPacket
{
public byte[] Buffer = new Byte[100];
public Socket Socket;

public SocketPacket(So cket socket)
{
Socket = socket;
}
}

public void Stop()
{
_socket.Shutdow n(SocketShutdow n.Both);
_socket.Close() ;
}

public void Start(string ipAddress, int port)
{
// Create socket and connect

_socket = new Socket(AddressF amily.InterNetw ork,SocketType. Stream,
ProtocolType.Tc p);

IPEndPoint endPoint = new IPEndPoint(IPAd dress.Parse(ipA ddress),
port);

_socket.Connect (endPoint);

System.IO.Strea mWriter sw;
sw = System.IO.File. AppendText("C:\ \Connection.log ");
sw.WriteLine("C onnection at " + DateTime.Now.To String());
sw.Close();

// set up a bunch of receive packets
for (int i=1;i<10;i++)
{
SocketPacket packet = new SocketPacket(_s ocket);
_socket.BeginRe ceive(
packet.Buffer, 0, packet.Buffer.L ength,
SocketFlags.Non e,
new AsyncCallback(E ndReceive),
packet
);
}

// send a message
SocketPacket packet2 = new SocketPacket(_s ocket);
packet2.Buffer = System.Text.Enc oding.ASCII.Get Bytes("FOL:1:FM FOL:IDONE-FOL:PWEXIT:VR10 0:\0")
; WriteBufferToLo g("SENT> ", packet2.Buffer) ;
_socket.BeginSe nd(
packet2.Buffer, 0, packet2.Buffer. Length,
SocketFlags.Non e,
new AsyncCallback(E ndSend),
packet2
);
}

public void EndSend(IAsyncR esult asyncResult)
{
SocketPacket packet = (SocketPacket)a syncResult.Asyn cState;
packet.Socket.E ndSend(asyncRes ult);
}

public void EndReceive(IAsy ncResult asyncResult)
{
// we seem to get EndReceive's while disconnecting
// is there a way to drop these before we shutdown
// so EndReceive doesn't get called?
if (_socket == null)
return;
if (!_socket.Conne cted)
return;

SocketPacket packet = (SocketPacket)a syncResult.Asyn cState;

packet.Socket.E ndSend(asyncRes ult);

WriteBufferToLo g("RCVD> ", packet.Buffer);

// put packet back on receive queue
_socket.BeginRe ceive(
packet.Buffer, 0, packet.Buffer.L ength,
SocketFlags.Non e,
new AsyncCallback(E ndReceive),
packet
);
}

public void WriteBufferToLo g(string prefix, byte[] buffer)
{
System.IO.Strea mWriter sw;
sw = System.IO.File. AppendText("C:\ \Connection.log ");
sw.WriteLine(pr efix + GetString(buffe r));
sw.Close();
}

public string GetString(byte[] buffer)
{
string result = "";

int index = 0;
while (index < buffer.Length && buffer[index] > 0)
{
char[] chars = new char[buffer.Length + 1];
System.Text.Dec oder d = System.Text.Enc oding.ASCII.Get Decoder();
int len = d.GetChars(buff er, index, buffer.Length - index, chars,
0);
string str = new System.String(c hars);

int n = str.IndexOf("\0 ");
if (n >= 0)
str = str.Substring(0 , n);

index += str.Length + 1;

if (index < buffer.Length)
result += str + @"\0";
else
result += str;
}

return result;
}
}
}

[Brian Rice]

> You should not send new packet before others are sent.

Currenlty you call BeginSend multiple times, you can't do this.
You must send all packets with single send, if this isn't possible, you need
to wait before first send completes and calls callback method.

In this example I am only doing ONE send.

BTW: If I up my buffer to, say, 512 bytes then my log looks like this:

Connection at 5/1/2004 1:39:33 PM
SENT> ZZZ:1:FMZZZ:ID1 234:PWAAAA:VR10 0:\0
RCVD> ZZZ:1:FMZZZ:SW2 4657:CNUS:TO480 :TX113731:DX050 12004:DEOCX
OPRACASHTESTSX: \0

But, of course the problem is that I can get really large packets and
still have the same problem. Has anybody else experienced this issue
of packets coming back on different threads and therefore not
neccesarilly being in the right order?

