The process-event API could use stricter validation

[martialblog]

The process-event API could use stricter validation. Here's what I mean:

cat 2.json 
{
}

curl -u 'source-2:whatisatypename123' -d '@2.json' 'http://localhost:5680/process-event'
invalid event: tags must not be empty

Ok good so far, but what about:

cat 3.json 
{
  "tags": {
    "": ""
  }
}

curl -i -u 'source-2:whatisatypename123' -d '@3.json' 'http://localhost:5680/process-event'
event processed successfully

Resulting in:

[julianbrost]

{
"tags": {
"": ""
}
}

That actually shows multiple problems:

1. This should result in an "must set severity or event type" error (I thought this was actually already there, but doesn't seem to be the case then)
2. Tag names should be non-empty.
3. ID tag values should probably be non-empty, for extra tags, at least not at the moment¹.

Footnotes

1. At the moment, we do something like hostgroup/Server so these don't have a value at the moment so we can't require this at the moment. However, this specific aspect will probably change in the future, see Allow multiple values for tags #217. However, I'm not 100% sure if we want to require that even then or if we want to allow something like boolean flag tags (i.e. present/not present), that could be used for something like production, testing instead of env=production, env=testing. ↩

[martialblog]

From what I can tell, the Validate() method only checks the slice length and the upper length of the tag's keys (not values).

func (e *Event) Validate() error {
        if len(e.Tags) == 0 {
                return fmt.Errorf("invalid event: tags must not be empty")
        }

        for tag := range e.Tags {
                if len(tag) > 255 {
                        return fmt.Errorf("invalid event: tag %q is too long, at most 255 chars allowed, %d given", tag, len(tag))
                }
        }

        for tag := range e.ExtraTags {
                if len(tag) > 255 {
                        return fmt.Errorf(
                                "invalid event: extra tag %q is too long, at most 255 chars allowed, %d given", tag, len(tag),
                        )
                }
        }
...

This method also could use some unittests