commit b8fe21e6cb27a3b0ff8fa8c5f41dd6103de6ed0f
Author: Brian C. Lane <bcl@brianlane.com>
Date: Mon, 23 Dec 2019 06:42:55 -0800
Very Simple SMTP to Maildir delivery is working
Diffstat:
| A | Makefile | | | 2 | ++ |
| A | go.mod | | | 11 | +++++++++++ |
| A | go.sum | | | 19 | +++++++++++++++++++ |
| A | main.go | | | 221 | +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ |
4 files changed, 253 insertions(+), 0 deletions(-)
diff --git a/Makefile b/Makefile
@@ -0,0 +1,2 @@
+all: main.go
+ go build
diff --git a/go.mod b/go.mod
@@ -0,0 +1,11 @@
+module github.com/bcl/letterbox
+
+go 1.13
+
+require (
+ github.com/BurntSushi/toml v0.3.1
+ github.com/bradfitz/go-smtpd v0.0.0-20170404230938-deb6d6237625
+ github.com/luksen/maildir v0.0.0-20180118131156-1859503b54bd
+ github.com/veandco/go-sdl2 v0.3.3 // indirect
+ golang.org/x/lint v0.0.0-20191125180803-fdd1cda4f05f // indirect
+)
diff --git a/go.sum b/go.sum
@@ -0,0 +1,19 @@
+github.com/BurntSushi/toml v0.3.1 h1:WXkYYl6Yr3qBf1K79EBnL4mak0OimBfB0XUf9Vl28OQ=
+github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
+github.com/McKael/madon v2.3.0+incompatible h1:xMUA+Fy4saDV+8tN3MMnwJUoYWC//5Fy8LeOqJsRNIM=
+github.com/bradfitz/go-smtpd v0.0.0-20170404230938-deb6d6237625 h1:ckJgFhFWywOx+YLEMIJsTb+NV6NexWICk5+AMSuz3ss=
+github.com/bradfitz/go-smtpd v0.0.0-20170404230938-deb6d6237625/go.mod h1:HYsPBTaaSFSlLx/70C2HPIMNZpVV8+vt/A+FMnYP11g=
+github.com/luksen/maildir v0.0.0-20180118131156-1859503b54bd h1:RjDnqXEJasth7m8Z+okAKdNCAg+Kt0w+qMvyvqW/QCI=
+github.com/luksen/maildir v0.0.0-20180118131156-1859503b54bd/go.mod h1:ZCFCeVAq3QI7TMtCH/6fr2sYqBCLeeGhda7tCQFC/m4=
+github.com/veandco/go-sdl2 v0.3.3 h1:4/TirgB2MQ7oww3pM3Yfgf1YbChMlAQAmiCPe5koK0I=
+github.com/veandco/go-sdl2 v0.3.3/go.mod h1:FB+kTpX9YTE+urhYiClnRzpOXbiWgaU3+5F2AB78DPg=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/lint v0.0.0-20191125180803-fdd1cda4f05f h1:J5lckAjkw6qYlOZNj90mLYNTEKDvWeuc1yieZ8qUzUE=
+golang.org/x/lint v0.0.0-20191125180803-fdd1cda4f05f/go.mod h1:5qLYkcX4OjUUV8bRuDixDT3tpyyb+LUpUlRWLxfhWrs=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/tools v0.0.0-20191125144606-a911d9008d1f h1:kDxGY2VmgABOe55qheT/TFqUMtcTHnomIPS1iv3G4Ms=
+golang.org/x/tools v0.0.0-20191125144606-a911d9008d1f/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
+golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
diff --git a/main.go b/main.go
@@ -0,0 +1,221 @@
+package main
+
+import (
+ "errors"
+ "flag"
+ "fmt"
+ "github.com/BurntSushi/toml"
+ "github.com/bradfitz/go-smtpd/smtpd"
+ "github.com/luksen/maildir"
+ "log"
+ "net"
+ "path"
+ "strings"
+)
+
+/* commandline flags */
+type cmdlineArgs struct {
+ Config string // Path to configuration file
+ Host string // Host IP or name to bind to
+ Port int // Port to bind to
+ Maildirs string // Path to top level of the user Maildirs
+}
+
+/* commandline defaults */
+var cmdline = cmdlineArgs{
+ Config: "letterbox.toml",
+ Host: "",
+ Port: 25,
+ Maildirs: "/var/spool/maildirs",
+}
+
+/* parseArgs handles parsing the cmdline args and setting values in the global cmdline struct */
+func parseArgs() {
+ flag.StringVar(&cmdline.Config, "config", cmdline.Config, "Path to configutation file")
+ flag.StringVar(&cmdline.Host, "host", cmdline.Host, "Host IP or name to bind to")
+ flag.IntVar(&cmdline.Port, "port", cmdline.Port, "Port to bind to")
+ flag.StringVar(&cmdline.Maildirs, "maildirs", cmdline.Maildirs, "Path to the top level of the user Maildirs")
+
+ flag.Parse()
+}
+
+type letterboxConfig struct {
+ Hosts []string `toml:"hosts"`
+ Emails []string `toml:"emails"`
+}
+
+var cfg letterboxConfig
+var allowedHosts []net.IP
+var allowedNetworks []*net.IPNet
+
+// reads a TOML configuration file and returns a slice of settings
+/*
+ Example TOML file:
+
+ hosts = ["192.168.101.0/24", "fozzy.brianlane.com", "192.168.103.15"]
+ emails = ["user@domain.com", "root@domain.com"]
+*/
+func readConfig(filename string) (letterboxConfig, error) {
+ var config letterboxConfig
+ if _, err := toml.DecodeFile(filename, &config); err != nil {
+ return config, err
+ }
+ return config, nil
+}
+
+type env struct {
