client: Accept empty file and ensure response on error

[arnaudgeiser]

Description

In case of TLS usage (ssl-context) and an empty file, a NullPointerException was raised on the following code because bs/to-byte-buffers was returning nil and a manifold.stream/->source cannot be build from it.

(send-streaming-body ch msg
      (-> file
        (bs/to-byte-buffers {:chunk-size (.-chunk-size file)})
        s/->source))

This issue has been reported here : https://github.com/clj-commons/aleph/issues/559

The following PR considers an empty file as a valid request when using TLS (it's already the case when TLS is not used).

Two other changes are included:

• We always log when there is a failure on aleph.http.core/send-message. [1]
• We always provide a response to the client when an Exception is raised - related to the issue [2]

Both of approaches have also been considered by @kachayev (#553) but I don't think it will be ever merged...

[1] https://github.com/clj-commons/aleph/pull/553/files#diff-f3c6a88143a34bab27cfd4dde73563c71de85a57da8133def509631b893d05ddR648 [2] https://github.com/clj-commons/aleph/pull/553/files#diff-2d6587452350a3603e05f940d19be2b98e6377dfc7efc3dc1eb099ff332e4b3bR654

[KingMob]

Thanks for working on this. Can you split it up into smaller pieces? It's easier to review when multiple concerns aren't bundled together. I'd prefer to keep the empty file fix and the additional error logging separate.

In particular, there's a lot of old code and notes from Kachayev about errors, and I'd like to look them over.

For the empty file fix, can you add non-TLS tests as well?

[arnaudgeiser]

Thank you @KingMob for the review, I will split this PR in two and add a test regarding non-TLS one. => PR turned into draft