Socket.Receive blocks sometimes on localhost

[Sven Groot]

I have a Windows Service application that acts as if it's an SMTP server.
Outlook connects to this service, which is always running on the localhost.
This works fine most of the time.
However, sometimes it will no longer receive anything from Outlook.
Socket.Receive would block indefinitely (actually, Socket.Poll times out,
because that's what I'm using). Outlook sends it, because when I'm stepping
through the code with the debugger, everything works.

Although this happens rarely, there is one situation where this always
happens: when Outlook has more than one message to send in a single
send/receive action, it will always block after the second MAIL command. An
example SMTP transcript:
220 localhost welcomes you to SignalMailSMTP
EHLO qualityweb
250 OK
MAIL FROM: <se****@signalmailsmtp.com>
250 Mail from se****@signalmailsmtp.com accepted
RCPT TO: <re******@signalmailsmtp.com>
250 Recipient re******@signalmailsmtp.com accepted
DATA
354 Start mail input; end with <CRLF>.<CRLF>
From: "SignalMail" <se****@signalmailsmtp.com>
To: <re******@signalmailsmtp.com>
Subject: AEX Enter Long alert
Date: Sat, 27 Sep 2003 14:03:28 +0200
Message-ID: <000701c384ef$5d1ae640$9dfc3850@qualityweb>
MIME-Version: 1.0
Content-Type: text/plain;
charset="us-ascii"
Content-Transfer-Encoding: 7bit
X-Priority: 3 (Normal)
X-MSMail-Priority: Normal
X-Mailer: Microsoft Outlook, Build 10.0.4510
X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2800.1165
Importance: Normal

..
250 OK
MAIL FROM: <se****@signalmailsmtp.com>
250 Mail from se****@signalmailsmtp.com accepted

The RCPT is never received. This has been reproduced on three separate
computers. Also, if you (or Outlook itself) retry too fast after this
failure, it will again fail, again at the RCPT command.

Now I can solve this by adding a delay (Thread.Sleep) but that's a highly
undesirable solution, as the exact delay value to make it work probably
depends on the speed of the computer it's running on. Also, it's a bit of a
hack.

Now I'm fresh out of ideas. It seems the message gets lost on the localhost
interface, but the question is, what can I do about it?
The code I'm using to receive:
Do
If mConnected.Poll(5000000, SelectMode.SelectRead) Then
BytesReceived = mConnected.Receive(Buffer)
Message &= Text.Encoding.ASCII.GetString(Buffer, 0, BytesReceived)
Else
mLogTransscript.Append("A timeout has occurred.")
mLogTransscript.Append(Environment.NewLine)
If Not mTransscript Is Nothing Then
mTransscript.WriteLine("A timeout has occurred.")
End If
mLogError = True
mState = SmtpState.Quit
Return Nothing
End If
Loop While Message.IndexOf(endSequence) = -1

Hopefully someone here can help.

--
Sven Groot

[Christine Nguyen]

Have you tried Thread.Sleep(0)? That way you don't have to calculate the
exact time to sleep for different machines.

"Sven Groot" <sv*******@gmx.net> wrote in message
news:#P**************@TK2MSFTNGP11.phx.gbl...

I have a Windows Service application that acts as if it's an SMTP server.
Outlook connects to this service, which is always running on the localhost. This works fine most of the time.
However, sometimes it will no longer receive anything from Outlook.
Socket.Receive would block indefinitely (actually, Socket.Poll times out,
because that's what I'm using). Outlook sends it, because when I'm stepping through the code with the debugger, everything works.

Although this happens rarely, there is one situation where this always
happens: when Outlook has more than one message to send in a single
send/receive action, it will always block after the second MAIL command. An example SMTP transcript:
220 localhost welcomes you to SignalMailSMTP
EHLO qualityweb
250 OK
MAIL FROM: <se****@signalmailsmtp.com>
250 Mail from se****@signalmailsmtp.com accepted
RCPT TO: <re******@signalmailsmtp.com>
250 Recipient re******@signalmailsmtp.com accepted
DATA
354 Start mail input; end with <CRLF>.<CRLF>
From: "SignalMail" <se****@signalmailsmtp.com>
To: <re******@signalmailsmtp.com>
Subject: AEX Enter Long alert
Date: Sat, 27 Sep 2003 14:03:28 +0200
Message-ID: <000701c384ef$5d1ae640$9dfc3850@qualityweb>
MIME-Version: 1.0
Content-Type: text/plain;
charset="us-ascii"
Content-Transfer-Encoding: 7bit
X-Priority: 3 (Normal)
X-MSMail-Priority: Normal
X-Mailer: Microsoft Outlook, Build 10.0.4510
X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2800.1165
Importance: Normal

.
250 OK
MAIL FROM: <se****@signalmailsmtp.com>
250 Mail from se****@signalmailsmtp.com accepted

The RCPT is never received. This has been reproduced on three separate
computers. Also, if you (or Outlook itself) retry too fast after this
failure, it will again fail, again at the RCPT command.

Now I can solve this by adding a delay (Thread.Sleep) but that's a highly
undesirable solution, as the exact delay value to make it work probably
depends on the speed of the computer it's running on. Also, it's a bit of a hack.

