Modernize error handling

.github/workflows/test.yml

@@ -26,7 +26,7 @@ jobs:
             go.mod
             go.sum
       - name: install
-        run: GOOS=linux GOARCH=${{ matrix.goarch }} make build
+        run: GOOS=linux GOARCH=${{ matrix.goarch }} go build
         if: "env.GIT_DIFF != ''"
 
   tests:

deepsubtree.go

@@ -1,15 +1,12 @@
 package smt
 
 import (
+	"errors"
 	"hash"
 )
 
-// BadProofError is returned when an invalid Merkle proof is supplied.
-type BadProofError struct{}
-
-func (e *BadProofError) Error() string {
-	return "bad proof"
-}
+// ErrBadProof is returned when an invalid Merkle proof is supplied.
+var ErrBadProof = errors.New("bad proof")
 
 // DeepSparseMerkleSubTree is a deep Sparse Merkle subtree for working on only a few leafs.
 type DeepSparseMerkleSubTree struct {
@@ -30,11 +27,11 @@ func NewDeepSparseMerkleSubTree(ms MapStore, hasher hash.Hash, root []byte) *Dee
 
 // AddBranch adds a branch to the tree.
 // These branches are generated by smt.ProveForRoot.
-// If the proof is invalid, a BadProofError is returned.
+// If the proof is invalid, a ErrBadProof is returned.
 func (dsmst *DeepSparseMerkleSubTree) AddBranch(proof SparseMerkleProof, key []byte, value []byte) error {
 	result, updates := verifyProofWithUpdates(proof, dsmst.Root(), key, value, dsmst.th.hasher)
 	if !result {
-		return &BadProofError{}
+		return ErrBadProof
 	}
 
 	for _, update := range updates {

deepsubtree_test.go

@@ -3,6 +3,7 @@ package smt
 import (
 	"bytes"
 	"crypto/sha256"
+	"errors"
 	"testing"
 )
 
@@ -131,7 +132,7 @@ func TestDeepSparseMerkleSubTreeBadInput(t *testing.T) {
 
 	dsmst := NewDeepSparseMerkleSubTree(NewSimpleMap(), sha256.New(), smt.Root())
 	err := dsmst.AddBranch(badProof, []byte("testKey1"), []byte("testValue1"))
-	if _, ok := err.(*BadProofError); !ok {
-		t.Error("did not return BadProofError for bad proof input")
+	if !errors.Is(err, ErrBadProof) {
+		t.Error("did not return ErrBadProof for bad proof input")
 	}
 }

proofs.go

@@ -2,7 +2,6 @@ package smt
 
 import (
 	"bytes"
-	"errors"
 	"hash"
 	"math"
 )
@@ -161,7 +160,7 @@ func CompactProof(proof SparseMerkleProof, hasher hash.Hash) (SparseCompactMerkl
 	th := newTreeHasher(hasher)
 
 	if !proof.sanityCheck(th) {
-		return SparseCompactMerkleProof{}, errors.New("bad proof")
+		return SparseCompactMerkleProof{}, ErrBadProof
 	}
 
 	bitMask := emptyBytes(int(math.Ceil(float64(len(proof.SideNodes)) / float64(8))))
@@ -189,7 +188,7 @@ func DecompactProof(proof SparseCompactMerkleProof, hasher hash.Hash) (SparseMer
 	th := newTreeHasher(hasher)
 
 	if !proof.sanityCheck(th) {
-		return SparseMerkleProof{}, errors.New("bad proof")
+		return SparseMerkleProof{}, ErrBadProof
 	}
 
 	decompactedSideNodes := make([][]byte, proof.NumSideNodes)

smt.go

@@ -3,6 +3,7 @@ package smt
 
 import (
 	"bytes"
+	"errors"
 	"hash"
 )
 
@@ -12,11 +13,7 @@ const (
 
 var defaultValue = []byte{}
 
-type keyAlreadyEmptyError struct{}
-
-func (e *keyAlreadyEmptyError) Error() string {
-	return "key already empty"
-}
+var errKeyAlreadyEmpty = errors.New("key already empty")
 
 // SparseMerkleTree is a Sparse Merkle tree.
 type SparseMerkleTree struct {
@@ -162,7 +159,7 @@ func (smt *SparseMerkleTree) UpdateForRoot(key []byte, value []byte, root []byte
 	if bytes.Equal(value, defaultValue) {
 		// Delete operation.
 		newRoot, err = smt.deleteWithSideNodes(path, sideNodes, oldLeafHash, oldLeafData)
-		if _, ok := err.(*keyAlreadyEmptyError); ok {
+		if errors.Is(err, errKeyAlreadyEmpty) {
 			// This key is already empty; return the old root.
 			return root, nil
 		}
@@ -181,10 +178,10 @@ func (smt *SparseMerkleTree) DeleteForRoot(key, root []byte) ([]byte, error) {
 func (smt *SparseMerkleTree) deleteWithSideNodes(path []byte, sideNodes [][]byte, oldLeafHash []byte, oldLeafData []byte) ([]byte, error) {
 	if bytes.Equal(oldLeafHash, smt.th.placeholder()) {
 		// This key is already empty as it is a placeholder; return an error.
-		return nil, &keyAlreadyEmptyError{}
+		return nil, errKeyAlreadyEmpty
 	} else if actualPath, _ := smt.th.parseLeaf(oldLeafData); !bytes.Equal(path, actualPath) {
 		// This key is already empty as a different key was found its place; return an error.
-		return nil, &keyAlreadyEmptyError{}
+		return nil, errKeyAlreadyEmpty
 	}
 
 	var currentHash, currentData []byte