Fix validate url

[freddyaboulton]

Description

ImgSerializable.serialize would fail on an image url because Path(load_dir) / x would strip out some of the slashes in the url which would cause the url to be treated as a file.

Doing Path(load_dir) / x basically assumes x is a filepath instead of a url but that has not been determined at the time that line is reached so I refactored the logic a bit so that Path(load_dir) / x is only called if x is not a url.

This comes at the cost of two get requests to the external url but the benefit is that we don't have to modify any of the public apis of our util functions.

Checklist:

• I have performed a self-review of my own code
• I have added a short summary of my change to the CHANGELOG.md
• My code follows the style guidelines of this project
• I have commented my code in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

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[gradio-pr-bot]

All the demos for this PR have been deployed at https://huggingface.co/spaces/gradio-pr-deploys/pr-2957-all-demos

[abidlabs]

This works great @freddyaboulton, nice catch!

Regarding the speed issue, we could change the validate_url method to use requests.head() instead of requests.get() so that it does not download the whole file when checking if the file exists:

def validate_url(possible_url: str) -> bool:
    headers = {"User-Agent": "gradio (https://gradio.app/; team@gradio.app)"}
    try:
        return requests.head(possible_url, headers=headers).ok
    except Exception:
        return False

Thoughts? A quick benchmark shows that the time to run validate_url on a 5 MB file drops from 1s to 0.3s if we use head():

import requests
import time

t = time.time()
headers = {"User-Agent": "gradio (https://gradio.app/; team@gradio.app)"}
requests.get("https://edmullen.net/test/rc.jpg", headers=headers).ok
print(time.time() - t)

t = time.time()
requests.head("https://edmullen.net/test/rc.jpg", headers=headers).ok
print(time.time() - t)

[freddyaboulton]

Thanks for the suggestion @abidlabs !

The one snag is that the gradio file route does not support head requests. I made that addition to the routes.py file but that means that we will first try head and if that's not supported we'll try with get.

Let me know what you think before I merge!

[abidlabs]

Great catch @freddyaboulton, LGTM

[freddyaboulton]

Thank you for the re-review!