[BUG][JAVA] IllegalArgumentException when using files with non-ascii chars for multipart requests.

Description

When using multipart requests the base ApiClient class throws an exception when building the body if the file contains non-ascii chars. A file named ítém.jpg will not be uploaded but item.jpg will work like a charm.

openapi-generator version

5.1.0

OpenAPI declaration file content or url

The bug is not related to any specific OpenAPI declaration file, but I can provide one if you want.

Generation Details

This is the config I'm using:

openApiGenerate {
    generatorName = "java"
    inputSpec = "$rootDir/specs/open-api.yaml".toString()
    outputDir = "$buildDir/generated/api".toString()
    apiPackage = "com.myapp.api"
    invokerPackage = "com.myapp.api.invoker"
    modelPackage = "com.myapp.api.model"
    configOptions = [
            dateLibrary: "legacy"
    ]
    globalProperties = [
            modelDocs: "false"
    ]
}

Steps to reproduce

Generate a Java client using any OpenAPI spec. Send a request using a file containing no-ascii chars and the client will throw an exception.

This is the exception thrown:

Caused by: java.lang.IllegalArgumentException: Unexpected char 0xed at 45 in Content-Disposition value: form-data; name="klisstItemImage"; filename="ítem.jpeg"
        at okhttp3.Headers$Companion.checkValue(Headers.kt:434)
        at okhttp3.Headers$Companion.of(Headers.kt:377)
        at okhttp3.Headers.of(Unknown Source:2)
        at com.klisst.api.invoker.ApiClient.buildRequestBodyMultipart(ApiClient.java:1230)
        at com.klisst.api.invoker.ApiClient.buildRequest(ApiClient.java:1074)
        at com.klisst.api.invoker.ApiClient.buildCall(ApiClient.java:1033)
        at com.klisst.api.DefaultApi.klisstItemUploadImageCall(DefaultApi.java:1579)
        at com.klisst.api.DefaultApi.klisstItemUploadImageValidateBeforeCall(DefaultApi.java:1601)
        at com.klisst.api.DefaultApi.klisstItemUploadImageWithHttpInfo(DefaultApi.java:1648)
        at com.klisst.api.DefaultApi.klisstItemUploadImage(DefaultApi.java:1625)
        at com.klisst.editklisstitem.api.KlisstItemApiClient$addPictureToItem$1.invoke(KlisstItemApiClient.kt:77)
        at com.klisst.editklisstitem.api.KlisstItemApiClient$addPictureToItem$1.invoke(KlisstItemApiClient.kt:76)
        at com.klisst.core.api.BaseApiClient.doEvaluateApiCall(BaseApiClient.kt:47)
        at com.klisst.core.api.BaseApiClient.doEvaluateApiCall$default(BaseApiClient.kt:36) 
        at com.klisst.core.api.BaseApiClient.evaluateApiCall(BaseApiClient.kt:19) 
        at com.klisst.editklisstitem.api.KlisstItemApiClient.addPictureToItem(KlisstItemApiClient.kt:76) 
        at com.klisst.editklisstitem.usecases.EditKlisstItem$uploadAndDeleteImagesAsynchronously$uploadJobs$1$1.invoke(EditKlisstItem.kt:62) 
        at com.klisst.editklisstitem.usecases.EditKlisstItem$uploadAndDeleteImagesAsynchronously$uploadJobs$1$1.invoke(EditKlisstItem.kt:61) 
        at com.klisst.core.coroutines.AsyncAwait$deferred$1.invokeSuspend(AsyncAwait.kt:25) 
        at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33) 
        at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:106) 
        at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:571) 
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:750) 
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:678) 
        at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:665) 

Related issues/PRs

None AFAIK.

Suggest a fix

The file name should be URL encoded before generating the part header or the non-ascii chars should be removed. ApiClient.java line 1230 should not crash if there are non-asccii chars as part of the file name.

Start in the generated Java ApiClient.java method buildRequestBodyMultipart, at the line identified in the stack trace, and reproduce the request with a filename such as ítém.jpeg. Trace how the multipart Content-Disposition header is built. Done means a generated Java client can send a multipart file whose name contains non-ASCII characters without throwing IllegalArgumentException.