How to read a utf-8 encoded binary string in tensorflow?

Question

I am trying to convert an encoded byte string back into the original array in the tensorflow graph (using tensorflow operations) in order to make a prediction in a tensorflow model. The array to byte conversion is based on this answer and it is the suggested input to tensorflow model prediction on google cloud's ml-engine.

def array_request_example(input_array):
    input_array = input_array.astype(np.float32)
    byte_string = input_array.tostring()
    string_encoded_contents = base64.b64encode(byte_string)
    return string_encoded_contents.decode('utf-8')}

Tensorflow code

byte_string = tf.placeholder(dtype=tf.string)
audio_samples = tf.decode_raw(byte_string, tf.float32)

audio_array = np.array([1, 2, 3, 4])
bstring = array_request_example(audio_array)
fdict = {byte_string: bstring}
with tf.Session() as sess:
    [tf_samples] = sess.run([audio_samples], feed_dict=fdict)

I have tried using decode_raw and decode_base64 but neither return the original values.

I have tried setting the the out_type of decode raw to the different possible datatypes and tried altering what data type I am converting the original array to.

So, how would I read the byte array in tensorflow? Thanks :)

Extra Info

The aim behind this is to create the serving input function for a custom Estimator to make predictions using gcloud ml-engine local predict (for testing) and using the REST API for the model stored on the cloud.

The serving input function for the Estimator is

def serving_input_fn():
    feature_placeholders = {'b64': tf.placeholder(dtype=tf.string,
                                                  shape=[None],
                                                  name='source')}
    audio_samples = tf.decode_raw(feature_placeholders['b64'], tf.float32)
    # Dummy function to save space
    power_spectrogram = create_spectrogram_from_audio(audio_samples)
    inputs = {'spectrogram': power_spectrogram}
    return tf.estimator.export.ServingInputReceiver(inputs, feature_placeholders)

Json request

I use .decode('utf-8') because when attempting to json dump the base64 encoded byte strings I receive this error

raise TypeError(repr(o) + " is not JSON serializable")
TypeError: b'longbytestring'

Prediction Errors

When passing the json request {'audio_bytes': 'b64': bytestring} with gcloud local I get the error

PredictionError: Invalid inputs: Expected tensor name: b64, got tensor name: [u'audio_bytes']

So perhaps google cloud local predict does not automatically handle the audio bytes and base64 conversion? Or likely somethings wrong with my Estimator setup.

And the request {'instances': [{'audio_bytes': 'b64': bytestring}]} to REST API gives

{'error': 'Prediction failed: Error during model execution: AbortionError(code=StatusCode.INVALID_ARGUMENT, details="Input to DecodeRaw has length 793713 that is not a multiple of 4, the size of float\n\t [[Node: DecodeRaw = DecodeRaw[_output_shapes=[[?,?]], little_endian=true, out_type=DT_FLOAT, _device="/job:localhost/replica:0/task:0/device:CPU:0"](_arg_source_0_0)]]")'}

which confuses me as I explicitly define the request to be a float and do the same in the serving input receiver.

Removing audio_bytes from the request and utf-8 encoding the byte strings allows me to get predictions, though in testing the decoding locally, I think the audio is being incorrectly converted from the byte string.

Demetrademetre

Answer 1

The answer that you referenced, is written assuming you are running the model on CloudML Engine's service. The service actually takes care of the JSON (including UTF-8) and base64 encoding.

To get your code working locally or in another environment, you'll need the following changes:

def array_request_example(input_array):
    input_array = input_array.astype(np.float32)
    return input_array.tostring()

byte_string = tf.placeholder(dtype=tf.string)
audio_samples = tf.decode_raw(byte_string, tf.float32)

audio_array = np.array([1, 2, 3, 4])
bstring = array_request_example(audio_array)
fdict = {byte_string: bstring}
with tf.Session() as sess:
    tf_samples = sess.run([audio_samples], feed_dict=fdict)

That said, based on your code, I suspect you are looking to send data as JSON; you can use gcloud local predict to simulate CloudML Engine's service. Or, if you prefer to write your own code, perhaps something like this:

def array_request_examples,(input_arrays):
  """input_arrays is a list (batch) of np_arrays)"""
  input_arrays = (a.astype(np.float32) for a in input_arrays)
  # Convert each image to byte strings
  bytes_strings = (a.tostring() for a in input_arrays)
  # Base64 encode the data
  encoded = (base64.b64encode(b) for b in bytes_strings)
  # Create a list of images suitable to send to the service as JSON:
  instances = [{'audio_bytes': {'b64': e}} for e in encoded]
  # Create a JSON request
  return json.dumps({'instances': instances})

def parse_request(request):
  # non-TF to simulate the CloudML Service which does not expect
  # this to be in the submitted graphs.
  instances = json.loads(request)['instances']
  return [base64.b64decode(i['audio_bytes']['b64']) for i in instances]

byte_strings = tf.placeholder(dtype=tf.string, shape=[None])
decode = lambda raw_byte_str: tf.decode_raw(raw_byte_str, tf.float32)
audio_samples = tf.map_fn(decode, byte_strings, dtype=tf.float32)

audio_array = np.array([1, 2, 3, 4])
request = array_request_examples([audio_array])
fdict = {byte_strings: parse_request(request)}
with tf.Session() as sess:
  tf_samples = sess.run([audio_samples], feed_dict=fdict)

Sleepy

Thanks :), you're correct I'm sending JSON to make predictions. What you suggested works locally to read the byte strings (once I add decode(utf-8)), but not in my Estimator's serving input function. I've updated the OP to explain why. From what I see the parsing gcloud should do automatically (if I've understood your answer right) is not happening as expected. – Demetrademetre