fix: Avoid crash then gzip-decompressing empty body

[niklas]

When doing a HEAD-request with "Accept-Encoding: gzip", some web servers set the content-encoding to gzip, but naturally transfer an empty body.

This makes :zlib.gunzip crash with

** (ErlangError) Erlang error: :data_error
    (erts 15.2.7) :zlib.inflateEnd_nif(#Reference<0.2948451012.2698379265.82762>)
    (erts 15.2.7) :zlib.gunzip/1
    iex:1: (file)

This PR skips decompression of an empty body.

[Copilot]

Pull Request Overview

This PR fixes a crash that occurs when decompressing gzip-encoded responses with empty bodies, which can happen with HEAD requests that include "Accept-Encoding: gzip" headers. The fix adds a guard clause to skip decompression when the response body is empty.

• Adds early return for empty body decompression to prevent :zlib.gunzip crashes
• Maintains existing decompression logic for non-empty bodies

Comments suppressed due to low confidence (1)

lib/tesla/middleware/compression.ex:87

• This new function clause that handles empty body decompression should have test coverage to verify it prevents the crash described in the PR and returns the expected result.

  defp decompress_body(_codecs, "" = body, acc) do

[yordis]

@niklas thank you so much for the help, I wonder if you could add a unit test to guarantee correctness.

[niklas]

Sure. Should I squash them?

[yordis]

@niklas ideally, yes, I need to figure out that situation to be honest, it helps with releasing automation but I can see that could be annoying.

Maybe I shouldn't check the Commits, and only enforce the title, I am unsure

[niklas]

\o/