Ktor - post unhanldled error with coroutines - kotlin

Question

I a new to Kotlin and Ktor in particular, so I have tried to do simple post request. As you can see below, there is nothing special.
routing {
post("/articles/add"){
val post = call.receive<ArticleRequest>()
println(post)
}
Error shown in logs is below and I don't understand why I should use here coroutines.
ERROR Application - Unhandled: POST - /articles/add
java.lang.IllegalStateException: Using blocking primitives on this dispatcher is not allowed. Consider using async channel instead or use blocking primitives in withContext(Dispatchers.IO) instead.
I am using 1.4.2 version. I would appreciate any help.

Answer 1

If you are using Jackson this is a bug and there is a suggested workaround:
routing {
post("/articles/add") {
with(Dispatchers.IO) {
val post = call.receive<ArticleRequest>()
println(post)
}
}
}
Or you can rollback to 1.4.1 until the bug is solved.

Answer 2

I've experienced the same issue after upgrading to ktor 1.4.2 and Kotlin 1.4.20, and I used both Moshi and Gson on this specific project but I don't believe they are causing this issue.
If you have a 'gradle.properties' file, add these ( or whatever version you wish to use ) :
ktor_version=1.3.2
kotlin_version=1.3.70.
Otherwise, in your 'build.gradle' file, create variables for different version :
buildscript {
ext.kotlin_version = '1.3.70'
ext.ktor_version = '1.3.2'
repositories {
jcenter()
}
dependencies {
classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
}
}
Then sync your gradle, run project.. all should be good.
However if you still experience some gradle-related issue, try this :
go to gradle (folder) -> wrapper -> open gradle_wrapper.properties and make sure the url has version 6.x.x or 5.x.x.
Mine looks like this currently:
distributionBase=GRADLE_USER_HOME
distributionPath=wrapper/dists
distributionUrl=https\://services.gradle.org/distributions/gradle-6.6.1-all.zip
zipStoreBase=GRADLE_USER_HOME
zipStorePath=wrapper/dists