Add opt-in JSON logging with structured DNS query fields (#8553)

* plugin/pkg/log: add opt-in JSON logging backend

Signed-off-by: houyuwushang <liuluoqianqiu@outlook.com>

* plugin/log: emit typed query records in JSON mode

Signed-off-by: houyuwushang <liuluoqianqiu@outlook.com>

* coremain: expose process-wide JSON logging

Signed-off-by: houyuwushang <liuluoqianqiu@outlook.com>

---------

Signed-off-by: houyuwushang <liuluoqianqiu@outlook.com>

core/dnsserver/onstartup.go

@@ -7,8 +7,17 @@ import (
 	"strings"
 
 	"github.com/coredns/coredns/plugin/pkg/dnsutil"
+	"github.com/coredns/coredns/plugin/pkg/log"
 )
 
+func printStartup(out string) {
+	if log.IsJSON() {
+		log.Info(strings.TrimSuffix(out, "\n"))
+		return
+	}
+	fmt.Print(out)
+}
+
 // checkZoneSyntax() checks whether the given string match 1035 Preferred Syntax or not.
 // The root zone, and all reverse zones always return true even though they technically don't meet 1035 Preferred Syntax
 func checkZoneSyntax(zone string) bool {

core/dnsserver/server.go

@@ -43,7 +43,6 @@ package dnsserver
 
 import (
 	"context"
-	"fmt"
 	"maps"
 	"net"
 	"runtime/debug"
@@ -504,7 +503,7 @@ func (s *Server) OnStartupComplete() {
 
 	out := startUpZones("", s.Addr, s.zones)
 	if out != "" {
-		fmt.Print(out)
+		printStartup(out)
 	}
 }
 

core/dnsserver/server_grpc.go

@@ -156,7 +156,7 @@ func (s *ServergRPC) OnStartupComplete() {
 
 	out := startUpZones(transport.GRPC+"://", s.Addr, s.zones)
 	if out != "" {
-		fmt.Print(out)
+		printStartup(out)
 	}
 }
 

core/dnsserver/server_https.go

@@ -185,7 +185,7 @@ func (s *ServerHTTPS) OnStartupComplete() {
 
 	out := startUpZones(transport.HTTPS+"://", s.Addr, s.zones)
 	if out != "" {
-		fmt.Print(out)
+		printStartup(out)
 	}
 }
 

core/dnsserver/server_https3.go

@@ -203,7 +203,7 @@ func (s *ServerHTTPS3) OnStartupComplete() {
 	}
 	out := startUpZones(transport.HTTPS3+"://", s.Addr, s.zones)
 	if out != "" {
-		fmt.Print(out)
+		printStartup(out)
 	}
 }
 

core/dnsserver/server_quic.go

@@ -315,7 +315,7 @@ func (s *ServerQUIC) OnStartupComplete() {
 
 	out := startUpZones(transport.QUIC+"://", s.Addr, s.zones)
 	if out != "" {
-		fmt.Print(out)
+		printStartup(out)
 	}
 }
 

core/dnsserver/server_tls.go

@@ -3,7 +3,6 @@ package dnsserver
 import (
 	"context"
 	"crypto/tls"
-	"fmt"
 	"net"
 	"time"
 
@@ -100,6 +99,6 @@ func (s *ServerTLS) OnStartupComplete() {
 
 	out := startUpZones(transport.TLS+"://", s.Addr, s.zones)
 	if out != "" {
-		fmt.Print(out)
+		printStartup(out)
 	}
 }