FIle multipart with OkHTTP

 protected String uploadFileOkHttp(String requestUrl, final String fileName) {

        final File file = new File(fileName);

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

        // using imageName because file name may be XXX.tmp, not XXX.jpg
        builder.addFormDataPart("file", fileName, new RequestBody() {
            @Override
            public MediaType contentType() {
                return MediaType.parse("application/octet-stream");
            }

            @Override
            public long contentLength() {
                return file.length();
            }

            @Override
            public void writeTo(BufferedSink sink) throws IOException {
                try {
                    Source source = Okio.source(file);
                    Buffer buf = new Buffer();

                    long totalRead = 0;
                    long totalSize = contentLength();
                    long remaining = totalSize;

                    for (long readCount; (readCount = source.read(buf, 32000)) != -1; ) {

                        totalRead += readCount;
                        remaining -= readCount;

                        sink.write(buf, readCount);
                        sink.flush();

//                        if (onEventListener != null) {
//                            onEventListener.publishProgress((int) ((totalRead / (float) totalSize) * 100));
//                        }
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });

        RequestBody requestBody = builder.build();
        Request httpRequest = new Request.Builder()
                .url(requestUrl)
                .post(requestBody)
                .build();

        String responseBody = null;
        try {
            OkHttpClient.Builder clientBuilder = new OkHttpClient.Builder();
            clientBuilder.connectTimeout(10, TimeUnit.SECONDS);
            clientBuilder.readTimeout(10, TimeUnit.SECONDS);
            OkHttpClient client = clientBuilder.build();

            okhttp3.Response httpResponse;
            try {
                Log.d(Constants.LOG_TAG, "REQUEST-1: " + requestUrl);
                httpResponse = client.newCall(httpRequest).execute();
            } catch (SSLException e) {
                requestUrl = requestUrl.replace("https://", "http://");
                httpRequest = new Request.Builder()
                        .url(requestUrl)
                        .post(requestBody)
                        .build();

                Log.d(Constants.LOG_TAG, "REQUEST-2: " + requestUrl);
                httpResponse = client.newCall(httpRequest).execute();
            }

            responseBody = httpResponse.body().string();

            if (TextUtils.isEmpty(responseBody)) {
                Log.d(Constants.LOG_TAG, "RESPONSE: NULL");
            } else {
                Log.d(Constants.LOG_TAG, "RESPONSE: " + responseBody);
            }

        } catch (IOException e) {
            e.printStackTrace();
        }

        return responseBody;
    }