Add fingerprint.StringFromHash

Inverse function of fingerprint.HashFromString.

pkg/crypto/fingerprint/hash.go

@@ -23,3 +23,13 @@ func HashFromString(s string) (crypto.Hash, error) {
 	}
 	return 0, errInvalidHashAlgorithm
 }
+
+// StringFromHash allows looking up a string representation of the crypto.Hash.
+func StringFromHash(hash crypto.Hash) (string, error) {
+	for s, h := range nameToHash {
+		if h == hash {
+			return s, nil
+		}
+	}
+	return "", errInvalidHashAlgorithm
+}

pkg/crypto/fingerprint/hash_test.go

@@ -22,3 +22,19 @@ func TestHashFromString(t *testing.T) {
 		}
 	})
 }
+
+func TestStringFromHash_Roundtrip(t *testing.T) {
+	for _, h := range nameToHash {
+		s, err := StringFromHash(h)
+		if err != nil {
+			t.Fatalf("Unexpected error for valid hash algorithm, got '%v'", err)
+		}
+		h2, err := HashFromString(s)
+		if err != nil {
+			t.Fatalf("Unexpected error for valid hash name, got '%v'", err)
+		}
+		if h != h2 {
+			t.Errorf("Hash value doesn't match, expected: 0x%x, got 0x%x", h, h2)
+		}
+	}
+}