1 files changed, 59 insertions, 0 deletions
diff --git a/app/message.go b/app/message.go
new file mode 100644
index 0000000..368eac0
--- /dev/null
+++ b/app/message.go
@@ -0,0 +1,59 @@
+package main
+
+import "encoding/binary"
+
+type DNSHeader struct {
+	ID      uint16
+	QR      uint8
+	OPCODE  uint8
+	AA      uint8
+	TC      uint8
+	RD      uint8
+	RA      uint8
+	Z       uint8
+	RCODE   uint8
+	QDCOUNT uint16
+	ANCOUNT uint16
+	NSCOUNT uint16
+	ARCOUNT uint16
+}
+
+type DNSMessage struct {
+	Header   DNSHeader
+	Question []byte
+}
+
+func (m *DNSHeader) Bytes() []byte {
+	bytes := make([]byte, 12)
+	binary.BigEndian.PutUint16(bytes[0:], m.ID)
+	binary.BigEndian.PutUint16(bytes[2:4], m.combineFlags())
+	binary.BigEndian.PutUint16(bytes[4:6], m.QDCOUNT)
+	binary.BigEndian.PutUint16(bytes[6:8], m.ANCOUNT)
+	binary.BigEndian.PutUint16(bytes[8:10], m.NSCOUNT)
+	binary.BigEndian.PutUint16(bytes[10:12], m.ARCOUNT)
+	return bytes
+}
+
+func (m *DNSHeader) combineFlags() uint16 {
+	return uint16(m.QR)<<15 | uint16(m.OPCODE)<<11 | uint16(m.AA)<<10 |
+		uint16(m.TC)<<9 | uint16(m.RD)<<8 | uint16(m.RA)<<7 | uint16(m.Z)<<4 |
+		uint16(m.RCODE)
+}
+
+func (m *DNSMessage) AddQuestion(q []byte) {
+	m.Question = q
+	m.Question = binary.BigEndian.AppendUint16(m.Question, 1)
+	m.Question = binary.BigEndian.AppendUint16(m.Question, 1)
+}
+
+func (m *DNSMessage) bytes() []byte {
+	headerBytes := m.Header.Bytes()
+	bytes := make([]byte, len(headerBytes)+len(m.Question))
+	copy(bytes, headerBytes)
+	copy(bytes[len(headerBytes):], m.Question)
+	return bytes
+}
+
+func MakeMessage(header DNSHeader) DNSMessage {
+	return DNSMessage{Header: header, Question: []byte{}}
+}