Support standard GRANIAN_* env vars and the rloop event loop

- Launcher now only injects --interface/--host/--port when the matching
  GRANIAN_* env var is unset, so every granian option (GRANIAN_LOOP,
  GRANIAN_WORKERS, GRANIAN_HTTP, GRANIAN_HOST, GRANIAN_PORT, ...) can be
  configured via granian's standard GRANIAN_* environment variables
- Add the rloop event loop as a runtime dependency so GRANIAN_LOOP=rloop
  works out of the box (previously failed with a missing 'rloop' package)

README.md

@@ -52,6 +52,35 @@ Configuration is read from environment variables:
 | `RBCS_DIGEST`           | *(unset)*     | Hash the key with this algorithm (e.g. `sha256`) |
 | `RBCS_MAX_AGE`          | `7d`          | Value TTL (`s`/`m`/`h`/`d`)         |
 
+### Configuring Granian
+
+The server runs on [Granian](https://github.com/emmett-framework/granian) via
+its RSGI interface. Any granian option can be configured with its standard
+`GRANIAN_*` environment variables (see `granian --help`), for example:
+
+```bash
+GRANIAN_LOOP=rloop GRANIAN_WORKERS=4 GRANIAN_HTTP=2 rbcs-server
+```
+
+Every granian CLI option has a matching `GRANIAN_*` variable
+(`GRANIAN_LOOP`, `GRANIAN_WORKERS`, `GRANIAN_HTTP`, `GRANIAN_TASK_IMPL`,
+`GRANIAN_RUNTIME_THREADS`, `GRANIAN_BLOCKING_THREADS`, `GRANIAN_LOG_LEVEL`,
+`GRANIAN_METRICS`, `GRANIAN_WS`, ...).
+
+When a `GRANIAN_*` variable and the corresponding `RBCS_*` variable are both
+set, the granian one wins:
+
+- `GRANIAN_HOST` overrides `RBCS_HOST` (default `127.0.0.1`)
+- `GRANIAN_PORT` overrides `RBCS_PORT` (default `8080`)
+- `GRANIAN_INTERFACE` overrides the default `rsgi` interface
+
+The Docker image ships the `rloop` event loop, so `GRANIAN_LOOP=rloop` works
+out of the box:
+
+```bash
+docker run -e GRANIAN_LOOP=rloop -e RBCS_MEMCACHE_HOST=memcached kaya-rbcs
+```
+
 The app is also a plain ASGI application, so it can be served by any ASGI
 server, e.g. `daphne kaya_rbcs.app:app`.
 

pyproject.toml

@@ -26,6 +26,7 @@ dependencies = [
 server = [
     "kaya-rsgi",
     "granian",
+    "rloop",
 ]
 dev = [
     "httpx",

requirements.in

@@ -4,3 +4,4 @@ kaya-core
 aiomcache
 kaya-rsgi
 granian
+rloop

requirements.txt

@@ -25,6 +25,8 @@ pwo==0.1.2
     # via
     #   kaya-core
     #   kaya-rsgi
+rloop==0.3.1
+    # via -r requirements.in
 typing-extensions==4.16.0
     # via
     #   kaya-core

src/kaya_rbcs/__main__.py

@@ -1,3 +1,4 @@
+import os
 import sys
 from typing import List, NoReturn
 
@@ -14,15 +15,17 @@ def main() -> NoReturn:
         ) from exc
 
     config = Config.from_env()
-    args: List[str] = [
-        '--interface',
-        'rsgi',
-        '--host',
-        config.host,
-        '--port',
-        str(config.port),
-        'kaya_rbcs.app:app',
-    ]
+    args: List[str] = []
+    # Only inject our own values when the equivalent GRANIAN_* environment
+    # variable is not set, so every granian option stays configurable via
+    # granian's standard GRANIAN_* environment variables.
+    if not os.getenv('GRANIAN_INTERFACE'):
+        args += ['--interface', 'rsgi']
+    if not os.getenv('GRANIAN_HOST'):
+        args += ['--host', config.host]
+    if not os.getenv('GRANIAN_PORT'):
+        args += ['--port', str(config.port)]
+    args.append('kaya_rbcs.app:app')
     sys.argv = [sys.argv[0], *args]
     entrypoint()  # type: ignore[no-untyped-call]
     raise SystemExit(0)