Add SystemD unit file

Handle signals and gracefully shut down, waiting for clients

.github/dependabot.yml

@@ -0,0 +1,11 @@
+version: 2
+updates:
+  - package-ecosystem: "gomod"
+    directory: "/"
+    schedule:
+      interval: "daily"
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "daily"

.github/workflows/codeql-analysis.yml

@@ -0,0 +1,66 @@
+name: "CodeQL"
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    # The branches below must be a subset of the branches above
+    branches: [master]
+  schedule:
+    - cron: '0 15 * * 5'
+
+jobs:
+  analyze:
+    name: Analyze
+    runs-on: ubuntu-latest
+
+    strategy:
+      fail-fast: false
+      matrix:
+        # Override automatic language detection by changing the below list
+        # Supported options are ['csharp', 'cpp', 'go', 'java', 'javascript', 'python']
+        language: ['go']
+        # Learn more...
+        # https://docs.github.com/en/github/finding-security-vulnerabilities-and-errors-in-your-code/configuring-code-scanning#overriding-automatic-language-detection
+
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v2
+      with:
+        # We must fetch at least the immediate parents so that if this is
+        # a pull request then we can checkout the head.
+        fetch-depth: 2
+
+    # If this run was triggered by a pull request event, then checkout
+    # the head of the pull request instead of the merge commit.
+    - run: git checkout HEAD^2
+      if: ${{ github.event_name == 'pull_request' }}
+
+    # Initializes the CodeQL tools for scanning.
+    - name: Initialize CodeQL
+      uses: github/codeql-action/init@v1
+      with:
+        languages: ${{ matrix.language }}
+        # If you wish to specify custom queries, you can do so here or in a config file.
+        # By default, queries listed here will override any specified in a config file. 
+        # Prefix the list here with "+" to use these queries and those in the config file.
+        # queries: ./path/to/local/query, your-org/your-repo/queries@main
+
+    # Autobuild attempts to build any compiled languages  (C/C++, C#, or Java).
+    # If this step fails, then you should remove it and run the build manually (see below)
+    - name: Autobuild
+      uses: github/codeql-action/autobuild@v1
+
+    # ℹ️ Command-line programs to run using the OS shell.
+    # 📚 https://git.io/JvXDl
+
+    # ✏️ If the Autobuild fails above, remove it and uncomment the following three lines
+    #    and modify them (or add more) to build your code if your project
+    #    uses a compiled language
+
+    #- run: |
+    #   make bootstrap
+    #   make release
+
+    - name: Perform CodeQL Analysis
+      uses: github/codeql-action/analyze@v1

.github/workflows/go.yml

@@ -0,0 +1,24 @@
+name: Go
+on: [push]
+jobs:
+
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+    steps:
+
+    - name: Set up Go 1.15
+      uses: actions/setup-go@v2.1.3
+      with:
+        go-version: 1.15
+      id: go
+
+    - name: Check out code into the Go module directory
+      uses: actions/checkout@v1
+
+    - name: Get dependencies
+      run: |
+        go get -v -t -d ./...
+
+    - name: Build
+      run: go build -v .

.github/workflows/release.yaml

@@ -0,0 +1,30 @@
+name: Release Go Binaries
+
+on: 
+  release:
+    types: [created]
+
+jobs:
+  releases-matrix:
+    name: Release Go Binary
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        goos: [freebsd, linux, windows]
+        goarch: ["386", amd64]
+    steps:
+    - uses: actions/checkout@v2
+    
+    - name: Set APP_VERSION env
+      run: echo APP_VERSION=$(echo ${GITHUB_REF} | rev | cut -d'/' -f 1 | rev ) >> ${GITHUB_ENV}
+    - name: Set BUILD_TIME env
+      run: echo BUILD_TIME=$(date) >> ${GITHUB_ENV}
+      
+    - uses: wangyoucao577/go-release-action@v1.15
+      with:
+        github_token: ${{ secrets.GITHUB_TOKEN }}
+        goos: ${{ matrix.goos }}
+        goarch: ${{ matrix.goarch }}
+        goversion: "https://golang.org/dl/go1.15.8.linux-amd64.tar.gz"
+        extra_files: LICENSE README.md smtprelay.ini
+        ldflags: -s -w -X "main.appVersion=${{ env.APP_VERSION }}" -X "main.buildTime=${{ env.BUILD_TIME }}"

README.md

@@ -1,5 +1,7 @@
 # smtprelay
 
+[![Go Report Card](https://goreportcard.com/badge/github.com/decke/smtprelay)](https://goreportcard.com/report/github.com/decke/smtprelay)
+
 Simple Golang based SMTP relay/proxy server that accepts mail via SMTP
 and forwards it directly to another SMTP server.
 

auth.go

@@ -13,6 +13,12 @@ var (
 	filename string
 )
 
+type AuthUser struct {
+	username         string
+	passwordHash     string
+	allowedAddresses []string
+}
+
 func AuthLoadFile(file string) error {
 	f, err := os.Open(file)
 	if err != nil {
@@ -28,41 +34,67 @@ func AuthReady() bool {
 	return (filename != "")
 }
 
