digest: register SHA1 digest algorithm

This algorithm is used by Git commit SHAs, and opens up the digest API
to work with these references.

Signed-off-by: Hidde Beydals <hello@hidde.co>

internal/digest/digest.go

@@ -17,6 +17,8 @@ limitations under the License.
 package digest
 
 import (
+	"crypto"
+	_ "crypto/sha1"
 	_ "crypto/sha256"
 	_ "crypto/sha512"
 	"fmt"
@@ -25,8 +27,19 @@ import (
 	_ "github.com/opencontainers/go-digest/blake3"
 )
 
-// Canonical is the primary digest algorithm used to calculate checksums.
-const Canonical = digest.SHA256
+const (
+	SHA1 digest.Algorithm = "sha1"
+)
+
+var (
+	// Canonical is the primary digest algorithm used to calculate checksums.
+	Canonical = digest.SHA256
+)
+
+func init() {
+	// Register SHA-1 algorithm for support of e.g. Git commit SHAs.
+	digest.RegisterAlgorithm(SHA1, crypto.SHA1)
+}
 
 // AlgorithmForName returns the digest algorithm for the given name, or an
 // error of type digest.ErrDigestUnsupported if the algorithm is unavailable.

internal/digest/writer_test.go

@@ -102,6 +102,10 @@ func benchmarkMultiDigesterWrite(b *testing.B, algos []digest.Algorithm, pSize i
 func BenchmarkMultiDigester_Write(b *testing.B) {
 	const pSize = 1024 * 2
 
+	b.Run("sha1", func(b *testing.B) {
+		benchmarkMultiDigesterWrite(b, []digest.Algorithm{SHA1}, pSize)
+	})
+
 	b.Run("sha256", func(b *testing.B) {
 		benchmarkMultiDigesterWrite(b, []digest.Algorithm{digest.SHA256}, pSize)
 	})