Gitea #561 ("production writes a 0-byte log") is closed as not-a-defect. The
production log on wonder-app-vd03 listed as 0 bytes with LastWriteTime ==
CreationTime; opening it showed 4,658,893 bytes of correct output, written
continuously since service start.
On Windows the directory entry's size and last-write time are not refreshed while
the writing process holds the file open, so Get-ChildItem, dir and FileInfo.Length
all report size-at-open for the life of the handle. A live, healthy log is
indistinguishable from a dead sink by metadata alone — which is what made the
false reading survive six weeks of investigation.
That same trap was in the 29a202f5 instrumentation: CheckFileSinkGrowth measured
with FileInfo.Length, so it would have reported "self-check FAILED: the sink did
not grow" at every boot on a perfectly healthy Windows service — and a
self-check's false positive reads as confirmation of the very bug it was added to
find. MeasureFamilyBytes now reads Length through an opened FileStream:
FileShare.ReadWrite to open it at all while the sink holds its write handle, and
FileShare.Delete so the probe never blocks a roll or retention delete.
Both instruments are kept. A sink that cannot write its file is still a real and
otherwise-invisible failure — a sibling repo reproduced it via handle contention,
where RollingFileSink logs the lock-out to SelfLog and falls through to _001. Only
the two doc claims that are now false are corrected: the class summary's
"production ran that way for six weeks" and the warning text's "#561 failure mode".
Tests: A_working_file_sink_passes already measured while Serilog held the file
open — precisely the broken case — and passed throughout, because it only ever ran
on macOS, where the length is honest. That platform blindness is now recorded in
the class summary, alongside two tests pinning the sharing contract the fix
depends on.
Production ran six weeks with a healthy process and a 0-byte log because
Serilog isolates per-sink failures: a file sink whose every write fails is
invisible from anywhere but SelfLog, which was not enabled. Two instruments:
- LogPipelineDiagnostics.EnableSelfLog (before the first logger builds):
SelfLog to logs/serilog-selflog.txt (rotated at 5 MB) + stderr — the only
channel that carries the exception the sink swallows.
- CheckFileSinkGrowth (after the startup banner): verifies each configured,
unbuffered file sink's rolled-file family physically grew across a marker
event; a silent sink is reported at boot via SelfLog/stderr and the
console sink instead of discovered months later. Growth-across-marker,
not existence — a previous run's bytes must not mask a silent sink (the
false pass an existence check would have given on wonder-app-vd03).
Never throws: both instruments swallow their own failures — a diagnostics
channel that can fail startup is worse than the defect it watches for.
The load-bearing test is the failure case (a sink that writes nothing IS
reported); a check that can only pass is indistinguishable from no check.
Joseph Doherty