How to fix 400 error in file uploading on flask server from android app

Question

I'm trying to upload file from android app with httpclient to flask server. I'm always gets 400 bad request error from server

public String send()
{
    try {
        url = "http://192.168.1.2:5000/audiostream";
        File file = new File(Environment.getExternalStorageDirectory().getAbsolutePath(), "/test.pcm");
        Log.d ("file" , file.getCanonicalPath());
        try {

            Log.d("transmission", "started");
            HttpClient httpclient = new DefaultHttpClient();

            HttpPost httppost = new HttpPost(url);
            ResponseHandler Rh = new BasicResponseHandler();

            InputStreamEntity reqEntity = new InputStreamEntity(new FileInputStream(file), -1);
            reqEntity.setContentType("binary/octet-stream");
            reqEntity.setChunked(true); // Send in multiple parts if needed

            httppost.setEntity(reqEntity);
            HttpResponse response = httpclient.execute(httppost);

            response.getEntity().getContentLength();
            StringBuilder sb = new StringBuilder();
            try {
                BufferedReader reader =
                        new BufferedReader(new InputStreamReader(response.getEntity().getContent()), 65728);
                String line;

                while ((line = reader.readLine()) != null) {
                    sb.append(line);
                }
            }
            catch (IOException e) { e.printStackTrace(); }
            catch (Exception e) { e.printStackTrace(); }


            Log.d("Response", sb.toString());
            Log.d("Response", "StatusLine : " + response.getStatusLine() + " Entity: " + response.getEntity()+ " Locate: " + response.getLocale() + " " + Rh);
            return sb.toString();
        } catch (Exception e) {
            // show error
            Log.d ("Error", e.toString());
            return e.toString();
        }
    }
    catch (Exception e)
    {
        Log.d ("Error", e.toString());
        return e.toString();
    }

}

But when I'm using curl file uploads correctly curl -i -F filedata=@"/home/rino/test.pcm" http://127.0.0.1:5000/audiostream Server configuration is

import os
from werkzeug.utils import secure_filename
from flask import Flask, jsonify, render_template, request, redirect,         url_for, make_response, send_file, flash
app = Flask(__name__)
app.debug = True


UPLOAD_FOLDER = '/home/rino/serv'
app.config['UPLOAD_FOLDER'] = UPLOAD_FOLDER

@app.route('/audiostream',methods=['GET', 'POST'])
def audiostream():
if request.method == 'POST':
    file = request.files['filedata']
    filename = secure_filename(file.filename)
    fullpath = os.path.join(app.config['UPLOAD_FOLDER'], filename)
    file.save(fullpath)
    return jsonify(results=['a','b'])

if request.method == 'GET':
    return "it's uploading page"

if __name__ == "__main__":
    app.run(host='0.0.0.0')

So, I'm think that my mistake is trivial but I can't recognize it.

Answer 1

Flask throws a 400 Bad Request when it can't access a key in the request. My guess (just by looking at the code) is that you're trying to pull out request.files['filedata'] but it doesn't exist in the Java request.

However it does in the curl request -F filedata.

Try taking a look at this: Http POST in Java (with file upload). It shows an example of how to add a part to your form upload using HttpClient and HttpPost.

According to this post you may need to add the encoding type of "multipart/form-data" as well.

tl;dr - Flask is looking for a filedata key in the request dict, you're not sending one.