为什么 protobuf 需要对消息中的类型信息进行编码？
Why protobuf needs to encode the type info in the message?
我正在阅读官方 protobuf encoding 文档。它声明 protobuf 消息对消息中每个字段的类型进行编码。但是，我认为客户端也有模式 class 文件，所以客户端应该已经知道类型了。为什么 protobuf 还要发送客户端已经知道的类型信息？
它在您的链接文档中说：
When the message is being decoded, the parser needs to be able to skip fields that it doesn't recognize. This way, new fields can be added to a message without breaking old programs that do not know about them. To this end, the "key" for each pair in a wire-format message is actually two values – the field number from your .proto file, plus a wire type that provides just enough information to find the length of the following value.
（强调我的）
我正在阅读官方 protobuf encoding 文档。它声明 protobuf 消息对消息中每个字段的类型进行编码。但是，我认为客户端也有模式 class 文件，所以客户端应该已经知道类型了。为什么 protobuf 还要发送客户端已经知道的类型信息？
它在您的链接文档中说：
When the message is being decoded, the parser needs to be able to skip fields that it doesn't recognize. This way, new fields can be added to a message without breaking old programs that do not know about them. To this end, the "key" for each pair in a wire-format message is actually two values – the field number from your .proto file, plus a wire type that provides just enough information to find the length of the following value.
（强调我的）