fix(server): add O_TRUNC when creating PID file to avoid stale content

[weim0000]

What problem does this change solve?

CreatePidFile opens the PID file with O_RDWR | O_CREAT but without O_TRUNC. If a stale PID file already exists from a previous run and the old PID string is longer than the new one, open() + write() will only overwrite the first N bytes of the file, leaving the trailing bytes from the old content intact. This results in a corrupted PID file.

Example:
Step File content Note
Previous run (PID=12345) 12345 correct
New run (PID=678), without O_TRUNC 67845 corrupted — trailing 45 is stale
New run (PID=678), with O_TRUNC 678 correct

A corrupted PID file can cause process management tools (e.g., kill $(cat pidfile), systemd, init scripts) to target the wrong process or fail to stop/restart the service.

How does this change fix the problem?

Add O_TRUNC to the open() flags in CreatePidFile so the file is truncated to zero length before writing the new PID, ensuring no stale bytes remain.

Changes

• src/cli/pid_util.h: Add O_TRUNC flag to the open() call in CreatePidFile.
• tests/cppunit/pid_util_test.cc: Add unit tests covering:
• • Truncation on existing file: Write a longer fake PID first, then call CreatePidFile and verify the content matches exactly the current PID with no leftover bytes.
• • Creation from scratch: Verify CreatePidFile works correctly when no file exists.
• • RemovePidFile: Verify the PID file is properly removed.

[github-actions]

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