Now I'm fresh out of ideas. It seems the message gets lost on the localhost interface, but the question is, what can I do about it?
The code I'm using to receive:
Do
If mConnected.Poll(5000000, SelectMode.SelectRead) Then
BytesReceived = mConnected.Receive(Buffer)
Message &= Text.Encoding.ASCII.GetString(Buffer, 0, BytesReceived)
Else
mLogTransscript.Append("A timeout has occurred.")
mLogTransscript.Append(Environment.NewLine)
If Not mTransscript Is Nothing Then
mTransscript.WriteLine("A timeout has occurred.")
End If
mLogError = True
mState = SmtpState.Quit
Return Nothing
End If
Loop While Message.IndexOf(endSequence) = -1

Hopefully someone here can help.

--
Sven Groot

[Ivar]

Hi,

Suggestions:
1)don't store message to string, stote it as byte[] in to MemoryStream.

2) Loop While Message.IndexOf(endSequence) = -1, if message gets
bigger(contains attachment) this code kill your computer.
Store only last 5 bytes (<CRLF>.<CRLF>), which can be used to check for data
terminator.

3) put in while loop Thread.Sleep(50) or other wise this code eats 100% of
your cpu.
(Sleep only if data not available to read)

4) Use Socket.Available to see if data must be readed or just wait to arrive
(Thread.Sleep(50) )
For complete solution see www.lumisoft.ee mail server project.
It provides SMTP/POP3/IMAP working server code.

This code is easy to follow, it's well commented, but it's in c#.

I'm sure you can find many good solutions,ideas from there or even may use
whole project.
(There isn't any need to invent bicycle, because of it already exists)

If you have some SMTP specific questions, you may email iv**@lumisoft.ee.
"Sven Groot" <sv*******@gmx.net> wrote in message
news:%2****************@TK2MSFTNGP11.phx.gbl...

I have a Windows Service application that acts as if it's an SMTP server.
Outlook connects to this service, which is always running on the localhost. This works fine most of the time.
However, sometimes it will no longer receive anything from Outlook.
Socket.Receive would block indefinitely (actually, Socket.Poll times out,
because that's what I'm using). Outlook sends it, because when I'm stepping through the code with the debugger, everything works.

Although this happens rarely, there is one situation where this always
happens: when Outlook has more than one message to send in a single
send/receive action, it will always block after the second MAIL command. An example SMTP transcript:
220 localhost welcomes you to SignalMailSMTP
EHLO qualityweb
250 OK
MAIL FROM: <se****@signalmailsmtp.com>
250 Mail from se****@signalmailsmtp.com accepted
RCPT TO: <re******@signalmailsmtp.com>
250 Recipient re******@signalmailsmtp.com accepted
DATA
354 Start mail input; end with <CRLF>.<CRLF>
From: "SignalMail" <se****@signalmailsmtp.com>
To: <re******@signalmailsmtp.com>
Subject: AEX Enter Long alert
Date: Sat, 27 Sep 2003 14:03:28 +0200
Message-ID: <000701c384ef$5d1ae640$9dfc3850@qualityweb>
MIME-Version: 1.0
Content-Type: text/plain;
charset="us-ascii"
Content-Transfer-Encoding: 7bit
X-Priority: 3 (Normal)
X-MSMail-Priority: Normal
X-Mailer: Microsoft Outlook, Build 10.0.4510
X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2800.1165
Importance: Normal

.
250 OK
MAIL FROM: <se****@signalmailsmtp.com>
250 Mail from se****@signalmailsmtp.com accepted

The RCPT is never received. This has been reproduced on three separate
computers. Also, if you (or Outlook itself) retry too fast after this
failure, it will again fail, again at the RCPT command.

Now I can solve this by adding a delay (Thread.Sleep) but that's a highly
undesirable solution, as the exact delay value to make it work probably
depends on the speed of the computer it's running on. Also, it's a bit of a hack.

Now I'm fresh out of ideas. It seems the message gets lost on the localhost interface, but the question is, what can I do about it?
The code I'm using to receive:
Do
If mConnected.Poll(5000000, SelectMode.SelectRead) Then
BytesReceived = mConnected.Receive(Buffer)
Message &= Text.Encoding.ASCII.GetString(Buffer, 0, BytesReceived)
Else
mLogTransscript.Append("A timeout has occurred.")
mLogTransscript.Append(Environment.NewLine)
If Not mTransscript Is Nothing Then
mTransscript.WriteLine("A timeout has occurred.")
End If
mLogError = True
mState = SmtpState.Quit
Return Nothing
End If
Loop While Message.IndexOf(endSequence) = -1

Hopefully someone here can help.

--
Sven Groot

[Pieter Philippaerts]

"Sven Groot" <sv*******@gmx.net> wrote

If mConnected.Poll(5000000, SelectMode.SelectRead) Then
BytesReceived = mConnected.Receive(Buffer)
Message &= Text.Encoding.ASCII.GetString(Buffer, 0, BytesReceived)
Else

Why do you use Poll with such a huge number? You can better call Receive
directly without using Poll. Receive will block until data is available.

BytesReceived = mConnected.Receive(Buffer)
If Buffer > 0 Then
Message &= Text.Encoding.ASCII.GetString(Buffer, 0, BytesReceived)
Else
' other side closed connection, or timeout
End If

I also agree with Ivar about the checking of only the last few bytes instead
of using IndexOf on the entire message.
You may also want to consider using a StringBuilder instance instead of
concatenating strings. This will greatly enhance the performance.

Regards,
Pieter Philippaerts
Managed SSL/TLS: http://www.mentalis.org/go.php?sl