Creating an aiohttp Application to Fetch and Validate NASA Mars Photos

We start by creating a new Python virtual environment (Python 3.5+ recommended) and installing aiohttp with pip install aiohttp . A basic nasa.py file is created containing an asynchronous request handler that returns a static text response.

The handler get_mars_photo is registered on the root path using app.router.add_get('/', get_mars_photo, name='mars_photo') . The application is run with web.run_app(app, host='127.0.0.1', port=8080) or via aiohttp-devtools for live reload.

To obtain real images we call the NASA Mars Rover API at https://api.nasa.gov/mars-photos/api/v1/rovers/curiosity/photos with required parameters sol (Martian day) and api_key . The following coroutine selects a random sol, fetches the JSON response, and returns a random img_src URL:

<code>import random
from aiohttp import web, ClientSession
NASA_API_KEY = 'DEMO_KEY'
ROVER_URL = 'https://api.nasa.gov/mars-photos/api/v1/rovers/curiosity/photos'

async def get_mars_image_url_from_nasa():
    while True:
        sol = random.randint(0, 1722)
        params = {'sol': sol, 'api_key': NASA_API_KEY}
        async with ClientSession() as session:
            async with session.get(ROVER_URL, params=params) as resp:
                resp_dict = await resp.json()
        if 'photos' not in resp_dict:
            raise Exception('No photos key')
        photos = resp_dict['photos']
        if not photos:
            continue
        return random.choice(photos)['img_src']
</code>

To ensure the image is suitable we validate its dimensions (≥1024 px) and that it is not grayscale. Pillow is installed with pip install pillow . The validation coroutine looks like:

<code>import io
from PIL import Image

async def validate_image(image_bytes):
    image = Image.open(io.BytesIO(image_bytes))
    return image.width >= 1024 and image.height >= 1024 and image.mode != 'L'
</code>

Another coroutine repeatedly fetches image bytes until a valid image is found:

<code>async def get_mars_photo_bytes():
    while True:
        image_url = await get_mars_image_url_from_nasa()
        async with ClientSession() as session:
            async with session.get(image_url) as resp:
                image_bytes = await resp.read()
        if await validate_image(image_bytes):
            break
    return image_bytes
</code>

The final request handler returns the image directly:

<code>async def get_mars_photo(request):
    image = await get_mars_photo_bytes()
    return web.Response(body=image, content_type='image/jpeg')
</code>

The complete application assembles the validation, image‑fetching, and routing logic, then starts the aiohttp server:

<code>import random
import io
from aiohttp import web, ClientSession
from PIL import Image

NASA_API_KEY = 'DEMO_KEY'
ROVER_URL = 'https://api.nasa.gov/mars-photos/api/v1/rovers/curiosity/photos'

# (validate_image, get_mars_image_url_from_nasa, get_mars_photo_bytes, get_mars_photo definitions as above)

app = web.Application()
app.router.add_get('/', get_mars_photo, name='mars_photo')
</code>

Running this script displays a random high‑resolution Mars photo in the browser, and the code can be extended with caching, dynamic sol selection, or additional filters.