Edge middleware

Edge middleware runs in front of a server service, before the request reaches your process: redirects, rewrites, header changes, and optionally a published function that can answer, continue or rewrite the request.

It is a structured rule set, so it is written as a file rather than a pile of flags:

miosa middleware shop API --from middleware.json
miosa middleware shop API           # what is configured now
miosa middleware shop API --off     # remove the rules and the function

{
  "rules": [
    { "path": "/old/*", "redirect": { "to": "/new", "status": 308 } },
    { "path": "/api/*", "request_headers": { "set": { "x-plan": "pro" } } }
  ],
  "function": { "slug": "gate", "paths": ["/app/*"], "timeout_ms": 250, "on_error": "closed" }
}

Rules run in order and there can be up to fifty of them. A path is either an exact path or a prefix ending in /*, where $1 is the rest of the path. Each rule carries exactly one of a redirect (with an optional 301, 302, 303, 307 or 308, default 307), a rewrite, and/or header changes.

The function answers x-miosa-middleware: next to let the request continue, and may add x-miosa-middleware-request-<name> or x-miosa-middleware-rewrite. Any other answer is returned to the client. With on_error: "closed", a failing function answers 503 edge_middleware_unavailable; with open, the request continues.

Protected header names are refused, including host, content-length, transfer-encoding, connection, upgrade, x-internal-*, x-miosa-* and x-forwarded-*.