Protocol Buffer内嵌消息二进制编码格式解析求助

First, let's recap how Protocol Buffer encodes nested messages correctly:

• For a nested field, the wire type is 2 (Length-delimited). Your edu field has tag 3, so the field key is calculated as (3 << 3) | 2 = 26 (hex 0x1a), which matches the value you see in your output.
• Right after the field key, Protocol Buffer should write a Varint-encoded length of the entire nested message content.
• Then follows the serialized bytes of the nested message itself.

What's Wrong with fd 96 d1 08? #

Your nested Education message's serialized content is:

0a 09 53 4f 4d 45 57 48 45 52 45

Counting these bytes: that's 11 total bytes. The Varint encoding for 11 is simply 0x0b (binary 1011), so the correct sequence after 0x1a should be 0x0b, not the four-byte sequence fd 96 d1 08.

Decoding fd 96 d1 08 as a Varint gives us the value 18107261, which is wildly larger than the actual length of your nested message. This is clearly incorrect behavior.

Why Does This Happen? #

Since you mentioned you've debugged the serialization process and filed a bug, this is almost certainly an issue with the Go Protocol Buffer library's XXX_Marshal method when using the true flag (which enables deterministic serialization). XXX_Marshal is an internal method, so unexpected behavior here points to a bug in the library's handling of nested messages during deterministic marshaling.

Correct Expected Encoding #

For your Person message, the valid hex encoding should be:

08 9a 05 12 03 54 6f 6d 1a 0b 0a 09 53 4f 4d 45 57 48 45 52 45

Where 0x0b replaces the incorrect fd 96 d1 08 sequence, representing the 11-byte length of the nested Education message.

内容的提问来源于stack exchange，提问作者Qiankun Zhang