5 files changed, 80 insertions, 10 deletions
diff --git a/lib/dns/message.go b/lib/dns/message.go
index 02a237c0..058a159e 100644
--- a/lib/dns/message.go
+++ b/lib/dns/message.go
@@ -5,7 +5,6 @@
 package dns
 
 import (
-	"errors"
 	"fmt"
 	"net"
 	"strconv"
@@ -1072,15 +1071,16 @@ func (msg *Message) String() string {
 // packet.  This method assume that message.packet already set to DNS raw
 // message.
 func (msg *Message) UnpackHeaderQuestion() (err error) {
-	if len(msg.packet) <= sectionHeaderSize {
-		return errors.New(`UnpackHeaderQuestion: missing question`)
-	}
+	var logp = `UnpackHeaderQuestion`
 
-	msg.Header.unpack(msg.packet)
+	err = msg.Header.unpack(msg.packet)
+	if err != nil {
+		return fmt.Errorf(`%s: %w`, logp, err)
+	}
 
 	err = msg.Question.unpack(msg.packet[sectionHeaderSize:])
 	if err != nil {
-		return err
+		return fmt.Errorf(`%s: %w`, logp, err)
 	}
 
 	return nil
diff --git a/lib/dns/message_header.go b/lib/dns/message_header.go
index c3c6f9cb..aa505aec 100644
--- a/lib/dns/message_header.go
+++ b/lib/dns/message_header.go
@@ -5,6 +5,9 @@
 package dns
 
 import (
+	"errors"
+	"fmt"
+
 	libbytes "git.sr.ht/~shulhan/pakakeh.go/lib/bytes"
 )
 
@@ -161,19 +164,31 @@ func (hdr *MessageHeader) pack() []byte {
 }
 
 // unpack the DNS header section.
-func (hdr *MessageHeader) unpack(packet []byte) {
+func (hdr *MessageHeader) unpack(packet []byte) (err error) {
+	if len(packet) < sectionHeaderSize {
+		return errors.New(`header too small`)
+	}
+	hdr.Op = OpCode((packet[2] & headerMaskOpCode) >> 3)
+	if hdr.Op < 0 || hdr.Op > OpCodeStatus {
+		return fmt.Errorf(`unknown op code=%d`, hdr.Op)
+	}
+	hdr.RCode = ResponseCode(headerMaskRCode & packet[3])
+	if hdr.RCode < 0 || hdr.RCode > RCodeRefused {
+		return fmt.Errorf(`unknown response code=%d`, hdr.RCode)
+	}
+
 	hdr.ID = libbytes.ReadUint16(packet, 0)
 
 	hdr.IsQuery = packet[2]&headerIsResponse != headerIsResponse
-	hdr.Op = OpCode((packet[2] & headerMaskOpCode) >> 3)
 	hdr.IsAA = packet[2]&headerIsAA == headerIsAA
 	hdr.IsTC = packet[2]&headerIsTC == headerIsTC
 	hdr.IsRD = packet[2]&headerIsRD == headerIsRD
 	hdr.IsRA = packet[3]&headerIsRA == headerIsRA
-	hdr.RCode = ResponseCode(headerMaskRCode & packet[3])
 
 	hdr.QDCount = libbytes.ReadUint16(packet, 4)
 	hdr.ANCount = libbytes.ReadUint16(packet, 6)
 	hdr.NSCount = libbytes.ReadUint16(packet, 8)
 	hdr.ARCount = libbytes.ReadUint16(packet, 10)
+
+	return nil
 }
diff --git a/lib/dns/message_header_test.go b/lib/dns/message_header_test.go
index cb30ece1..95fbe113 100644
--- a/lib/dns/message_header_test.go
+++ b/lib/dns/message_header_test.go
@@ -262,7 +262,10 @@ func TestMessageHeader_unpack(t *testing.T) {
 
 	for _, c = range cases {
 		got = MessageHeader{}
-		got.unpack(c.packet)
+		var err = got.unpack(c.packet)
+		if err != nil {
+			t.Fatal(err)
+		}
 		test.Assert(t, c.desc, c.hdr, got)
 	}
 }
diff --git a/lib/dns/message_test.go b/lib/dns/message_test.go
index 8a1d47b2..a2f07b8b 100644
--- a/lib/dns/message_test.go
+++ b/lib/dns/message_test.go
@@ -1210,6 +1210,42 @@ func TestMessageSetResponseCode(t *testing.T) {
 	}
 }
 
+func TestMessage_UnpackHeaderQuestion(t *testing.T) {
+	var tdata *test.Data
+	var err error
+	tdata, err = test.LoadData(`testdata/message/UnpackHeaderQuestion_test.txt`)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var name string
+	var rawb []byte
+	var msg Message
+	for name, rawb = range tdata.Input {
+		t.Run(name, func(t *testing.T) {
+			msg.packet, err = hexdump.Parse(rawb, true)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			err = msg.UnpackHeaderQuestion()
+			if err != nil {
+				var expError = tdata.Output[name+`Error`]
+				test.Assert(t, `error`, string(expError),
+					err.Error())
+				return
+			}
+
+			rawb, err = json.MarshalIndent(&msg, ``, `  `)
+			if err != nil {
+				t.Fatal(err)
+			}
+			test.Assert(t, `message`, string(tdata.Output[name]),
+				string(rawb))
+		})
+	}
+}
+
 func TestUnpackMessage(t *testing.T) {
 	type testCase struct {
 		exp    *Message
diff --git a/lib/dns/testdata/message/UnpackHeaderQuestion_test.txt b/lib/dns/testdata/message/UnpackHeaderQuestion_test.txt
new file mode 100644
index 00000000..01dae739
--- /dev/null
+++ b/lib/dns/testdata/message/UnpackHeaderQuestion_test.txt
@@ -0,0 +1,16 @@
+Various invalid messages that we receive on our server.
+
+>>> invalidHeader001
+0000000 5420 2f20 4854 5450 2f31 2e31 0d0a 486f
+0000010 7374 3a20 3139 342e 3233 332e 3638 2e31
+0000020 3834 3a35 330d 0a55 7365 722d 4167 656e
+0000030 743a 204d 6f7a 696c 6c61 2f35 2e30 2028
+0000040 636f 6d70 6174 6962 6c65 3b20 4d6f 6461
+0000050 7453 6361 6e6e 6572 2f31 2e30 3b20 2b68
+0000060 7474 7073 3a2f 2f6d 6f64 6174 2e69 6f2f
+0000070 290d 0a41 6363 6570 743a 202a 2f2a 0d0a
+0000080 4163 6365 7074 2d45 6e63 6f64 696e 673a
+0000090 2067 7a69 700d 0a0d 0a
+
+<<< invalidHeader001Error
+UnpackHeaderQuestion: unknown op code=5