如何在没有模式的情况下从 protobuf 消息中提取字段

Question

根据 this issue, the protoreflect 包提供了用于访问 protobuf 消息的“未知字段”的 API，但如果没有任何现有模式，我看不到任何使用它的方法。基本上，我想执行“弱解码”，类似于 JSON 解组器在输出类型为 map[string]interface{}.

时所做的事情

the documentation 中的示例如下所示：

err := UnmarshalOptions{DiscardUnknown: true}.Unmarshal(b, m)

其中 b 是输入字节切片，m 是输出消息，需要以某种方式初始化，如您所见 . I was thinking that dynamicpb can be used for this purpose, but it doesn't look possible without having an existing MessageDescriptor，这就是我被卡住的地方。 ..

Answer 1

我能够使用原始模式中的低级别 protowire package. Here is a full example, where I extract two fields of type uint64 (which happen to be assigned field numbers 4 和 5 实现此目的):

import "google.golang.org/protobuf/encoding/protowire"

func getData(src []byte) (creationTime, expiryTime uint64, err error) {
    remaining := src
    for len(remaining) > 0 {
        fieldNum, wireType, n := protowire.ConsumeTag(remaining)
        if n < 0 {
            return 0, 0, fmt.Errorf("failed to consume tag: %w", protowire.ParseError(n))
        }
        remaining = remaining[n:]

        switch fieldNum {
        case 4: // Expiry time
            if wireType != protowire.VarintType {
                return 0, 0, fmt.Errorf("unexpected type for expiry time field: %d", wireType)
            }
            expiryTime, n = protowire.ConsumeVarint(remaining)
        case 5: // Creation time
            if wireType != protowire.VarintType {
                return 0, 0, fmt.Errorf("unexpected type for creation time field: %d", wireType)
            }
            creationTime, n = protowire.ConsumeVarint(remaining)
        default:
            n = protowire.ConsumeFieldValue(fieldNum, wireType, remaining)
        }
        if n < 0 {
            return 0, 0, fmt.Errorf("failed to consume value for field %d: %w", fieldNum, protowire.ParseError(n))
        }
        remaining = remaining[n:]
    }

    return
}

如何在没有模式的情况下从 protobuf 消息中提取字段

How to extract field from protobuf message without schema

go

reflection

protocol-buffers

unmarshalling

proto