[Brian Rice]

Ok... I think you meant I was doing multiple BeginReceive's. ..
because, now, when I only do one BeginReceive and then do another
*only* after I have completed an EndReceive it works. So, my thinking
of having a pool of "BeginRecei ve" packets is probably fine as long as
I don't care about the order that I get them... but I do care so the
pool idea is bad for me.

Here is my revised code... and it works really well.

using System;
using System.Net;
using System.Net.Sock ets;

namespace UnitTest
{
/// <summary>
/// Summary description for SocketTest.
/// </summary>
public class SocketTest
{
public SocketTest()
{
}

protected Socket _socket = null;

public class SocketPacket
{
public byte[] Buffer = new Byte[30];
public Socket Socket;

public SocketPacket(So cket socket)
{
Socket = socket;
}
}

public void Stop()
{
_socket.Shutdow n(SocketShutdow n.Both);
_socket.Close() ;
}

public void Start(string ipAddress, int port)
{
// Create socket and connect

_socket = new Socket(AddressF amily.InterNetw ork,SocketType. Stream,
ProtocolType.Tc p);

IPEndPoint endPoint = new IPEndPoint(IPAd dress.Parse(ipA ddress),
port);

_socket.Connect (endPoint);

System.IO.Strea mWriter sw;
sw = System.IO.File. AppendText("C:\ \Connection.log ");
sw.WriteLine("C onnection at " + DateTime.Now.To String());
sw.Close();

// set up one receive packet
SocketPacket packet = new SocketPacket(_s ocket);
_socket.BeginRe ceive(
packet.Buffer, 0, packet.Buffer.L ength,
SocketFlags.Non e,
new AsyncCallback(E ndReceive),
packet
);

// send a message
SocketPacket packet2 = new SocketPacket(_s ocket);
packet2.Buffer = System.Text.Enc oding.ASCII.Get Bytes("FOL:1:FM FOL:IDONE-FOL:PWEXIT:VR10 0:\0");
WriteBufferToLo g("SENT> ", packet2.Buffer) ;
_socket.BeginSe nd(
packet2.Buffer, 0, packet2.Buffer. Length,
SocketFlags.Non e,
new AsyncCallback(E ndSend),
packet2
);
}

public void EndSend(IAsyncR esult asyncResult)
{
SocketPacket packet = (SocketPacket)a syncResult.Asyn cState;
packet.Socket.E ndSend(asyncRes ult);
}

public void EndReceive(IAsy ncResult asyncResult)
{
// we seem to get EndReceive's while disconnecting
if (_socket == null)
return;
if (!_socket.Conne cted)
return;

SocketPacket packet = (SocketPacket)a syncResult.Asyn cState;
packet.Socket.E ndSend(asyncRes ult);

WriteBufferToLo g("RCVD> ", packet.Buffer);

// put packet back on receive queue
packet.Buffer.I nitialize();
for (int i=0;i<packet.Bu ffer.Length;i++ )
packet.Buffer[i] = 0;
_socket.BeginRe ceive(
packet.Buffer, 0, packet.Buffer.L ength,
SocketFlags.Non e,
new AsyncCallback(E ndReceive),
packet
);
}

public void WriteBufferToLo g(string prefix, byte[] buffer)
{
System.IO.Strea mWriter sw;
sw = System.IO.File. AppendText("C:\ \Connection.log ");
sw.WriteLine(pr efix + GetString(buffe r));
sw.Close();
}

public string GetString(byte[] buffer)
{
string result = "";

int index = 0;
while (index < buffer.Length && buffer[index] > 0)
{
char[] chars = new char[buffer.Length + 1];
System.Text.Dec oder d = System.Text.Enc oding.ASCII.Get Decoder();
int len = d.GetChars(buff er, index, buffer.Length - index, chars,
0);
string str = new System.String(c hars);

int n = str.IndexOf("\0 ");
if (n >= 0)
str = str.Substring(0 , n);

index += str.Length + 1;

if (index < buffer.Length)
result += str + @"\0";
else
result += str;
}

return result;
}
}
}

[Ivar]

Ok... I think you meant I was doing multiple BeginReceive's. .. Yes.

