August 11, 2024

XML-RPC in Rust and Python

A lazy Sunday afternoon and my interest was piqued by XML-RPC

Client

A very basic XML-RPC client wrapped in a Cloud Functions function:

main.py:

import functions_framework
import os
import xmlrpc.client


endpoint = os.get_env("ENDPOINT")

proxy = xmlrpc.client.ServerProxy(endpoint)

@functions_framework.http
def add(request):
    print(request)
    rqst = request.get_json(silent=True)

    resp = proxy.add(
        {"x":{
            "real":rqst["x"]["real"],
            "imag":rqst["x"]["imag"]
        },
        "y":{
            "real":rqst["y"]["real"],
            "imag":rqst["y"]["imag"]
        }
    })

    return resp

requirements.txt:

functions-framework==3.*

Run it:

python3 -m venv venv
source venv/bin/activate
python3 -m pip install --requirement requirements.txt

export ENDPOINT="..."

python3 main.py

Server

Forcing myself to go Rust first and there’s an (old) xml-rpc crate.

Securing gRPC services using Tailscale

This is so useful that it’s worth its own post.

I write many gRPC services. As these generally run securely, it’s best to test them that way too but, even with e.g. Let’s Encrypt, it can be challenging to generate appropriate TLS certs.

Tailscale makes this trivial.

Assuming there’s a gRPC service running on localhost:50051, we want to avoid -plaintext:

PORT="50051"

grpcurl \
-plaintext 0.0.0.0:${PORT} \
list

NOTE I’m using list and assuming your service has reflection enabled but you can, of course, use relevant methods.

`curl`'ing a Tailscale Webhook

[Tailscale] is really good. I’ve been using it as a virtual private network to span 2 home networks and to securely (!) access my hosts when I’m remote.

Recently Tailscale added Webhook functionality to permit processing subscribed-to (Tailscale) events. I’m always a sucker for a webhook ;-)

Here’s a curl command to send a test event to a Tailscale Webhook:

URL=""

# From Tailscale's docs
# https://tailscale.com/kb/1213/webhooks/#events-payload
BODY='
[
  {
    "timestamp": "2022-09-21T13:37:51.658918-04:00",
    "version": 1,
    "type": "test",
    "tailnet": "example.com",
    "message": "This is a test event",
    "data": null
  }
]
'

T=$(date +%s)
V=$(\
  printf "${T}.${BODY}" \
  | openssl dgst -sha256 -hmac "${SECRET}" -hex -r \
  | head --bytes=64)

curl \
--request POST \
--header "Tailscale-Webhook-Signature:t=${T},v1=${V}" \
--header "Content-Type: application/json" \
--data "${BODY}" \
https://${URL}

There must be a better way of extracting the hashed value from the openssl output.