mda-lmtp: Add a very basic MDA that uses LMTP to do the mail delivery.

mda-lmtp is a very basic MDA that uses LMTP to do the mail delivery.

It takes command line arguments similar to maildrop or procmail, reads an
email via standard input, and sends it over the given LMTP server.
Supports connecting to LMTP servers over UNIX sockets and TCP.

Since chasquid does not support direct LMTP local delivery, this can be
used as a workaround instead.

Example of use:
$ mda-lmtp --addr localhost:1234 -f juan@casa -d jose < email

cmd/mda-lmtp/.gitignore

@@ -0,0 +1,2 @@
+mda-lmtp
+*.log

cmd/mda-lmtp/mda-lmtp.go

@@ -0,0 +1,125 @@
+// mda-lmtp is a very basic MDA that uses LMTP to do the delivery.
+//
+// See the usage below for details.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"net"
+	"net/textproto"
+	"os"
+	"strings"
+)
+
+// Command-line flags
+var (
+	fromwhom  = flag.String("f", "", "Whom the message is from")
+	recipient = flag.String("d", "", "Recipient")
+
+	addrNetwork = flag.String("addr_network", "",
+		"Network of the LMTP address (e.g. unix or tcp)")
+	addr = flag.String("addr", "", "LMTP server address")
+)
+
+func usage() {
+	fmt.Fprintf(os.Stderr, `
+mda-lmtp is a very basic MDA that uses LMTP to do the mail delivery.
+
+It takes command line arguments similar to maildrop or procmail, reads an
+email via standard input, and sends it over the given LMTP server.
+Supports connecting to LMTP servers over UNIX sockets and TCP.
+
+It can be used when your mail server does not support LMTP directly.
+
+Example of use:
+$ mda-lmtp --addr localhost:1234 -f juan@casa -d jose < email
+
+Flags:
+`)
+	flag.PrintDefaults()
+}
+
+// Exit with EX_TEMPFAIL.
+func tempExit(format string, args ...interface{}) {
+	fmt.Printf(format+"\n", args...)
+	// 75 = EX_TEMPFAIL "temporary failure" exit code (sysexits.h).
+	os.Exit(75)
+}
+
+func main() {
+	flag.Usage = usage
+	flag.Parse()
+
+	if *addr == "" {
+		fmt.Printf("No LMTP server address given (use --addr)\n")
+		os.Exit(2)
+	}
+
+	// Try to autodetect the network if it's missing.
+	if *addrNetwork == "" {
+		*addrNetwork = "tcp"
+		if strings.HasPrefix(*addr, "/") {
+			*addrNetwork = "unix"
+		}
+	}
+
+	conn, err := net.Dial(*addrNetwork, *addr)
+	if err != nil {
+		tempExit("Error connecting to (%s, %s): %v",
+			*addrNetwork, *addr, err)
+	}
+
+	tc := textproto.NewConn(conn)
+
+	// Expect the hello from the server.
+	_, _, err = tc.ReadResponse(220)
+	if err != nil {
+		tempExit("Server greeting error: %v", err)
+	}
+
+	hostname, err := os.Hostname()
+	if err != nil {
+		tempExit("Could not get hostname: %v", err)
+	}
+
+	cmd(tc, 250, "LHLO %s", hostname)
+	cmd(tc, 250, "MAIL FROM:<%s>", *fromwhom)
+	cmd(tc, 250, "RCPT TO:<%s>", *recipient)
+	cmd(tc, 354, "DATA")
+
+	w := tc.DotWriter()
+	_, err = io.Copy(w, os.Stdin)
+	w.Close()
+	if err != nil {
+		tempExit("Error writing DATA: %v", err)
+	}
+
+	// This differs from SMTP: here we get one reply per recipient, with the
+	// result of the delivery. Since we deliver to only one recipient, read
+	// one code.
+	_, _, err = tc.ReadResponse(250)
+	if err != nil {
+		tempExit("Delivery failed remotely: %v", err)
+	}
+
+	cmd(tc, 221, "QUIT")
+
+	tc.Close()
+}
+
+// cmd sends a command and checks it matched the expected code.
+func cmd(conn *textproto.Conn, expectCode int, format string, args ...interface{}) {
+	id, err := conn.Cmd(format, args...)
+	if err != nil {
+		tempExit("Sent %q, got %v", fmt.Sprintf(format, args...), err)
+	}
+	conn.StartResponse(id)
+	defer conn.EndResponse(id)
+
+	_, _, err = conn.ReadResponse(expectCode)
+	if err != nil {
+		tempExit("Sent %q, got %v", fmt.Sprintf(format, args...), err)
+	}
+}

cmd/mda-lmtp/test.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+
+set -e
+. $(dirname ${0})/../../test/util/lib.sh
+
+init
+
+# Build the binary once, so we can use it and launch it in chamuyero scripts.
+# Otherwise, we not only spend time rebuilding it over and over, but also "go
+# run" masks the exit code, which is something we care about.
+go build
+
+for i in *.cmy; do
+	if ! chamuyero $i > $i.log 2>&1 ; then
+		echo "# Test $i failed, log follows"
+		cat $i.log
+		exit 1
+	fi
+done
+
+success

cmd/mda-lmtp/test_tcp_success.cmy

@@ -0,0 +1,32 @@
+
+nc tcp_listen localhost:14932
+
+mda |= ./mda-lmtp --addr=localhost:14932 -f from -d to < .data
+
+nc -> 220 Hola desde expect
+
+nc <~ LHLO .*
+nc -> 250-Bienvenido!
+nc -> 250 Contame...
+
+nc <- MAIL FROM:<from>
+nc -> 250 Aja
+
+nc <- RCPT TO:<to>
+nc -> 250 Aja
+
+nc <- DATA
+nc -> 354 Dale
+
+nc <- Subject: test
+nc <-
+nc <- This is a test.
+nc <- .
+
+nc -> 250 Recibido
+
+nc <- QUIT
+nc -> 221 Chauchas
+
+mda wait 0
+

cmd/mda-lmtp/test_unix_failure.cmy

@@ -0,0 +1,31 @@
+
+nc unix_listen .test-sock
+
+mda = ./mda-lmtp --addr=.test-sock --addr_network=unix \
+        -f from -d to < .data
+
+nc -> 220 Hola desde expect
+
+nc <~ LHLO .*
+nc -> 250-Bienvenido!
+nc -> 250 Contame...
+
+nc <- MAIL FROM:<from>
+nc -> 250 Aja
+
+nc <- RCPT TO:<to>
+nc -> 250 Aja
+
+nc <- DATA
+nc -> 354 Dale
+
+nc <- Subject: test
+nc <-
+nc <- This is a test.
+nc <- .
+
+nc -> 452 Nananana
+
+mda <- Delivery failed remotely: 452 Nananana
+mda wait 75
+

cmd/mda-lmtp/test_unix_success.cmy

@@ -0,0 +1,33 @@
+
+nc unix_listen .test-sock
+
+mda |= ./mda-lmtp --addr=.test-sock --addr_network=unix \
+        -f from -d to < .data
+
+nc -> 220 Hola desde expect
+
+nc <~ LHLO .*
+nc -> 250-Bienvenido!
+nc -> 250 Contame...
+
+nc <- MAIL FROM:<from>
+nc -> 250 Aja
+
+nc <- RCPT TO:<to>
+nc -> 250 Aja
+
+nc <- DATA
+nc -> 354 Dale
+
+nc <- Subject: test
+nc <-
+nc <- This is a test.
+nc <- .
+
+nc -> 250 Recibido
+
+nc <- QUIT
+nc -> 221 Chauchas
+
+mda wait 0
+