Extend .debug.* flags and hide them by default

Allow to override DNS resolver address via the -debug.dnsoverride flag
and SMTP port via -debug.smtpport.

All flags are not available unless maddy is built using the 'debugflags'
tag.

docs/man/maddy.1.scd

@@ -41,10 +41,6 @@ emptor.*
 *-debug*
 	Enable debug log. You want to use it when reporting bugs.
 
-*-debug.pprof, -debug.blockprofrate, -debug.mutexproffract*
-	These options are meant for use by developers and are not interesting for
-	end users.
-
 # Modules
 
 maddy is built of many small components called "modules". Each module does one

internal/check/dnsbl/dnsbl.go

@@ -52,7 +52,7 @@ func NewDNSBL(_, instName string, _, inlineArgs []string) (module.Module, error)
 		instName:  instName,
 		inlineBls: inlineArgs,
 
-		resolver: net.DefaultResolver,
+		resolver: dns.DefaultResolver(),
 		log:      log.Logger{Name: "dnsbl"},
 	}, nil
 }

internal/check/spf/spf.go

@@ -215,7 +215,7 @@ func (s *state) relyOnDMARC(hdr textproto.Header) bool {
 		return false
 	}
 
-	policyDomain, record, err := maddydmarc.FetchRecord(net.DefaultResolver, context.Background(), fromDomain)
+	policyDomain, record, err := maddydmarc.FetchRecord(dns.DefaultResolver(), context.Background(), fromDomain)
 	if err != nil {
 		s.log.Error("DMARC fetch", err, "from_domain", fromDomain)
 		return false

internal/check/stateless_check.go

@@ -2,7 +2,6 @@ package check
 
 import (
 	"fmt"
-	"net"
 
 	"github.com/emersion/go-message/textproto"
 	"github.com/foxcpp/maddy/internal/buffer"
@@ -152,7 +151,7 @@ func RegisterStatelessCheck(name string, defaultFailAction FailAction, connCheck
 		return &statelessCheck{
 			modName:  modName,
 			instName: instName,
-			resolver: net.DefaultResolver,
+			resolver: dns.DefaultResolver(),
 			logger:   log.Logger{Name: modName},
 
 			defaultFailAction: defaultFailAction,

internal/dns/debugflags.go

@@ -0,0 +1,11 @@
+//+build debugflags
+
+package dns
+
+import (
+	"flag"
+)
+
+func init() {
+	flag.StringVar(&overrideServ, "debug.dnsoverride", "system-default", "replace the DNS resolver address")
+}

internal/dns/dnssec.go

@@ -174,6 +174,16 @@ func NewExtResolver() (*ExtResolver, error) {
 	if err != nil {
 		return nil, err
 	}
+
+	if overrideServ != "" && overrideServ != "system-default" {
+		host, port, err := net.SplitHostPort(overrideServ)
+		if err != nil {
+			panic(err)
+		}
+		cfg.Servers = []string{host}
+		cfg.Port = port
+	}
+
 	cl := new(dns.Client)
 	cl.Dialer = &net.Dialer{
 		Timeout: time.Duration(cfg.Timeout) * time.Second,

internal/dns/override.go

@@ -0,0 +1,36 @@
+package dns
+
+import (
+	"context"
+	"net"
+	"time"
+)
+
+var (
+	overrideServ string
+)
+
+// override globally overrides the used DNS server address with one provided.
+// This function is meant only for testing. It should be called before any modules are
+// initialized to have full effect.
+//
+// The server argument is in form of "IP:PORT". It is expected that the server
+// will be available both using TCP and UDP on the same port.
+func override(server string) {
+	net.DefaultResolver.Dial = func(ctx context.Context, network, address string) (net.Conn, error) {
+		dialer := net.Dialer{
+			// This is localhost, it is either running or not. Fail quickly if
+			// we can't connect.
+			Timeout: 1 * time.Second,
+		}
+
+		switch network {
+		case "udp", "udp4", "udp6":
+			return dialer.DialContext(ctx, "udp4", server)
+		case "tcp", "tcp4", "tcp6":
+			return dialer.DialContext(ctx, "tcp4", server)
+		default:
+			panic("OverrideDNS.Dial: unknown network")
+		}
+	}
+}

internal/dns/resolver.go

@@ -2,7 +2,7 @@
 // lookups.
 //
 // Currently, there is only Resolver interface which is implemented
-// by net.DefaultResolver. In the future, DNSSEC-enabled stub resolver
+// by dns.DefaultResolver(). In the future, DNSSEC-enabled stub resolver
 // implementation will be added here.
 package dns
 
