Download file with Retrofit 2, OkHttp, Okio and RxJava

DownloadFileWithRetrofit2RxJava.java

import com.squareup.okhttp.ResponseBody;
import okio.BufferedSink;
import okio.Okio;
import retrofit.Response;
import retrofit.http.GET;
import retrofit.http.Query;
import rx.Observable;

interface ApiService {

    @GET("/media/download")
    Observable<Response<ResponseBody>> download(@Query("id") String id);

}

public Observable<File> download(String id) {
    return service.download(id)
            .flatMap(this::saveFile);
}

public Observable<File> saveFile(Response<ResponseBody> response) {
    return Observable.create((Observable.OnSubscribe<File>) subscriber -> {
        try {
            // you can access headers of response
            String header = response.headers().get("Content-Disposition");
            // this is specific case, it's up to you how you want to save your file
            // if you are not downloading file from direct link, you might be lucky to obtain file name from header
            String fileName = header.replace("attachment; filename=", "");
            // will create file in global Music directory, can be any other directory, just don't forget to handle permissions
            File file = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MUSIC).getAbsoluteFile(), fileName);
            
            BufferedSink sink = Okio.buffer(Okio.sink(file));
            // you can access body of response
            sink.writeAll(response.body().source());
            sink.close();
            subscriber.onNext(file);
            subscriber.onCompleted();
        } catch (IOException e) {
            e.printStackTrace();
            subscriber.onError(e);
        }
    });
}

What happens when the file is big??. I think with this approach will cause an OOM.

Any way to listen download progress? And can we show the download notification with this?

Up for listen download progress and download notification @lsurvila