fix(langchain): type check chain.invoke() input argument name

[Yun-Kim]

This PR fixes the langchain integration's patched chain method to check for the correct input argument name.

In LangChain<0.1, we patch langchain.Chain.__call__(), which uses inputs: Union[Dict[str, Any], str] as the argument to the chain invocation. However in LangChain>=0.1, we patch langchain.Chain.invoke(), which uses input: Dict[str, Any] as the argument to the chain invocation. We use the same traced function to patch both methods, but this subtle change broke our argument parsing, which expected the name inputs instead of input.

Checklist

• Change(s) are motivated and described in the PR description
• Testing strategy is described if automated tests are not included in the PR
• Risks are described (performance impact, potential for breakage, maintainability)
• Change is maintainable (easy to change, telemetry, documentation)
• Library release note guidelines are followed or label changelog/no-changelog is set
• Documentation is included (in-code, generated user docs, public corp docs)
• Backport labels are set (if applicable)
• If this PR changes the public interface, I've notified @DataDog/apm-tees.
• If change touches code that signs or publishes builds or packages, or handles credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.

Reviewer Checklist

• Title is accurate
• All changes are related to the pull request's stated goal
• Description motivates each change
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Change is maintainable (easy to change, telemetry, documentation)
• Release note makes sense to a user of the library
• Author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: yunkim/fix-langchain-chain-inputs
Commit report: 37b90ae
Test service: dd-trace-py

✅ 0 Failed, 272 Passed, 133 Skipped, 0s Wall Time

[sabrenner]

lgtm, one nonblocking question

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-04-02 22:13:13

Comparing candidate commit 37b90ae in PR branch yunkim/fix-langchain-chain-inputs with baseline commit 1c1f54a in branch main.

Found 7 performance improvements and 4 performance regressions! Performance is the same for 190 metrics, 9 unstable metrics.

scenario:flasksimple-appsec-telemetry

• 🟩 execution_time [-256.159µs; -210.144µs] or [-3.933%; -3.226%]

scenario:flasksimple-tracer

• 🟥 execution_time [+202.964µs; +252.187µs] or [+3.228%; +4.010%]

scenario:httppropagationextract-datadog_tracecontext_tracestate_not_propagated_on_trace_id_no_match

• 🟩 max_rss_usage [-693.461KB; -469.393KB] or [-3.177%; -2.150%]

scenario:httppropagationextract-invalid_span_id_header

• 🟩 max_rss_usage [-767.353KB; -618.323KB] or [-3.509%; -2.827%]

scenario:httppropagationextract-medium_valid_headers_all

• 🟩 max_rss_usage [-719.715KB; -501.303KB] or [-3.293%; -2.293%]

scenario:httppropagationextract-valid_headers_all

• 🟥 max_rss_usage [+727.535KB; +808.055KB] or [+3.442%; +3.823%]

scenario:httppropagationextract-wsgi_invalid_trace_id_header

• 🟥 max_rss_usage [+664.764KB; +746.718KB] or [+3.144%; +3.531%]

scenario:sethttpmeta-all-disabled

• 🟩 max_rss_usage [-733.373KB; -475.357KB] or [-3.314%; -2.148%]

scenario:sethttpmeta-obfuscation-send-querystring-disabled

• 🟥 max_rss_usage [+480.507KB; +756.895KB] or [+2.212%; +3.484%]

scenario:sethttpmeta-useragentvariant_exists_2

• 🟩 max_rss_usage [-827.870KB; -597.538KB] or [-3.733%; -2.695%]

scenario:sethttpmeta-useragentvariant_exists_3

• 🟩 max_rss_usage [-712.610KB; -451.474KB] or [-3.224%; -2.042%]