@@ -14,7 +14,7 @@ import (
 
 // Resolver is an interface that describes DNS-related methods used by maddy.
 //
-// It is implemented by net.DefaultResolver. Methods behave the same way.
+// It is implemented by dns.DefaultResolver(). Methods behave the same way.
 type Resolver interface {
 	LookupAddr(ctx context.Context, addr string) (names []string, err error)
 	LookupHost(ctx context.Context, host string) (addrs []string, err error)
@@ -33,3 +33,11 @@ func LookupAddr(ctx context.Context, r Resolver, ip net.IP) (string, error) {
 	}
 	return strings.TrimRight(names[0], "."), nil
 }
+
+func DefaultResolver() Resolver {
+	if overrideServ != "" && overrideServ != "system-default" {
+		override(overrideServ)
+	}
+
+	return net.DefaultResolver
+}

internal/endpoint/smtp/smtp.go

@@ -451,7 +451,7 @@ func New(modName string, addrs []string) (module.Module, error) {
 		addrs:      addrs,
 		submission: modName == "submission",
 		lmtp:       modName == "lmtp",
-		resolver:   net.DefaultResolver,
+		resolver:   dns.DefaultResolver(),
 		Log:        log.Logger{Name: modName},
 	}
 	return endp, nil

internal/msgpipeline/msgpipeline.go

@@ -1,8 +1,6 @@
 package msgpipeline
 
 import (
-	"net"
-
 	"github.com/emersion/go-message/textproto"
 	"github.com/emersion/go-smtp"
 	"github.com/foxcpp/maddy/internal/address"
@@ -50,7 +48,7 @@ func New(globals map[string]interface{}, cfg []config.Node) (*MsgPipeline, error
 	parsedCfg, err := parseMsgPipelineRootCfg(globals, cfg)
 	return &MsgPipeline{
 		msgpipelineCfg: parsedCfg,
-		Resolver:       net.DefaultResolver,
+		Resolver:       dns.DefaultResolver(),
 	}, err
 }
 

internal/storage/sql/sql.go

@@ -12,7 +12,6 @@ import (
 	"encoding/hex"
 	"errors"
 	"fmt"
-	"net"
 	"os"
 	"path/filepath"
 	"strconv"
@@ -145,7 +144,7 @@ func New(_, instName string, _, inlineArgs []string) (module.Module, error) {
 	store := &Storage{
 		instName: instName,
 		Log:      log.Logger{Name: "sql"},
-		resolver: net.DefaultResolver,
+		resolver: dns.DefaultResolver(),
 	}
 	if len(inlineArgs) != 0 {
 		if len(inlineArgs) == 1 {

internal/target/remote/debugflags.go

@@ -0,0 +1,9 @@
+//+build debugflags
+
+package remote
+
+import "flag"
+
+func init() {
+	flag.StringVar(&smtpPort, "debug.smtpport", "25", "SMTP port to use for connections in tests")
+}

internal/target/remote/remote.go

@@ -79,9 +79,9 @@ func New(_, instName string, _, inlineArgs []string) (module.Module, error) {
 	}
 	return &Target{
 		name:        instName,
-		resolver:    net.DefaultResolver,
+		resolver:    dns.DefaultResolver(),
 		dialer:      net.Dial,
-		mtastsCache: mtasts.Cache{Resolver: net.DefaultResolver},
+		mtastsCache: mtasts.Cache{Resolver: dns.DefaultResolver()},
 		Log:         log.Logger{Name: "remote"},
 
 		stsCacheUpdateDone: make(chan struct{}),

maddy.go

@@ -80,9 +80,10 @@ var (
 	// only for purposes of modification using -X linker flag.
 	DefaultLibexecDirectory = "/usr/lib/maddy"
 
-	profileEndpoint   = flag.String("debug.pprof", "", "enable live profiler HTTP endpoint and listen on the specified endpoint")
-	blockProfileRate  = flag.Int("debug.blockprofrate", 0, "set blocking profile rate")
-	mutexProfileFract = flag.Int("debug.mutexproffract", 0, "set mutex profile fraction)")
+	enableDebugFlags  = false
+	profileEndpoint   *string
+	blockProfileRate  *int
+	mutexProfileFract *int
 )
 
 func BuildInfo() string {
@@ -107,6 +108,13 @@ func Run() int {
 		logTargets   = flag.String("log", "stderr", "default logging target(s)")
 		printVersion = flag.Bool("v", false, "print version and exit")
 	)
+
+	if enableDebugFlags {
+		profileEndpoint = flag.String("debug.pprof", "", "enable live profiler HTTP endpoint and listen on the specified address")
+		blockProfileRate = flag.Int("debug.blockprofrate", 0, "set blocking profile rate")
+		mutexProfileFract = flag.Int("debug.mutexproffract", 0, "set mutex profile fraction")
+	}
+
 	flag.Parse()
 
 	if len(flag.Args()) != 0 {
@@ -156,6 +164,10 @@ func Run() int {
 }
 
 func initDebug() {
+	if !enableDebugFlags {
+		return
+	}
+
 	if *profileEndpoint != "" {
 		go func() {
 			log.Println("listening on", "http://"+*profileEndpoint, "for profiler requests")

maddy_debug.go

@@ -0,0 +1,11 @@
+//+build debugflags
+
+package maddy
+
+import (
+	_ "net/http/pprof"
+)
+
+func init() {
+	enableDebugFlags = true
+}