How to properly manage a Retrofit POST request?

Question

Actually i'm trying to post a text file to my server and i would be able to handle the error when i've sent the file but i didn't get the response (In case the file has been sent the network is gone down so the server received the file but the device don't know it)

Because for now i'm getting an issue because if i don't get the response when the device return online it send again the same file and i would prevent it.

Seems it's hidely retry to send the file on connection fail or something like that.

Here is my method which i use onClick to send the file:

 public void sendPost() {
        @SuppressLint({"SdCardPath", "DefaultLocale"}) final File file = new File("/data/data/com.example.igardini.visualposmobile/files/"+String.format("%03d", Integer.valueOf(nTerminalino))+"_"+nTavoli.getText().toString()+".txt");

        final MultipartBody.Builder builder = new MultipartBody.Builder();
        builder.setType(MultipartBody.FORM);

        final RequestBody fbody = RequestBody.create(MediaType.parse("text/*"), file);
        builder.addFormDataPart(String.format("%03d", Integer.valueOf(nTerminalino))+"_"+nTavoli.getText().toString(), file.getName(),fbody);

        final MultipartBody requestBody = builder.build();

        final APIService apiService = ApiUtils.getAPIService(ipCASSA);

        final Call<Void> calls = apiService.savePost(requestBody);



        calls.enqueue(new Callback<Void>() {
            @Override
            public void onResponse(@NonNull Call<Void> call, @NonNull Response<Void> response) {
                if (response.isSuccessful()) {
                    Log.i("RESPONSE: ", response.toString());


                    Print();
                    dialogLoading.dismiss();
                    Runtime.getRuntime().gc();


//                    checkFile task = new checkFile();
//                    task.execute();

                }else {
                    Toast.makeText(pterm.this,"ERRORE",Toast.LENGTH_LONG).show();
                }
            }

            @Override
            public void onFailure(@NonNull Call<Void> call, @NonNull Throwable t) {
                    if(t instanceof IOException) {
                        Log.e("TAG", t.toString());
                        MediaPlayer mpFound = MediaPlayer.create(pterm.this, R.raw.errorsound);
                        mpFound.start();
                        Vibrator v = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
                        if (v.hasVibrator()) {
                            v.vibrate(6000);
                        }
                        new GlideToast.makeToast(pterm.this, "CONNESSIONE FALLITA!", GlideToast.LENGTHLONG, GlideToast.FAILTOAST).show();
                        dialogLoading.dismiss();
                    }

            }
        });
    }

While here are my other useful classes:

class ApiUtils {

    private ApiUtils() {}



    static APIService getAPIService(String ipCASSA) {

        String BASE_URL = "http://"+ipCASSA+"/web/";

        final OkHttpClient okHttpClient = new OkHttpClient.Builder()
                .connectTimeout(10000, TimeUnit.MILLISECONDS)
                .writeTimeout(10000, TimeUnit.MILLISECONDS)
                .readTimeout(10000, TimeUnit.MILLISECONDS)
                .retryOnConnectionFailure(false)
                .build();


        return RetrofitClient.getClient(BASE_URL,okHttpClient).create(APIService.class);
    }
}

public interface APIService {

    @POST("CART=PTERM")
    Call<Void> savePost(@Body RequestBody text);

}

class RetrofitClient {

    private static Retrofit retrofit = null;


    static Retrofit getClient(String baseUrl, OkHttpClient okHttpClient) {
        if (retrofit==null) {
            retrofit = new Retrofit.Builder()
                    .baseUrl(baseUrl)
                    .client(okHttpClient)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
        }
        return retrofit;
    }
}

Answer 1

In that case I would add to file some sort of device generated random ID, and send it along with request.

On server side I would change logic to first try to locate file in DB using this ID, if there is none, store it and return status OK along with maybe server side id (might come handy later).

If there is file with ID provided on request, just return server side ID with status 200 - that way you will not store it twice.

You can even go further - if you have not stable connection (it seems like it from description) you could even make seperate REST call to check if file is on server side by generated id or checksum, and if not then start to send it - it will safe bandwitch.

It does not have to be generated ID - it can be checksum of a file for example. Whatever is easier for you.

For generating ID you could use Android's UUID https://developer.android.com/reference/java/util/UUID

For checksum check this answer: How to generate an MD5 checksum for a file in Android?

BTW - I would not do 10 seconds timeout limit - it is way too much, and user experience will be terrible