support encrypted streams with SRTP and MIKEY (#520) (#809)

pkg/mikey/message.go

@@ -0,0 +1,91 @@
+// Package mikey contains functions to decode and encode MIKEY messages.
+package mikey
+
+import "fmt"
+
+// Message is a MIKEY message.
+type Message struct {
+	Header   Header
+	Payloads []Payload
+}
+
+// Unmarshal decodes a Message.
+func (m *Message) Unmarshal(buf []byte) error {
+	n, nextPayloadType, err := m.Header.unmarshal(buf)
+	if err != nil {
+		return err
+	}
+
+	for nextPayloadType != 0 {
+		var payload Payload
+
+		switch nextPayloadType {
+		case payloadTypeKEMAC:
+			payload = &PayloadKEMAC{}
+		case payloadTypeT:
+			payload = &PayloadT{}
+		case payloadTypeSP:
+			payload = &PayloadSP{}
+		case payloadTypeRAND:
+			payload = &PayloadRAND{}
+		default:
+			return fmt.Errorf("unsupported payload type: %d", nextPayloadType)
+		}
+
+		payloadLen, err := payload.unmarshal(buf[n:])
+		if err != nil {
+			return fmt.Errorf("unable to parse payload %d: %w", nextPayloadType, err)
+		}
+
+		nextPayloadType = payloadType(buf[n])
+		n += payloadLen
+		m.Payloads = append(m.Payloads, payload)
+	}
+
+	if n < len(buf) {
+		return fmt.Errorf("detected %d unparsed bytes", len(buf)-n)
+	}
+
+	return nil
+}
+
+func (m *Message) marshalSize() int {
+	n := m.Header.marshalSize()
+	for _, pl := range m.Payloads {
+		n += pl.marshalSize()
+	}
+	return n
+}
+
+// Marshal encodes a Message.
+func (m *Message) Marshal() ([]byte, error) {
+	buf := make([]byte, m.marshalSize())
+
+	var nextPayloadType payloadType
+	if len(m.Payloads) != 0 {
+		nextPayloadType = m.Payloads[0].typ()
+	}
+
+	n, err := m.Header.marshalTo(buf, nextPayloadType)
+	if err != nil {
+		return nil, err
+	}
+
+	for i, pl := range m.Payloads {
+		if i != len(m.Payloads)-1 {
+			nextPayloadType = m.Payloads[i+1].typ()
+		} else {
+			nextPayloadType = 0
+		}
+
+		buf[n] = byte(nextPayloadType)
+
+		n2, err := pl.marshalTo(buf[n:])
+		if err != nil {
+			return nil, err
+		}
+		n += n2
+	}
+
+	return buf, nil
+}