[fix] workaround for missing tokenDecimal for tokentx calls

Note on a Etherscan bug:
Some ERC20 contract does not have valid decimals information in Etherscan.
When that happen TokenName, TokenSymbol are empty strings,
and TokenDecimal is 0.

More information can be found at:
nanmu42#8

Author: nanmu42

account.go

@@ -79,6 +79,14 @@ func (c *Client) InternalTxByAddress(address string, startBlock *int, endBlock *
 // contract address and/or from/to address.
 //
 // leave undesired condition to nil.
+//
+// Note on a Etherscan bug:
+// Some ERC20 contract does not have valid decimals information in Etherscan.
+// When that happen TokenName, TokenSymbol are empty strings,
+// and TokenDecimal is 0.
+//
+// More information can be found at:
+// https://github.com/nanmu42/etherscan-api/issues/8
 func (c *Client) ERC20Transfers(contractAddress, address *string, startBlock *int, endBlock *int, page int, offset int) (txs []ERC20Transfer, err error) {
 	param := M{
 		"page":   page,

account_e2e_test.go

@@ -73,6 +73,7 @@ func TestClient_ERC20Transfers(t *testing.T) {
 	const (
 		wantLen1 = 3
 		wantLen2 = 458
+		wantLen3 = 2
 	)
 
 	var a, b = 3273004, 3328071
@@ -92,6 +93,17 @@ func TestClient_ERC20Transfers(t *testing.T) {
 	if len(txs) != wantLen2 {
 		t.Errorf("got txs length %v, want %v", len(txs), wantLen2)
 	}
+
+	// some ERC20 contract does not have valid decimals information in Etherscan,
+	// which brings errors like `json: invalid use of ,string struct tag, trying to unmarshal "" into uint8`
+	var specialContract = "0x5eac95ad5b287cf44e058dcf694419333b796123"
+	var specialStartHeight = 6024142
+	var specialEndHeight = 6485274
+	txs, err = api.ERC20Transfers(&specialContract, nil, &specialStartHeight, &specialEndHeight, 1, 500)
+	noError(t, err, "api.ERC20Transfers 2")
+	if len(txs) != wantLen3 {
+		t.Errorf("got txs length %v, want %v", len(txs), wantLen3)
+	}
 }
 
 func TestClient_BlocksMinedByAddress(t *testing.T) {

client.go

@@ -134,7 +134,12 @@ func (c *Client) call(module, action string, param map[string]interface{}, outco
 		return
 	}
 
-	err = json.Unmarshal(envelope.Result, outcome)
+	// workaround for missing tokenDecimal for some tokentx calls
+	if action == "tokentx" {
+		err = json.Unmarshal(bytes.Replace(envelope.Result, []byte(`"tokenDecimal":""`), []byte(`"tokenDecimal":"0"`), -1), outcome)
+	} else {
+		err = json.Unmarshal(envelope.Result, outcome)
+	}
 	if err != nil {
 		err = wrapErr(err, "json unmarshal outcome")
 		return