One of the easiest high-level TCP protocols to use is SMTP for sending an email message. This application simply connects to an SMTP server via TCP, identifies itself, and identifies who the message is for, sends the text of the message, and finally says goodbye. As each line of text is sent to the server, it returns a status code and message to indicate progress. The following code demonstrates this:
' Be sure to change the following two string equates
' to the name of your SMTP mail server and your email
' address.
#COMPILE EXE
$mailhost = "mailserver.mydomain.com"
$mailfrom = "email@address.com"
FUNCTION PBMAIN() AS LONG
' Get the local computer's IP address and name
HOST ADDR TO ip&
HOST NAME ip& TO hostname$
' ** Connect to the mailhost
hTCP& = FREEFILE
TCP OPEN "smtp" AT $mailhost AS hTCP&
IF ERR THEN
MSGBOX "Error connecting to mailhost"
EXIT FUNCTION
ELSE
TCP LINE hTCP&, buffer$
IF LEFT$(buffer$, 3) <> "220" THEN
MSGBOX "Mailhost Error: " & buffer$
EXIT FUNCTION
END IF
END IF
' Get the local computer's IP address and name
HOST NAME TO hostname$
' ** Greet the mailhost
TCP PRINT hTCP&, "HELO " + hostname$
TCP LINE hTCP&, buffer$
IF LEFT$(buffer$, 3) <> "250" THEN
MSGBOX "HELO Error: " & buffer$
TCP CLOSE hTCP&
EXIT FUNCTION
END IF
' ** Tell the mailhost who we are
TCP PRINT hTCP&, "MAIL FROM:<" & $mailfrom & ">"
TCP LINE hTCP&, buffer$
IF LEFT$(buffer$, 3) <> "250" THEN
MSGBOX "MAIL FROM Error: " & buffer$
TCP CLOSE hTCP&
EXIT FUNCTION
END IF
' ** Tell the mailhost who we want to send the message to
TCP PRINT hTCP&, "RCPT TO:<info@powerbasic.com>"
TCP LINE hTCP&, buffer$
IF LEFT$(buffer$, 3) <> "250" THEN
MSGBOX "RCPT TO Error: " & buffer$
TCP CLOSE hTCP&
EXIT FUNCTION
END IF
' ** Now we can send the message
TCP PRINT hTCP&, "DATA"
TCP LINE hTCP&, buffer$
IF LEFT$(buffer$, 3) <> "354" THEN
MSGBOX "DATA Error: " & buffer$
TCP CLOSE hTCP&
EXIT FUNCTION
END IF
TCP PRINT hTCP&, "From: " & $mailfrom
TCP PRINT hTCP&, "To: info@powerbasic.com"
TCP PRINT hTCP&, "Subject: Greetings!"
TCP PRINT hTCP&, ""
TCP PRINT hTCP&, "Just wanted to say hello."
TCP PRINT hTCP&, "This TCP stuff is great!
' ** End of the message
TCP PRINT hTCP&, "."
TCP LINE hTCP&, buffer$
IF LEFT$(buffer$, 3) <> "250" THEN
MSGBOX "DATA Error: " & buffer$
TCP CLOSE hTCP&
EXIT FUNCTION
END IF
' ** Say goodbye
TCP PRINT hTCP&, "QUIT"
TCP LINE hTCP&, buffer$
IF LEFT$(buffer$, 3) <> "221" THEN
MSGBOX "QUIT Error: " & buffer$
TCP CLOSE hTCP&
EXIT FUNCTION
END IF
TCP CLOSE hTCP&
END FUNCTION
The SMTP protocol is fully described in RFC 821 http://www.powerbasic.com/files/pub/docs/rfc/800/rfc821.zip
See Also
An ECHO client and server using TCP