New

• Add support for Datadog Synthetics distributed tracing HTTP header (#781)
• Add diagnostic logs at tracer startup for cross-language tracer consistency (#769, #776)

Fixes

• Improve logic in outbound HTTP automatic instrumentation to generate exactly one automatic instrumentation span (#780)
• Ensure IIS applications run the automatic instrumentation startup hook only once at application start (#775, #778)

Performance Overhead

• Reduce heap allocations in the following methods:
  • MethodBuilder, used throughout all integrations (#760)
  • ObjectExtensions, used throughout all integrations (#759)
  • SpanExtensions.AddTagsFromDbCommand, used in the AdoNet integration (#774)
  • UriHelpers.GetRelativeUrl, used in the AspNet, AspNetWebApi2, AspNetMvc, and AspNetCore integrations (#783)
  • AspNetCoreDiagnosticObserver, used in the AspNetCore integration (#779)
  • StringExtensions.ToBoolean (#789)
• Improve performance in Span.Finish (#763)

Build / Test

• Increase timeouts in smoke tests and read their output asynchronously (#788, #768)
• Improve reliability of RateLimiter unit tests (#787)

Known Issues and Workarounds

• Application fails to start with System.IO.FileNotFoundException System.Net.Http 4.0.0.0 (#876)
  • This issue has been fixed in .NET Tracer 1.19.2

Changes since 1.18.0