Embedded message compression

Almon

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Jul 30, 2019, 2:57:35 AM7/30/19

to Protocol Buffers

Hi everyone,

In my project, I use Grpc to exchange messages between server and client by ethernet and I want to dissect in Wireshark all the messages (and embedded messages) who are exchanged.

I have some troubles to dissect embedded message because I see it compressed. For example, my embedded message is 24 bytes length but I see it at 8 bytes length. Althrough, in wireshark, I see the main message not compressed...

Someone know if it's a parameter to set or if it's a grpc internal process?

Else, do we could find the compression algorithm to uncompress embedded message?

Thank you for your help.

Alexandre.

Adam Cozzette

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Jul 30, 2019, 5:46:08 PM7/30/19

to Almon, Protocol Buffers

I'm not sure what kind of compression gRPC does, but there is a GitHub issue here with some instructions on decoding gRPC packets with Wireshark: https://github.com/grpc/grpc/issues/13586

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Alexandre SIMON

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Jul 31, 2019, 4:02:58 AM7/31/19

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Thanks for your reply, I already found why it doesn't work: uint32 in proto file is converted in varint in line... So I changed uint32 to fixed32 but a second question happen:

How to force enum to be a fixed32 and not a uint32 (converted in varint)?

Le mardi 30 juillet 2019 23:46:08 UTC+2, Adam Cozzette a écrit :

I'm not sure what kind of compression gRPC does, but there is a GitHub issue here with some instructions on decoding gRPC packets with Wireshark: https://github.com/grpc/grpc/issues/13586

On Mon, Jul 29, 2019 at 11:57 PM Almon <Alexandr...@gmail.com> wrote:

Hi everyone,

In my project, I use Grpc to exchange messages between server and client by ethernet and I want to dissect in Wireshark all the messages (and embedded messages) who are exchanged.
I have some troubles to dissect embedded message because I see it compressed. For example, my embedded message is 24 bytes length but I see it at 8 bytes length. Althrough, in wireshark, I see the main message not compressed...

Someone know if it's a parameter to set or if it's a grpc internal process?
Else, do we could find the compression algorithm to uncompress embedded message?

Thank you for your help.

Alexandre.

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Adam Cozzette

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Jul 31, 2019, 10:49:46 AM7/31/19

to Alexandre SIMON, Protocol Buffers

I don't think there is any way to force enums to use the fixed32 format; they will always be serialized as varints.

One thing to note is that varints are not an optional compression step, they're an important part of the wire format. I suspect it would be much easier to get Wireshark to decode the varints for you than it would be to try to avoid all varints.

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