+ rcpts []smtpd.MailAddress
+ destDirs []*maildir.Dir
+ deliveries []*maildir.Delivery
+ tmpfile string
+}
+
+func (e *env) AddRecipient(rcpt smtpd.MailAddress) error {
+ if strings.HasPrefix(rcpt.Email(), "bad@") {
+ return errors.New("we don't send email to bad@")
+ }
+ // Check the recipients against the whitelist. Only append ones that pass
+ e.rcpts = append(e.rcpts, rcpt)
+ return nil
+}
+
+func (e *env) BeginData() error {
+ if len(e.rcpts) == 0 {
+ return smtpd.SMTPError("554 5.5.1 Error: no valid recipients")
+ }
+
+ for _, rcpt := range e.rcpts {
+ if !strings.Contains(rcpt.Email(), "@") {
+ log.Printf("Skipping recipient: %s", rcpt)
+ continue
+ }
+ // Eliminate anything that looks like a path
+ user := path.Base(path.Clean(strings.Split(rcpt.Email(), "@")[0]))
+
+ // TODO filter recipients based on a whitelist
+
+ // Add a new maildir for each recipient
+ userDir := maildir.Dir(path.Join(cmdline.Maildirs, user))
+ if err := userDir.Create(); err != nil {
+ log.Printf("Error creating maildir for %s: %s", user, err)
+ return smtpd.SMTPError("450 Error: maildir unavailable")
+ }
+ e.destDirs = append(e.destDirs, &userDir)
+ delivery, err := userDir.NewDelivery()
+ if err != nil {
+ log.Printf("Error creating delivery for %s: %s", user, err)
+ return smtpd.SMTPError("450 Error: maildir unavailable")
+ }
+ e.deliveries = append(e.deliveries, delivery)
+ }
+ if len(e.deliveries) == 0 {
+ return smtpd.SMTPError("554 5.5.1 Error: no valid recipients")
+ }
+
+ return nil
+}
+
+func (e *env) Write(line []byte) error {
+ for _, delivery := range e.deliveries {
+ _, err := delivery.Write(line)
+ if err != nil {
+ // Delivery failed, need to close all the deliveries
+ e.Close()
+ return err
+ }
+ }
+ return nil
+}
+
+// The server really should call this with error status from outside
+func (e *env) Close() error {
+ for _, delivery := range e.deliveries {
+ err := delivery.Close()
+ if err != nil {
+ return err
+ }
+ }
+ return nil
+}
+
+func onNewConnection(c smtpd.Connection) error {
+ client, _, err := net.SplitHostPort(c.Addr().String())
+ if err != nil {
+ log.Printf("Problem parsing client address %s: %s", c.Addr().String(), err)
+ return errors.New("Problem parsing client address")
+ }
+ clientIP := net.ParseIP(client)
+ log.Printf("Connection from %s\n", clientIP.String())
+ for _, h := range allowedHosts {
+ if h.Equal(clientIP) {
+ log.Printf("Connection from %s allowed by hosts\n", clientIP.String())
+ return nil
+ }
+ }
+
+ for _, n := range allowedNetworks {
+ if n.Contains(clientIP) {
+ log.Printf("Connection from %s allowed by network\n", clientIP.String())
+ return nil
+ }
+ }
+
+ log.Printf("Connection from %s rejected\n", clientIP.String())
+ return errors.New("Client IP not allowed")
+}
+
+func onNewMail(c smtpd.Connection, from smtpd.MailAddress) (smtpd.Envelope, error) {
+ log.Printf("letterbox: new mail from %q", from)
+ return &env{}, nil
+}
+
+func main() {
+ parseArgs()
+ cfg, err := readConfig(cmdline.Config)
+ if err != nil {
+ log.Fatalf("Error reading config file %s: %s\n", cmdline.Config, err)
+ }
+ // Convert the hosts entries into IP and IPNet
+ for _, h := range cfg.Hosts {
+ // Does it look like a CIDR?
+ _, ipv4Net, err := net.ParseCIDR(h)
+ if err == nil {
+ allowedNetworks = append(allowedNetworks, ipv4Net)
+ continue
+ }
+
+ // Does it look like an IP?
+ ip := net.ParseIP(h)
+ if ip != nil {
+ allowedHosts = append(allowedHosts, ip)
+ continue
+ }
+
+ // Does it look like a hostname?
+ ips, err := net.LookupIP(h)
+ if err == nil {
+ for _, ip := range ips {
+ allowedHosts = append(allowedHosts, ip)
+ }
+ }
+ }
+ fmt.Printf("letterbox: %s:%d\n", cmdline.Host, cmdline.Port)
+ log.Println("Allowed Hosts")
+ for _, h := range allowedHosts {
+ log.Printf(" %s\n", h.String())
+ }
+ log.Println("Allowed Networks")
+ for _, n := range allowedNetworks {
+ log.Printf(" %s\n", n.String())
+ }
+
+ s := &smtpd.Server{
+ Addr: fmt.Sprintf("%s:%d", cmdline.Host, cmdline.Port),
+ OnNewConnection: onNewConnection,
+ OnNewMail: onNewMail,
+ }
+ err = s.ListenAndServe()
+ if err != nil {
+ log.Fatalf("ListenAndServe: %v", err)
+ }
+}