-func AuthFetch(username string) (string, string, error) {
-	if ! AuthReady() {
-		return "", "", errors.New("Authentication file not specified. Call LoadFile() first")
+// Split a string and ignore empty results
+// https://stackoverflow.com/a/46798310/119527
+func splitstr(s string, sep rune) []string {
+	return strings.FieldsFunc(s, func(c rune) bool { return c == sep })
+}
+
+func parseLine(line string) *AuthUser {
+	parts := strings.Fields(line)
+
+	if len(parts) < 2 || len(parts) > 3 {
+		return nil
+	}
+
+	user := AuthUser{
+		username:         parts[0],
+		passwordHash:     parts[1],
+		allowedAddresses: nil,
+	}
+
+	if len(parts) >= 3 {
+		user.allowedAddresses = splitstr(parts[2], ',')
+	}
+
+	return &user
+}
+
+func AuthFetch(username string) (*AuthUser, error) {
+	if !AuthReady() {
+		return nil, errors.New("Authentication file not specified. Call LoadFile() first")
 	}
 
 	file, err := os.Open(filename)
 	if err != nil {
-		return "", "", err
+		return nil, err
 	}
 	defer file.Close()
 
 	scanner := bufio.NewScanner(file)
 	for scanner.Scan() {
-		parts := strings.Fields(scanner.Text())
-
-		if len(parts) != 3 {
+		user := parseLine(scanner.Text())
+		if user == nil {
 			continue
 		}
 
-		if strings.ToLower(username) == strings.ToLower(parts[0]) {
-			return parts[1], parts[2], nil
+		if strings.ToLower(username) != strings.ToLower(user.username) {
+			continue
 		}
+
+		return user, nil
 	}
 
-	return "", "", errors.New("User not found")
+	return nil, errors.New("User not found")
 }
 
 func AuthCheckPassword(username string, secret string) error {
-	hash, _, err := AuthFetch(username)
+	user, err := AuthFetch(username)
 	if err != nil {
 		return err
 	}
-	if bcrypt.CompareHashAndPassword([]byte(hash), []byte(secret)) == nil {
+	if bcrypt.CompareHashAndPassword([]byte(user.passwordHash), []byte(secret)) == nil {
 		return nil
 	}
 	return errors.New("Password invalid")
 }
-

auth_test.go

@@ -0,0 +1,89 @@
+package main
+
+import (
+	"testing"
+)
+
+func stringsEqual(a, b []string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}
+
+func TestParseLine(t *testing.T) {
+	var tests = []struct {
+		name       string
+		expectFail bool
+		line       string
+		username   string
+		addrs      []string
+	}{
+		{
+			name:       "Empty line",
+			expectFail: true,
+			line:       "",
+		},
+		{
+			name:       "Too few fields",
+			expectFail: true,
+			line:       "joe",
+		},
+		{
+			name:       "Too many fields",
+			expectFail: true,
+			line:       "joe xxx joe@example.com whatsthis",
+		},
+		{
+			name:     "Normal case",
+			line:     "joe xxx joe@example.com",
+			username: "joe",
+			addrs:    []string{"joe@example.com"},
+		},
+		{
+			name:     "No allowed addrs given",
+			line:     "joe xxx",
+			username: "joe",
+			addrs:    []string{},
+		},
+		{
+			name:     "Trailing comma",
+			line:     "joe xxx joe@example.com,",
+			username: "joe",
+			addrs:    []string{"joe@example.com"},
+		},
+		{
+			name:     "Multiple allowed addrs",
+			line:     "joe xxx joe@example.com,@foo.example.com",
+			username: "joe",
+			addrs:    []string{"joe@example.com", "@foo.example.com"},
+		},
+	}
+
+	for i, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			user := parseLine(test.line)
+			if user == nil {
+				if !test.expectFail {
+					t.Errorf("parseLine() returned nil unexpectedly")
+				}
+				return
+			}
+
+			if user.username != test.username {
+				t.Errorf("Testcase %d: Incorrect username: expected %v, got %v",
+					i, test.username, user.username)
+			}
+
+			if !stringsEqual(user.allowedAddresses, test.addrs) {
+				t.Errorf("Testcase %d: Incorrect addresses: expected %v, got %v",
+					i, test.addrs, user.allowedAddresses)
+			}
+		})
+	}
+}

cmd/README.md

@@ -0,0 +1,6 @@
+
+To run the hasher, do like this
+
+```bash
+$ go run hasher.go hunter2
+```

cmd/hasher.go

@@ -0,0 +1,22 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"golang.org/x/crypto/bcrypt"
+)
+
+func main() {
+	if len(os.Args) != 2 {
+		fmt.Fprintln(os.Stderr, "Usage: hasher PASSWORD")
+		os.Exit(1)
+	}
+	password := os.Args[1]
+
+	hash, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, "Error generating hash: %s", err)
+	}
+	fmt.Println(string(hash))
+}

config.go

@@ -2,32 +2,145 @@ package main
 
 import (
 	"flag"
+	"net"
+	"regexp"
+	"net/smtp"
 
 	"github.com/vharitonsky/iniflags"
-)
-
-const (
-	VERSION = "1.2.0"
+	"github.com/sirupsen/logrus"
 )
 
 var (
-	logFile    = flag.String("logfile", "/var/log/smtprelay.log", "Path to logfile")
-	hostName   = flag.String("hostname", "localhost.localdomain", "Server hostname")
-	welcomeMsg = flag.String("welcome_msg", "", "Welcome message for SMTP session")
-	listen     = flag.String("listen", "127.0.0.1:25 [::1]:25", "Address and port to listen for incoming SMTP")
-	localCert  = flag.String("local_cert", "", "SSL certificate for STARTTLS/TLS")
-	localKey   = flag.String("local_key", "", "SSL private key for STARTTLS/TLS")
-	localForceTLS = flag.Bool("local_forcetls", false, "Force STARTTLS (needs local_cert and local_key)")
-	allowedNets = flag.String("allowed_nets", "127.0.0.1/8 ::1/128", "Networks allowed to send mails")
-	allowedSender = flag.String("allowed_sender", "", "Regular expression for valid FROM EMail adresses")
-	allowedRecipients = flag.String("allowed_recipients", "", "Regular expression for valid TO EMail adresses")
-	allowedUsers = flag.String("allowed_users", "", "Path to file with valid users/passwords")
-	remoteHost = flag.String("remote_host", "smtp.gmail.com:587", "Outgoing SMTP server")
-	remoteUser = flag.String("remote_user", "", "Username for authentication on outgoing SMTP server")
-	remotePass = flag.String("remote_pass", "", "Password for authentication on outgoing SMTP server")
-	versionInfo= flag.Bool("version", false, "Show version information")
+	appVersion = "unknown"
+	buildTime  = "unknown"
 )
 
