Implement Rate Limit per remote

.gitignore

@@ -0,0 +1,2 @@
+.env
+smtprelay

Dockerfile

@@ -0,0 +1,22 @@
+FROM golang:1.22-alpine AS build
+
+WORKDIR /app
+
+COPY go.mod ./
+COPY go.sum ./
+
+RUN go mod download
+
+COPY *.go ./
+
+RUN go build -o smtprelay
+
+FROM golang:1.22-alpine
+
+WORKDIR /app
+
+COPY --from=build /app/smtprelay ./
+
+EXPOSE 25
+
+ENTRYPOINT ["./smtprelay"]

README.md

@@ -5,7 +5,6 @@
 Simple Golang based SMTP relay/proxy server that accepts mail via SMTP
 and forwards it directly to another SMTP server.
 
-
 ## Why another SMTP server?
 
 Outgoing mails are usually send via SMTP to an MTA (Mail Transfer Agent)
@@ -19,7 +18,6 @@ cron via msmtp/sSMTP/dma, mails from various services and network printers
 via a remote SMTP server without giving away my mail credentials to each
 device which produces mail.
 
-
 ## Main features
 
 * Simple configuration with ini file .env file or environment variables
@@ -30,3 +28,7 @@ device which produces mail.
 * Forwards all mail to a smarthost (any SMTP server)
 * Small codebase
 * IPv6 support
+
+## Rate Limit
+
+* Add rate limit option in remote (?rate=1/1h) using <https://github.com/sethvargo/go-limiter>

go.mod

@@ -10,12 +10,16 @@ require (
 )
 
 require (
+	github.com/Hepri/rate_limiter v0.0.0-20170628005159-cf154f46b333 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/kr/pretty v0.3.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/sethvargo/go-limiter v1.0.0 // indirect
 	golang.org/x/sys v0.19.0 // indirect
 	gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )
 
-go 1.20
+go 1.22
+
+toolchain go1.22.2

go.sum

@@ -1,3 +1,5 @@
+github.com/Hepri/rate_limiter v0.0.0-20170628005159-cf154f46b333 h1:JlFmeHM9nEHCfGlMYlZBHSqb1T7JtwdSMtQKVl829IU=
+github.com/Hepri/rate_limiter v0.0.0-20170628005159-cf154f46b333/go.mod h1:SSFHoCFNk9cmyeMoZcuhDiInWAF/JdyFEG7kHfu9rp4=
 github.com/chrj/smtpd v0.3.1 h1:kogHFkbFdKaoH3bgZkqNC9uVtKYOFfM3uV3rroBdooE=
 github.com/chrj/smtpd v0.3.1/go.mod h1:JtABvV/LzvLmEIzy0NyDnrfMGOMd8wy5frAokwf6J9Q=
 github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ33E=
@@ -20,6 +22,8 @@ github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZb
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/rogpeppe/go-internal v1.9.0 h1:73kH8U+JUqXU8lRuOHeVHaa/SZPifC7BkcraZVejAe8=
 github.com/rogpeppe/go-internal v1.9.0/go.mod h1:WtVeX8xhTBvf0smdhujwtBcq4Qrzq/fJaraNFVN+nFs=
+github.com/sethvargo/go-limiter v1.0.0 h1:JqW13eWEMn0VFv86OKn8wiYJY/m250WoXdrjRV0kLe4=
+github.com/sethvargo/go-limiter v1.0.0/go.mod h1:01b6tW25Ap+MeLYBuD4aHunMrJoNO5PVUFdS9rac3II=
 github.com/sirupsen/logrus v1.9.3 h1:dueUQJ1C2q9oE3F7wvmSGAaVtTmUizReu6fjN8uqzbQ=
 github.com/sirupsen/logrus v1.9.3/go.mod h1:naHLuLoDiP4jHNo9R0sCBMtWGeIprob74mVsIT4qYEQ=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=

main.go

@@ -195,7 +195,7 @@ func mailHandler(peer smtpd.Peer, env smtpd.Envelope) error {
 		environ = append(environ, fmt.Sprintf("%s=%s", "SMTPRELAY_PEER", peerIP))
 
 		cmd := exec.Cmd{
-			Env: environ,
+			Env:  environ,
 			Path: *command,
 		}
 

remotes.go

@@ -4,16 +4,23 @@ import (
 	"fmt"
 	"net/smtp"
 	"net/url"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/sethvargo/go-limiter"
+	"github.com/sethvargo/go-limiter/memorystore"
 )
 
 type Remote struct {
-	SkipVerify bool
-	Auth       smtp.Auth
-	Scheme     string
-	Hostname   string
-	Port       string
-	Addr       string
-	Sender     string
+	SkipVerify  bool
+	Auth        smtp.Auth
+	Scheme      string
+	Hostname    string
+	Port        string
+	Addr        string
+	Sender      string
+	RateLimiter *limiter.Store
 }
 
 // ParseRemote creates a remote from a given url in the following format:
@@ -25,6 +32,7 @@ type Remote struct {
 // Supported Params:
 // - skipVerify: can be "true" or empty to prevent ssl verification of remote server's certificate.
 // - auth: can be "login" to trigger "LOGIN" auth instead of "PLAIN" auth
+// - rate: an optional rate limiter in the format <msgs>/<time unit> like 100/1h
 func ParseRemote(remoteURL string) (*Remote, error) {
 	u, err := url.Parse(remoteURL)
 	if err != nil {
@@ -79,5 +87,22 @@ func ParseRemote(remoteURL string) (*Remote, error) {
 		r.Sender = u.Path[1:]
 	}
 
+	if hasVal, rate := q.Has("rate"), q.Get("rate"); hasVal && strings.Contains(rate, "/") {
+		i, err := strconv.ParseInt(strings.Split(rate, "/")[0], 10, 32)
+		if err == nil {
+			t, err := time.ParseDuration(strings.Split(rate, "/")[1])
+			log.Infof("Configuring rate limiter %v/%v", i, t)
+			if err == nil {
+				store, err := memorystore.New(&memorystore.Config{
+					Tokens:   uint64(i),
+					Interval: t,
+				})
+				if err == nil {
+					r.RateLimiter = &store
+				}
+			}
+		}
+	}
+
 	return r, nil
 }

smtp.go

@@ -18,6 +18,7 @@
 package main
 
 import (
+	"context"
 	"crypto/tls"
 	"encoding/base64"
 	"errors"
@@ -27,6 +28,8 @@ import (
 	"net/smtp"
 	"net/textproto"
 	"strings"
+
+	"github.com/chrj/smtpd"
 )
 
 // A Client represents a client connection to an SMTP server.
@@ -321,6 +324,13 @@ var testHookStartTLS func(*tls.Config) // nil, except for tests
 // functionality. Higher-level packages exist outside of the standard
 // library.
 func SendMail(r *Remote, from string, to []string, msg []byte) error {
+	if r.RateLimiter != nil {
+		tokens, remaining, _, ok, err := (*r.RateLimiter).Take(context.Background(), "")
+		if err != nil || !ok {
+			return smtpd.Error{Code: 452, Message: "Rate limit reached"}
+		}
+		log.Debugf("Remaining %v tokens of %v", remaining, tokens)
+	}
 	if r.Sender != "" {
 		from = r.Sender
 	}