Better error reporting for missing query string parameters

[candlerb]

Proposal

Use case. Why is this important?

Currently a missing query parameter is reported as if the query parameter was present with empty string. Furthermore, the error message does not include the name of the faulty parameter. This makes it hard to identify the problem with the query.

This affects people experimenting with the API for the first time.

Bug Report

What did you do?

curl -s 'http://localhost:9090/api/v1/query_range?query=ifHCInOctets%7bifDescr%3d"pppoe-out1"%7d' | python3 -mjson.tool

What did you expect to see?

Something like:

"error": "missing parameter 'start'"

What did you see instead? Under which circumstances?

{
    "status": "error",
    "errorType": "bad_data",
    "error": "cannot parse \"\" to a valid timestamp"
}

Environment

• System information:

    Linux 4.4.0-138-generic x86_64
  

• Prometheus version:

  prometheus, version 2.4.3 (branch: HEAD, revision: 167a4b4e73a8eca8df648d2d2043e21bdb9a7449)
    build user:       root@1e42b46043e9
    build date:       20181004-08:42:02
    go version:       go1.11.1
  

[BrianHa94]

@brian-brazil I would like to take this one up

[codwu]

@BrianHa94 Are you still working on it? I would like to open a PR for this issue.

[BrianHa94]

@codwu Yes, I have a fix. I just need to test before opening a PR.

[gouthamve]

Hi @BrianHa94 could you submit the patch? This is still an issue on 2.7.1

[palash25]

Hi @gouthamve I would like to work on this

Just to be sure this change would require using errors.New with appropriate messages and adding it to the apiError struct wherever params are checked like in this snippet start, err := parseTime(r.FormValue("start")) right? and ofcourse changing the error response in these test cases

[geekodour]

@gouthamve @palash25 Would it be useful if we set start to minTime and end to time.Now or something because otherwise I think the error message is helpful only?

[codesome]

@palash25 you can go ahead if @BrianHa94 is not working on it. @BrianHa94 are you still on it?

[BrianHa94]

@palash25 please go ahead.