+var (
+	logFile           = flag.String("logfile", "", "Path to logfile")
+	logFormat         = flag.String("log_format", "default", "Log output format")
+	logLevel          = flag.String("log_level", "info", "Minimum log level to output")
+	hostName          = flag.String("hostname", "localhost.localdomain", "Server hostname")
+	welcomeMsg        = flag.String("welcome_msg", "", "Welcome message for SMTP session")
+	listen            = flag.String("listen", "127.0.0.1:25 [::1]:25", "Address and port to listen for incoming SMTP")
+	localCert         = flag.String("local_cert", "", "SSL certificate for STARTTLS/TLS")
+	localKey          = flag.String("local_key", "", "SSL private key for STARTTLS/TLS")
+	localForceTLS     = flag.Bool("local_forcetls", false, "Force STARTTLS (needs local_cert and local_key)")
+	allowedNetsStr    = flag.String("allowed_nets", "127.0.0.0/8 ::1/128", "Networks allowed to send mails")
+	allowedNets       = []*net.IPNet{}
+	allowedSenderStr  = flag.String("allowed_sender", "", "Regular expression for valid FROM EMail addresses")
+	allowedSender     *regexp.Regexp
+	allowedRecipStr   = flag.String("allowed_recipients", "", "Regular expression for valid TO EMail addresses")
+	allowedRecipients *regexp.Regexp
+	allowedUsers      = flag.String("allowed_users", "", "Path to file with valid users/passwords")
+	remoteHost        = flag.String("remote_host", "", "Outgoing SMTP server")
+	remoteUser        = flag.String("remote_user", "", "Username for authentication on outgoing SMTP server")
+	remotePass        = flag.String("remote_pass", "", "Password for authentication on outgoing SMTP server")
+	remoteAuthStr     = flag.String("remote_auth", "none", "Auth method on outgoing SMTP server (none, plain, login)")
+	remoteAuth        smtp.Auth
+	remoteSender      = flag.String("remote_sender", "", "Sender e-mail address on outgoing SMTP server")
+	versionInfo       = flag.Bool("version", false, "Show version information")
+)
+
+
+func setupAllowedNetworks() {
+	for _, netstr := range splitstr(*allowedNetsStr, ' ') {
+		baseIP, allowedNet, err := net.ParseCIDR(netstr)
+		if err != nil {
+			log.WithField("netstr", netstr).
+				WithError(err).
+				Fatal("Invalid CIDR notation in allowed_nets")
+		}
+
+		// Reject any network specification where any host bits are set,
+		// meaning the address refers to a host and not a network.
+		if !allowedNet.IP.Equal(baseIP) {
+			log.WithFields(logrus.Fields{
+				"given_net": netstr,
+				"proper_net": allowedNet,
+			}).Fatal("Invalid network in allowed_nets (host bits set)")
+		}
+
+		allowedNets = append(allowedNets, allowedNet)
+	}
+}
+
+func setupAllowedPatterns() {
+	var err error
+
+	if (*allowedSenderStr != "") {
+		allowedSender, err = regexp.Compile(*allowedSenderStr)
+		if err != nil {
+			log.WithField("allowed_sender", *allowedSenderStr).
+				WithError(err).
+				Fatal("allowed_sender pattern invalid")
+		}
+	}
+
+	if (*allowedRecipStr != "") {
+		allowedRecipients, err = regexp.Compile(*allowedRecipStr)
+		if err != nil {
+			log.WithField("allowed_recipients", *allowedRecipStr).
+				WithError(err).
+				Fatal("allowed_recipients pattern invalid")
+		}
+	}
+}
+
+
+func setupRemoteAuth() {
+	logger := log.WithField("remote_auth", *remoteAuthStr)
+
+	// Remote auth disabled?
+	if *remoteAuthStr == "" || *remoteAuthStr == "none" {
+		if *remoteUser != "" {
+			logger.Fatal("remote_user given but not used")
+		}
+		if *remotePass != "" {
+			logger.Fatal("remote_pass given but not used")
+		}
+
+		// No auth; use empty default
+		return
+	}
+
+	// We need a username, password, and remote host
+	if *remoteUser == "" {
+		logger.Fatal("remote_user required but empty")
+	}
+	if *remotePass == "" {
+		logger.Fatal("remote_pass required but empty")
+	}
+	if *remoteHost == "" {
+		logger.Fatal("remote_auth without remote_host is pointless")
+	}
+
+	host, _, err := net.SplitHostPort(*remoteHost)
+	if err != nil {
+		logger.WithField("remote_host", *remoteHost).
+			   Fatal("Invalid remote_host")
+	}
+
+	switch *remoteAuthStr {
+	case "plain":
+		remoteAuth = smtp.PlainAuth("", *remoteUser, *remotePass, host)
+	case "login":
+		remoteAuth = LoginAuth(*remoteUser, *remotePass)
+	default:
+		logger.Fatal("Invalid remote_auth type")
+	}
+}
+
 func ConfigLoad() {
 	iniflags.Parse()
+
+	// Set up logging as soon as possible
+	setupLogger()
+
+	if (*remoteHost == "") {
+		log.Warn("remote_host not set; mail will not be forwarded!")
+	}
+
+	setupAllowedNetworks()
+	setupAllowedPatterns()
+	setupRemoteAuth()
 }

go.mod

@@ -1,7 +1,11 @@
-module code.bluelife.at/decke/smtprelay
+module github.com/decke/smtprelay
 
