Sockets Hanging with SMTP server code

[Dave]

Hello,

I am trying to write an application that will talk to an SMTP server
using sockets. I can connect to the server just fine, then I can
receive the first message from the server. I can then send out a
command to the server, but after that the thing just hangs when I am
waiting for a response. I can't understand why this is happening. I am
new to this language, so this might be something obvious that I am
overlooking. Any help would be great. Here is the code. I based this
code off an example from msdn.

Imports System.Net
Imports System.Net.Sock ets
Imports System.Text

Module Module1

Sub Main()
Connect("smtpse rver", "")
End Sub

Sub Connect(ByVal server As [String], ByVal message As [String])
Try
' Create a TcpClient.
' Note, for this client to work you need to have a TcpServer
' connected to the same address as specified by the server, port
' combination.
Dim port As Int32 = 25
Dim client As New TcpClient(serve r, port)

' Translate the passed message into ASCII and store it as a Byte
array.
Dim data As [Byte]() = System.Text.Enc oding.ASCII.Get Bytes(message)

' Get a client stream for reading and writing.
' Stream stream = client.GetStrea m();
Dim stream As NetworkStream = client.GetStrea m()
' Receive the TcpServer.respo nse.
' Buffer to store the response bytes.
data = New [Byte](256) {}

' String to store the response ASCII representation.
Dim responseData As [String] = [String].Empty

' Read the first batch of the TcpServer response bytes.
Dim bytes As Int32 = stream.Read(dat a, 0, data.Length)
responseData = System.Text.Enc oding.ASCII.Get String(data, 0, bytes)
Console.WriteLi ne("Received: {0}", responseData)
data = System.Text.Enc oding.ASCII.Get Bytes("HELO smtpserver.com" )
stream.Write(da ta, 0, data.Length)
stream.Flush()
'This next line prints out just fine
Console.WriteLi ne("Sent -> HELO smtpserver.com" )

Here is the part that is hanging
------------------------------------------------------------------------
bytes = stream.Read(dat a, 0, data.Length)
responseData = System.Text.Enc oding.ASCII.Get String(data, 0, bytes)
---------------------------------------------------------------------------

Console.WriteLi ne("Received: {0}", responseData)

'Never gets here
Console.WriteLi ne("Never gets here")

' Close everything.
client.Close()
Catch e As ArgumentNullExc eption
Console.WriteLi ne("ArgumentNul lException: {0}", e)
Catch e As SocketException
Console.WriteLi ne("SocketExcep tion: {0}", e)
End Try

Console.WriteLi ne(ControlChars .Cr + " Press Enter to continue...")
Console.Read()
End Sub 'Connect

[Rulin Hong]

data = System.Text.Enc oding.ASCII.Get Bytes("HELO smtpserver.com" & vbCrLf)
vbCrLf means end of command. Otherwise SMTP server never responds your
command.

"Dave" wrote:

Hello,

I am trying to write an application that will talk to an SMTP server
using sockets. I can connect to the server just fine, then I can
receive the first message from the server. I can then send out a
command to the server, but after that the thing just hangs when I am
waiting for a response. I can't understand why this is happening. I am
new to this language, so this might be something obvious that I am
overlooking. Any help would be great. Here is the code. I based this
code off an example from msdn.

Imports System.Net
Imports System.Net.Sock ets
Imports System.Text

Module Module1

Sub Main()
Connect("smtpse rver", "")
End Sub

Sub Connect(ByVal server As [String], ByVal message As [String])
Try
' Create a TcpClient.
' Note, for this client to work you need to have a TcpServer
' connected to the same address as specified by the server, port
' combination.
Dim port As Int32 = 25
Dim client As New TcpClient(serve r, port)

' Translate the passed message into ASCII and store it as a Byte
array.
Dim data As [Byte]() = System.Text.Enc oding.ASCII.Get Bytes(message)

' Get a client stream for reading and writing.
' Stream stream = client.GetStrea m();
Dim stream As NetworkStream = client.GetStrea m()
' Receive the TcpServer.respo nse.
' Buffer to store the response bytes.
data = New [Byte](256) {}

' String to store the response ASCII representation.
Dim responseData As [String] = [String].Empty

' Read the first batch of the TcpServer response bytes.
Dim bytes As Int32 = stream.Read(dat a, 0, data.Length)
responseData = System.Text.Enc oding.ASCII.Get String(data, 0, bytes)
Console.WriteLi ne("Received: {0}", responseData)
data = System.Text.Enc oding.ASCII.Get Bytes("HELO smtpserver.com" )
stream.Write(da ta, 0, data.Length)
stream.Flush()
'This next line prints out just fine
Console.WriteLi ne("Sent -> HELO smtpserver.com" )

Here is the part that is hanging
------------------------------------------------------------------------
bytes = stream.Read(dat a, 0, data.Length)
responseData = System.Text.Enc oding.ASCII.Get String(data, 0, bytes)
---------------------------------------------------------------------------

Console.WriteLi ne("Received: {0}", responseData)

'Never gets here
Console.WriteLi ne("Never gets here")

' Close everything.
client.Close()
Catch e As ArgumentNullExc eption
Console.WriteLi ne("ArgumentNul lException: {0}", e)
Catch e As SocketException
Console.WriteLi ne("SocketExcep tion: {0}", e)
End Try

Console.WriteLi ne(ControlChars .Cr + " Press Enter to continue...")
Console.Read()
End Sub 'Connect

[Tom Shelton]

In article <3c************ **************@ posting.google. com>, Dave wrote:

Hello,

I am trying to write an application that will talk to an SMTP server
using sockets. I can connect to the server just fine, then I can
receive the first message from the server. I can then send out a
command to the server, but after that the thing just hangs when I am
waiting for a response. I can't understand why this is happening. I am
new to this language, so this might be something obvious that I am
overlooking. Any help would be great. Here is the code. I based this
code off an example from msdn.

<snip>

Simple code example:

Option Strict On
Option Explicit On

Imports System
Imports System.IO
Imports System.Text
Imports System.Net
Imports System.Net.Sock ets

Module Module1

Sub Main()
' Declare a socket, and get our servers address
Dim connection As New Socket(AddressF amily.InterNetw ork,
SocketType.Stre am, ProtocolType.Tc p)
Dim serverIP As IPAddress =
Dns.GetHostByNa me("smtpserver. com").AddressLi st(0)

' Connect the socket
connection.Conn ect(New IPEndPoint(serv erIP, 25))

' Create a reader and a writer
Dim reader As New StreamReader(Ne w NetworkStream(c onnection,
False))
Dim writer As New StreamWriter(Ne w NetworkStream(c onnection,
True))

writer.AutoFlus h = True
writer.NewLine = vbCrLf ' so this will be protable to Unix :)

writer.WriteLin e("HELO smtpserver.com" )
Console.WriteLi ne(reader.ReadL ine())

connection.Clos e()
End Sub

End Module

SMTP commands need to be terminated with a CrLF pair :)
HTH
--
Tom Shelton [MVP]