feat(errors): Use custom erorrs to allow errors.Is() (#19)

errors.go

@@ -0,0 +1,14 @@
+package gohashtree
+
+import "errors"
+
+var (
+	// ErrOddChunks is returned when the number of chunks is odd.
+	ErrOddChunks = errors.New("odd number of chunks")
+	// ErrNotEnoughDigests is returned when the number of digests is not enough.
+	ErrNotEnoughDigests = errors.New("not enough digest length")
+	// ErrChunksNotMultipleOf64 is returned when the chunks are not multiple of 64 bytes.
+	ErrChunksNotMultipleOf64 = errors.New("chunks not multiple of 64 bytes")
+	// ErrDigestsNotMultipleOf32 is returned when the digests are not multiple of 32 bytes.
+	ErrDigestsNotMultipleOf32 = errors.New("digests not multiple of 32 bytes")
+)

hash.go

@@ -38,10 +38,10 @@ func Hash(digests [][32]byte, chunks [][32]byte) error {
 	}
 
 	if len(chunks)%2 == 1 {
-		return fmt.Errorf("odd number of chunks")
+		return ErrOddChunks
 	}
 	if len(digests) < len(chunks)/2 {
-		return fmt.Errorf("not enough digest length, need at least %v, got %v", len(chunks)/2, len(digests))
+		return fmt.Errorf("%w: need at least %v, got %v", ErrNotEnoughDigests, len(chunks)/2, len(digests))
 	}
 	if supportedCPU {
 		_hash(&digests[0][0], chunks, uint32(len(chunks)/2))
@@ -64,14 +64,17 @@ func HashByteSlice(digests []byte, chunks []byte) error {
 	if len(chunks) == 0 {
 		return nil
 	}
+
 	if len(chunks)%64 != 0 {
-		return fmt.Errorf("chunks not multiple of 64 bytes")
+		return ErrChunksNotMultipleOf64
 	}
+
 	if len(digests)%32 != 0 {
-		return fmt.Errorf("digests not multiple of 32 bytes")
+		return ErrDigestsNotMultipleOf32
 	}
+
 	if len(digests) < len(chunks)/2 {
-		return fmt.Errorf("not enough digest length, need at least %d, got %d", len(chunks)/2, len(digests))
+		return fmt.Errorf("%w: need at least %v, got %v", ErrNotEnoughDigests, len(chunks)/2, len(digests))
 	}
 	// We use an unsafe pointer to cast []byte to [][32]byte. The length and
 	// capacity of the slice need to be divided accordingly by 32.

hash_test.go

@@ -24,6 +24,7 @@ SOFTWARE.
 package gohashtree_test
 
 import (
+	"errors"
 	"reflect"
 	"testing"
 
@@ -283,7 +284,7 @@ func TestNotAllocatedDigest(t *testing.T) {
 	chunks := make([][32]byte, 4)
 	err := gohashtree.Hash(digests, chunks)
 	expected := "not enough digest length, need at least 2, got 1"
-	if err.Error() != expected {
+	if !errors.Is(err, gohashtree.ErrNotEnoughDigests) {
 		t.Logf("expected error: \"%s\", got: \"%s\"", expected, err)
 		t.Fail()
 	}