 require (
-	github.com/chrj/smtpd v0.1.2
+	github.com/chrj/smtpd v0.3.0
+	github.com/google/uuid v1.2.0
+	github.com/sirupsen/logrus v1.8.1
 	github.com/vharitonsky/iniflags v0.0.0-20180513140207-a33cd0b5f3de
-	golang.org/x/crypto v0.0.0-20181203042331-505ab145d0a9
+	golang.org/x/crypto v0.0.0-20201221181555-eec23a3978ad
 )
+
+go 1.13

go.sum

@@ -1,7 +1,24 @@
-github.com/chrj/smtpd v0.1.2 h1:yWaMOCmnPlcNgJzkak1TBhhkObAfomd+NmZG5epdO88=
-github.com/chrj/smtpd v0.1.2/go.mod h1:jt4ydELuZmqhn9hn3YpEPV1dY00aOB+Q1nWXnBDFKeY=
+github.com/chrj/smtpd v0.3.0 h1:cw1LSHDOz7N3XbkcZSF/bue9dh7ATKk5ZksfBztV6b0=
+github.com/chrj/smtpd v0.3.0/go.mod h1:1hmG9KbrE10JG1SmvG79Krh4F6713oUrw2+gRp1oSYk=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/eaigner/dkim v0.0.0-20150301120808-6fe4a7ee9cfb/go.mod h1:FSCIHbrqk7D01Mj8y/jW+NS1uoCerr+ad+IckTHTFf4=
+github.com/google/uuid v1.2.0 h1:qJYtXnJRWmpe7m/3XlyhrsLrEURqHRM2kxzoxXqyUDs=
+github.com/google/uuid v1.2.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/sirupsen/logrus v1.8.1 h1:dJKuHgqk1NNQlqoA6BTlM1Wf9DOH3NBjQyu0h9+AZZE=
+github.com/sirupsen/logrus v1.8.1/go.mod h1:yWOB1SBYBC5VeMP7gHvWumXLIWorT60ONWic61uBYv0=
+github.com/stretchr/testify v1.2.2 h1:bSDNvY7ZPG5RlJ8otE/7V6gMiyenm9RtJ7IUVIAoJ1w=
+github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
 github.com/vharitonsky/iniflags v0.0.0-20180513140207-a33cd0b5f3de h1:fkw+7JkxF3U1GzQoX9h69Wvtvxajo5Rbzy6+YMMzPIg=
 github.com/vharitonsky/iniflags v0.0.0-20180513140207-a33cd0b5f3de/go.mod h1:irMhzlTz8+fVFj6CH2AN2i+WI5S6wWFtK3MBCIxIpyI=
-golang.org/x/crypto v0.0.0-20181203042331-505ab145d0a9 h1:mKdxBk7AujPs8kU4m80U72y/zjbZ3UcXC7dClwKbUI0=
-golang.org/x/crypto v0.0.0-20181203042331-505ab145d0a9/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/crypto v0.0.0-20201221181555-eec23a3978ad h1:DN0cp81fZ3njFcrLCytUHRSUkqBjfTo4Tx9RJTWs0EY=
+golang.org/x/crypto v0.0.0-20201221181555-eec23a3978ad/go.mod h1:jdWPYTVW3xRLrWPugEBEK3UY2ZEsg3UU495nc5E+M+I=
+golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20191026070338-33540a1f6037 h1:YyJpGZS1sBuBCzLAR1VEpK193GlqGZbnPFnPV/5Rsb4=
+golang.org/x/sys v0.0.0-20191026070338-33540a1f6037/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/term v0.0.0-20201117132131-f5c789dd3221/go.mod h1:Nr5EML6q2oocZ2LXRh80K7BxOlk5/8JxuGnuhpl+muw=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=

logger.go

@@ -0,0 +1,60 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"time"
+
+	"github.com/sirupsen/logrus"
+)
+
+var (
+	log *logrus.Logger
+)
+
+func setupLogger() {
+	log = logrus.New()
+
+	// Handle logfile
+	if (*logFile == "") {
+		log.SetOutput(os.Stderr)
+	} else {
+		writer, err := os.OpenFile(*logFile, os.O_CREATE|os.O_RDWR|os.O_APPEND, 0600)
+		if err != nil {
+			fmt.Printf("cannot open log file: %s\n", err)
+			os.Exit(1)
+		}
+
+		log.SetOutput(writer)
+	}
+
+	// Handle log_format
+	switch *logFormat {
+	case "json":
+		log.SetFormatter(&logrus.JSONFormatter{
+			TimestampFormat:   time.RFC3339Nano,
+			DisableHTMLEscape: true,
+		})
+	case "plain":
+		log.SetFormatter(&logrus.TextFormatter{
+			DisableTimestamp: true,
+		})
+	case "", "default":
+		log.SetFormatter(&logrus.TextFormatter{
+			FullTimestamp: true,
+		})
+	default:
+		fmt.Fprintf(os.Stderr, "Invalid log_format: %s\n", *logFormat)
+		os.Exit(1)
+	}
+
+	// Handle log_level
+	level, err := logrus.ParseLevel(*logLevel)
+	if err != nil {
+		level = logrus.InfoLevel
+
+		log.WithField("given_level", *logLevel).
+			Warn("could not parse log level, defaulting to 'info'")
+	}
+	log.SetLevel(level)
+}

main.go

@@ -3,161 +3,292 @@ package main
 import (
 	"crypto/tls"
 	"fmt"
-	"io"
-	"log"
 	"net"
-	"net/smtp"
+	"net/textproto"
 	"os"
-	"regexp"
+	"os/signal"
 	"strings"
-	"time"
+	"syscall"
 
