Support for configuring all command line flags via environment variab…

Dockerfile

@@ -14,7 +14,7 @@ COPY . .
 RUN CGO_ENABLED=0 go build -ldflags="-s -w" -o /bin/aws-smtp-relay
 
 FROM scratch
-COPY --from=build /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
 COPY --from=build /bin/aws-smtp-relay /bin/
-USER 65534
+COPY --from=build /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
+USER 1001
 ENTRYPOINT ["aws-smtp-relay"]

main.go

@@ -7,6 +7,8 @@ import (
 	"os"
 	"regexp"
 	"strings"
+	"strconv"
+	"log"
 
 	"github.com/blueimp/aws-smtp-relay/internal/auth"
 	"github.com/blueimp/aws-smtp-relay/internal/relay"
@@ -16,19 +18,19 @@ import (
 )
 
 var (
-	addr      = flag.String("a", ":1025", "TCP listen address")
-	name      = flag.String("n", "AWS SMTP Relay", "SMTP service name")
-	host      = flag.String("h", "", "Server hostname")
-	certFile  = flag.String("c", "", "TLS cert file")
-	keyFile   = flag.String("k", "", "TLS key file")
-	startTLS  = flag.Bool("s", false, "Require TLS via STARTTLS extension")
-	onlyTLS   = flag.Bool("t", false, "Listen for incoming TLS connections only")
-	relayAPI  = flag.String("r", "ses", "Relay API to use (ses|pinpoint)")
-	setName   = flag.String("e", "", "Amazon SES Configuration Set Name")
-	ips       = flag.String("i", "", "Allowed client IPs (comma-separated)")
-	user      = flag.String("u", "", "Authentication username")
-	allowFrom = flag.String("l", "", "Allowed sender emails regular expression")
-	denyTo    = flag.String("d", "", "Denied recipient emails regular expression")
+	addr      = flag.String("a", LookupEnvOrString("LISTEN_ADDRESS", ":1025"), "TCP listen address")
+	name      = flag.String("n", LookupEnvOrString("SMTP_SERVICE_NAME", "AWS SMTP Relay"), "SMTP service name")
+	host      = flag.String("h", LookupEnvOrString("HOSTNAME", ""), "Server hostname")
+	certFile  = flag.String("c", LookupEnvOrString("CERT_FILE", ""), "TLS cert file")
+	keyFile   = flag.String("k", LookupEnvOrString("KEY_FILE", ""), "TLS key file")
+	startTLS  = flag.Bool("s", LookupEnvOrBool("REQUIRE_STARTTLS", false), "Require TLS via STARTTLS extension (TCP PASSTHROUGH)")
+	onlyTLS   = flag.Bool("t", LookupEnvOrBool("REQUIRE_TLS", false), "Listen for incoming TLS connections only (false by default)")
+	relayAPI  = flag.String("r", LookupEnvOrString("RELAY_API", "ses"), "Relay API to use (ses|pinpoint)")
+	setName   = flag.String("e", LookupEnvOrString("SES_CONFIGURATION_SET_NAME", ""), "Amazon SES Configuration Set Name")
+	ips       = flag.String("i", LookupEnvOrString("ALLOWED_IPS", ""), "Allowed client IPs (comma-separated)")
+	user      = flag.String("u", LookupEnvOrString("AUTH_USERNAME", ""), "Authentication username")
+	allowFrom = flag.String("l", LookupEnvOrString("ALLOWED_SENDERS_REGEX", ""), "Allowed sender emails regular expression")
+	denyTo    = flag.String("d", LookupEnvOrString("DENIED_RECIPIENTS_REGEX", ""), "Denied recipient emails regular expression")
 )
 
 var ipMap map[string]bool
@@ -41,6 +43,18 @@ func server() (srv *smtpd.Server, err error) {
 	if *user != "" && len(bcryptHash) > 0 && len(password) == 0 {
 		authMechs["CRAM-MD5"] = false
 	}
+
+	// force-enable the login mechanism: only needed if there is no external routing and TLS is not configured
+	if LookupEnvOrString("ENABLE_LOGIN", "") == "true" {
+		authMechs["LOGIN"] = true
+	}
+
+	version := LookupEnvOrString("GIT_REV", "")
+	if version == "" {
+		log.Printf("Listening on %v\r\n", *addr)
+	}else{
+		log.Printf("(Revision: %s) Listening on %v\r\n", version, *addr)
+	}
 	srv = &smtpd.Server{
 		Addr:         *addr,
 		Handler:      relayClient.Send,
@@ -98,6 +112,38 @@ func configure() error {
 	return nil
 }
 
+// returns the value of an environment variable or the default value
+func LookupEnvOrString(key string, defaultVal string) string {
+	if val, ok := os.LookupEnv(key); ok {
+		return val
+	}
+	return defaultVal
+}
+
+func LookupEnvOrInt(key string, defaultVal int) int {
+	if val, ok := os.LookupEnv(key); ok {
+		v, err := strconv.Atoi(val)
+		if err != nil {
+			log.Fatalf("LookupEnvOrInt[%s]: %v", key, err)
+		}
+		return v
+	}
+	return defaultVal
+}
+
+func LookupEnvOrBool(key string, defaultVal bool) bool {
+	if val, ok := os.LookupEnv(key); ok {
+		val = strings.ToLower(val)
+		if val == "true" {
+			return true
+		}else if val == "false" {
+			return false
+		}
+		log.Fatalf("LookupEnvOrBool[%s]: invalid value %v", key, val)
+	}
+	return defaultVal
+}
+
 func main() {
 	flag.Parse()
 	var srv *smtpd.Server