File is not correctly uploaded using POST-request

I am trying to upload a .zip file from an Android phone using a POST-request. I found through some scouting through the forums okhttp which should make it quite easy.

The file that arrives at the server is a zip-file with the correct name, but there is no content in the file (it is 0kb). I suspect that the stream is not correctly flushed when sending by okhttp.

public class FileSender extends AsyncTask<String, String, String> {

@Override
protected String doInBackground(String... params) {
    String zipPath = params[0];
    String zipName = params[1];
    String serverUrl = "http://192.168.1.109:5000"+"/files/"+zipName;
    File file = new File(zipPath+zipName);
    Log.d("File name", "zipName: "+zipName+" file.getName(): "+file.getName());

    // TODO file is not send properly...
    RequestBody postBody = new MultipartBody.Builder()
            .setType(MultipartBody.FORM)
            .addFormDataPart(zipName, file.getName(),
                    RequestBody.create(MediaType.parse("application/octet-stream"), file))
            .build();

    OkHttpClient client = new OkHttpClient();

    Request request = new Request.Builder()
            .url(serverUrl)
            .post(postBody)
            // TODO insert API-key here
            .addHeader("API-key", "<my-api-key>")
            .build();


    try {
        Response response = client.newCall(request).execute();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return "Request Submitted";
   
}}

I basically implemented it with this, this as template.

Am I doing something wrong? What is another way to upload files this way?

Using Insomnia I am able to send files and there the Content-Type is also "application/octet-stream".

I managed to make it work. The issue was on my Flask-server side. This is the code that accepts the file:

@api.route("/files", methods=["POST"])
def post_file():
"""Upload a file."""
zipfile = request.files["zip"]
filename = secure_filename(zipfile.filename)
# Check if user has correct key
user_key = request.headers.get("API-key")
if user_key not in ALLOWED_KEYS:
return f"Permission denied. Key '{user_key}' has no access.", 401
if "/" in filename:
# Return 400 BAD REQUEST
abort(400, "no subdirectories directories allowed")
zipfile.save(os.path.join(UPLOAD_DIRECTORY, filename))
# Before I tried this (which does not work):
# with open(os.path.join(UPLOAD_DIRECTORY, secure_filename(filename)), "wb") as fp:	    
#     fp.write(request.data)
# Return 201 CREATED
return "Successfully uploaded file.", 201

Here the code of my Android side:

public class FileSender extends AsyncTask<String, Boolean, Boolean> {
@Override
protected Boolean doInBackground(String... params) {
String zipPath = params[0];
String zipName = params[1];
// TODO put ip in env-variable
String serverUrl = "http://IP:Port"+"/files";
File file = new File(zipPath+zipName);
Log.d("File name", "zipName: "+zipName+" file.getName(): "+file.getName());
RequestBody postBody = new MultipartBody.Builder()
.setType(MultipartBody.FORM)
.addFormDataPart("zip", file.getName(),
RequestBody.create(MediaType.parse("application/zip"), file))
.build();
OkHttpClient client = new OkHttpClient();
Request request = new Request.Builder()
.url(serverUrl)
.post(postBody)
// TODO insert API-key here
.addHeader("API-key", "<API-Key>")
.build();
try {
Response response = client.newCall(request).execute();
Log.d("SendToServer", "Worked: "+response.body().string());
return true;
} catch (IOException e) {
Log.d("SendToServer", "Error: "+e.toString());
e.printStackTrace();
return false;
}
}

}