Incorrect protocol and port detection when APP_WEB_URL is unset behind Nginx

[osaimi]

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1. Is this request related to a challenge you're experiencing? Tell me about your story.

The Dify frontend relies on the backend to generate some frontend URLs. If APP_WEB_URL is not set, the backend uses request.url_root to determine the URL. However, when running Dify in a Docker environment behind Nginx, request.url_root fails to correctly detect the protocol and port.
 

• Protocol Issue: When Nginx uses HTTP but the external proxy uses HTTPS, the protocol is incorrectly detected as HTTP instead of HTTPS.
• Port Issue: The port is incorrectly determined because it is tied to NGINX_PORT.
   
  I cannot set APP_WEB_URL because clients access my Dify instance from multiple hosts and ports. As a result, leaving APP_WEB_URL unset causes incorrect frontend URL generation in dynamic setups with multiple hosts, ports, or proxies.
   
  Here is a screenshot of what’s happening:

2. Additional context or comments

I propose that we remove APP_WEB_URL completely and let the frontend use window.location.origin instead. Here is a proof of concept for the proposal: #13065

3. Can you help us with this feature?

• I am interested in contributing to this feature.

[osaimi]

Werkzeug’s ProxyFix middleware uses X-Forwarded-* headers to update the WSGI environ. By default, it tries to use two headers: X-Forwarded-For and X-Forwarded-Proto. This was added to Dify’s extensions in this PR.

def __init__(
   self,
   app: WSGIApplication,
   x_for: int = 1,
   x_proto: int = 1,
   x_host: int = 0,
   x_port: int = 0,
   x_prefix: int = 0,
) -> None:

 
It might be worth extending ext_proxy_fix.py to handle additional X-Forwarded-* headers.
 
 
The integer values in the ProxyFix configuration indicate the number of reverse proxies the middleware should trust. As a result, this setup will not work correctly beyond a single reverse proxy without further configuration.