How to decode binary/raw google protobuf data

Question

I have a coredump with encoded protobuf data and I want to decode this data and see the content. I have the .proto file which defines this message in raw protocol buffer. My proto file looks like this:

$  cat my.proto 
message header {
  required uint32 u1 = 1;
  required uint32 u2 = 2;
  optional uint32 u3 = 3 [default=0];
  optional bool   b1 = 4 [default=true];
  optional string s1 = 5;
  optional uint32 u4 = 6;
  optional uint32 u5 = 7;
  optional string s2 = 9;
  optional string s3   = 10; 
  optional uint32 u6 = 8;
}

And protoc version:

$  protoc --version
libprotoc 2.3.0

I have tried the following:

1. Dump the raw data from the core

   (gdb) dump memory b.bin 0x7fd70db7e964 0x7fd70db7e96d

2. Pass it to protoc

   //proto file (my.proto) is in the current dir
$ protoc --decode --proto_path=$pwd my.proto < b.bin
Missing value for flag: --decode
To decode an unknown message, use --decode_raw.

   $ protoc --decode_raw < /tmp/b.bin
Failed to parse input.

Any thoughts on how to decode it? The documentation doesn’t explain much on how to go about it.

Edit: Data in binary format (10 bytes)

(gdb) x/10xb 0x7fd70db7e964
0x7fd70db7e964: 0x08    0xff    0xff    0x01    0x10    0x08    0x40    0xf7
0x7fd70db7e96c: 0xd4    0x38

Answer 1

You used --decode_raw correctly, but your input does not seem to be a protobuf.

For --decode, you need to specify the type name, like:

protoc --decode header my.proto < b.bin

However, if --decode_raw reports a parse error than --decode will too.

It would seem that the bytes you extracted via gdb are not a valid protobuf. Perhaps your addresses aren't exactly right: if you added or removed a byte at either end, it probably won't parse.

I note that according to the addresses you specified, the protobuf is only 9 bytes long, which is only enough space for three or four of the fields to be set. Is that what you are expecting? Perhaps you could post the bytes here.

EDIT:

The 10 bytes you added to your question appear to decode successfully using --decode_raw:

$ echo 08ffff01100840f7d438 | xxd -r -p | protoc --decode_raw
1: 32767
2: 8
8: 928375

Cross-referencing the field numbers, we get:

u1: 32767
u2: 8
u6: 928375