From dca3dfbc6acc24a116640805bc9896df7e8fc244 Mon Sep 17 00:00:00 2001
From: Atsushi Watanabe <atsushi.w@ieee.org>
Date: Thu, 6 Feb 2020 14:07:44 +0900
Subject: [PATCH] Add fingerprint.StringFromHash

Inverse function of fingerprint.HashFromString.
---
 pkg/crypto/fingerprint/hash.go      | 10 ++++++++++
 pkg/crypto/fingerprint/hash_test.go | 16 ++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/pkg/crypto/fingerprint/hash.go b/pkg/crypto/fingerprint/hash.go
index 7f336b897..99e7fa51d 100644
--- a/pkg/crypto/fingerprint/hash.go
+++ b/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
+}
diff --git a/pkg/crypto/fingerprint/hash_test.go b/pkg/crypto/fingerprint/hash_test.go
index 1280252e3..e9617b7cd 100644
--- a/pkg/crypto/fingerprint/hash_test.go
+++ b/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)
+		}
+	}
+}