I'm developing an app by enables the user to take a photo and send it to a Keras model for prediction. This model is already deployed in a Google App Engine Service with a Python script that uses Flask for receiving via POST request the image and calling the model to make the prediction. Here's the Python code:
import numpy as np
import flask
import io
import logging
import tensorflow as tf
from keras.preprocessing.image import img_to_array
from keras.applications import imagenet_utils
from keras.models import load_model
from PIL import Image
# initialize our Flask application and the Keras model
app = flask.Flask(__name__)
app.config['PROPAGATE_EXCEPTIONS'] = True
model = None
def recortar(image):
# Function that centers and crop image. Please, asume that it works properly. Return is a numpy array.
return image
@app.route("/predict", methods=["POST"])
def predict():
model = load_model('modelo_1.h5')
graph = tf.get_default_graph()
data = {"success": False}
if flask.request.method == "POST":
if flask.request.files.get("image"):
# read the image in PIL format
image = flask.request.files["image"].read()
image = Image.open(io.BytesIO(image))
image = recortar(image)
app.logger.info('Tamaño: '+str(image.size))
image = img_to_array(image)
image = np.expand_dims(image, axis=0)
with graph.as_default():
preds = model.predict(image)
data['predictions'] = str(np.squeeze(preds).tolist())
data["success"] = True
return flask.jsonify(data)
else:
return "No se ha obtenido la imagen"
else:
return "El HTTP request no era POST"
# if this is the main thread of execution first load the model and
# then start the server
if __name__ == "__main__":
print(("* Loading Keras model and Flask starting server..."
"please wait until server has fully started"))
app.debug = True
app.run()
Sending the image via curl works perfectly: as expected, I obtain a JSON response from the server containing the prediction. Here's the CURL command and the server response:
>> curl -X POST -F image=@nevus.jpg 'https://example.com/predict'
{"predictions":"[0.7404708862304688, 0.25952914357185364]","success":true}
Then I try to repeat the same process, but through an Android app, but I get a 500 error as response. When checking the logs on Stackdriver Error Reporting, I see the following stacktrace:AttributeError:
'NoneType' object has no attribute 'size'
at predict (/home/vmagent/app/main.py:73)
at dispatch_request (/env/lib/python3.6/site-packages/flask/app.py:1799)
at full_dispatch_request (/env/lib/python3.6/site-packages/flask/app.py:1813)
at reraise (/env/lib/python3.6/site-packages/flask/_compat.py:35)
at handle_user_exception (/env/lib/python3.6/site-packages/flask/app.py:1718)
at full_dispatch_request (/env/lib/python3.6/site-packages/flask/app.py:1815)
at wsgi_app (/env/lib/python3.6/site-packages/flask/app.py:2292)
at reraise (/env/lib/python3.6/site-packages/flask/_compat.py:35)
at handle_exception (/env/lib/python3.6/site-packages/flask/app.py:1741)
at wsgi_app (/env/lib/python3.6/site-packages/flask/app.py:2295)
at __call__ (/env/lib/python3.6/site-packages/flask/app.py:2309)
at handle_request (/env/lib/python3.6/site-packages/gunicorn/workers/sync.py:176)
at handle (/env/lib/python3.6/site-packages/gunicorn/workers/sync.py:135)
This error refers to image object, so I assume that, as the code was working properly before, the error must be in the way I send the image through the HTTP request. Recall that the image is taken when a user click a button, because this button sends an intent for taking the photo. When the photo is taken, the user can click a send button, whose code I post bellow. Note that orientedBitmap corresponds to the photo taken in bitmap format.
