fix(reverseproxy): set is_proxied=True when X-Forwarded-Proto is present

[austin-rt]

Problem

When Calibre-Web is served through a Cloudflare Tunnel (or any reverse proxy that sends X-Forwarded-Proto without X-Forwarded-Host), the Kobo sync URL is generated with localhost:8083 instead of the public HTTPS URL.

Root cause: ReverseProxied.is_proxied only returns True when HTTP_X_FORWARDED_HOST is present. Cloudflare Tunnel (and most standard reverse proxy configurations including nginx, Caddy, and Traefik in their default configs) sends X-Forwarded-Proto but not X-Forwarded-Host, so is_proxied stays False. This causes kobo.py:get_download_url_for_book() to fall back to an explicit host:port URL, appending the internal container port (default 8083) — e.g. https://books.example.com:8083/kobo/.... This breaks Kobo wireless sync silently: books appear in the library but fail to download.

My Setup

• Raspberry Pi running Calibre-Web in Docker
• Cloudflare Tunnel exposing it externally (no port forwarding)
• Kobo Clara BW syncing via the external URL

Changes

1. cps/reverseproxy.py — Core fix

Also check X-Forwarded-Proto when determining scheme, and set self.proxied = True whenever any proxy header is detected — consistent with the existing X-Forwarded-Host behaviour.

# Before
scheme = environ.get('HTTP_X_SCHEME', '')
if scheme:
    environ['wsgi.url_scheme'] = scheme

# After
scheme = environ.get('HTTP_X_SCHEME', '') or environ.get('HTTP_X_FORWARDED_PROTO', '')
if scheme:
    environ['wsgi.url_scheme'] = scheme
    self.proxied = True

2. cps/config_sql.py — Schema default change

Changed config_external_port column default from 8083 to None. The old default was misleading behind a proxy — it caused the port to always be appended to URLs even when it shouldn't be.

3. cps/kobo.py — Runtime fallback

Fall back to DEFAULT_PORT (8083) at runtime when config_external_port is None, preserving existing behavior for non-proxied setups.

4. cps/admin.py — Blank port handling + proxy context

• Passes is_proxied to config_edit.html and admin.html templates
• Handles blank External Port submission as NULL instead of crashing (int('') threw ValueError)

5. cps/templates/config_edit.html — Port field UX

• Port field is no longer required; value is blank when NULL; placeholder shows 8083
• Help text shown when proxy detected:

  "A reverse proxy was detected. Leave blank unless you need to override the port for direct access."

6. cps/templates/admin.html — Config display

• Shows stored value if set
• Shows "Not set — reverse proxy detected" (italic) if proxied and not set
• Falls back to 8083 if not proxied and not set

Notes

• ProxyFix in __init__.py already correctly handles X-Forwarded-Proto for scheme detection, and TRUSTED_PROXY_COUNT is documented for Cloudflare Tunnel. This closes the gap in is_proxied, which is a separate check used by kobo.py.
• X-Forwarded-Proto is the most universally forwarded proxy header — this fix broadens is_proxied detection to cover Cloudflare Tunnel and the majority of standard proxy setups that don't explicitly set X-Forwarded-Host.
• I've raised the same fix against Calibre-Web Automated: fix: set is_proxied=True when X-Forwarded-Proto header is present crocodilestick/Calibre-Web-Automated#1143.

Verified

Tested end-to-end on a fresh Docker install behind a Cloudflare Tunnel:

Test	Result
Reverse proxy auto-detected via X-Forwarded-Proto	✅
Help text "A reverse proxy was detected..." shown on config page	✅
Port field blank by default with placeholder 8083	✅
Config saves cleanly with blank port (previously crashed)	✅
Kobo Auth URL uses public hostname (https://...)	✅
Kobo download URLs use public hostname (not localhost:8083)	✅
E2E tested on fresh Docker install with empty library	✅
Kobo device sync confirmed — books downloaded to device (Kobo Clara BW)	✅

---

Note: Python isn't my primary language so apologies if the implementation isn't idiomatic — happy to iterate based on feedback.

[austin-rt]

Status: All changes verified via automated e2e testing against a fresh Docker install behind a Cloudflare Tunnel — Kobo sync URLs correctly use the public hostname, config saves cleanly with a blank port field, and reverse proxy detection works.

Keeping this as a draft until I can confirm full end-to-end sync onto a physical Kobo device. Will mark ready for review once that's verified.