Show errors in a consistent way

[cstenglein]

Currently, the error comes in weird formats, depending on the endpoint.

Do not send an error array. but only one error at a time.

[fusion44]

Can you give some examples? What is a not weird format?

Not sure I can do anything about the error array response... that's a FastAPI thing. Will check.

[cstenglein]

There are currently 3 ways a error is displayed: just in detail, as detail.msg, and detail[X].msg (X is an integer).

As a user of blitz_api, I would like to have consistent error messages, either in detail or in detail.msg. Multiple errors are not really necessary IMO, since you could just show the "next" error.

Scenario 1

When I call system/login with a wrong password, I get the following response:

{
  "detail": [
    {
      "loc": [
        "body",
        "password"
      ],
      "msg": "ensure this value has at least 8 characters",
      "type": "value_error.any_str.min_length",
      "ctx": {
        "limit_value": 8
      }
    }
  ]
}

=> So I access detail.msg.

When I get an unauthenticated error, e.g. by calling system/change-password, I get the following response:

{
  "detail": "Not authenticated"
}

=> So I need to access just detail.

Scenario 2

When I call system/change-password and I enter the wrong old_password:

{
  "detail": "old password format invalid"
}

=> So I need to access just detail. again

When I call /lightning/new-address with the request body

{
  "type": "p2w2"
}

I get the details as an array:

{
  "detail": [
    {
      "loc": [
        "body",
        "type"
      ],
      "msg": "value is not a valid enumeration member; permitted: 'p2wkh', 'np2wkh'",
      "type": "type_error.enum",
      "ctx": {
        "enum_values": [
          "p2wkh",
          "np2wkh"
        ]
      }
    }
  ]
}

=> So there I need to access detail[0].msg

[fusion44]

That there are multiple errors returned is a Fastapi thing. If you call an endpoint with multiple wrong query args then you'll get an error array with an error message for each. We can't change this without forking FastAPI.

What we can do is always return an array where the first element is the actual error message. Need to look into this more.

[fusion44]

Issues related to this:

• Better error responses in /apps endpoints #148
• API behaviour is undefined when LN node is not reachable #205
• lnd grpc api remains in undefined state on given invalid macaroon path #220
• Error cases while fetching warmup data for new SSE clients aren't handled properly #245
• list-all-tx 500 on lnd startup #247

[fusion44]

TIL: https://www.rfc-editor.org/rfc/rfc9457.html

This standard describes error handling for apis.

Here's more some information:
https://blog.frankel.ch/problem-details-http-apis/

Might be a good idea to implement this standard.