KDSingleApplication: Do not exceed maximum socket name length

[PatBlankdeCas]

Under MacOS (Sequoia) the app cannot start under certain conditions.

Start attempt with:
The following start attempt: OPENCLOUD_HTTP_VERBOSE=1 /Applications/OpenCloud.app/Contents/MacOS/opencloud --logdebug --logfile -

Error message:
QLocalServer::listen: Name error
gui.main: Already running, exiting...
kdsingleapplication.localsocket: Connection timed out

When starting the app with sudo, the app can be started successfully.
The app can also be started as follows:
export TMPDIR=/tmp
/Applications/OpenCloud.app/Contents/MacOS/OpenCloud

Solution approach 1:
New user with a shorter name: successful.

Solution 2:
User directory name shortened. Also successful.

The previous user name had 28 characters. Together with kdsingleapp-username-OpenCloud it is a total of 50 characters. This seems to be the problem.

[michaelstingl]

Technical Analysis: macOS Socket Name Length Issue

Disclaimer

This analysis was conducted with AI assistance based on:

• 🤖 Analysis of https://github.com/opencloud-eu/desktop
• 🤖 Analysis of https://github.com/KDAB/KDSingleApplication
• 🤖 Web research

Root Cause

The issue occurs due to Unix Domain Socket path length limitations on macOS. The application fails to start with the error:

QLocalServer::listen: Name error
gui.main: Already running, exiting...
kdsingleapplication.localsocket: Connection timed out

Technical Details

1. Socket Path Length Limits:

   • macOS: 104 bytes (sizeof(sockaddr_un.sun_path))
   • Linux: 108 bytes
   • Portable recommendation: 92 bytes

2. Current Socket Name Pattern:

   • Format: kdsingleapp-<username>-OpenCloud
   • Example with 28-char username:
     • Base: "kdsingleapp-" (12 chars)
     • Username: 28 chars
     • Separator: "-" (1 char)
     • App name: "OpenCloud" (9 chars)
     • Total: 50 chars

3. macOS Temporary Path:

   • Typical length: ~49 chars (e.g., /var/folders/xx/xxxxxxxxxx/T/)
   • Combined with socket name: 49 + 50 = 99 chars
   • Very close to the 104-byte limit

Current Status

• OpenCloud Desktop 1.0.0: Uses KDSingleApplication 1.1.0 (April 2024)
• KDSingleApplication: Fix was merged on November 16, 2024 (commit 32141cc)
• Problem: The fix is not yet in a released version

Solution Already Implemented Upstream

KDAB has already fixed this issue in KDSingleApplication:

• Commit: KDAB/KDSingleApplication@32141cc
• The fix:
  • Uses UID instead of username when the path would be too long
  • Truncates the socket name if necessary
  • Properly handles different OS limits

Recommendations

1. Short-term (Immediate):

   • Update the desktop app to use a shorter application name:

   // Instead of:
   KDSingleApplication singleApplication;
   
   // Use:
   KDSingleApplication singleApplication("OC");
   // or
   KDSingleApplication singleApplication("OpenCloud", 
       KDSingleApplication::Option::IncludeSessionInSocketName);

2. Medium-term (Preferred):

   • Wait for KDSingleApplication 1.1.1 or 1.2.0 release
   • Update the Craft blueprint to use the new version
   • Rebuild OpenCloud Desktop with the updated library

3. Alternative (If urgent):

   • Update Craft blueprint to use KDSingleApplication from git master
   • This would include the fix immediately

References

• KDSingleApplication fix: KDAB/KDSingleApplication@32141cc
• Unix socket documentation: https://man7.org/linux/man-pages/man7/unix.7.html
• Related issue in Strawberry Music Player: Strawberry 1.1.3 crashes on launch (Paid) strawberrymusicplayer/strawberry#1603

Testing

The issue can be reproduced by:

1. Creating a macOS user with a username of 25+ characters
2. Attempting to start OpenCloud Desktop
3. The application will fail with the socket error

The fix has been tested by KDAB on both Linux and macOS.

[TheOneRing]

I contacted KDAB and asked whether the can release a new version including KDAB/KDSingleApplication#45