ddtrace/tracer: fix trace_agent_url on startup log

[rachelyangdog]

What does this PR do?

Updates the start up log so that it logs the correct value for "agent_url"

Motivation

When DD_TRACE_AGENT_URL is set to a valid unix socket (e.g, unix:///var/run/datadog/apm.socket), the startup log on dd-trace-go contains: "agent_url":"http://uds__var_run_datadog_apm.socket/v0.4/traces". We wanted the startup log to reflect the actual, un-normalized socket value instead.

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

Unsure? Have a question? Request a review!

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-11-07 20:11:30

Comparing candidate commit 728d921 in PR branch rachel.yang/fix-trace-agent-url with baseline commit bebced4 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 58 metrics, 1 unstable metrics.

[mtoffl01]

Good work! Your comments make things extra-clear which I appreciate 😉 .
Let's just add a few more test cases to ensure the changes are robust.

Btw, would change the Motivation section of the PR description to this, instead:

When DD_TRACE_AGENT_URL is set to a valid unix socket (e.g, unix:///var/run/datadog/apm.socket), the startup log on dd-trace-go contains: "agent_url":"http://uds__var_run_datadog_apm.socket/v0.4/traces". We wanted the startup log to reflect the actual, un-normalized socket value instead.

[mtoffl01]

one more small nit 😄

[mtoffl01]

one more small nit 😄

[mtoffl01]

Approving, just waiting to be sure CI is green.