Improve hash-entry implementation

1. make the algorithm identifiers visible to dependent packages
2. check compatibility of algID and hashValue on Set so that we cannot
   end up in an unwanted state

Fixes #20

Also, improve coverage - therefore partially addressing #12.

.github/workflows/ci-go-cover.yml

@@ -14,7 +14,7 @@
 # 1. Change workflow name from "cover 100%" to "cover ≥92.5%". Script will automatically use 92.5%.  
 # 2. Update README.md to use the new path to badge.svg because the path includes the workflow name.
 
-name: cover ≥78%
+name: cover ≥78.8%
 on: [push, pull_request]
 jobs:
 

entity_test.go

@@ -21,7 +21,7 @@ func TestEntity_RoundtripOneRoleUint(t *testing.T) {
 	err = tv.SetRegID("https://acme.example")
 	assert.Nil(t, err)
 
-	err = tv.SetThumbprint(0, []byte{0x00, 0x01})
+	err = tv.SetThumbprint(Sha256_32, []byte{0x00, 0x01, 0x02, 0x03})
 	assert.Nil(t, err)
 
 	// When only one element is present role does not use the array wrap:
@@ -36,15 +36,15 @@ func TestEntity_RoundtripOneRoleUint(t *testing.T) {
 	//    01                  # unsigned(1)
 	//	  18 22               # unsigned(34)
 	//	  82                  # array(2)
-	//	     00               # unsigned(0)
-	//       42               # bytes(2)
-	//          0001          # "\x00\x01"
+	//	     06               # unsigned(6)
+	//       44               # bytes(4)
+	//          00010203      # "\x00\x01\x02\x03"
 	expectedCBOR := []byte{
 		0xa4, 0x18, 0x1f, 0x68, 0x41, 0x43, 0x4d, 0x45, 0x20, 0x4c, 0x74,
 		0x64, 0x18, 0x20, 0x74, 0x68, 0x74, 0x74, 0x70, 0x73, 0x3a, 0x2f,
 		0x2f, 0x61, 0x63, 0x6d, 0x65, 0x2e, 0x65, 0x78, 0x61, 0x6d, 0x70,
-		0x6c, 0x65, 0x18, 0x21, 0x01, 0x18, 0x22, 0x82, 0x00, 0x42, 0x00,
-		0x01,
+		0x6c, 0x65, 0x18, 0x21, 0x01, 0x18, 0x22, 0x82, 0x06, 0x44, 0x00,
+		0x01, 0x02, 0x03,
 	}
 
 	actual := roundTripper(t, tv, expectedCBOR).(Entity)

hashentry.go

@@ -28,56 +28,94 @@ type HashEntry struct {
 // Named Information Hash Algorithm Registry
 // https://www.iana.org/assignments/named-information/named-information.xhtml#hash-alg
 const (
-	sha256 = uint64(iota + 1)
-	sha256_128
-	sha256_120
-	sha256_96
-	sha256_64
-	sha256_32
-	sha384
-	sha512
-	sha3_224
-	sha3_256
-	sha3_384
-	sha3_512
+	Sha256 uint64 = (iota + 1)
+	Sha256_128
+	Sha256_120
+	Sha256_96
+	Sha256_64
+	Sha256_32
+	Sha384
+	Sha512
+	Sha3_224
+	Sha3_256
+	Sha3_384
+	Sha3_512
 )
 
 var (
+	algToValueLen = map[uint64]int{
+		Sha256:     32,
+		Sha256_128: 16,
+		Sha256_120: 15,
+		Sha256_96:  12,
+		Sha256_64:  8,
+		Sha256_32:  4,
+		Sha384:     48,
+		Sha512:     64,
+		Sha3_224:   28,
+		Sha3_256:   32,
+		Sha3_384:   48,
+		Sha3_512:   64,
+	}
+
 	algToString = map[uint64]string{
-		sha256:     "sha-256",
-		sha256_128: "sha-256-128",
-		sha256_120: "sha-256-120",
-		sha256_96:  "sha-256-96",
-		sha256_64:  "sha-256-64",
-		sha256_32:  "sha-256-32",
-		sha384:     "sha-384",
-		sha512:     "sha-512",
-		sha3_224:   "sha3-224",
-		sha3_256:   "sha3-256",
-		sha3_384:   "sha3-384",
-		sha3_512:   "sha3-512",
+		Sha256:     "sha-256",
+		Sha256_128: "sha-256-128",
+		Sha256_120: "sha-256-120",
+		Sha256_96:  "sha-256-96",
+		Sha256_64:  "sha-256-64",
+		Sha256_32:  "sha-256-32",
+		Sha384:     "sha-384",
+		Sha512:     "sha-512",
+		Sha3_224:   "sha3-224",
+		Sha3_256:   "sha3-256",
+		Sha3_384:   "sha3-384",
+		Sha3_512:   "sha3-512",
 	}
 
 	stringToAlg = map[string]uint64{
-		"sha-256":     sha256,
-		"sha-256-128": sha256_128,
-		"sha-256-120": sha256_120,
-		"sha-256-96":  sha256_96,
-		"sha-256-64":  sha256_64,
-		"sha-256-32":  sha256_32,
-		"sha-384":     sha384,
-		"sha-512":     sha512,
-		"sha3-224":    sha3_224,
-		"sha3-256":    sha3_256,
-		"sha3-384":    sha3_384,
-		"sha3-512":    sha3_512,
+		"sha-256":     Sha256,
+		"sha-256-128": Sha256_128,
+		"sha-256-120": Sha256_120,
+		"sha-256-96":  Sha256_96,
+		"sha-256-64":  Sha256_64,
+		"sha-256-32":  Sha256_32,
+		"sha-384":     Sha384,
+		"sha-512":     Sha512,
+		"sha3-224":    Sha3_224,
+		"sha3-256":    Sha3_256,
+		"sha3-384":    Sha3_384,
+		"sha3-512":    Sha3_512,
 	}
 )
 
 // Set assigns the supplied algID and hash value to the HashEntry receiver
 func (h *HashEntry) Set(algID uint64, value []byte) error {
+	if err := ValidHashEntry(algID, value); err != nil {
+		return err
+	}
+
 	h.HashAlgID = algID
 	h.HashValue = value
+
+	return nil
+}
+
+func ValidHashEntry(algID uint64, value []byte) error {
+	wantLen, ok := algToValueLen[algID]
+	if !ok {
+		return fmt.Errorf("unknown hash algorithm %d", algID)
+	}
+
+	gotLen := len(value)
+
+	if wantLen != gotLen {
+		return fmt.Errorf(
+			"length mismatch for hash algorithm %s: want %d bytes, got %d",
+			algToString[algID], wantLen, gotLen,
+		)
+	}
+
 	return nil
 }