Forward validation errors to agents

[beniwohli]

The apm server helpfully spits out great validation error messages if a payload fails the JSON Schema validation:

2017/09/13 09:12:20.138559 server.go:164: INFO Data validation error: Problem validating JSON document against schema: I[#] S[#] doesn't validate with "error#"
  I[#/errors/0/log] S[#/properties/errors/items/properties/log/required] missing properties: "message", code=400

This is great, but all the agent gets back is an empty 400 Bad Request response. It would be great if the validation error message could be returned to the agent, e.g. as a JSON payload.

[watson]

We had a discussion about error responses in #6 and we implemented changes in #37, so it should already reply with the validation error. But maybe something broke along the way?

[beniwohli]

Weird. Just verified that I get back an empty response. Can you check with the Node agent, @watson?

[watson]

@beniwohli I just tested it with curl from the latest master. Here's the results. I think the issue is that the server sends back Content-Type: text/plain; charset=utf-8 even though the body is JSON -
which obviously is wrong.

With curl default (Accept: */*):

$ curl -v -X POST -H 'Content-Type: application/json' -d '{"app":{"name":"foo","agent":{"name":"foo","version":"1"}},"errors":[{"timestamp":"2017-01-01T00:00:00+00:00","log":{"message":"foo"}}]}' localhost:8200/v1/errors
> POST /v1/errors HTTP/1.1
> Host: localhost:8200
> User-Agent: curl/7.54.0
> Accept: */*
> Content-Type: application/json
> Content-Length: 136
>
< HTTP/1.1 400 Bad Request
< Date: Wed, 13 Sep 2017 11:09:06 GMT
< Content-Length: 325
< Content-Type: text/plain; charset=utf-8
<
{"error":"Data Validation error: Problem validating JSON document against schema: I[#] S[#] doesn't validate with \"error#\"\n  I[#/errors/0/timestamp] S[#/properties/errors/items/properties/timestamp/pattern] does not match pattern \"^(\\\\d{4})-(\\\\d{2})-(\\\\d{2})T(\\\\d{2}):(\\\\d{2}):(\\\\d{2})(\\\\.\\\\d{1,6})?Z$\""}%

With curl and the header Accept: application/json:

$ curl -v -X POST -H 'Content-Type: application/json' -H 'Accept: application/json' -d '{"app":{"name":"foo","agent":{"name":"foo","version":"1"}},"errors":[{"timestamp":"2017-01-01T00:00:00+00:00","log":{"message":"foo"}}]}' localhost:8200/v1/errors
> POST /v1/errors HTTP/1.1
> Host: localhost:8200
> User-Agent: curl/7.54.0
> Content-Type: application/json
> Accept: application/json
> Content-Length: 136
>
< HTTP/1.1 400 Bad Request
< Date: Wed, 13 Sep 2017 11:09:30 GMT
< Content-Length: 325
< Content-Type: text/plain; charset=utf-8
<
{"error":"Data Validation error: Problem validating JSON document against schema: I[#] S[#] doesn't validate with \"error#\"\n  I[#/errors/0/timestamp] S[#/properties/errors/items/properties/timestamp/pattern] does not match pattern \"^(\\\\d{4})-(\\\\d{2})-(\\\\d{2})T(\\\\d{2}):(\\\\d{2}):(\\\\d{2})(\\\\.\\\\d{1,6})?Z$\""}%

[watson]

I changed this to a bug as it's not working as intended

[beniwohli]

OK, turns out I was using urllib3 wrong :( (in my defense, there are several stackoverflow questions and urllib3 bug reports that are similarly confused)

@watson should we close this and open another issue specific to the buggy content-type?

[watson]

@beniwohli good idea