OTLP tonic metadata from env variable

[harscoet]

Fixes #1336

Changes

As per the specs, the custom headers for OTLP exporter can be specified through env variables - OTEL_EXPORTER_OTLP_HEADERS, OTEL_EXPORTER_OTLP_TRACES_HEADERS, OTEL_EXPORTER_OTLP_METRICS_HEADERS.
This PR completes the work already done in PR #1290 adding support for tonic metadata
To reproduce the same behavior as http exporter, the env-variable takes precedence (as discussed in open-telemetry/opentelemetry-rust-contrib#10)

I moved common code for http and tonic exporters in exporter/mod.rs (function to parse header from string and test helper to run tests with isolated env variables)
I wanted to minimize the changes but maybe it should be a good idea to use a crate like https://crates.io/crates/temp-env for environment related testing

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: harscoet (53b832d, a2c56e2, 1449ba0, 3599ed1, bed4f5a, da09f04, 43b57f0, 76c0573)

[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (c06c04b) 55.4% compared to head (76c0573) 55.6%.
Report is 2 commits behind head on main.

Files	Patch %	Lines
opentelemetry-sdk/src/metrics/periodic_reader.rs	0.0%	6 Missing ⚠️
opentelemetry-otlp/src/exporter/tonic/mod.rs	97.7%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1377     +/-   ##
=======================================
+ Coverage   55.4%   55.6%   +0.2%     
=======================================
  Files        147     145      -2     
  Lines      18083   18022     -61     
=======================================
+ Hits       10021   10037     +16     
+ Misses      8062    7985     -77     

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[shaun-cox]

Thanks for the contribution!

[shaun-cox]

Overall, I love the cleanup. I wonder if one more little step here could eliminate the for loop by leveraging the std::iter::Extend trait that HashMap implements? Something like:

headers.extend(
    parse_header_string(input)
        .filter_map(|(k,v)| { 
           let key = HeaderName::from_str(k)?;
           let value = HeaderName::from_str(v)?;
           Some((key, value))
        )
    );

(I may have the .filter_map lambda totally wrong, but hopefully the gist comes across.

[harscoet]

Good suggestion, I updated it

fn add_header_from_string(input: &str, headers: &mut HashMap<HeaderName, HeaderValue>) {
    headers.extend(parse_header_string(input).filter_map(|(key, value)| {
        Some((
            HeaderName::from_str(key).ok()?,
            HeaderValue::from_str(value).ok()?,
        ))
    }));
}

[harscoet]

Both http and tonic modules are using HeaderName/HeaderValue so I just pushed some updates to simplify the code of parse_header_string to return impl Iterator<Item = (HeaderName, HeaderValue)> + '_ (instead of impl Iterator<Item = (&str, &str)>)

[hdost]

🤕 latest tests fail.

[harscoet]

🤕 latest tests fail.

There seem to be random failures during opentelemetry-jaeger tests, due to environment variable updates from parallel tests.
I created a PR #1384

[harscoet]

Both http and tonic modules are using HeaderName/HeaderValue so I just pushed some updates to simplify the code of parse_header_string to return impl Iterator<Item = (HeaderName, HeaderValue)> + '_ (instead of impl Iterator<Item = (&str, &str)>)

I finally reverted to use impl Iterator<Item = (&str, &str)> after realizing that grpcio is using HashMap<String, String> for headers, it's better to stay generic for all exporters

For grpcio we will be able to use something like that

fn add_headers_from_string(input: &str, headers: &mut HashMap<String, String>) {
    headers.extend(
        parse_header_string(&input).map(|(key, value)| (key.to_string(), value.to_string())),
    );
}

[lalitb]

Nicely done. Thanks.

[hdost]

Thank you again!