 	"github.com/chrj/smtpd"
+	"github.com/google/uuid"
+	"github.com/sirupsen/logrus"
 )
 
 func connectionChecker(peer smtpd.Peer) error {
-	var peerIP net.IP
-	if addr, ok := peer.Addr.(*net.TCPAddr); ok {
-		peerIP = net.ParseIP(addr.IP.String())
-	} else {
-		return smtpd.Error{Code: 421, Message: "Denied"}
+	// This can't panic because we only have TCP listeners
+	peerIP := peer.Addr.(*net.TCPAddr).IP
+
+	if len(allowedNets) == 0 {
+		// Special case: empty string means allow everything
+		return nil
 	}
 
-	nets := strings.Split(*allowedNets, " ")
-
-	for i := range(nets) {
-		_, allowedNet, _ := net.ParseCIDR(nets[i])
-
+	for _, allowedNet := range allowedNets {
 		if allowedNet.Contains(peerIP) {
 			return nil
 		}
 	}
 
+	log.WithFields(logrus.Fields{
+		"ip": peerIP,
+	}).Warn("Connection refused from address outside of allowed_nets")
 	return smtpd.Error{Code: 421, Message: "Denied"}
 }
 
+func addrAllowed(addr string, allowedAddrs []string) bool {
+	if allowedAddrs == nil {
+		// If absent, all addresses are allowed
+		return true
+	}
+
+	addr = strings.ToLower(addr)
+
+	// Extract optional domain part
+	domain := ""
+	if idx := strings.LastIndex(addr, "@"); idx != -1 {
+		domain = strings.ToLower(addr[idx+1:])
+	}
+
+	// Test each address from allowedUsers file
+	for _, allowedAddr := range allowedAddrs {
+		allowedAddr = strings.ToLower(allowedAddr)
+
+		// Three cases for allowedAddr format:
+		if idx := strings.Index(allowedAddr, "@"); idx == -1 {
+			// 1. local address (no @) -- must match exactly
+			if allowedAddr == addr {
+				return true
+			}
+		} else {
+			if idx != 0 {
+				// 2. email address (user@domain.com) -- must match exactly
+				if allowedAddr == addr {
+					return true
+				}
+			} else {
+				// 3. domain (@domain.com) -- must match addr domain
+				allowedDomain := allowedAddr[idx+1:]
+				if allowedDomain == domain {
+					return true
+				}
+			}
+		}
+	}
+
+	return false
+}
+
 func senderChecker(peer smtpd.Peer, addr string) error {
 	// check sender address from auth file if user is authenticated
 	if *allowedUsers != "" && peer.Username != "" {
-		_, email, err := AuthFetch(peer.Username)
+		user, err := AuthFetch(peer.Username)
 		if err != nil {
+			// Shouldn't happen: authChecker already validated username+password
+			log.WithFields(logrus.Fields{
+				"peer": peer.Addr,
+				"username": peer.Username,
+			}).WithError(err).Warn("could not fetch auth user")
 			return smtpd.Error{Code: 451, Message: "Bad sender address"}
 		}
 
-		if strings.ToLower(addr) != strings.ToLower(email) {
+		if !addrAllowed(addr, user.allowedAddresses) {
+			log.WithFields(logrus.Fields{
+				"peer": peer.Addr,
+				"username": peer.Username,
+				"sender_address": addr,
+			}).Warn("sender address not allowed for authenticated user")
 			return smtpd.Error{Code: 451, Message: "Bad sender address"}
 		}
 	}
 
-	if *allowedSender == "" {
+	if allowedSender == nil {
+		// Any sender is permitted
 		return nil
 	}
 
-	re, err := regexp.Compile(*allowedSender)
-	if err != nil {
-		log.Printf("allowed_sender invalid: %v\n", err)
-		return smtpd.Error{Code: 451, Message: "Bad sender address"}
-	}
-
-	if re.MatchString(addr) {
+	if allowedSender.MatchString(addr) {
+		// Permitted by regex
 		return nil
 	}
 
+	log.WithFields(logrus.Fields{
+		"sender_address": addr,
+		"peer": peer.Addr,
+	}).Warn("sender address not allowed by allowed_sender pattern")
 	return smtpd.Error{Code: 451, Message: "Bad sender address"}
 }
 
 func recipientChecker(peer smtpd.Peer, addr string) error {
-	if *allowedRecipients == "" {
+	if allowedRecipients == nil {
+		// Any recipient is permitted
 		return nil
 	}
 
-	re, err := regexp.Compile(*allowedRecipients)
-	if err != nil {
-		log.Printf("allowed_recipients invalid: %v\n", err)
-		return smtpd.Error{Code: 451, Message: "Bad recipient address"}
-	}
-
-	if re.MatchString(addr) {
+	if allowedRecipients.MatchString(addr) {
+		// Permitted by regex
 		return nil
 	}
 
+	log.WithFields(logrus.Fields{
+		"peer": peer.Addr,
+		"recipient_address": addr,
+	}).Warn("recipient address not allowed by allowed_recipients pattern")
 	return smtpd.Error{Code: 451, Message: "Bad recipient address"}
 }
 
 func authChecker(peer smtpd.Peer, username string, password string) error {
 	err := AuthCheckPassword(username, password)
 	if err != nil {
-		log.Printf("Auth error: %v\n", err)
+		log.WithFields(logrus.Fields{
+			"peer": peer.Addr,
+			"username": username,
+		}).WithError(err).Warn("auth error")
 		return smtpd.Error{Code: 535, Message: "Authentication credentials invalid"}
 	}
 	return nil
 }
 
 func mailHandler(peer smtpd.Peer, env smtpd.Envelope) error {
-	if *allowedUsers != "" && peer.Username == "" {
-		return smtpd.Error{Code: 530, Message: "Authentication Required"}
-	}
-
 	peerIP := ""
 	if addr, ok := peer.Addr.(*net.TCPAddr); ok {
 		peerIP = addr.IP.String()
 	}
 
