api_server.py

import os
import time
import numpy as np
from PIL import Image

from pathlib import Path

# Disable tensorflow warnings
os.environ['TF_CPP_MIN_LOG_LEVEL'] = '3'

from tensorflow import keras
from flask import Flask, jsonify, request, render_template

load_type = 'remote_hub_from_pretrained'
"""
local;
remote_hub_download; 
remote_hub_from_pretrained;
remote_hub_pipeline; - needs config.json and this is not easy to grasp how to do it with custom models
https://discuss.huggingface.co/t/how-to-create-a-config-json-after-saving-a-model/10459/4
"""

REPO_ID = "1vash/mnist_demo_model"
MODEL_DIR = "./artifacts/models"

# Load the saved model into memory
if load_type == 'local':
    model = keras.models.load_model(f'{MODEL_DIR}/mnist_model.h5')
elif load_type == 'remote_hub_download':
    from huggingface_hub import hf_hub_download

    model = keras.models.load_model(hf_hub_download(repo_id=REPO_ID, filename="saved_model.pb"))
elif load_type == 'remote_hub_from_pretrained':
    # https://huggingface.co/docs/hub/keras
    os.environ['TRANSFORMERS_CACHE'] = str(Path(MODEL_DIR).absolute())
    from huggingface_hub import from_pretrained_keras
    model = from_pretrained_keras(REPO_ID, cache_dir=MODEL_DIR)
elif load_type == 'remote_hub_pipeline':
    from transformers import pipeline

    model = pipeline("image-classification", model=REPO_ID)
else:
    raise AssertionError('No load type is specified!')

# Initialize the Flask application
app = Flask(__name__)


# API route for prediction
@app.route('/predict', methods=['POST'])
def predict():
    """
    Predicts the class label of an input image.

    Request format:
    {
        "image": [[pixel_values_gray]]
    }

    Response format:
    {
        "label": predicted_label,
        "pred_proba" prediction class probability
        "ml-latency-ms": latency_in_milliseconds
            (Measures time only for ML operations preprocessing with predict)
    }
    """
    if 'image' not in request.files:
        # Handle if no file is selected
        return 'No file selected'

    start_time = time.time()

    file = request.files['image']

    # Get pixels out of file
    image_data = Image.open(file)

    # Check image shape
    if image_data.size != (28, 28):
        return "Invalid image shape. Expected (28, 28), take from 'demo images' folder."

    # Preprocess the image
    processed_image = preprocess_image(image_data)

    # Make a prediction, verbose=0 to disable progress bar in logs
    prediction = model.predict(processed_image, verbose=0)

    # Get the predicted class label
    predicted_label = np.argmax(prediction)
    proba = prediction[0][predicted_label]

    # Calculate latency in milliseconds
    latency_ms = (time.time() - start_time) * 1000

    # Return the prediction result and latency as dictionary response
    response = {
        'label': int(predicted_label),
        'pred_proba': float(proba),
        'ml-latency-ms': round(latency_ms, 4)
    }

    # dictionary is not a JSON: https://www.quora.com/What-is-the-difference-between-JSON-and-a-dictionary
    # flask.jsonify vs json.dumps https://sentry.io/answers/difference-between-json-dumps-and-flask-jsonify/
    # The flask.jsonify() function returns a Response object with Serializable JSON and content_type=application/json.
    return jsonify(response)


# Helper function to preprocess the image
def preprocess_image(image_data):
    """Preprocess image for Model Inference

    :param image_data: Raw image
    :return: image: Preprocessed Image
    """
    # Resize the image to match the input shape of the model
    image = np.array(image_data).reshape(1, 28, 28)

    # Normalize the pixel values
    image = image.astype('float32') / 255.0

    return image


# API route for health check
@app.route('/health', methods=['GET'])
def health():
    """
    Health check API to ensure the application is running.
    Returns "OK" if the application is healthy.
    Demo Usage: "curl http://localhost:5000/health" or using alias "curl http://127.0.0.1:5000/health"
    """
    return 'OK'


# API route for version
@app.route('/version', methods=['GET'])
def version():
    """
    Returns the version of the application.
    Demo Usage: "curl http://127.0.0.1:5000/version" or using alias "curl http://127.0.0.1:5000/version"
    """
    return '1.0'


@app.route("/")
def hello_world():
    return render_template("index.html")
    # return "<p>Hello, Team!</p>"


# Start the Flask application
if __name__ == '__main__':
    app.run(debug=True)