x-pack/filebeat/input/httpjson: Close connections properly

[shmsr]

Proposed commit message

Fix potential connection leaks in case of errors or when the response has been read but the connection remains unclosed.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Related issues

[botelastic]

This pull request doesn't have a Team:<team> label.

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @shmsr? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit

[efd6]

The callees here all follow the normal invariant that if err is nil, then the response is non-nil. So the condition can go away. If the response is non-nil, the body should be non-nil (this is documented as a property of http.Response values returned by http.Client and http.Transport and if we are not following that, it is a bug).

Suggested change

	defer func() {
	if httpResp != nil && httpResp.Body != nil {
	httpResp.Body.Close()
	}
	}()
	defer httpResp.Body.Close()

Actually, looking closer, I do not believe that this ever needs to happen; all responses come from httpClient.do which passes all bodies through drainBody which both completely drains (which is not done here) and closes it.

[shmsr]

Oh, right. Now that I look more closely, I see:

beats/x-pack/filebeat/input/httpjson/request.go

Line 503 in df064b8

err = resp.Body.Close()

in getIdsFromResponses, which we can get rid of since we are already draining the body and closing it with drainBody?

I'll remove my changes as well.

[efd6]

Do we want a note in changelog dev?