Decode basic milter packet structure

.gitignore

@@ -1 +1,5 @@
+# Ignore .vagrant folder
+.vagrant
+
+# Ignore build result
 milter-experiment

Vagrantfile

@@ -0,0 +1,40 @@
+# -*- mode: ruby -*-
+# vi: set ft=ruby :
+
+Vagrant.configure("2") do |config|
+  config.vm.box = "debian/buster64"
+
+  config.vm.synced_folder "./", "/vagrant", type: "rsync"
+
+  # Export postfix port 25 (guest) to port 2525 (host)
+  # This is useful for throwing swaks and other tools against postfix
+  config.vm.network "forwarded_port", guest: 25, host: 2525
+
+  config.vm.provision "shell", inline: <<-SHELL
+    # Give that vagrant box an apparently good FQDN
+    echo "local-vagrant.example.com" > /etc/hostname
+    echo "local-vagrant.example.com" > /etc/mailname
+    echo "127.0.1.2 local-vagrant.example.com local-vagrant" > /etc/hosts
+    hostnamectl set-hostname local-vagrant.example.com
+
+    # Basic preparations
+    apt-get update
+
+    # Install postfix
+    DEBIAN_FRONTEND=noninteractive apt-get install -y postfix
+
+    # Add milter to configuration
+    postconf smtpd_milters=inet:127.0.0.1:7777
+    postconf non_smtpd_milters=inet:127.0.0.1:7777
+
+    # Enable and launch postfix
+    systemctl enable postfix.service
+    systemctl start postfix.service
+
+    # Install swaks
+    DEBIAN_FRONTEND=noninteractive apt-get install -y swaks
+
+    # That's it
+    echo "That's it. We're set up. Enjoy your test environment."
+  SHELL
+end

main.go

@@ -5,11 +5,8 @@ import (
 	"bytes"
 	"encoding/binary"
 	"encoding/hex"
-	"os"
-)
-
-import (
 	"milter-experiment/logging"
+	"os"
 )
 
 var (
@@ -37,13 +34,24 @@ func handleMtaConnection(clientConnection *bufio.ReadWriter) {
 				logger.Errorln(err.Error())
 			}
 			logger.Debugf("Parsed length: %d\n", packetLength)
+
+			// Next up is a character, indicating the milter command
+			logger.Debugf("Parsing command from byte: %X\n", buf[4])
+			command := string(buf[4])
+			logger.Debugf("Parsed packet command: %s\n", command)
+
+			// Last part is data with lenght len-1
+			data := make([]byte, packetLength)
+			data = buf[5 : 5+packetLength-1]
+			logger.Debugf("Hexdump of packet payload read:\n%s", hex.Dump(data))
+
 		}
 	}
 }
 
 func main() {
 	logger = logging.NewLogger(os.Stdout, os.Stderr, logging.DEBUG)
-	err := runServer()
+	err := runServer("127.0.0.1:7777")
 	if err != nil {
 		logger.Errorf("Could not run server: %s\n", err.Error())
 		os.Exit(1)

socket.go

@@ -6,8 +6,8 @@ import (
 	"net"
 )
 
-func runServer() error {
+func runServer(listenAddr string) error {
-	serverSocket, err := net.Listen("tcp", "127.0.0.1:7777")
+	serverSocket, err := net.Listen("tcp", listenAddr)
 	if err != nil {
 		myError := fmt.Errorf("could not create listening socket: %s", err.Error())
 		return myError