Github release assets model autodownload

[Ownmarc]

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Simplified and robust pretrained model downloading in Ultralytics YOLOv5.

📊 Key Changes

• Removed deprecated Google Drive download logic for pretrained YOLOv5 models.
• Added direct download from GitHub releases as the primary method.
• Included a fallback to Google Cloud Storage if GitHub download fails.
• Implemented assertions and improved error handling for download integrity checks.

🎯 Purpose & Impact

• 🔄 Streamlining Download Process: The update aims to simplify how users download pretrained models by using GitHub, which may offer a more reliable service compared to the previous method.
• 🛠 Enhanced Reliability: By asserting file existence and size after download, users are less likely to encounter issues due to incomplete or failed downloads.
• 🐛 Better Error Messaging: Clear error messages can help diagnose problems during the download process, improving user experience.
• 🔗 Fallback Option: In case of GitHub issues, the code now attempts to download from Google Cloud Storage, providing an alternative to ensure that the process is less prone to failure.

[glenn-jocher]

Ok I think this looks good now, but unfortunately I'm seeing an error locally that doesn't show up in the checks. I get this on a python detect.py command.

Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/urllib/request.py", line 1350, in do_open
    h.request(req.get_method(), req.selector, req.data, headers,
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/http/client.py", line 1255, in request
    self._send_request(method, url, body, headers, encode_chunked)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/http/client.py", line 1301, in _send_request
    self.endheaders(body, encode_chunked=encode_chunked)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/http/client.py", line 1250, in endheaders
    self._send_output(message_body, encode_chunked=encode_chunked)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/http/client.py", line 1010, in _send_output
    self.send(msg)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/http/client.py", line 950, in send
    self.connect()
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/http/client.py", line 1424, in connect
    self.sock = self._context.wrap_socket(self.sock,
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/ssl.py", line 500, in wrap_socket
    return self.sslsocket_class._create(
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/ssl.py", line 1040, in _create
    self.do_handshake()
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/ssl.py", line 1309, in do_handshake
    self._sslobj.do_handshake()
ssl.SSLCertVerificationError: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (_ssl.c:1123)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/glennjocher/PycharmProjects/yolov5/detect.py", line 171, in <module>
    detect()
  File "/Users/glennjocher/PycharmProjects/yolov5/detect.py", line 33, in detect
    model = attempt_load(weights, map_location=device)  # load FP32 model
  File "/Users/glennjocher/PycharmProjects/yolov5/models/experimental.py", line 136, in attempt_load
    attempt_download(w)
  File "/Users/glennjocher/PycharmProjects/yolov5/utils/google_utils.py", line 31, in attempt_download
    hub.download_url_to_file('https://github.com/ultralytics/yolov5/releases/download/v2.0/' + file, weights)
  File "/Users/glennjocher/PycharmProjects/yolov5/venv/lib/python3.8/site-packages/torch/hub.py", line 379, in download_url_to_file
    u = urlopen(req)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/urllib/request.py", line 222, in urlopen
    return opener.open(url, data, timeout)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/urllib/request.py", line 525, in open
    response = self._open(req, data)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/urllib/request.py", line 542, in _open
    result = self._call_chain(self.handle_open, protocol, protocol +
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/urllib/request.py", line 502, in _call_chain
    result = func(*args)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/urllib/request.py", line 1393, in https_open
    return self.do_open(http.client.HTTPSConnection, req,
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/urllib/request.py", line 1353, in do_open
    raise URLError(err)
urllib.error.URLError: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (_ssl.c:1123)>

It looks like the problem is specific to MacOS with python requests (I'm running on a Macbook). We may have to ditch the torch downloader for the existing curl commands, which I've never seen anyone report problems with.
https://stackoverflow.com/questions/42098126/mac-osx-python-ssl-sslerror-ssl-certificate-verify-failed-certificate-verify

[glenn-jocher]

I dropped all this into a try, except, finally clause. Try GitHub, except GCP, finally check and return

[glenn-jocher]

CI is passing, everything seems good, merging.