Error: The inputs have already been written to an output stream and can not be consumed again.

[davgia]

Hi, I have an Android application that needs to upload a local temp file to a server. At runtime I receive the following error:

The inputs have already been written to an output stream and can not be consumed again.
	com.github.kittinunf.fuel.core.FuelError$Companion.wrap(FuelError.kt:86)
	com.github.kittinunf.fuel.core.FuelError$Companion.wrap$default(FuelError.kt:83)
Caused by: java.lang.IllegalStateException: The inputs have already been written to an output stream and can not be consumed again.
	com.github.kittinunf.fuel.core.requests.UploadBody.writeTo(UploadBody.kt:100)
	com.github.kittinunf.fuel.toolbox.HttpClient.setBodyIfDoOutput(HttpClient.kt:273)
	com.github.kittinunf.fuel.toolbox.HttpClient.sendRequest(HttpClient.kt:140)
	com.github.kittinunf.fuel.toolbox.HttpClient.doRequest(HttpClient.kt:79)
	com.github.kittinunf.fuel.toolbox.HttpClient.executeRequest(HttpClient.kt:37)
	com.github.kittinunf.fuel.core.requests.RequestTask.executeRequest(RequestTask.kt:23)
	com.github.kittinunf.fuel.core.requests.RequestTask.call(RequestTask.kt:44)
	com.github.kittinunf.fuel.core.requests.RequestTask.call(RequestTask.kt:14)
	com.github.kittinunf.fuel.core.requests.RequestTaskCallbacks.call(RequestTaskCallbacks.kt:28)
	com.github.kittinunf.fuel.core.requests.RequestTaskCallbacks.call(RequestTaskCallbacks.kt:20)
	java.util.concurrent.FutureTask.run(FutureTask.java:266)
	java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
	java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
	java.lang.Thread.run(Thread.java:764)

The android version is the following:

android {
    defaultConfig {
        compileSdk 34
        minSdkVersion 21
        targetSdkVersion 34
    }
}

Those are my dependencies:

dependencies {
    implementation "org.jetbrains.kotlin:kotlin-reflect:1.9.21"
    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:1.8.0"
    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:1.8.0"

    implementation 'com.github.kittinunf.fuel:fuel:2.3.1'
    implementation 'com.github.kittinunf.fuel:fuel-android:2.3.1'
    implementation 'com.github.kittinunf.fuel:fuel-gson:2.3.1'
    implementation 'com.github.kittinunf.fuel:fuel-coroutines:2.3.1'
}

And this is the code I'm using to upload:

private suspend fun uploadFile(localPath: String): String {
    val bearerToken = authenticate() //retrieves a jwt bearer token
    val url = "***REDACTED***" //simple upload endpoint that accepts multipart/form-data file and saves it elsewhere

    withContext(Dispatchers.IO) {
        Fuel.upload(url, Method.POST)
            .authentication()
            .bearer(bearerToken)
            .upload()
            .add { FileDataPart(File(localPath), name = "file", filename = "input.pdf", contentType = PDF_MIME_TYPE) }
            .progress { readBytes, totalBytes ->
                if (readBytes > 0 && totalBytes > 0) {
                    val progress: Int = (readBytes.toFloat() / totalBytes.toFloat() * 100).toInt()
                    Log.d(TAG, "Upload progress: $progress%")
                }
            }
            .responseString { _, _, result ->
                result.fold({
                    Log.d(TAG, "Upload completed")
                }, { error ->
                    Log.e(TAG, "Unable to upload the file", error)
                })
            }
            .awaitUnit()
    }
}

The file localPath should not be locked by anyone else. I've even make a copy of it and pass the copy to Fuel to double check but it returns the same error. Could it be a bug?

Thanks in advance

[davgia]

UPDATE: the problem seems to be caused by multiple calls of the .add {} function. I have yet to understand why... seems to be related to coroutines