Steam user unable to connect via HTTP Proxy, erroring HPE_INVALID_CONSTANT

[anubis-dev]

I'm trying to use residential proxies sourced from smartproxy with steam-user to fetch CSGO Item floats. 

The problem is, my steam client refuses to connect through my proxy. The proxy works normally through curl, but get this error when used in httpProxy for steam-user:

Parse Error: Expected HTTP/
    at Socket.socketOnData (node:_http_client:541:22)
    at Socket.emit (node:events:517:28)
    at addChunk (node:internal/streams/readable:368:12)
    at readableAddChunk (node:internal/streams/readable:341:9)
    at Socket.Readable.push (node:internal/streams/readable:278:10)
    at TCP.onStreamRead (node:internal/stream_base_commons:190:23) {
  bytesParsed: 0,
  code: 'HPE_INVALID_CONSTANT',
  reason: 'Expected HTTP/',
  rawPacket: <Buffer 05 01>,
  proxyConnecting: true
}

I've tried monkey-patching into steam-user and node-stdlib to enhance the logging, but it appears this is an error internal to node's http. 

From some googling I can see some people talking about Content-length being incorrect, but I would assume its a more specific issue to my proxy?

I've tried http and https. I have tried whitelisting my IP so no URL credentials are even used (httpProxy = "http://gate.smartproxy.com:10000") and all get the same error. 

 

Sanity check, this is my instantiation: 

    this.client = new SteamUser({
      httpProxy,
      enablePicsCache: true,
    });

[Dr. McKay]

Sounds like your proxies aren't standards-compliant HTTP proxies.