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fix: Allow loki.source.file to read renaming lines of a deleted file before it tries to re open a new one #5270

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Merged
kalleep merged 3 commits into from
Jan 16, 2026
+49 −19
Merged

fix: Allow loki.source.file to read renaming lines of a deleted file before it tries to re open a new one #5270

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dd573be
fix: tail.File now return buffered lines before reopening new file.
kalleep Jan 15, 2026
159cc2e
add a small sleep before append and delete happens
kalleep Jan 15, 2026
0430f7d
fix comment
kalleep Jan 15, 2026
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8 changes: 7 additions & 1 deletion internal/component/loki/source/file/internal/tail/file.go
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Original file line number Diff line number Diff line change
Expand Up @@ -163,8 +163,14 @@ func (f *File) wait() error {
return f.reopen(true)
case eventDeleted:
level.Debug(f.logger).Log("msg", "file deleted")
// if a file is deleted we want to make sure we drain what's remaining in the open file.
// If a file is deleted we want to make sure we drain what's remaining in the open file.
f.drain()
// If we have any buffered lines after drain we can return here to make sure they are consumed and
// we are not blocking on reopening the new file.
if len(f.bufferedLines) > 0 {
level.Debug(f.logger).Log("msg", "finish reading deleted file before reopen")
return nil
}
// In polling mode we could miss events when a file is deleted, so before we give up
// we try to reopen the file.
return f.reopen(false)
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60 changes: 42 additions & 18 deletions internal/component/loki/source/file/internal/tail/file_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -199,24 +199,6 @@ func TestFile(t *testing.T) {
require.ErrorIs(t, err, context.Canceled)
})

t.Run("UTF-16LE", func(t *testing.T) {
file, err := NewFile(log.NewNopLogger(), &Config{
Filename: "testdata/mssql.log",
Encoding: unicode.UTF16(unicode.LittleEndian, unicode.IgnoreBOM),
})
require.NoError(t, err)
defer file.Stop()

verify(t, file, &Line{Text: "2025-03-11 11:11:02.58 Server Microsoft SQL Server 2019 (RTM) - 15.0.2000.5 (X64) ", Offset: 180}, nil)
verify(t, file, &Line{Text: " Sep 24 2019 13:48:23 ", Offset: 228}, nil)
verify(t, file, &Line{Text: " Copyright (C) 2019 Microsoft Corporation", Offset: 314}, nil)
verify(t, file, &Line{Text: " Enterprise Edition (64-bit) on Windows Server 2022 Standard 10.0 <X64> (Build 20348: ) (Hypervisor)", Offset: 518}, nil)
verify(t, file, &Line{Text: "", Offset: 522}, nil)
verify(t, file, &Line{Text: "2025-03-11 11:11:02.71 Server UTC adjustment: 1:00", Offset: 636}, nil)
verify(t, file, &Line{Text: "2025-03-11 11:11:02.71 Server (c) Microsoft Corporation.", Offset: 762}, nil)
verify(t, file, &Line{Text: "2025-03-11 11:11:02.72 Server All rights reserved.", Offset: 876}, nil)
})

t.Run("calls to next after stop", func(t *testing.T) {
name := createFile(t, "stopped", "hello\n")
defer removeFile(t, name)
Expand Down Expand Up @@ -261,6 +243,48 @@ func TestFile(t *testing.T) {
verify(t, file, &Line{Text: "newline2", Offset: 18}, nil)
})

t.Run("deleted while reading", func(t *testing.T) {
name := createFile(t, "removed", "1\n2\n")
file, err := NewFile(log.NewNopLogger(), &Config{
Offset: 0,
Filename: name,
WatcherConfig: WatcherConfig{
MinPollFrequency: 50 * time.Millisecond,
MaxPollFrequency: 50 * time.Millisecond,
},
})
require.NoError(t, err)

go func() {
time.Sleep(50 * time.Millisecond)
appendToFile(t, name, "3\n4\n")
removeFile(t, name)
}()

verify(t, file, &Line{Text: "1", Offset: 2}, nil)
verify(t, file, &Line{Text: "2", Offset: 4}, nil)
verify(t, file, &Line{Text: "3", Offset: 6}, nil)
verify(t, file, &Line{Text: "4", Offset: 8}, nil)
})

t.Run("UTF-16LE", func(t *testing.T) {
file, err := NewFile(log.NewNopLogger(), &Config{
Filename: "testdata/mssql.log",
Encoding: unicode.UTF16(unicode.LittleEndian, unicode.IgnoreBOM),
})
require.NoError(t, err)
defer file.Stop()

verify(t, file, &Line{Text: "2025-03-11 11:11:02.58 Server Microsoft SQL Server 2019 (RTM) - 15.0.2000.5 (X64) ", Offset: 180}, nil)
verify(t, file, &Line{Text: " Sep 24 2019 13:48:23 ", Offset: 228}, nil)
verify(t, file, &Line{Text: " Copyright (C) 2019 Microsoft Corporation", Offset: 314}, nil)
verify(t, file, &Line{Text: " Enterprise Edition (64-bit) on Windows Server 2022 Standard 10.0 <X64> (Build 20348: ) (Hypervisor)", Offset: 518}, nil)
verify(t, file, &Line{Text: "", Offset: 522}, nil)
verify(t, file, &Line{Text: "2025-03-11 11:11:02.71 Server UTC adjustment: 1:00", Offset: 636}, nil)
verify(t, file, &Line{Text: "2025-03-11 11:11:02.71 Server (c) Microsoft Corporation.", Offset: 762}, nil)
verify(t, file, &Line{Text: "2025-03-11 11:11:02.72 Server All rights reserved.", Offset: 876}, nil)
})

t.Run("should detect UTF-16LE encoding from BOM", func(t *testing.T) {
enc := unicode.UTF16(unicode.LittleEndian, unicode.UseBOM).NewEncoder()
encoded, err := enc.String("Hello, 世界\r\n")
Expand Down
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