dns: add debugging for request, forwarding, and response

If debug.Value is set to value greater than 1, server will print each
processed request, forward, and response.
The debug information prefixed with single character to differentiate
single action,

	< : incoming request from client
	> : the answer is sent to client
	! : no answer found on cache and the query is not recursive
	^ : request is forwarded to parent name server
	- : answer exist on cache but its expired
	+ : new answer is added to caches
	# : the expired answer is renewed and updated on caches

Following the prefix is message ID and question, separated by colon.

1 files changed, 75 insertions, 8 deletions

diff --git a/lib/dns/server.go b/lib/dns/server.go
index df98d0e1..d5650e6a 100644
--- a/lib/dns/server.go
+++ b/lib/dns/server.go
@@ -17,6 +17,8 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+
+	"github.com/shuLhan/share/lib/debug"
 )
 
 //
@@ -40,6 +42,23 @@ import (
 // it is used to prune least frequently accessed answers.
 // Local caches will never get pruned.
 //
+// Debugging
+//
+// If debug.Value is set to value greater than 1, server will print each
+// processed request, forward, and response.
+// The debug information prefixed with single character to differentiate
+// single action,
+//
+//	< : incoming request from client
+//	> : the answer is sent to client
+//	! : no answer found on cache and the query is not recursive
+//	^ : request is forwarded to parent name server
+//	- : answer exist on cache but its expired
+//	+ : new answer is added to caches
+//	# : the expired answer is renewed and updated on caches
+//
+// Following the prefix is message ID and question, separated by colon.
+//
 type Server struct {
 	opts        *ServerOptions
 	errListener chan error
@@ -499,6 +518,11 @@ func (srv *Server) processRequest() {
 	)
 
 	for req := range srv.requestq {
+		if debug.Value >= 1 {
+			fmt.Printf("dns: < %d:%s\n", req.message.Header.ID,
+				req.message.Question)
+		}
+
 		ans, an := srv.caches.get(string(req.message.Question.Name),
 			req.message.Question.Type,
 			req.message.Question.Class)
@@ -521,14 +545,29 @@ func (srv *Server) processRequest() {
 			req.message.SetQuery(false)
 			req.message.SetAuthorativeAnswer(true)
 			res = req.message
+
+			if debug.Value >= 1 {
+				fmt.Printf("dns: ! %d:%s\n",
+					res.Header.ID, res.Question)
+			}
 		} else {
 			if an.msg.IsExpired() && srv.hasForwarders {
+				if debug.Value >= 1 {
+					fmt.Printf("dns: - %d:%s\n",
+						req.message.Header.ID,
+						req.message.Question)
+				}
 				srv.forwardq <- req
 				continue
 			}
 
 			an.msg.SetID(req.message.Header.ID)
 			res = an.msg
+
+			if debug.Value >= 1 {
+				fmt.Printf("dns: > %d:%s\n",
+					res.Header.ID, res.Question)
+			}
 		}
 
 		srv.processResponse(req, res, true)
@@ -538,6 +577,9 @@ func (srv *Server) processRequest() {
 func (srv *Server) processResponse(req *request, res *Message, isLocal bool) {
 	if !isLocal {
 		if !isResponseValid(req, res) {
+			log.Printf("dns: invalid response, got %d:%s, want %d:%s\n",
+				req.message.Header.ID, req.message.Question,
+				res.Header.ID, res.Question)
 			return
 		}
 	}
@@ -548,15 +590,25 @@ func (srv *Server) processResponse(req *request, res *Message, isLocal bool) {
 		return
 	}
 
-	if !isLocal {
-		if res.Header.RCode != 0 {
-			log.Printf("dns: response error %s, code: %s\n",
-				res.Question, rcodeNames[res.Header.RCode])
-			return
-		}
+	if isLocal {
+		return
+	}
+
+	if res.Header.RCode != 0 {
+		log.Printf("dns: response error %s, code: %s\n",
+			res.Question, rcodeNames[res.Header.RCode])
+		return
+	}
 
-		an := newAnswer(res, false)
-		srv.caches.upsert(an)
+	an := newAnswer(res, false)
+	inserted := srv.caches.upsert(an)
+
+	if debug.Value >= 1 {
+		if inserted {
+			fmt.Printf("dns: + %d:%s\n", res.Header.ID, res.Question)
+		} else {
+			fmt.Printf("dns: # %d:%s\n", res.Header.ID, res.Question)
+		}
 	}
 }
 
@@ -589,6 +641,11 @@ func (srv *Server) runDohForwarder(nameserver string) {
 	}
 
 	for req := range srv.forwardq {
+		if debug.Value >= 1 {
+			fmt.Printf("dns: ^ %d:%s\n", req.message.Header.ID,
+				req.message.Question)
+		}
+
 		res, err := forwarder.Query(req.message)
 		if err != nil {
 			log.Println("dns: failed to query DoH: " + err.Error())
@@ -601,6 +658,11 @@ func (srv *Server) runDohForwarder(nameserver string) {
 
 func (srv *Server) runTCPForwarder(remoteAddr *net.TCPAddr) {
 	for req := range srv.forwardq {
+		if debug.Value >= 1 {
+			fmt.Printf("dns: ^ %d:%s\n", req.message.Header.ID,
+				req.message.Question)
+		}
+
 		cl, err := NewTCPClient(remoteAddr.String())
 		if err != nil {
 			log.Println("dns: failed to create TCP client: " + err.Error())
@@ -625,6 +687,11 @@ func (srv *Server) runUDPForwarder(remoteAddr *net.UDPAddr) {
 	}
 
 	for req := range srv.forwardq {
+		if debug.Value >= 1 {
+			fmt.Printf("dns: ^ %d:%s\n", req.message.Header.ID,
+				req.message.Question)
+		}
+
 		res, err := forwarder.Query(req.message)
 		if err != nil {
 			log.Println("dns: failed to query UDP: " + err.Error())