btn_enviarfoto.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Log.d(TAG, "Botón \"enviar\" pulsado. Codificando imagen.");
ByteArrayOutputStream stream = new ByteArrayOutputStream();
orientedBitmap.compress(Bitmap.CompressFormat.PNG, 100, stream);
byte[] byteArray = stream.toByteArray();
orientedBitmap.recycle();
uploadToServer(byteArray);
}
});
uploadToServer just calls the execute methong of AsynchTask class as shown bellow:
private void uploadToServer(byte[] data) {
Bitmap bitmapOrg = BitmapFactory.decodeByteArray(data, 0, data.length);
Log.d(TAG, "Imagen codificada. Enviando al servidor.");
ObtenerPrediccionTask task = new ObtenerPrediccionTask();
task.execute(bitmapOrg);
}
And finally and most important, this is the code for the ObtenerPrediccionTask class:
public class ObtenerPrediccionTask extends AsyncTask<Bitmap, Void, String> {
@Override
protected String doInBackground(Bitmap... imagen) {
ByteArrayOutputStream bao = new ByteArrayOutputStream();
HttpURLConnection connection = null;
DataOutputStream outputStream = null;
String probabilidad_melanoma = "";
JsonReader jsonReader = null;
try {
for (int i = 0; i < imagen.length; i++) {
Bitmap imagen2 = imagen[i];
imagen2.compress(Bitmap.CompressFormat.JPEG, 90, bao);
byte[] ba = bao.toByteArray();
InputStream fileInputStream = new ByteArrayInputStream(ba);
URL url = new URL("https://example.com/predict"); // not the real URL
String lineEnd = "\r\n";
String twoHyphens = "--";
String boundary = "xxxxxxxx";
String str = twoHyphens + boundary + lineEnd;
connection = (HttpURLConnection) url.openConnection();
// Allow Inputs & Outputs
connection.setDoInput(true);
connection.setDoOutput(true);
connection.setUseCaches(false);
// Enable POST method
connection.setRequestMethod("POST");
connection.setRequestProperty("Connection", "Keep-Alive");
connection.setRequestProperty("Content-Type", "multipart/form-data;boundary=" + boundary);
outputStream = new DataOutputStream(connection.getOutputStream());
outputStream.writeBytes(twoHyphens + boundary + lineEnd);
outputStream.writeBytes("Content-Disposition: form-data; name=\"" +
"image" + "\";filename=\"" +
"foto.jpg" + "\"" + lineEnd);
outputStream.writeBytes(lineEnd);
int bytesAvailable = fileInputStream.available();
int bufferSize = Math.min(bytesAvailable, 1024);
byte[] buffer = new byte[bufferSize];
// Read file
int bytesRead = fileInputStream.read(buffer, 0, bufferSize);
while (bytesRead > 0) {
outputStream.write(buffer, 0, bufferSize);
bytesAvailable = fileInputStream.available();
bufferSize = Math.min(bytesAvailable, 1024);
bytesRead = fileInputStream.read(buffer, 0, bufferSize);
}
outputStream.writeBytes(lineEnd);
outputStream.writeBytes(twoHyphens + boundary + twoHyphens + lineEnd);
// Responses from the server (code and message)
int responseCode = connection.getResponseCode();
connection.getResponseMessage();
fileInputStream.close();
outputStream.flush();
outputStream.close();
if (responseCode == HttpURLConnection.HTTP_OK) {
InputStream responseStream = new
BufferedInputStream(connection.getInputStream());
BufferedReader responseStreamReader =
new BufferedReader(new InputStreamReader(responseStream));
String line = "";
StringBuilder stringBuilder = new StringBuilder();
while ((line = responseStreamReader.readLine()) != null) {
stringBuilder.append(line).append("\n");
}
responseStreamReader.close();
String response = stringBuilder.toString();
Log.d(TAG, "Imagen recibida por el servidor y pasada al modelo. Esta es la respuesta: " + response);
jsonReader = new JsonReader(new StringReader(response));
probabilidad_melanoma = readJson(jsonReader);
} else {
Log.d(TAG, Integer.toString(responseCode));
}
}
return probabilidad_melanoma;
} catch (MalformedURLException malformedURLException) {
Log.e(TAG, malformedURLException.toString());
return null;
} catch (IOException io) {
Log.e(TAG, io.toString());
return null;
} finally {
if (connection != null) {
connection.disconnect();
}
}
}
protected void onPostExecute(String probabilidad_melanoma) {
if (probabilidad_melanoma != null) {
Log.d(TAG, "Probabilidad melanoma: " + probabilidad_melanoma);
} else {
Log.w(TAG, "La respuesta ha sido nula");
}
}
}
readJson function is also working properly, so don't get bothered by it.
This last chunk of code is the result of an extensive search in SO of a way to properly send an image, but as nothing has worked yet, I've run out of ideas. What's the problem with my code?