Implement proper error response for server endpoints

[GregoryAlbouy]

Description

Tasks

Suggestions

Dependencies

• Blocked by #12

Notes

[moreirathomas]

Also: we need to define how to handle non-critical errors (the client sends invalid data, it needs to send it again correctly shaped) vs critical errors (aka status 500 errors).

Notably is there a reconnection procedure?

[moreirathomas]

Types of error a run can produce:

• ErrUnknownField or ErrUnknownPredicate when parsing the config json/yaml
• InvalidConfigError: the config is invalid, it holds an array of errors (currently produces a pre-formatted string)
• native error on config.Request.Value(): we cannot create the request for any reason
• ErrConnection: when the recorder fails to connect to the url requested
• NO error on context.DeadlineExceeded: we simply stop the run where we are and continue on with the metrics and the tests
• ErrCanceled: when the run is explicitly canceled
• native error on internal errors

Types of error the server can produce:

• all of the above are forwarded
• internal error on io.ReadAll(r.Body) error
• internal error on configparse.JSON(body) error
• internal error on encoding any response (report or progress)

---

Goal:

• flag client errors differently than internal errors
• provide maximum context on client errors
• handle ErrCanceled differently than other errors
• handle server and runner errors differently (?)
• settle on if how we deal with context.DeadlineExceeded currently is what we want (ie: should going above the global timeout be an error ?)

[moreirathomas]

graph TD;
  A(start)-->B{parse input config}
  B-->|invalid|BB[ParseConfigError: ErrUnknownField, ErrUnknownPredicate, error]
  B-->C{validate config}
  C-->|invalid|CC[InvalidConfigError]
  C-->D{create request}
  D-->|invalid|DD[ErrInternal, InvalidConfigError]
  D-->E{record requests}
  E-->|dead ping|EE[ErrConnection]
  E-->|canceled|EEE[ErrCanceled]
  E-->|unexpected|EEEE[ErrInternal]
  E-->F{respond}
  F-->|unexpected|FF[ErrInternal]
  F-->G(end)

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[moreirathomas]

Improvements can be found but the issue is viewed as implemented for now.