How to download PDF file with Retrofit and Kotlin coroutines?

Question

I saw topics like How to download file in Android using Retrofit library?, they use @Streaming and RxJava / callbacks.

I have Kotlin, coroutines, Retrof

Answer 1

Thanks to @AndreiTanana I found a mistake. A problem was in suspend in the request definition. All other requests retain their suspend modifier, but this request removed it. I changed the code so.

interface Api {
    @FormUrlEncoded
    @Streaming
    @POST("export-pdf/")
    fun exportPdf(
        @Field("token") token: String
    ): Call

    // Any another request. Note 'suspend' here.
    @FormUrlEncoded
    @POST("reject/")
    suspend fun reject(): RejectResponse
}

Then in it's implementation, ApiImpl:

class ApiImpl : Api {

    private val retrofit by lazy { ApiClient.getRetrofit().create(Api::class.java) }

    override fun exportPdf(
        token: String
    ): Call =
        retrofit.exportPdf(token)

    override suspend fun reject(): RejectResponse =
        // Here can be another instance of Retrofit.
        retrofit.reject()
}

Retrofit client:

class ApiClient {

    companion object {

        private val retrofit: Retrofit


        init {

            val okHttpClient = OkHttpClient().newBuilder()
                .connectTimeout(60, TimeUnit.SECONDS)
                .readTimeout(60, TimeUnit.SECONDS)
                .writeTimeout(60, TimeUnit.SECONDS)
                .build()

            val gson = GsonBuilder().setLenient().create()

            retrofit = Retrofit.Builder()
                .baseUrl(SERVER_URL)
                .client(okHttpClient)
                // .addConverterFactory(GsonConverterFactory.create(gson)) - you can add this line, I think.
                .build()
        }

        fun getRetrofit(): Retrofit = retrofit
}

Interactor:

interface Interactor {
    // Note 'suspend' here. This is for coroutine chain.
    suspend fun exportPdf(
        token: String
    ): Call
}

class InteractorImpl(private val api: Api) : Interactor {
    override suspend fun exportPdf(
        token: String
    ): Call =
        api.exportPdf(token)
}

Then in fragment:

private fun exportPdf(view: View, token: String) {
    showProgress(view)
    launch(Dispatchers.IO) {
        try {
            val response = interactor.exportPdf(token).execute()
            var error: String? = null
            if (response.headers().get("Content-Type")?.contains(
                    "application/json") == true) {
                // Received JSON with an error.
                val json: String? = response.body()?.string()
                error = json?.let {
                    val export = ApiClient.getGson().fromJson(json,
                        ExportPdfResponse::class.java)
                    export.errors?.common?.firstOrNull()
                } ?: getString(R.string.request_error)
            } else {
                // Received PDF.
                val buffer = response.body()?.byteStream()
                if (buffer != null) {
                    val file = context?.let { createFile(it, "pdf") }
                    if (file != null) {
                        copyStreamToFile(buffer, file)
                        launch(Dispatchers.Main) {
                            if (isAdded) {
                                hideProgress(view)
                            }
                        }
                    }
                }
            }
            if (error != null) {
                launch(Dispatchers.Main) {
                    if (isAdded) {
                        hideProgress(view)
                        showErrorDialog(error)
                    }
                }
            }
        } catch (e: Exception) {
            launch(Dispatchers.Main) {
                if (isAdded) {
                    showErrorDialog(getString(R.string.connection_timeout))
                    hideProgress(view)
                }
            }
        }
    }
}