Add json_lines webhook input format

[JensErat]

fluent-bit allows two JSON log formats: a stream of JSON objects not separated at all,
and one with a single JSON object per line. None of those was compatible with
grok_exporter so far. This change implements the json_lines format that is compatible
with fluent-bit.

I did not implement for v2 config, is this considered deprecated regarding new features or should the change also be included there? Runs fine with json_lines configuration and fluent-bit in our integration stage with some millions of log records by now.

I'd also be fine adding up some refactoring regarding duplicate code, but I wanted to propose/discuss the change first.

[coveralls]

Coverage decreased (-0.2%) to 66.948% when pulling 5cb8fc1 on JensErat:json_lines into 44b195e on fstab:master.

[Skeen]

I assume this PR is implementing support for Newline Delimited JSON (ndjson).

I think we could consider implementing a webhook_format: auto or webhook_format: detect for automatically determining the format, based upon the given Content-Type, in this case that would be application/x-ndjson.

• I am not suggesting that it should be done with this PR, I'm just making sure that the format here is indeed ndjson.

[JensErat]

Yes, looks like. Although fluent-bit not really calls it that way. fluent-bit allows sending custom headers, so using the header should also be a valid route for us. I'll check next week how fluent-bit really behaves regarding content type headers. I assume a way to "force overwrite" any incoming headers in grok_exporter would be a good thing, anyway.

I'm totally fine with providing a new patch taking HTTP headers into account.

I didn't know or even expect somebody wrote a spec for newline separated json records. :) But a common naming definitely is a good thing to have.

[Skeen]

JensErat wrote:
Yes, looks like. Although fluent-bit not really calls it that way. fluent-bit allows sending custom headers, so using the header should also be a valid route for us. I'll check next week how fluent-bit really behaves regarding content type headers. I assume a way to "force overwrite" any incoming headers in grok_exporter would be a good thing, anyway.

I don't know the specifics of the fluent-bit http module, but I imagine it behaves somewhat similar to the fluentd one; which seems to send the header for ndjson, as quoted below:

FluentD documentation:
Content-Type for HTTP request. out_http automatically set Content-Type for built-in formatters when this parameter is not specified. Here is a table:

• json: application/x-ndjson
• ...

But yes, I'm not suggesting that auto / detect replaces a pre-configured value, rather that it might be a reasonable default.

I didn't know or even expect somebody wrote a spec for newline separated json records. :) But a common naming definitely is a good thing to have.

Ofcourse someone wrote a spec for it, it's always nice when things are standardized.

[Skeen]

I have been running this change for a while now, and it seems good and rock stable. 👍

[fstab]

Thanks a lot and sorry for the delay. It's merged now.