internal/exp/service/activity/{github,gerrit}: walkSegMail can fail with EOF

[dmitshur]

The following error was observed on 2021-02-02 11:15:

GitHub Activity Service: walkSegMail(github.fileSeg{file:"/2021-02.reclog", skip:0, size:4096}): truncated record at offset 0: EOF
Gerrit Activity Service: ok

Restarting fixed the issue.

It's looks like a possible race condition: the file length was determined to be 4096 bytes yet reading at offset 0 returned EOF. Maybe the file was still being written after being created, and the buffers weren't flushed?

[dmitshur]

This was observed again on 2023-03-01 12:38 AM UTC:

GitHub Activity Service: ok
Gerrit Activity Service: walkSegMail(gerrit.fileSeg{file:"/2023-03.reclog", skip:0, size:4096}): truncated record at offset 0: EOF

Like the last time, it happened at the very beginning of a new month. Perhaps this race can only happen under conditions when a new file is being created.