Unable to limit streamed request size

[Dave Yao]

I have implemented an envoy filter that aims to limit layer size for upload to a registry (CNCF), I cannot use the pre-exisiting max_request_body_bytes filter because the size limit is huge and I do not want to buffer the whole request. I have come up with the following approach but it doesnt seem to work, docker push ends up pushing bigger layers than is permitted by the filter.

```

- applyTo: HTTP_FILTER
    match:
      context: SIDECAR_INBOUND
      listener:
        filterChain:
          filter:
            name: envoy.filters.network.http_connection_manager
    patch:
      operation: INSERT_BEFORE
      value:
        name: envoy.filters.http.lua
        typed_config:
          '@type': type.googleapis.com/envoy.extensions.filters.http.lua.v3.Lua
          default_source_code:
            inline_string: |
              function envoy_on_request(request_handle)
                  local max_bytes = 10 * 1024 * 1024 #10MB for testing purpose would be >10GB in actual.
                  local total = 0
                  for chunk in request_handle:bodyChunks() do
                    total = total + chunk:length()
                    if total > max_bytes then
                      request_handle:respond(
                      { [":status"] = 413,
                        ["content-type"] = "application/json"},
                        "{\"errors\":[{\"code\":\"TOOBIG\",\"message\":\"Layer exceeds maximum allowed size\"}]}"
                      )
                      return
                    end
                  end
                end

```

The logs show the following error:
```

 error   envoy lua external/envoy/source/extensions/filters/common/lua/lua.cc:32 script log: [string "function envoy_on_request(request_handle)..."]:7: respond() cannot be called if headers have been continued        thread=23
```
Is the lua script correct, is there some other way I should be using to restrict the size of uploads?