podman

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// Copyright (c) 2019 FOSS contributors of https://github.com/nxadm/tail
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// Copyright (c) 2015 HPE Software Inc. All rights reserved.
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// Copyright (c) 2013 ActiveState Software Inc. All rights reserved.
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package watch
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import (
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	"os"
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	"runtime"
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	"time"
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	"github.com/nxadm/tail/util"
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	"gopkg.in/tomb.v1"
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)
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// PollingFileWatcher polls the file for changes.
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type PollingFileWatcher struct {
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	Filename string
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	Size     int64
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}
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func NewPollingFileWatcher(filename string) *PollingFileWatcher {
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	fw := &PollingFileWatcher{filename, 0}
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	return fw
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}
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var POLL_DURATION time.Duration
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func (fw *PollingFileWatcher) BlockUntilExists(t *tomb.Tomb) error {
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	for {
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		if _, err := os.Stat(fw.Filename); err == nil {
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			return nil
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		} else if !os.IsNotExist(err) {
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			return err
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		}
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		select {
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		case <-time.After(POLL_DURATION):
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			continue
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		case <-t.Dying():
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			return tomb.ErrDying
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		}
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	}
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	panic("unreachable")
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}
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func (fw *PollingFileWatcher) ChangeEvents(t *tomb.Tomb, pos int64) (*FileChanges, error) {
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	origFi, err := os.Stat(fw.Filename)
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	if err != nil {
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		return nil, err
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	}
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	changes := NewFileChanges()
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	var prevModTime time.Time
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	// XXX: use tomb.Tomb to cleanly manage these goroutines. replace
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	// the fatal (below) with tomb's Kill.
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	fw.Size = pos
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	go func() {
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		prevSize := fw.Size
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		for {
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			select {
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			case <-t.Dying():
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				return
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			default:
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			}
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			time.Sleep(POLL_DURATION)
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			fi, err := os.Stat(fw.Filename)
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			if err != nil {
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				// Windows cannot delete a file if a handle is still open (tail keeps one open)
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				// so it gives access denied to anything trying to read it until all handles are released.
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				if os.IsNotExist(err) || (runtime.GOOS == "windows" && os.IsPermission(err)) {
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					// File does not exist (has been deleted).
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					changes.NotifyDeleted()
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					return
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				}
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				// XXX: report this error back to the user
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				util.Fatal("Failed to stat file %v: %v", fw.Filename, err)
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			}
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			// File got moved/renamed?
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			if !os.SameFile(origFi, fi) {
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				changes.NotifyDeleted()
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				return
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			}
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			// File got truncated?
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			fw.Size = fi.Size()
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			if prevSize > 0 && prevSize > fw.Size {
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				changes.NotifyTruncated()
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				prevSize = fw.Size
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				continue
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			}
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			// File got bigger?
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			if prevSize > 0 && prevSize < fw.Size {
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				changes.NotifyModified()
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				prevSize = fw.Size
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				continue
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			}
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			prevSize = fw.Size
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			// File was appended to (changed)?
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			modTime := fi.ModTime()
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			if modTime != prevModTime {
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				prevModTime = modTime
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				changes.NotifyModified()
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			}
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		}
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	}()
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	return changes, nil
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}
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func init() {
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	POLL_DURATION = 250 * time.Millisecond
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}
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