2 files changed, 16 insertions, 0 deletions
diff --git a/plumbing/hash.go b/plumbing/hash.go
index 637a425..afc602a 100644
--- a/plumbing/hash.go
+++ b/plumbing/hash.go
@@ -71,3 +71,13 @@ type HashSlice []Hash
 func (p HashSlice) Len() int           { return len(p) }
 func (p HashSlice) Less(i, j int) bool { return bytes.Compare(p[i][:], p[j][:]) < 0 }
 func (p HashSlice) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }
+
+// IsHash returns true if the given string is a valid hash.
+func IsHash(s string) bool {
+	if len(s) != 40 {
+		return false
+	}
+
+	_, err := hex.DecodeString(s)
+	return err == nil
+}
diff --git a/plumbing/hash_test.go b/plumbing/hash_test.go
index fc2428b..0f836b0 100644
--- a/plumbing/hash_test.go
+++ b/plumbing/hash_test.go
@@ -52,3 +52,9 @@ func (s *HashSuite) TestHashesSort(c *C) {
 	c.Assert(i[0], Equals, NewHash("1111111111111111111111111111111111111111"))
 	c.Assert(i[1], Equals, NewHash("2222222222222222222222222222222222222222"))
 }
+
+func (s *HashSuite) TestIsHash(c *C) {
+	c.Assert(IsHash("8ab686eafeb1f44702738c8b0f24f2567c36da6d"), Equals, true)
+	c.Assert(IsHash("foo"), Equals, false)
+	c.Assert(IsHash("zab686eafeb1f44702738c8b0f24f2567c36da6d"), Equals, false)
+}