Execute Redis commands over the Upstash Redis REST API from a serverless or edge function

Documented steps

1. Create/open an Upstash Redis database in the console and copy its REST URL (e.g. https://us1-merry-cat-32748.upstash.io) and REST token into UPSTASH_REDIS_REST_URL / UPSTASH_REDIS_REST_TOKEN.
2. Single-command endpoint shape is REST_URL/COMMAND/arg1/arg2/.../argN, e.g. https://<REST_URL>/set/foo/bar.
3. Authenticate every request with header 'Authorization: Bearer $TOKEN'; the query param ?_token=$TOKEN is also accepted.
4. GET form: curl https://<REST_URL>/get/foo -H "Authorization: Bearer $TOKEN".
5. POST form with the value in the body: curl -X POST -d '$VALUE' https://<REST_URL>/set/foo -H "Authorization: Bearer $TOKEN".
6. POST form with the whole command as a JSON array in the body: curl -X POST -d '["SET","foo","bar","EX",100]' https://<REST_URL> -H "Authorization: Bearer $TOKEN".
7. Parse the JSON response: success is {"result": <null|integer|string|array>}; failure is {"error": "ERR ..."}. Check for the 'error' key before reading 'result'.
8. Only HEAD, GET, POST and PUT methods are allowed; other verbs return 405. Missing/invalid token returns 401; command syntax errors return 400.
9. For binary or non-UTF8 values, send header 'Upstash-Encoding: base64' — all strings in the response are then base64-encoded except the literal 'OK'; decode client-side.
10. Header 'Upstash-Response-Format: resp2' returns raw RESP2 bytes (application/octet-stream) instead of JSON; it cannot be combined with base64 encoding.
11. Use the database's read-only token for read-only workloads; it permits read commands only and restricts powerful read operations.
12. Do not attempt blocking commands over REST: BLPOP, BRPOP, BRPOPLPUSH, BZPOPMAX and BZPOPMIN are not supported — poll instead.
13. Keep any single request (including body) under the documented 10MB max request size; chunk larger payloads across multiple commands.
14. Official docs: https://upstash.com/docs/redis/features/restapi | https://upstash.com/docs/redis/troubleshooting/max_request_size_exceeded | https://upstash.com/docs/redis/troubleshooting/max_daily_request_limit