-	log.Printf("new mail from=<%s> to=%s peer=[%s]\n", env.Sender,
-		env.Recipients, peerIP)
+	logger := log.WithFields(logrus.Fields{
+		"from": env.Sender,
+		"to": env.Recipients,
+		"peer": peerIP,
+		"host": *remoteHost,
+		"uuid": generateUUID(),
+	})
 
-	var auth smtp.Auth
-	host, _, _ := net.SplitHostPort(*remoteHost)
-
-	if *remoteUser != "" && *remotePass != "" {
-		auth = smtp.PlainAuth("", *remoteUser, *remotePass, host)
+	if (*remoteHost == "") {
+		logger.Warning("remote_host not set; discarding mail")
+		return nil
 	}
 
+	logger.Info("delivering mail from peer using smarthost")
+
 	env.AddReceivedLine(peer)
 
-	log.Printf("delivering using smarthost %s\n", *remoteHost)
+	var sender string
+
+	if *remoteSender == "" {
+		sender = env.Sender
+	} else {
+		sender = *remoteSender
+	}
 
 	err := SendMail(
 		*remoteHost,
-		auth,
-		env.Sender,
+		remoteAuth,
+		sender,
 		env.Recipients,
 		env.Data,
 	)
 	if err != nil {
-		log.Printf("delivery failed: %v\n", err);
-		return smtpd.Error{Code: 554, Message: "Forwarding failed"}
+		var smtpError smtpd.Error
+
+		switch err.(type) {
+		case *textproto.Error:
+			err := err.(*textproto.Error)
+			smtpError = smtpd.Error{Code: err.Code, Message: err.Msg}
+
+			logger.WithFields(logrus.Fields{
+				"err_code": err.Code,
+				"err_msg": err.Msg,
+			}).Error("delivery failed")
+		default:
+			smtpError = smtpd.Error{Code: 554, Message: "Forwarding failed"}
+
+			logger.WithError(err).
+				Error("delivery failed")
+		}
+
+		return smtpError
 	}
 
-	log.Printf("%s delivery successful\n", env.Recipients)
-
+	logger.Debug("delivery successful")
 	return nil
 }
 
-func main() {
+func generateUUID() string {
+	uniqueID, err := uuid.NewRandom()
 
+	if err != nil {
+		log.WithError(err).
+			Error("could not generate UUIDv4")
+
+		return ""
+	}
+
+	return uniqueID.String()
+}
+
+func getTLSConfig() *tls.Config {
+	// Ciphersuites as defined in stock Go but without 3DES and RC4
+	// https://golang.org/src/crypto/tls/cipher_suites.go
+	var tlsCipherSuites = []uint16{
+		tls.TLS_AES_128_GCM_SHA256,
+		tls.TLS_AES_256_GCM_SHA384,
+		tls.TLS_CHACHA20_POLY1305_SHA256,
+		tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256,
+		tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256,
+		tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
+		tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
+		tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
+		tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
+		tls.TLS_RSA_WITH_AES_128_GCM_SHA256, // does not provide PFS
+		tls.TLS_RSA_WITH_AES_256_GCM_SHA384, // does not provide PFS
+	}
+
+	if *localCert == "" || *localKey == "" {
+		log.WithFields(logrus.Fields{
+			"cert_file": *localCert,
+			"key_file": *localKey,
+		}).Fatal("TLS certificate/key file not defined in config")
+	}
+
+	cert, err := tls.LoadX509KeyPair(*localCert, *localKey)
+	if err != nil {
+		log.WithField("error", err).
+			Fatal("cannot load X509 keypair")
+	}
+
+	return &tls.Config{
+		PreferServerCipherSuites: true,
+		MinVersion:               tls.VersionTLS12,
+		CipherSuites:             tlsCipherSuites,
+		Certificates:             []tls.Certificate{cert},
+	}
+}
+
+func main() {
 	ConfigLoad()
 
 	if *versionInfo {
-		fmt.Printf("smtprelay/%s\n", VERSION)
+		fmt.Printf("smtprelay/%s (%s)\n", appVersion, buildTime)
 		os.Exit(0)
 	}
 
-	if *logFile != "" {
-		f, err := os.OpenFile(*logFile, os.O_WRONLY | os.O_CREATE | os.O_APPEND, 0600)
-		if err != nil {
-			log.Fatalf("Error opening logfile: %v", err)
-		}
-		defer f.Close()
+	log.WithField("version", appVersion).
+		Debug("starting smtprelay")
 
-		log.SetOutput(io.MultiWriter(os.Stdout, f))
+	// Load allowed users file
+	if *allowedUsers != "" {
+		err := AuthLoadFile(*allowedUsers)
+		if err != nil {
+			log.WithField("file", *allowedUsers).
+				WithError(err).
+				Fatal("cannot load allowed users file")
+		}
 	}
 
-	listeners := strings.Split(*listen, " ")
-
-	for i := range(listeners) {
-		listener := listeners[i]
+	var servers []*smtpd.Server
 
+	// Create a server for each desired listen address
+	for _, listenAddr := range strings.Split(*listen, " ") {
 		server := &smtpd.Server{
 			Hostname:          *hostName,
 			WelcomeMessage:    *welcomeMsg,
@@ -168,67 +299,84 @@ func main() {
 		}
 
 		if *allowedUsers != "" {
-			err := AuthLoadFile(*allowedUsers)
-			if err != nil {
-				log.Fatalf("Authentication file: %s\n", err)
-			}
-
 			server.Authenticator = authChecker
 		}
 
-		if strings.Index(listeners[i], "://") == -1 {
-			log.Printf("Listen on %s ...\n", listener)
-			go server.ListenAndServe(listener)
-		} else if strings.HasPrefix(listeners[i], "starttls://") {
-			listener = strings.TrimPrefix(listener, "starttls://")
+		var lsnr net.Listener
+		var err error
 
