Include which slot the query is accurate "as of"

[Quantumplation]

Describe your idea, in simple words.

In the body or header of the response to the /matches endpoint, include the tip that the result is accurate up to.

Why is it a good idea?

When integrating data from multiple sources, or when implementing time-sensitive / event-sourced applications, it is often important to know at what time the data received is accurate as of. There is a difference between:

• a set of matches for a wallet that has had no activity for a long time
• a set of matches for a wallet against a kupo instance that is not yet up to date

This can also be identified by hitting the health endpoint, but given latency, it can be difficult to know "for sure" that your results are in sync.

That is, the results you get back from /matches could be as of a different slot than the response from /health issued shortly before or shortly after.

Are you willing to work on it yourself?

Willing? yes; Able? probably not.

[KtorZ]

>>> curl -v http://localhost:1442/v1/checkpoints | jq

> GET /v1/checkpoints HTTP/1.1
> Host: localhost:1442
> User-Agent: curl/7.84.0
> Accept: */*
> 
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< Transfer-Encoding: chunked
< Date: Sat, 16 Jul 2022 10:36:16 GMT
< Server: kupo
< X-Most-Recent-Checkpoint: 63598532
< Content-Type: application/json;charset=utf-8

[
  {
    "slot_no": 63598532,
    "header_hash": "329001bf94409d4d8ab35aaf7a3127cf83ce1ba260bde2d5df389195dce5d59e"
  },
  {
    "slot_no": 63598493,
    "header_hash": "4fe48af2e2a580df43da4b958ecb32732b08b458c64273d304d4d5d60543e82a"
  },
  {
    "slot_no": 63598456,
    "header_hash": "020b553875c4b821e99c9c80619aed9bedbefe73d16623cad508c14a1652e4b1"
  },
  {
    "slot_no": 63598269,
    "header_hash": "ed2b6f4ff07967bbe694a72da2ccc9897ee4817ca37f8a797c184bbc9d75c083"
  },
  {
    "slot_no": 63597879,
    "header_hash": "12271f8c66b862c0a1ea5e2f0ec36f46ac14b88e381ee8f8141d04b098c4a703"
  },
  {
    "slot_no": 63597192,
    "header_hash": "10b40329d6a5930512df373f1be08545b60ae2cb4a66020ad84103776a10d3d9"
  },
  {
    "slot_no": 63595845,
    "header_hash": "4f2d3481623be1e81b73e370cca7006bfb1996a4636f7cd393f8cc841e4d0c05"
  },
  {
    "slot_no": 63593182,
    "header_hash": "f9cb9c6033442dadf2fbb39281d386fcd074bda006b60912c9a892ef8264e0aa"
  },
  {
    "slot_no": 63587836,
    "header_hash": "cafa60959b81726699f06f93ce654a04ec21ffcb3fb80314816512f6e693f5a5"
  },
  {
    "slot_no": 63576932,
    "header_hash": "cc7a6ab3107165fb2b3f4ba6be6663148c61326c26892d6d54ae78cfe5aa6a3e"
  },
  {
    "slot_no": 63555346,
    "header_hash": "afba24da7cc98a25f8f25be434f143d5c1c18c5c83113a33c0d0f28442575ae5"
  }
]