How to retrieve error message in HTTP4S client? - scala

Question

I am trying to use Blaze client for http4s to make http calls. It works fine when 200 response is returned but in case of HTTP 500 or 400 I am not able to figure out how to retrieve the detailed error message returned from server.
I am can only see folllwing in the logs for this client.
2022-11-10 23:37:40 INFO - Shutting down connection pool:
curAllocated=1 idleQueues.size=1 waitQueue.size=0
maxWaitQueueLimit=256 closed=false org.http4s.client.UnexpectedStatus:
unexpected HTTP status: 500 Internal Server Error
def callEffect(client: Client[IO]): IO[String] = {
val uri = serverUrl
.withPath("/abc")
val request = GET(uri, Accept(MediaType.application.json))
client.expect[String](request).map { res =>
println(res)
res
}
}
def deploy(implicit cs: ContextShift[IO]): IO[ExitCode] = {
BlazeClientBuilder[IO](scala.concurrent.ExecutionContext.global).resource
.map(x => println(callEffect(x).unsafeRunSync()))
.use(_ => IO.unit.as(ExitCode.Success))
}

Answer 1

Since the result is provided inside an IO, you can use any of IO's error handling features to handle the issues, for example with redeem
def run(args: List[String]): IO[ExitCode] = {
BlazeClientBuilder[IO].resource
.use(client =>
for {
result <- callEffect(client).redeem(
error => "could not get a result",
something => s"this is what I got: $something"
)
_ <- IO.println(result)
} yield ExitCode.Success
)
}
There's a great article on this topic here:
https://softwaremill.com/practical-guide-to-error-handling-in-scala-cats-and-cats-effect/
For even more control, you can handle errors from the client itself, for example using expectOr() instead of expect(), which gives you access to a convenient onError: Response[F] => F[Throwable].