Creation time of images

[jmozmoz]

Is there a way to access the creation time of the images? By this one could wait 3 hours before downloading a new file.

Currently the images do not contain EXIF data and the server response with this header:

t = 'https://clouds.matteason.co.uk/images/2048x1024/clouds.jpg'
response = requests.head(t, allow_redirects=True)
print(json.dumps(dict(response.headers), indent=4))

{
    "Date": "Sun, 07 Jan 2024 15:03:36 GMT",
    "Content-Type": "image/jpeg",
    "Content-Length": "453521",
    "Connection": "keep-alive",
    "last-modified": "Sun, 07 Jan 2024 14:40:10 GMT",
    "access-control-allow-origin": "*",
    "etag": "\"659ab7ca-6eb91\"",
    "expires": "Sun, 07 Jan 2024 14:56:22 GMT",
    "Cache-Control": "max-age=600",
    "x-proxy-cache": "MISS",
    "x-github-request-id": "D7A6:3CB921:4663A39:478CE79:659AB93E",
    "via": "1.1 varnish",
    "x-served-by": "cache-fra-eddf8230113-FRA",
    "x-cache": "MISS",
    "x-cache-hits": "0",
    "x-timer": "S1704638782.245013,VS0,VE116",
    "vary": "Accept-Encoding",
    "x-fastly-request-id": "d37c7c93eee1d54d41bbf3af796af759af214a7b",
    "CF-Cache-Status": "REVALIDATED",
    "Accept-Ranges": "bytes",
    "Report-To": "{\"endpoints\":[{\"url\":\"https:\\/\\/a.nel.cloudflare.com\\/report\\/v3?s=HcZUwe2O41bkdngpsz%2FeRquqDosFjSkMRrYWri%2FNvekWfdQ91DnaRhMtXxdsYvD7ussoKqgzLnrtu6yxtNp4Uii2pJvcg2uhh%2F%2BfiVW%2FXcUl8waPfh%2Bxc4MDJ5zSgU6C1N%2FfYWvlE3CW\"}],\"group\":\"cf-nel\",\"max_age\":604800}",
    "NEL": "{\"success_fraction\":0,\"report_to\":\"cf-nel\",\"max_age\":604800}",
    "Server": "cloudflare",
    "CF-RAY": "841d16a639d16d6e-MUC",
    "alt-svc": "h3=\":443\"; ma=86400"
}

Date is the time of downloading and last-modified seems to change every 30 minutes. It would be best, if this information were available in the header sent by the server. Of perhaps in a separate text/json file on the server.

[jmozmoz]

Okay, I guess the 30 minutes interval of new images results from this: https://github.com/matteason/live-cloud-maps/blob/main/.github/workflows/generate-images.yml#L6

So in fact it is a new image every 30 minutes. So I guess it would require more work to determine if the base images have changed and store this information somewhere.

[matteason]

Hi @jmozmoz - yes, this is a good idea. Ostensibly the source data is updated every three hours, but the workflow runs more frequently because sometimes the base images contain holes which later get filled in.

What I could do is take a hash of the newly generated file, compare it to the currently published file, and only republish if it's changed. Then the last-modified should be accurate and you could issue a HEAD request to determine if you need to refetch.

[jmozmoz]

See jmozmoz/cloudmap#12 (comment)