golang protobuf序列化分析

1. data.proto

message ColumnarValue {
  uint32 id= 1;
  int32 typ = 2;
  repeated bytes values = 3;
}

data.go.proto

type ColumnarValue struct {
  Id   uint32   `protobuf:"varint,1,opt,name=id,json=id,proto3" json:"id,omitempty"`
	Typ int32    `protobuf:"varint,2,opt,name=typ,json=typ,proto3" json:"typ,omitempty"`
	Values  [][]byte `protobuf:"bytes,3,rep,name=values,proto3" json:"values,omitempty"`
}

2. 序列化

func (m *ColumnarValue) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
	b = b[:cap(b)]
	n, err := m.MarshalTo(b)
	if err != nil {
		return nil, err
	}
	return b[:n], nil
}

func (m *ColumnarValue) MarshalTo(dAtA []byte) (int, error) {
	var i int
	_ = i
	var l int
	_ = l
	if m.Id != 0 {
		dAtA[i] = 0x8
		i++
		i = encodeVarintData(dAtA, i, uint64(m.Id))
	}
	if m.Typ != 0 {
		dAtA[i] = 0x10
		i++
		i = encodeVarintData(dAtA, i, uint64(m.Typ))
	}
	if len(m.Values) > 0 {　　// [][]byte序列化
		for _, b := range m.Values {
			dAtA[i] = 0x1a
			i++
			i = encodeVarintData(dAtA, i, uint64(len(b)))  // 对byte Slice的长度(int值)编码
			i += copy(dAtA[i:], b)              // 直接复制b(bytes)切片
		}
	}
	return i, nil
}

编码(slice长度)

func encodeVarintData(dAtA []byte, offset int, v uint64) int {
	for v >= 1<<7 {
		dAtA[offset] = uint8(v&0x7f | 0x80)
		v >>= 7
		offset++
	}
	dAtA[offset] = uint8(v)
	return offset + 1
}

3. 反序列化

func (m *VecValue) XXX_Unmarshal(b []byte) error {
	return m.Unmarshal(b)
}

func (m *VecValue) Unmarshal(dAtA []byte) error {
	l := len(dAtA)
	iNdEx := 0
	for iNdEx < l {
		preIndex := iNdEx
		var wire uint64
		for shift := uint(0); ; shift += 7 {
			if shift >= 64 {
				return ErrIntOverflowData
			}
			if iNdEx >= l {
				return io.ErrUnexpectedEOF
			}
			b := dAtA[iNdEx]
			iNdEx++
			wire |= (uint64(b) & 0x7F) << shift
			if b < 0x80 {
				break
			}
		}
		fieldNum := int32(wire >> 3)
		wireType := int(wire & 0x7)
		if wireType == 4 {
			return fmt.Errorf("proto: VecValue: wiretype end group for non-group")
		}
		if fieldNum <= 0 {
			return fmt.Errorf("proto: VecValue: illegal tag %d (wire type %d)", fieldNum, wire)
		}
		switch fieldNum {
		case 1:
			if wireType != 0 {
				return fmt.Errorf("proto: wrong wireType = %d for field Id", wireType)
			}
			m.Id = 0
			for shift := uint(0); ; shift += 7 {
				if shift >= 64 {
					return ErrIntOverflowData
				}
				if iNdEx >= l {
					return io.ErrUnexpectedEOF
				}
				b := dAtA[iNdEx]
				iNdEx++
				m.Id |= (uint32(b) & 0x7F) << shift
				if b < 0x80 {
					break
				}
			}
		case 2:
			if wireType != 0 {
				return fmt.Errorf("proto: wrong wireType = %d for field Typ", wireType)
			}
			m.Typ = 0
			for shift := uint(0); ; shift += 7 {
				if shift >= 64 {
					return ErrIntOverflowData
				}
				if iNdEx >= l {
					return io.ErrUnexpectedEOF
				}
				b := dAtA[iNdEx]
				iNdEx++
				m.Typ |= (int32(b) & 0x7F) << shift
				if b < 0x80 {
					break
				}
			}
		case 3:
			if wireType != 2 {
				return fmt.Errorf("proto: wrong wireType = %d for field Values", wireType)
			}
			var byteLen int
			for shift := uint(0); ; shift += 7 {
				if shift >= 64 {
					return ErrIntOverflowData
				}
				if iNdEx >= l {
					return io.ErrUnexpectedEOF
				}
				b := dAtA[iNdEx]
				iNdEx++
				byteLen |= (int(b) & 0x7F) << shift
				if b < 0x80 {
					break
				}
			}
			if byteLen < 0 {
				return ErrInvalidLengthData
			}
			postIndex := iNdEx + byteLen
			if postIndex > l {
				return io.ErrUnexpectedEOF
			}
			m.Values = append(m.Values, make([]byte, postIndex-iNdEx))
			copy(m.Values[len(m.Values)-1], dAtA[iNdEx:postIndex])　　// 直接复制dAtA切片中指定内容, go层内部　内存复制
			iNdEx = postIndex
		default:
			iNdEx = preIndex
			skippy, err := skipData(dAtA[iNdEx:])
			if err != nil {
				return err
			}
			if skippy < 0 {
				return ErrInvalidLengthData
			}
			if (iNdEx + skippy) > l {
				return io.ErrUnexpectedEOF
			}
			iNdEx += skippy
		}
	}

	if iNdEx > l {
		return io.ErrUnexpectedEOF
	}
	return nil
}