beangle-setline 0.0.2

setline

setline is a small Linux-only local HTTP path router written in D.

It listens on a local address, matches requests by path prefix, and forwards them to local backend services. A route can also return a prebuilt direct response for fast local endpoints such as health checks.

Scope

• Linux only.
• Local only: the listener must bind to loopback or localhost.
• HTTP/1.x only in this first version.
• Path-prefix routing with longest-prefix priority.
• Local HTTP backends only.
• Multiple backends use simple round-robin selection. No weight support.
• Direct responses are supported for fast local short-circuit paths.
• stripPrefix is intentionally unsupported.

Build

dub build

Run

dub run -- --config config.example.json

Config

{
  "listen": "127.0.0.1:8080",
  "adminToken": "change-me",
  "routes": [
    {
      "prefix": "/healthz",
      "directResponse": {
        "status": 200,
        "contentType": "application/json",
        "body": "{\"status\":\"ok\"}"
      }
    },
    {
      "prefix": "/api/edu",
      "backends": [
        "http://127.0.0.1:9002",
        "http://127.0.0.1:9003"
      ]
    },
    {
      "prefix": "/api",
      "backend": "http://127.0.0.1:9001"
    }
  ]
}

Every route must define exactly one action:

• backend: forward to one local backend.
• backends: forward to multiple local backends with round-robin selection.
• directResponse: return a prepared local response.

Because routes are sorted by longest prefix first, /api/edu wins over /api.

Direct response fields:

• status: HTTP status code, default 200.
• contentType: response content type, default text/plain; charset=utf-8.
• body: response body, default empty.
• headers: optional extra response headers.

For direct responses, the complete HTTP response is built when the config is loaded or when a route is registered.

Runtime Route Registration

curl -X PUT http://127.0.0.1:8080/__setline/routes \
  -H 'Content-Type: application/json' \
  -H 'X-Setline-Token: change-me' \
  -d '{"prefix":"/api/edu","backends":["http://127.0.0.1:9002","http://127.0.0.1:9003"]}'

List routes:

curl -H 'X-Setline-Token: change-me' http://127.0.0.1:8080/__setline/routes

Notes

This project is deliberately narrow: local-only HTTP path routing, local backend selection, transparent proxying, and optional direct responses.

See also:

• doc/transparent-proxy-design.md
• doc/project-constraints.md