pbyrne84.github.io

Smithy4s ZIO Opentracing (ZIO 2/Scala/tracing/layering/logging/testing)

This utilises the knowledge learnt from Zio2Playground.html and applies it to https://disneystreaming.github.io/smithy4s/.

The teason for being interested in Smithy is it handles ADTs in requests and responses. One of the joys of Scala is ADTs. Having payloads that can have values in some circumstances and not others is difficult otherwise. Errors should happen at deserialization not in the app on random edge cases.

Full readme can be found at https://github.com/pbyrne84/smithy4s-zio-opentracing

Test exercising everything can be found at ZioMainSpec.scala.

Challenges faced include

1. All examples of ZIO with http4s seems to be Blaze not Ember.
2. Starting traces from the request. ZIO has tracing as a first class citizen but requires the request headers at least for open tracing.
3. Layering is not compatible with TASK[_]. The dependencies need to be provided to create that signature. The easiest way seems to using the ZIO smithy compatible implementation as a facade that gives live layers and then the lower level actual business services can be tested singularly with custom layering.
4. Managing trace info on successful route responses, this makes sure we are not bad citizens breaking the tracing chain.
5. Managing trace info on BadRequest responses that never get into the route implementation. This logic can be found at ZioRoutes.scala.