-			if *localCert == "" || *localKey == "" {
-				log.Fatal("TLS certificate/key not defined in config")
-			}
+		if strings.Index(listenAddr, "://") == -1 {
+			log.WithField("address", listenAddr).
+				Info("listening on address")
 
-			cert, err := tls.LoadX509KeyPair(*localCert, *localKey)
-			if err != nil {
-				log.Fatal(err)
-			}
+			lsnr, err = net.Listen("tcp", listenAddr)
+		} else if strings.HasPrefix(listenAddr, "starttls://") {
+			listenAddr = strings.TrimPrefix(listenAddr, "starttls://")
 
-			server.TLSConfig = &tls.Config {
-				Certificates: [] tls.Certificate{cert},
-			}
+			server.TLSConfig = getTLSConfig()
 			server.ForceTLS = *localForceTLS
 
-			log.Printf("Listen on %s (STARTSSL) ...\n", listener)
-			lsnr, err := net.Listen("tcp", listener)
-			defer lsnr.Close()
+			log.WithField("address", listenAddr).
+				Info("listening on address (STARTTLS)")
+			lsnr, err = net.Listen("tcp", listenAddr)
+		} else if strings.HasPrefix(listenAddr, "tls://") {
+			listenAddr = strings.TrimPrefix(listenAddr, "tls://")
 
-			go server.Serve(lsnr)
-		} else if strings.HasPrefix(listeners[i], "tls://") {
+			server.TLSConfig = getTLSConfig()
 
-			listener = strings.TrimPrefix(listener, "tls://")
-
-			if *localCert == "" || *localKey == "" {
-				log.Fatal("TLS certificate/key not defined in config")
-			}
-
-			cert, err := tls.LoadX509KeyPair(*localCert, *localKey)
-			if err != nil {
-				log.Fatal(err)
-			}
-
-			server.TLSConfig = &tls.Config {
-				Certificates: [] tls.Certificate{cert},
-			}
-
-			log.Printf("Listen on %s (TLS) ...\n", listener)
-			lsnr, err := tls.Listen("tcp", listener, server.TLSConfig)
-			defer lsnr.Close()
-
-			go server.Serve(lsnr)
+			log.WithField("address", listenAddr).
+				Info("listening on address (TLS)")
+			lsnr, err = tls.Listen("tcp", listenAddr, server.TLSConfig)
 		} else {
-			log.Fatal("Unknown protocol in listener ", listener)
+			log.WithField("address", listenAddr).
+				Fatal("unknown protocol in listen address")
+		}
+
+		if err != nil {
+			log.WithFields(logrus.Fields{
+				"address": listenAddr,
+			}).WithError(err).Fatal("error starting listener")
+		}
+		servers = append(servers, server)
+
+		go func() {
+			server.Serve(lsnr)
+		}()
+	}
+
+	handleSignals()
+
+	// First close the listeners
+	for _, server := range servers {
+		logger := log.WithField("address", server.Address())
+		logger.Debug("Shutting down server")
+		err := server.Shutdown(false)
+		if err != nil {
+			logger.WithError(err).
+				Warning("Shutdown failed")
 		}
 	}
 
-	for true {
-		time.Sleep(time.Minute)
+	// Then wait for the clients to exit
+	for _, server := range servers {
+		logger := log.WithField("address", server.Address())
+		logger.Debug("Waiting for server")
+		err := server.Wait()
+		if err != nil {
+			logger.WithError(err).
+				Warning("Wait failed")
+		}
 	}
+
+	log.Debug("done")
+}
+
+func handleSignals() {
+	// Wait for SIGINT, SIGQUIT, or SIGTERM
+	sigs := make(chan os.Signal, 1)
+	signal.Notify(sigs, syscall.SIGINT, syscall.SIGQUIT, syscall.SIGTERM)
+	sig := <-sigs
+
+	log.WithField("signal", sig).
+		Info("shutting down in response to received signal")
 }

main_test.go

@@ -0,0 +1,94 @@
+package main
+
+import (
+	"testing"
+)
+
+func TestAddrAllowedNoDomain(t *testing.T) {
+	allowedAddrs := []string{"joe@abc.com"}
+	if addrAllowed("bob.com", allowedAddrs) {
+		t.FailNow()
+	}
+}
+
+func TestAddrAllowedSingle(t *testing.T) {
+	allowedAddrs := []string{"joe@abc.com"}
+
+	if !addrAllowed("joe@abc.com", allowedAddrs) {
+		t.FailNow()
+	}
+	if addrAllowed("bob@abc.com", allowedAddrs) {
+		t.FailNow()
+	}
+}
+
+func TestAddrAllowedDifferentCase(t *testing.T) {
+	allowedAddrs := []string{"joe@abc.com"}
+	testAddrs := []string{
+		"joe@ABC.com",
+		"Joe@abc.com",
+		"JOE@abc.com",
+		"JOE@ABC.COM",
+	}
+	for _, addr := range testAddrs {
+		if !addrAllowed(addr, allowedAddrs) {
+			t.Errorf("Address %v not allowed, but should be", addr)
+		}
+	}
+}
+
+func TestAddrAllowedLocal(t *testing.T) {
+	allowedAddrs := []string{"joe"}
+
+	if !addrAllowed("joe", allowedAddrs) {
+		t.FailNow()
+	}
+	if addrAllowed("bob", allowedAddrs) {
+		t.FailNow()
+	}
+}
+
+func TestAddrAllowedMulti(t *testing.T) {
+	allowedAddrs := []string{"joe@abc.com", "bob@def.com"}
+	if !addrAllowed("joe@abc.com", allowedAddrs) {
+		t.FailNow()
+	}
+	if !addrAllowed("bob@def.com", allowedAddrs) {
+		t.FailNow()
+	}
+	if addrAllowed("bob@abc.com", allowedAddrs) {
+		t.FailNow()
+	}
+}
+
+func TestAddrAllowedSingleDomain(t *testing.T) {
+	allowedAddrs := []string{"@abc.com"}
+	if !addrAllowed("joe@abc.com", allowedAddrs) {
+		t.FailNow()
+	}
+	if addrAllowed("joe@def.com", allowedAddrs) {
+		t.FailNow()
+	}
+}
+
+func TestAddrAllowedMixed(t *testing.T) {
+	allowedAddrs := []string{"app", "app@example.com", "@appsrv.example.com"}
+	if !addrAllowed("app", allowedAddrs) {
+		t.FailNow()
+	}
+	if !addrAllowed("app@example.com", allowedAddrs) {
+		t.FailNow()
+	}
+	if addrAllowed("ceo@example.com", allowedAddrs) {
+		t.FailNow()
+	}
+	if !addrAllowed("root@appsrv.example.com", allowedAddrs) {
+		t.FailNow()
+	}
+	if !addrAllowed("dev@appsrv.example.com", allowedAddrs) {
+		t.FailNow()
+	}
+	if addrAllowed("appsrv@example.com", allowedAddrs) {
+		t.FailNow()
+	}
+}

