Fixed ReadSymbol binary decoding and Symbol encoding

A Symbol is encoded using a single 64 bits value. However, the decoder
was instead assuming a precision 8 bits followed by a string encoded
binary data.

In fact, a symbol is encoded using a single 64 bits value, the most
significant byte being the precision and the rest is interpreted as a
SymbolCode.

abidecoder_test.go

@@ -629,6 +629,16 @@ func TestABI_Read_TimePointSec(t *testing.T) {
 	assert.Equal(t, `{"name":"2018-10-30T18:06:09"}`, string(out))
 }
 
+func TestABI_Read_Symbol(t *testing.T) {
+	abi := ABI{}
+	data, err := hex.DecodeString("04454f5300000000")
+	require.NoError(t, err)
+
+	out, err := abi.decodeField(NewDecoder(data), "name", "symbol", false, false, []byte("{}"))
+	require.NoError(t, err)
+	assert.Equal(t, `{"name":"4,EOS"}`, string(out))
+}
+
 func TestABIDecoder_analyseFieldType(t *testing.T) {
 
 	testCases := []map[string]interface{}{

abiencoder_test.go

@@ -284,7 +284,7 @@ func TestABI_Write(t *testing.T) {
 		{"caseName": "public_key err", "typeName": "public_key", "expectedValue": "", "json": "{\"testField\":\"EOS1111111111111111111111114T1Anm\"}", "expectedError": fmt.Errorf("writing field: public_key: checkDecode: invalid checksum")},
 		{"caseName": "signature", "typeName": "signature", "expectedValue": "000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000", "json": "{\"testField\":\"SIG_K1_111111111111111111111111111111111111111111111111111111111111111116uk5ne\"}", "expectedError": nil},
 		{"caseName": "signature err", "typeName": "signature", "expectedValue": "", "json": "{\"testField\":\"SIG_K1_BADX11111111111111111111111111111111111111111111111111111111111116uk5ne\"}", "expectedError": fmt.Errorf("writing field: public_key: signature checksum failed, found 3aea1e96 expected e72f76ff")},
-		{"caseName": "symbol", "typeName": "symbol", "expectedValue": "0403454f53", "json": "{\"testField\":\"4,EOS\"}", "expectedError": nil},
+		{"caseName": "symbol", "typeName": "symbol", "expectedValue": "04454f5300000000", "json": "{\"testField\":\"4,EOS\"}", "expectedError": nil},
 		{"caseName": "symbol format error", "typeName": "symbol", "expectedValue": "", "json": "{\"testField\":\"4EOS\"}", "expectedError": fmt.Errorf("writing field: symbol: symbol should be of format '4,EOS'")},
 		{"caseName": "symbol format error", "typeName": "symbol", "expectedValue": "", "json": "{\"testField\":\"abc,EOS\"}", "expectedError": fmt.Errorf("writing field: symbol: strconv.ParseUint: parsing \"abc\": invalid syntax")},
 		{"caseName": "symbol_code", "typeName": "symbol_code", "expectedValue": "ffffffffffffffff", "json": "{\"testField\":18446744073709551615}", "expectedError": nil},

decoder.go

@@ -793,26 +793,24 @@ func (d *Decoder) ReadExtendedAsset() (out ExtendedAsset, err error) {
 }
 
 func (d *Decoder) ReadSymbol() (out *Symbol, err error) {
-
-	precision, err := d.ReadUInt8()
-	if err != nil {
-		return out, fmt.Errorf("read symbol: read precision: %s", err)
-	}
-	symbol, err := d.ReadString()
+	rawValue, err := d.ReadUint64()
 	if err != nil {
-		return out, fmt.Errorf("read symbol: read symbol: %s", err)
+		return out, fmt.Errorf("read symbol: %s", err)
 	}
 
+	precision := uint8(rawValue & 0xFF)
+	symbolCode := SymbolCode(rawValue >> 8).String()
+
 	out = &Symbol{
 		Precision: precision,
-		Symbol:    symbol,
+		Symbol:    symbolCode,
 	}
-	decoderLog.Debug("read symbol", zap.String("symbol", symbol), zap.Uint8("precision", precision))
+
+	decoderLog.Debug("read symbol", zap.String("symbol", symbolCode), zap.Uint8("precision", precision))
 	return
 }
 
 func (d *Decoder) ReadSymbolCode() (out SymbolCode, err error) {
-
 	n, err := d.ReadUint64()
 	out = SymbolCode(n)
 

encoder.go

@@ -128,6 +128,13 @@ func (e *Encoder) Encode(v interface{}) (err error) {
 		return e.writeBlockTimestamp(cv)
 	case CurrencyName:
 		return e.writeCurrencyName(cv)
+	case Symbol:
+		value, err := cv.ToUint64()
+		if err != nil {
+			return fmt.Errorf("encoding symbol: %s", err)
+		}
+
+		return e.writeUint64(value)
 	case SymbolCode:
 		return e.writeUint64(uint64(cv))
 	case Asset: