Make som more unpack functions for messages and envelopes

msg/envelope.go

@@ -28,6 +28,37 @@ func UnmarshalEnvelopeFromCBOR(data []byte) (*Envelope, error) {
 	return e, nil
 }
 
+func UnmarshalAndVerifyEnvelopeFromCBOR(data []byte) (*Envelope, error) {
+
+	e, err := UnmarshalEnvelopeFromCBOR(data)
+	if err != nil {
+		return nil, fmt.Errorf("envelope: error unmarshalling envelope: %s", err)
+	}
+
+	err = e.Verify()
+	if err != nil {
+		return nil, fmt.Errorf("envelope: error verifying envelope: %s", err)
+	}
+
+	return e, nil
+}
+
+func (e *Envelope) Verify() error {
+	if e.EphemeralKey == nil || e.EncryptedContent == nil || e.EncryptedHeaders == nil {
+		return fmt.Errorf("envelope: missing fields in envelope")
+	}
+
+	if len(e.EphemeralKey) != 32 {
+		return fmt.Errorf("envelope: invalid ephemeral key length")
+	}
+
+	return nil
+}
+
+func (e *Envelope) IsValid() bool {
+	return e.Verify() == nil
+}
+
 func (e *Envelope) getContent(privkey []byte) ([]byte, error) {
 	return decrypt(e.EncryptedContent, e.EphemeralKey, privkey)
 }

msg/message.go

@@ -6,6 +6,7 @@ import (
 	"time"
 
 	"github.com/bahner/go-ma"
+	cbor "github.com/fxamacker/cbor/v2"
 	nanoid "github.com/matoous/go-nanoid/v2"
 )
 
@@ -111,3 +112,28 @@ func newFromHeaders(h *Headers) (*Message, error) {
 	}
 	return m, nil
 }
+
+// UnmarshalMessageFromCBOR unmarshals a Message from a CBOR byte slice
+// and verifies the signature
+func UnmarshalMessageFromCBOR(b []byte) (*Message, error) {
+	var m *Message = new(Message)
+	err := cbor.Unmarshal(b, m)
+	if err != nil {
+		return nil, fmt.Errorf("msg_unmarshal_message_from_cbor: failed to unmarshal message: %w", err)
+	}
+	return m, nil
+}
+
+func UnmarshalAndVerifyMessageFromCBOR(b []byte) (*Message, error) {
+	m, err := UnmarshalMessageFromCBOR(b)
+	if err != nil {
+		return nil, fmt.Errorf("msg_unmarshal_message_from_cbor_and_verify_signature: failed to unmarshal message: %w", err)
+	}
+
+	err = m.Verify()
+	if err != nil {
+		return nil, fmt.Errorf("msg_unmarshal_message_from_cbor_and_verify_signature: failed to verify message: %w", err)
+	}
+
+	return m, nil
+}