service_files/smtprelay.service

@@ -0,0 +1,11 @@
+[Unit]
+Description=SMTP Relay
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+ExecStart=/opt/smtprelay/bin/smtprelay -config /etc/smtprelay/smtprelay.ini
+
+[Install]
+WantedBy=multi-user.target

smtp.go

@@ -242,7 +242,8 @@ func (c *Client) Auth(a smtp.Auth) error {
 
 // Mail issues a MAIL command to the server using the provided email address.
 // If the server supports the 8BITMIME extension, Mail adds the BODY=8BITMIME
-// parameter.
+// parameter. If the server supports the SMTPUTF8 extension, Mail adds the
+// SMTPUTF8 parameter.
 // This initiates a mail transaction and is followed by one or more Rcpt calls.
 func (c *Client) Mail(from string) error {
 	if err := validateLine(from); err != nil {
@@ -256,6 +257,9 @@ func (c *Client) Mail(from string) error {
 		if _, ok := c.ext["8BITMIME"]; ok {
 			cmdStr += " BODY=8BITMIME"
 		}
+		if _, ok := c.ext["SMTPUTF8"]; ok {
+			cmdStr += " SMTPUTF8"
+		}
 	}
 	_, _, err := c.cmd(250, cmdStr, from)
 	return err
@@ -451,3 +455,30 @@ func validateLine(line string) error {
 	}
 	return nil
 }
+
+// LOGIN authentication
+type loginAuth struct {
+	username, password string
+}
+
+func LoginAuth(username, password string) smtp.Auth {
+	return &loginAuth{username, password}
+}
+
+func (a *loginAuth) Start(server *smtp.ServerInfo) (string, []byte, error) {
+	return "LOGIN", []byte{}, nil
+}
+
+func (a *loginAuth) Next(fromServer []byte, more bool) ([]byte, error) {
+	if more {
+		switch string(fromServer) {
+		case "Username:":
+			return []byte(a.username), nil
+		case "Password:":
+			return []byte(a.password), nil
+		default:
+			return nil, errors.New("Unknown fromServer")
+		}
+	}
+	return nil, nil
+}

smtprelay.ini

@@ -1,7 +1,13 @@
 ; smtprelay configuration
 
-; Logfile
-;logfile = /var/log/smtprelay.log
+; Logfile (blank/default is stderr)
+;logfile = 
+
+; Log format: default, plain (no timestamp), json
+;log_format = "default"
+
+; Log level: panic, fatal, error, warn, info, debug, trace
+;log_level = "info"
 
 ; Hostname for this SMTP server
 ;hostname = "localhost.localdomain"
@@ -25,22 +31,33 @@
 ;local_forcetls = false
 
 ; Networks that are allowed to send mails to us
-;allowed_nets = 127.0.0.1/8 ::1/128
+; Defaults to localhost. If set to "", then any address is allowed.
+;allowed_nets = 127.0.0.0/8 ::1/128
 
-; Regular expression for valid FROM EMail adresses
+; Regular expression for valid FROM EMail addresses
+; If set to "", then any sender is permitted.
 ; Example: ^(.*)@localhost.localdomain$
 ;allowed_sender =
 
-; Regular expression for valid TO EMail adresses
+; Regular expression for valid TO EMail addresses
+; If set to "", then any recipient is permitted.
 ; Example: ^(.*)@localhost.localdomain$
 ;allowed_recipients =
 
 ; File which contains username and password used for
 ; authentication before they can send mail.
-; File format: username bcrypt-hash email
+; File format: username bcrypt-hash [email[,email[,...]]]
+;   username: The SMTP auth username
+;   bcrypt-hash: The bcrypt hash of the pasword (generate with "./hasher password")
+;   email: Comma-separated list of allowed "from" addresses:
+;          - If omitted, user can send from any address
+;          - If @domain.com is given, user can send from any address @domain.com
+;          - Otherwise, email address must match exactly (case-insensitive)
+;          E.g. "app@example.com,@appsrv.example.com"
 ;allowed_users =
 
-; Relay all mails to this SMTP server
+; Relay all mails to this SMTP server.
+; If not set, mails are discarded.
 
 ; GMail
 ;remote_host = smtp.gmail.com:587
@@ -54,3 +71,10 @@
 ; Authentication credentials on outgoing SMTP server
 ;remote_user =
 ;remote_pass =
+
+; Authentication method on outgoing SMTP server
+; (none, plain, login)
+;remote_auth = none
+
+; Sender e-mail address on outgoing SMTP server
+;remote_sender =