How to unmarshal protobuf header on envoy

I have a custom header that is marshaled with protobuf (in a lua script inside an openresty plugin), called x-internal-state-bin.

Now I want to have access to this header in an inline lua code on my envoy, how can I unmarshal this custom proto (I have the proto file)? Or if there are other solutions with other filters than lua.

I came up with unmarshalling the proto inside the inline lua code.

Note that this solution needs lua-protobuf module to unmarshal the proto header and this module is not present in envoy docker image. According to this issue, I changed the docker file and installed this module.

Dockerfile content:

FROM docker.io/envoyproxy/envoy-dev:c89cc2ab48769efd726a0db8c8d75d516554a529 # note that this should be the dev tag

RUN apt update && apt install -y \
    luarocks git

RUN luarocks install lua-protobuf
RUN luarocks install base64

Lua inline code to unmarshal protobuf:

function envoy_on_request(request_handle)
  local pb = require "pb"
  local protoc = require "protoc"
  local base64 = require "base64"

  -- My proto definitioned copied from my .pb file
  assert(protoc:load [[
    syntax = "proto3";

    message RequestState {
      repeated int32 ids = 2;
  } ]])

  local rawh = request_handle:headers():get("x-state-bin")
  -- Some magics for base64 padding, ignore it
  while (string.len(rawh) % 4 ~= 0) do
    rawh = rawh .. "="
  end
  local bhead = base64.decode(rawh)
  -- RequestState is the name of the proto message that is defined above
  local message = assert(pb.decode("RequestState", bhead))

  local ids = table.concat(message.ids, ",")
  request_handle:headers():add("x-ids", "ids-"..ids)
end