all: add CLI flags for no config start

This commit adds the ability to start `ctrld` without config file. All
necessary information can be provided via command line flags, either in
base64 encoded config or launch arguments.

cmd/ctrld/cli.go

@@ -1,11 +1,15 @@
 package main
 
 import (
+	"bytes"
+	"encoding/base64"
 	"fmt"
 	"log"
+	"net"
 	"os"
 	"os/exec"
 	"runtime"
+	"strconv"
 
 	"github.com/go-playground/validator/v10"
 	"github.com/kardianos/service"
@@ -38,6 +42,7 @@ func initCLI() {
 		`verbose log output, "-v" means query logging enabled, "-vv" means debug level logging enabled`,
 	)
 
+	basicModeFlags := []string{"listen", "primary_upstream", "secondary_upstream", "domains", "log"}
 	runCmd := &cobra.Command{
 		Use:   "run",
 		Short: "Run the DNS proxy server",
@@ -49,14 +54,18 @@ func initCLI() {
 			if configPath != "" {
 				v.SetConfigFile(configPath)
 			}
-			if err := v.ReadInConfig(); err != nil {
-				if _, ok := err.(viper.ConfigFileNotFoundError); ok {
-					writeConfigFile()
-					defaultConfigWritten = true
-				} else {
-					log.Fatalf("failed to decode config file: %v", err)
+			noConfigStart := func() bool {
+				for _, flagName := range basicModeFlags {
+					if cmd.Flags().Lookup(flagName).Changed {
+						return true
+					}
 				}
-			}
+				return false
+			}()
+
+			readConfigFile(!noConfigStart && configBase64 == "")
+			readBase64Config()
+			processNoConfigFlags(noConfigStart)
 			if err := v.Unmarshal(&cfg); err != nil {
 				log.Fatalf("failed to unmarshal config: %v", err)
 			}
@@ -106,6 +115,12 @@ func initCLI() {
 	}
 	runCmd.Flags().BoolVarP(&daemon, "daemon", "d", false, "Run as daemon")
 	runCmd.Flags().StringVarP(&configPath, "config", "c", "", "Path to config file")
+	runCmd.Flags().StringVarP(&configBase64, "base64_config", "", "", "base64 encoded config")
+	runCmd.Flags().StringVarP(&listenAddress, "listen", "", "", "listener address and port, in format: address:port")
+	runCmd.Flags().StringVarP(&primaryUpstream, "primary_upstream", "", "", "primary upstream endpoint")
+	runCmd.Flags().StringVarP(&secondaryUpstream, "secondary_upstream", "", "", "secondary upstream endpoint")
+	runCmd.Flags().StringSliceVarP(&domains, "domains", "", nil, "list of domain to apply in a split DNS policy")
+	runCmd.Flags().StringVarP(&logPath, "log", "", "", "path to log file")
 
 	rootCmd.AddCommand(runCmd)
 
@@ -125,3 +140,78 @@ func writeConfigFile() {
 		log.Printf("failed to write config file: %v\n", err)
 	}
 }
+
+func readConfigFile(configWritten bool) {
+	err := v.ReadInConfig()
+	if err == nil || !configWritten {
+		return
+	}
+	if _, ok := err.(viper.ConfigFileNotFoundError); ok {
+		writeConfigFile()
+		defaultConfigWritten = true
+		return
+	}
+	log.Fatalf("failed to decode config file: %v", err)
+}
+
+func readBase64Config() {
+	if configBase64 == "" {
+		return
+	}
+	configStr, err := base64.StdEncoding.DecodeString(configBase64)
+	if err != nil {
+		log.Fatalf("invalid base64 config: %v", err)
+	}
+	if err := v.ReadConfig(bytes.NewReader(configStr)); err != nil {
+		log.Fatalf("failed to read base64 config: %v", err)
+	}
+}
+
+func processNoConfigFlags(noConfigStart bool) {
+	if !noConfigStart {
+		return
+	}
+	if listenAddress == "" || primaryUpstream == "" {
+		log.Fatal(`"listen" and "primary_upstream" flags must be set in no config mode`)
+	}
+	host, portStr, err := net.SplitHostPort(listenAddress)
+	if err != nil {
+		log.Fatalf("invalid listener address: %v", err)
+	}
+	port, err := strconv.Atoi(portStr)
+	if err != nil {
+		log.Fatalf("invalid port number: %v", err)
+	}
+	lc := &ctrld.ListenerConfig{
+		IP:   host,
+		Port: port,
+	}
+	v.Set("listener", map[string]*ctrld.ListenerConfig{
+		"0": lc,
+	})
+
+	upstream := map[string]*ctrld.UpstreamConfig{
+		"0": {
+			Name:     primaryUpstream,
+			Endpoint: primaryUpstream,
+			Type:     ctrld.ResolverTypeDOH,
+		},
+	}
+	if secondaryUpstream != "" {
+		upstream["1"] = &ctrld.UpstreamConfig{
+			Name:     secondaryUpstream,
+			Endpoint: secondaryUpstream,
+			Type:     ctrld.ResolverTypeLegacy,
+		}
+		rules := make([]ctrld.Rule, 0, len(domains))
+		for _, domain := range domains {
+			rules = append(rules, ctrld.Rule{domain: []string{"upstream.1"}})
+		}
+		lc.Policy = &ctrld.ListenerPolicyConfig{Name: "My Policy", Rules: rules}
+	}
+	v.Set("upstream", upstream)
+
+	if logPath != "" {
+		v.Set("service", ctrld.ServiceConfig{LogLevel: "debug", LogPath: logPath})
+	}
+}

cmd/ctrld/main.go

@@ -12,10 +12,16 @@ import (
 )
 
 var (
-	configPath string
-	daemon     bool
-	cfg        ctrld.Config
-	verbose    int
+	configPath        string
+	configBase64      string
+	daemon            bool
+	listenAddress     string
+	primaryUpstream   string
+	secondaryUpstream string
+	domains           []string
+	logPath           string
+	cfg               ctrld.Config
+	verbose           int
 
 	bootstrapDNS = "76.76.2.0"