Allow Content-Encoding to be unset when CompressionAlgorithms: []string{}

[mterhar]

Description

When a receiver uses the empty array for CompessionAlgorithm, it tells the middleware to pass any compressed body through to the receiver. This works fine for any body that has a Conent-Encoding header set, but when that header is missing, an empty string, or Identity, it will return a 400 response to the client without passing it along to the receiver.

This change bypasses the error when Content-Encoding is unset, empty, or Identity.

Link to tracking issue

Fixes #14131 and open-telemetry/opentelemetry-collector-contrib#44010

Testing

Added some test cases to ensure the missing content-encoding doesn't error out. The test fails with the original code and passes with the minimal change in the compression.go file.

Documentation

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.24%. Comparing base (6258454) to head (b3f109b).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14132      +/-   ##
==========================================
- Coverage   92.25%   92.24%   -0.01%     
==========================================
  Files         658      658              
  Lines       41184    41186       +2     
==========================================
- Hits        37995    37994       -1     
- Misses       2183     2185       +2     
- Partials     1006     1007       +1     

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[codeboten]

@axw can you confirm that your comments have been addressed?

[axw]

Looks good, just a few minor things.

[axw]

Could we just not add the decompressor in the first place, if the configured list is empty?
(Happy for this to be done in a followup.)

[mterhar]

I tried to do that, but it was skipping decompression too much sometimes. I am happy to take another stab at it but I’d like to make it a follow-up.

[axw]

LGTM, thanks!