add typ and validation

Signed-off-by: Orie Steele <orie@transmute.industries>

cwt_test.go

@@ -17,10 +17,10 @@ func ExampleCWTMessage() {
 	msgToSign.Payload = []byte("hello world")
 	msgToSign.Headers.Protected.SetAlgorithm(cose.AlgorithmES512)
 
+	msgToSign.Headers.Protected.SetType("application/cwt")
 	claims := make(cose.CWTClaims)
 	claims[cose.CWTClaimIssuer] = "issuer.example"
 	claims[cose.CWTClaimSubject] = "subject.example"
-
 	msgToSign.Headers.Protected.SetCWTClaims(claims)
 
 	msgToSign.Headers.Unprotected[cose.HeaderLabelKeyID] = []byte("1")
@@ -41,12 +41,14 @@ func ExampleCWTMessage() {
 		panic(err)
 	}
 	sig, err := msgToSign.MarshalCBOR()
+	// uncomment to review EDN
+	// coseSign1Diagnostic, err := cbor.Diagnose(sig)
+	// fmt.Println(coseSign1Diagnostic)
 	if err != nil {
 		panic(err)
 	}
 	fmt.Println("message signed")
 
-
 	// create a verifier from a trusted public key
 	publicKey := privateKey.Public()
 	verifier, err := cose.NewVerifier(cose.AlgorithmES512, publicKey)

headers.go

@@ -24,6 +24,7 @@ const (
 	HeaderLabelCounterSignatureV2  int64 = 11
 	HeaderLabelCounterSignature0V2 int64 = 12
 	HeaderLabelCWTClaims           int64 = 15
+	HeaderLabelType                int64 = 16
 	HeaderLabelX5Bag               int64 = 32
 	HeaderLabelX5Chain             int64 = 33
 	HeaderLabelX5T                 int64 = 34
@@ -103,10 +104,28 @@ func (h ProtectedHeader) SetAlgorithm(alg Algorithm) {
 	h[HeaderLabelAlgorithm] = alg
 }
 
+// SetType sets the type of the cose object in the protected header.
+func (h ProtectedHeader) SetType(typ any) (any, error) {
+	if !canTstr(typ) && !canUint(typ) {
+		return typ, errors.New("header parameter: type: require tstr / uint type")
+	}
+	h[HeaderLabelType] = typ
+	return typ, nil
+}
+
 // SetCWTClaims sets the CWT Claims value of the protected header.
-func (h ProtectedHeader) SetCWTClaims(claims CWTClaims) {
-	// TODO: validate claims, for example ensuring that 1 and 2 are tstr, not bstr
+func (h ProtectedHeader) SetCWTClaims(claims CWTClaims) (CWTClaims, error) {
+	iss, hasIss := claims[1]
+	if hasIss && !canTstr(iss) {
+		return claims, errors.New("cwt claim: iss: require tstr")
+	}
+	sub, hasSub := claims[2]
+	if hasSub && !canTstr(sub) {
+		return claims, errors.New("cwt claim: sub: require tstr")
+	}
+	// TODO: validate claims, other claims
 	h[HeaderLabelCWTClaims] = claims
+	return claims, nil
 }
 
 // Algorithm gets the algorithm value from the algorithm header.
@@ -478,6 +497,25 @@ func validateHeaderParameters(h map[any]any, protected bool) error {
 			if err := ensureCritical(value, h); err != nil {
 				return fmt.Errorf("header parameter: crit: %w", err)
 			}
+		case HeaderLabelType:
+			is_tstr := canTstr(value)
+			if !is_tstr && !canUint(value) {
+				return errors.New("header parameter: type: require tstr / uint type")
+			}
+			if is_tstr {
+				v := value.(string)
+				if len(v) == 0 {
+					return errors.New("header parameter: type: require non-empty string")
+				}
+				if v[0] == ' ' || v[len(v)-1] == ' ' {
+					return errors.New("header parameter: type: require no leading/trailing whitespace")
+				}
+				// Basic check that the content type is of form type/subtype.
+				// We don't check the precise definition though (RFC 6838 Section 4.2).
+				if strings.Count(v, "/") != 1 {
+					return errors.New("header parameter: type: require text of form type/subtype")
+				}
+			}
 		case HeaderLabelContentType:
 			is_tstr := canTstr(value)
 			if !is_tstr && !canUint(value) {