[BUILD] allow building with -DWITH_OTLP_HTTP_COMPRESSION=OFF without zlib

[cfstras]

Issue

Currently, when building -DWITH_OTLP_HTTP_COMPRESSION=OFF, and not providing the libz dependency, we get this error:

...\opentelemetry-cpp\ext\src\http\client\curl\http_
client_curl.cc(6,10): error C1083: Cannot open include file: 'zconf.h': No such file or directory [...opentelemetry-cpp\build\ext\src\http\client\curl\opentelemetry_http_cli
ent_curl.vcxproj]

Changes

This fixes the issue by moving the #include <zconf.h> inside the corresponding #ifdef block, letting the build pass.

Do I need to do any of these? LMK, happy to :)

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

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[marcalff]

This makes sense.

Note however that ENABLE_OTLP_COMPRESSION_PREVIEW is what we call a "feature flag":

• the extra code path is protected with an ifdef, for now
• building without the feature is allowed, for now

By the time the compression code is deemed stable, the feature flag will be removed, so the dependency at build time on zlib will become mandatory.

[marcalff]

LGTM, thanks for the fix.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.88%. Comparing base (497eaf4) to head (d059280).
Report is 152 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3120      +/-   ##
==========================================
+ Coverage   87.12%   87.88%   +0.76%     
==========================================
  Files         200      195       -5     
  Lines        6109     6137      +28     
==========================================
+ Hits         5322     5393      +71     
+ Misses        787      744      -43     

see 99 files with indirect coverage changes

[cfstras]

Hi @marcalff Thanks for the note. I guess once it's stable, we'll have to bite the bullet and add that to our build scripts.

FWIW, for our situation compression is pretty unnecessary, we have a native binary running alongside a DataDog daemon on the same box, so data never leaves the box. More dependencies just complicate the already quite complex build process. Anyway, thanks for maintaining this, it's very helpful for us! :)