A wrong Server URL can land on the host's static web UI, which answers
200 OK with an HTML page. connect() treated any 2xx from /users/auth (or
/users/create) as a successful login, so the user was silently
"connected" to an endpoint that can never sync: pulls report 0% and
pushes fail with no error surfaced. This is the root of the symptom in
#4692 (KOReader sync to a Grimmory/Booklore server failing on Android).
Validate that the auth/registration response is an actual KOReader Sync
JSON object (a real server replies e.g. {"authorized":"OK"}; an HTML
page fails JSON parsing) and otherwise return a clear
"Not a KOReader Sync server. Check the Server URL." message.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Huang Xin
316ca3c941