DownloadProxy

DownloadProxy is a small local HTTP caching proxy for Factorio server environments.

It is designed to sit on the same machine as a Factorio server or related automation and reduce repeated upstream downloads by caching allowed Factorio assets locally. In this deployment, it is used on a trusted LAN behind the ChatWire server manager. The allowlist is intentionally narrow and focused on Factorio endpoints such as game downloads, mod downloads, and selected API responses.

Purpose

This project exists to help Factorio servers avoid repeatedly fetching the same upstream files:

• Factorio release downloads
• Factorio checksum files
• Factorio mod downloads
• Selected Factorio API responses

The proxy is intended specifically for Factorio server use behind ChatWire on a trusted local network. It is not a general-purpose open proxy and is not intended for direct Internet exposure.

How It Works

• Only requests from localhost are accepted.
• Only explicitly allowed upstream Factorio URLs are fetched.
• Cache hits are served from disk.
• Cache misses are throttled before contacting the upstream server.
• Successful responses are stored with a body file and metadata sidecar.
• Useful upstream headers such as Content-Type, Content-Disposition, ETag, and Last-Modified are preserved.

Running

Build:

go build ./...

Run with defaults:

./goHTTPCacher

The default bind address is:

127.0.0.1:55555

Useful launch flags:

./goHTTPCacher \
  -listen-addr=127.0.0.1:55555 \
  -upstream-rate=1s \
  -upstream-burst=1 \
  -fetch-timeout=2m \
  -metrics-interval=1m

Cache Behavior

• Short-lived cache entries are stored in ./shortCache/
• Long-lived cache entries are stored in ./longCache/
• Cached bodies use the .cache suffix
• Cached metadata uses the .cache.meta.json suffix

Older body-only cache entries are still readable.

Notes

• This service is intentionally restrictive.
• It should be run locally on the same host as the Factorio server or supporting automation, typically under ChatWire.
• Design choices are intentionally scoped to that environment: localhost-only access, a narrow allowlist, simple process-local locking, and local disk-backed cache state.
• If you need additional upstream endpoints, they should be added deliberately to the allowlist in the source rather than opening the proxy broadly.