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Fix OSError race condition in file polling between fileExists and getLastModificationTime #15

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Fix OSError race condition in file polling between fileExists and getLastModificationTime #15

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Copilot Jan 10, 2026
94669cd
Fix race condition where getLastModificationTime can raise OSError
Copilot Jan 10, 2026
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33 changes: 25 additions & 8 deletions src/fsnotify/filepoll.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,11 @@ proc initFileEventData*(name: string, cb: EventCallback): PathEventData =
result.cb = cb

if fileExists(name):
init(result)
try:
init(result)
except OSError:
# File was removed between fileExists check and init call
discard

# proc initFileEventData*(args: seq[tuple[name: string, cb: EventCallback]]): seq[FileEventData] =
# result = newSeq[FileEventData](args.len)
Expand All @@ -36,10 +40,14 @@ proc close*(data: PathEventData) =
proc filecb*(data: var PathEventData) =
if data.exists:
if fileExists(data.name):
let now = getLastModificationTime(data.name)
if now != data.lastModificationTime:
data.lastModificationTime = now
call(data, @[initPathEvent(data.name, FileEventAction.Modify)])
try:
let now = getLastModificationTime(data.name)
if now != data.lastModificationTime:
data.lastModificationTime = now
call(data, @[initPathEvent(data.name, FileEventAction.Modify)])
except OSError:
# File was removed between fileExists check and getLastModificationTime call
discard
else:
data.exists = false
var event = initPathEvent(data.name, FileEventAction.Remove)
Expand All @@ -48,13 +56,22 @@ proc filecb*(data: var PathEventData) =
for kind, name in walkDir(dir):
if kind == pcFile and getUniqueFileId(name) == data.uniqueId:
data.exists = true
data.lastModificationTime = getLastModificationTime(name)
try:
data.lastModificationTime = getLastModificationTime(name)
except OSError:
# File was removed between walkDir and getLastModificationTime call
data.exists = false
continue
event = initPathEvent(data.name, FileEventAction.Rename, name)
data.name = name
break

call(data, @[event])
else:
if fileExists(data.name):
init(data)
call(data, @[initPathEvent(data.name, FileEventAction.Create)])
try:
init(data)
call(data, @[initPathEvent(data.name, FileEventAction.Create)])
except OSError:
# File was removed between fileExists check and init call
discard