Question

Following is the java code on android side. It uploads file from the smartphone to a Flask server(a web server built on Flask framework). On Flask server side, how can I receive the file correctly? I worked on it for several days, but couldn’t figure out how to do it correctly. The request.headers gave me the correct parsed header data, but request.data or request.stream couldn’t give me the expected data. Any help will be appreciated!

public void doUpload(String filename)
{
    HttpURLConnection conn = null;
    DataOutputStream os = null;
    DataInputStream inputStream = null;

    String urlServer = "http://216.96.***.***:8000/upload";

    String lineEnd = "\r\n";
    String twoHyphens = "--";
    String boundary =  "*****";
    int bytesRead, bytesAvailable, bufferSize, bytesUploaded = 0;
    byte[] buffer;
    int maxBufferSize = 2*1024*1024;

    String uploadname = filename.substring(23);

    try
    {
        FileInputStream fis = new FileInputStream(new File(filename) );

        URL url = new URL(urlServer);
        conn = (HttpURLConnection) url.openConnection();
        conn.setChunkedStreamingMode(maxBufferSize);

        // POST settings.
        conn.setDoInput(true);
        conn.setDoOutput(true);
        conn.setUseCaches(false);
        conn.setRequestMethod("POST");
        conn.setRequestProperty("Connection", "Keep-Alive");
        conn.setRequestProperty("Content-Type", "multipart/form-data; boundary="+boundary);
        conn.addRequestProperty("username", Username);
        conn.addRequestProperty("password", Password);
        conn.connect();

        os = new DataOutputStream(conn.getOutputStream());
        os.writeBytes(twoHyphens + boundary + lineEnd);
        os.writeBytes("Content-Disposition: form-data; name=\"uploadedfile\";filename=\"" + uploadname +"\"" + lineEnd);
        os.writeBytes(lineEnd);

        bytesAvailable = fis.available();
        System.out.println("available: " + String.valueOf(bytesAvailable));
        bufferSize = Math.min(bytesAvailable, maxBufferSize);
        buffer = new byte[bufferSize];

        bytesRead = fis.read(buffer, 0, bufferSize);
        bytesUploaded += bytesRead;
        while (bytesRead > 0)
        {
            os.write(buffer, 0, bufferSize);
            bytesAvailable = fis.available();
            bufferSize = Math.min(bytesAvailable, maxBufferSize);
            buffer = new byte[bufferSize];
            bytesRead = fis.read(buffer, 0, bufferSize);
            bytesUploaded += bytesRead;
        }
        System.out.println("uploaded: "+String.valueOf(bytesUploaded));
        os.writeBytes(lineEnd);
        os.writeBytes(twoHyphens + boundary + twoHyphens + lineEnd);

        // Responses from the server (code and message)
        conn.setConnectTimeout(2000); // allow 2 seconds timeout.
        int rcode = conn.getResponseCode();
        if (rcode == 200) Toast.makeText(getApplicationContext(), "Success!!", Toast.LENGTH_LONG).show();
        else Toast.makeText(getApplicationContext(), "Failed!!", Toast.LENGTH_LONG).show();
        fis.close();
        os.flush();
        os.close();
        Toast.makeText(getApplicationContext(), "Record Uploaded!", Toast.LENGTH_LONG).show();
    }
    catch (Exception ex)
    {
        //ex.printStackTrace();
        //return false;
    }
}
}

My server side code:

@app.route('/cell_upload', methods=['GET', 'POST'])
def cell_upload():
    """Uploads a new file for the user from cellphone."""
    if request.method == 'POST':
        int_message = 1
        print "Data uploading"
        print request.headers
        logdata = request.stream.readline()
        while(logdata):
            print "uploading"
            print logdata
            logdata = request.stream.readline()
        print "Uploading done"
        return Response(str(int_message), mimetype='text/plain')
    int_message = 0
    return Response(str(int_message), mimetype='text/plain')

Answer 1

I’m not sure what your exact problem is, but I was able to get things to work by using the java (client) code taken from this SO question and by slightly modifying your flask code as follows:

if request.method == 'POST':
        int_message = 1
        print "Data uploading"
        print request.headers
        for v in request.values:
          print v
        #logdata = request.stream.readline()
        #while(logdata):
        #    print "uploading"
        #    print logdata
        #    logdata = request.stream.readline()
        print "Uploading done"
        return Response(str(int_message), mimetype='text/plain')

I wouldn’t consider this “the final answer”, but hopefully it will give you a shove in the right direciton.