I've found an issue related to serving SPAs from t...

# kotlin-toolchain

[Lucas Silva]

I've found an issue related to serving SPAs from the resources folder in Ktor. In short, the fat jar built with kotlin package isn't serving my web ui correctly. Instead of displaying the HTML file, it's triggering a download because the content type is, for some reason, application/octet-stream . The problem doesn't occur when running with kotlin run though, as the content type stays as html.

The workaround was to add call.respondResource as follows:

get("/") {
    call.respondResource("webui/index.html")
}

singlePageApplication {
    useResources = true
    filesPath = "webui"
    defaultPage = "index.html"
}

To be sure this is an issue with KTC, I tried the same in a normal KMP project with Gradle (without the workaround) and it worked just fine with both the buildFatJar and runFatJar tasks.

[joffrey]

Hi Lucas! Thanks for the report. Where is webui/index.html declared? Is it in the resources of the Ktor server module? Or in another local module that the server depends on?

[Lucas Silva]

In the resources of the ktor module. Full path is ktor-backend/resources/webui/index.html. It's a vue frontend built with vite - nothing unusual.

[joffrey]

Thanks. I'm suspecting the difference in behavior is due to the JAR format used. The JAR produced in the Gradle setup is a fat JAR with all the contents merged in a single jar. The JAR produced by kotlin package is an executable JAR following the Spring Executable JAR format (which contains nested JARs).

[joffrey]

Ok I think that my suspicion is correct. There is an issue on Ktor side to support the jar:nested: protocol to serve resources from this type of JAR: youtrack.jetbrains.com/issue/KTOR-8883

It seems to be implemented already but not released yet. It should be released in Ktor 3.6.0. @Bruce could you please confirm all this?

[joffrey]

Side note: maybe I'm mistaken and the problem comes from the fact that Ktor is serving the directory entry webui instead of ignoring it and falling back to the default. @Bruce, is this expected?

[Bruce]

Yep, that looks right. Maybe you could try on 3.6.0-eap-1675 with the EAP repository? https://redirector.kotlinlang.org/maven/ktor-eap

[Lucas Silva]

Same issue on 3.6.0-eap-1675.

[joffrey]

Yeah it seems to be about Ktor serving the directory entry. It's not only the wrong content type, it's also an empty content. I think there is something to fix on Ktor side here. @Bruce, could you please have a look?

[Bruce]

yeah I'll log a new issue

[Bruce]

I've got a hunch on what's going on there

[Bruce]

https://youtrack.jetbrains.com/issue/KTOR-9884/Directories-are-returned-as-empty-binaries-when-using-nested-jars

[joffrey]

Thanks, perfect!