Basic Question Concerning Extending Envoy

[Danny]

Hi,

I've been trying to extend the Envoy proxy utilizing C++ rather than web assembly. My project uses Istio and I've plugged in my Envoy version. However, the big problem I have been having is that I am receiving errors that point to the empty Http filter not being able to be found. For reference, I am using this blog as a reference: [https://medium.com/@alishananda/implementing-filters-in-envoy-dcd8fc2d8fda]

I also used the paradigms that are discussed in the repo following repo... [https://github.com/envoyproxy/envoy/blob/main/DEVELOPER.md]. However, I am missing the fundamental understanding to be able to do the following. I create a directory, called a_filter, I create the supporting files a_filter.cc, a_filter.h, and a BUILD file. The Protobuf file is in a subdirectory v2 with its appropriate BUILD file. I need to know what changes have to be made to the Envoy static files so that when I apply the CRD:

---

apiVersion: networking.istio.io/v1alpha3

kind: EnvoyFilter

metadata:

  name: trial

spec:

  workloadLabels: { app: my_app }

  filters:

  - filterType: HTTP

    filterName: "a_filter"

    insertPosition: {index: FIRST }

    listernerMatch: { listenerProtocol: HTTP, listenerType: ANY, portNumber: 5678 }

    filterConfig:

       destination: "my manager"

       header: "header-name"

---

I do not get the following failure: 

10.0.67.96_42422: Didn't find a registered implementation for name: ‘a_filter'

Any help on this matter would be greatly appreciated. 

[Zizon Qiu]

1. To make bazel aware of your custom filter, you need to list it in extensions_build_config.bzl,

under source/extensions or your standalone project root.

2.  Register it explicitly like 

https://github.com/envoyproxy/envoy/blob/main/source/extensions/filters/http/csrf/config.cc#L34-L36

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