"Brian Rice" <ma**@brianrice .com> wrote in message
news:dc******** *************** **@posting.goog le.com... Ok... I think you meant I was doing multiple BeginReceive's. ..
because, now, when I only do one BeginReceive and then do another
*only* after I have completed an EndReceive it works. So, my thinking
of having a pool of "BeginRecei ve" packets is probably fine as long as
I don't care about the order that I get them... but I do care so the
pool idea is bad for me.

Here is my revised code... and it works really well.

using System;
using System.Net;
using System.Net.Sock ets;

namespace UnitTest
{
/// <summary>
/// Summary description for SocketTest.
/// </summary>
public class SocketTest
{
public SocketTest()
{
}

protected Socket _socket = null;

public class SocketPacket
{
public byte[] Buffer = new Byte[30];
public Socket Socket;

public SocketPacket(So cket socket)
{
Socket = socket;
}
}

public void Stop()
{
_socket.Shutdow n(SocketShutdow n.Both);
_socket.Close() ;
}

public void Start(string ipAddress, int port)
{
// Create socket and connect

_socket = new Socket(AddressF amily.InterNetw ork,SocketType. Stream,
ProtocolType.Tc p);

IPEndPoint endPoint = new IPEndPoint(IPAd dress.Parse(ipA ddress),
port);

_socket.Connect (endPoint);

System.IO.Strea mWriter sw;
sw = System.IO.File. AppendText("C:\ \Connection.log ");
sw.WriteLine("C onnection at " + DateTime.Now.To String());
sw.Close();

// set up one receive packet
SocketPacket packet = new SocketPacket(_s ocket);
_socket.BeginRe ceive(
packet.Buffer, 0, packet.Buffer.L ength,
SocketFlags.Non e,
new AsyncCallback(E ndReceive),
packet
);

// send a message
SocketPacket packet2 = new SocketPacket(_s ocket);
packet2.Buffer = System.Text.Enc oding.ASCII.Get Bytes("FOL:1:FM FOL:IDONE-FOL:PWEXIT:VR10 0:\0")
; WriteBufferToLo g("SENT> ", packet2.Buffer) ;
_socket.BeginSe nd(
packet2.Buffer, 0, packet2.Buffer. Length,
SocketFlags.Non e,
new AsyncCallback(E ndSend),
packet2
);
}

public void EndSend(IAsyncR esult asyncResult)
{
SocketPacket packet = (SocketPacket)a syncResult.Asyn cState;
packet.Socket.E ndSend(asyncRes ult);
}

public void EndReceive(IAsy ncResult asyncResult)
{
// we seem to get EndReceive's while disconnecting
if (_socket == null)
return;
if (!_socket.Conne cted)
return;

SocketPacket packet = (SocketPacket)a syncResult.Asyn cState;
packet.Socket.E ndSend(asyncRes ult);

WriteBufferToLo g("RCVD> ", packet.Buffer);

// put packet back on receive queue
packet.Buffer.I nitialize();
for (int i=0;i<packet.Bu ffer.Length;i++ )
packet.Buffer[i] = 0;
_socket.BeginRe ceive(
packet.Buffer, 0, packet.Buffer.L ength,
SocketFlags.Non e,
new AsyncCallback(E ndReceive),
packet
);
}

public void WriteBufferToLo g(string prefix, byte[] buffer)
{
System.IO.Strea mWriter sw;
sw = System.IO.File. AppendText("C:\ \Connection.log ");
sw.WriteLine(pr efix + GetString(buffe r));
sw.Close();
}

public string GetString(byte[] buffer)
{
string result = "";

int index = 0;
while (index < buffer.Length && buffer[index] > 0)
{
char[] chars = new char[buffer.Length + 1];
System.Text.Dec oder d = System.Text.Enc oding.ASCII.Get Decoder();
int len = d.GetChars(buff er, index, buffer.Length - index, chars,
0);
string str = new System.String(c hars);

int n = str.IndexOf("\0 ");
if (n >= 0)
str = str.Substring(0 , n);

index += str.Length + 1;

if (index < buffer.Length)
result += str + @"\0";
else
result += str;
}

return result;
}
}
}