Using the .NET managed TCP/IP classes in a managed C++ appplication

Using the managed TCP/IP classes in a managed C++ appplication
Igor Chouvalov, Dundas Software Ltd

This sample demonstrates a basic technique of networking
using the TCP/IP protocol. It implements a simple POP3 client
that connects to the POP3 mail server and retrieves the number
of messages in your mailbox.

The sample is based on the Managed C++ Application created by
Application Wizard.

All changes are made in the main source file. In our case this is the
POP3Client.cpp file.

All functionality is implemented in the CPOP3Client class. This class 
has four properties:

POP3HostName  - POP3 server address,
UserName      - User Name,
Password      - User Password,
Status        - Error message (read-only)

and public property NumberOfMessages to retrieve the number
of messages in the mailbox.

The TcpClient class from .NET Framework is used to create a client
connection to a remote host. Inside of the NumberOfMessages function
we create connection, get access to the buffer to read the data,
read the response from the server, and check it. If it is positive value
we return true, otherwise we return false.

	bool ConnectToServer()
	{
		String *strReadBuffer;
		StreamReader *streamRead;

		// Close exist connection.
		if(m_Client != NULL)
		{
			m_Client->Close();
			m_Client = NULL;
		}

		// Create connection to the server.
		m_Client = new TcpClient(m_strPOP3HostName, 110);

		// Create stream to read.
		streamRead = new StreamReader(m_Client->GetStream(), Encoding::ASCII );

		strReadBuffer = streamRead->ReadLine();

		// Ignore rest of the buffer.
		streamRead->DiscardBufferedData();

		// Check response for +OK reply.
		if(strReadBuffer->StartsWith("+OK"))
			return true;
		else
		{
			m_Client->Close();
			m_Client = NULL;
			return false;
		}
	}

The DisconnectFromServer function just sends a QUIT command to the server.

	void DisconnectFromServer()
	{
		String *strResponse = String::Empty;

		SendCommand("QUIT", &strResponse);
		
		m_Client->Close();
		m_Client = NULL;
	}

After connecting to the server we get access to the mailbox by sending
USER and PASS commands to the server. The SendCommand class member takes care of this.
It uses two streams one for reading from the socket (an instance of
the StreamReader class) and another stream for writing to the socket
(an instance of the NetworkStream class). It writes the command to the output
stream and gets the response from the input streams. For our current needs
it reads only the first line of the response and discards rest
of the buffer. To get multiline response, you should read data in a loop
until end of the stream.

	bool SendCommand(String *strCommand, String** pstrOutput)
	{
		Byte outbuffer __gc[];

		StreamReader	*streamRead;
		NetworkStream	*streamWrite;
		String		*strRequest;

		// Add crlf to the command.
		strRequest = String::Concat(strCommand, S"\r\n");

		// Create streams to read from socket and write to it.
		streamWrite = m_Client->GetStream();
		streamRead = new StreamReader(streamWrite, Encoding::ASCII);

		// Convert from the string to the byte stream and write to socket.
		outbuffer = Encoding::ASCII->GetBytes(strRequest);
		streamWrite->Write(outbuffer, 0, outbuffer->Length);

		// read response from the socket.
		*pstrOutput = streamRead->ReadLine();

		// Ignore rest of the buffer.
		streamRead->DiscardBufferedData();

		return (*pstrOutput)->StartsWith(S"+OK") ? true : false;
	}

Inside main function we read the parameters from a command line
POP3 server address, user name, and password,
create instance of CPOP3Client, set its properties based  on the
command line parameters and call the NumberOfMessages method to retrieve
number of messages in the mailbox.

If an error occurs we print whatever useful information we can.

int main(int argc, char *argv[ ])
{
	CPOP3Client* pPOP3Client;
	int nNrOfMessages;

	// Check parameters.
	if(argc != 4)
	{
		Console::WriteLine(S"Wrong argument number.");
		Console::WriteLine(S"Use following command line:");
		Console::WriteLine(S"pop3client.exe POP3Hostname username password");
		return 0;
	}

	// Create POP3Client object.
	pPOP3Client = new CPOP3Client();

	// Set properties from command line.
	pPOP3Client->set_POP3HostName(new String(argv[1]));
	pPOP3Client->set_UserName(new String(argv[2]));
	pPOP3Client->set_Password(new String(argv[3]));

	// Get number of messages in the mailbox.
	nNrOfMessages = pPOP3Client->GetNumberOfMessages();

	// If -1 returned, error occurred, then print error message.
	// otherwise 
	if(nNrOfMessages < 0)
		Console::Write(String::Concat(S"Error occured: ", pPOP3Client->get_Status()));
	else
	{
		Console::Write(S"You have ");
		Console::Write(nNrOfMessages);
		Console::WriteLine(S" messages in your mailbox.");
	}
    return 0;

}