forked from hpcloud/tail
/
tail.go
277 lines (244 loc) · 6 KB
/
tail.go
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// Copyright (c) 2013 ActiveState Software Inc. All rights reserved.
package tail
import (
"bufio"
"fmt"
"github.com/ActiveState/tail/watch"
"io"
"launchpad.net/tomb"
"log"
"os"
"time"
)
var (
ErrStop = fmt.Errorf("tail should now stop")
)
type Line struct {
Text string
Time time.Time
}
// Config is used to specify how a file must be tailed.
type Config struct {
Location int // Tail from last N lines (tail -n)
Follow bool // Continue looking for new lines (tail -f)
ReOpen bool // Reopen recreated files (tail -F)
MustExist bool // Fail early if the file does not exist
Poll bool // Poll for file changes instead of using inotify
MaxLineSize int // If non-zero, split longer lines into multiple lines
}
type Tail struct {
Filename string
Lines chan *Line
Config
file *os.File
reader *bufio.Reader
watcher watch.FileWatcher
changes *watch.FileChanges
tomb.Tomb // provides: Done, Kill, Dying
}
// TailFile begins tailing the file. Output stream is made available
// via the `Tail.Lines` channel. To handle errors during tailing,
// invoke the `Wait` or `Err` method after finishing reading from the
// `Lines` channel.
func TailFile(filename string, config Config) (*Tail, error) {
if !(config.Location == 0 || config.Location == -1) {
panic("only 0/-1 values are supported for Location.")
}
if config.ReOpen && !config.Follow {
panic("cannot set ReOpen without Follow.")
}
t := &Tail{
Filename: filename,
Lines: make(chan *Line),
Config: config}
if t.Poll {
t.watcher = watch.NewPollingFileWatcher(filename)
} else {
t.watcher = watch.NewInotifyFileWatcher(filename)
}
if t.MustExist {
var err error
t.file, err = os.Open(t.Filename)
if err != nil {
return nil, err
}
}
go t.tailFileSync()
return t, nil
}
// Stop stops the tailing activity.
func (tail *Tail) Stop() error {
tail.Kill(nil)
return tail.Wait()
}
func (tail *Tail) close() {
close(tail.Lines)
if tail.file != nil {
tail.file.Close()
}
}
func (tail *Tail) reopen() error {
if tail.file != nil {
tail.file.Close()
}
for {
var err error
tail.file, err = os.Open(tail.Filename)
if err != nil {
if os.IsNotExist(err) {
log.Printf("Waiting for %s to appear...", tail.Filename)
if err := tail.watcher.BlockUntilExists(tail.Tomb); err != nil {
return fmt.Errorf("Failed to detect creation of %s: %s", tail.Filename, err)
}
continue
}
return fmt.Errorf("Unable to open file %s: %s", tail.Filename, err)
}
break
}
return nil
}
func (tail *Tail) readLine() ([]byte, error) {
line, _, err := tail.reader.ReadLine()
return line, err
}
func (tail *Tail) tailFileSync() {
defer tail.Done()
defer tail.close()
if !tail.MustExist {
// deferred first open.
err := tail.reopen()
if err != nil {
tail.Kill(err)
return
}
}
// Seek to requested location on first open of the file.
var offset int64
var whence int
if tail.Location >= 0 {
whence = 0
offset = int64(tail.Location)
} else {
whence = 2
offset = -1*int64(tail.Location) - 1
}
_, err := tail.file.Seek(offset, whence) // Seek to the file beginning/end
if err != nil {
tail.Killf("Seek error on %s: %s", tail.Filename, err)
return
}
tail.reader = bufio.NewReader(tail.file)
// Read line by line.
for {
line, err := tail.readLine()
switch err {
case nil:
if line != nil {
tail.sendLine(line)
}
case io.EOF:
if !tail.Follow {
return
}
// When EOF is reached, wait for more data to become
// available. Wait strategy is based on the `tail.watcher`
// implementation (inotify or polling).
err := tail.waitForChanges()
if err != nil {
if err != ErrStop {
tail.Kill(err)
}
return
}
default: // non-EOF error
tail.Killf("Error reading %s: %s", tail.Filename, err)
return
}
select {
case <-tail.Dying():
return
default:
}
}
}
// waitForChanges waits until the file has been appended, deleted,
// moved or truncated. When moved or deleted - the file will be
// reopened if ReOpen is true. Truncated files are always reopened.
func (tail *Tail) waitForChanges() error {
if tail.changes == nil {
st, err := tail.file.Stat()
if err != nil {
return err
}
tail.changes = tail.watcher.ChangeEvents(tail.Tomb, st)
}
select {
case <-tail.changes.Modified:
return nil
case <-tail.changes.Deleted:
tail.changes = nil
if tail.ReOpen {
// XXX: we must not log from a library.
log.Printf("Re-opening moved/deleted file %s ...", tail.Filename)
if err := tail.reopen(); err != nil {
return err
}
log.Printf("Successfully reopened %s", tail.Filename)
tail.reader = bufio.NewReader(tail.file)
return nil
} else {
log.Printf("Stopping tail as file no longer exists: %s", tail.Filename)
return ErrStop
}
case <-tail.changes.Truncated:
// Always reopen truncated files (Follow is true)
log.Printf("Re-opening truncated file %s ...", tail.Filename)
if err := tail.reopen(); err != nil {
return err
}
log.Printf("Successfully reopened truncated %s", tail.Filename)
tail.reader = bufio.NewReader(tail.file)
return nil
case <-tail.Dying():
return ErrStop
}
panic("unreachable")
}
// sendLine sends the line(s) to Lines channel, splitting longer lines
// if necessary.
func (tail *Tail) sendLine(line []byte) {
now := time.Now()
lines := []string{string(line)}
// Split longer lins
if tail.MaxLineSize > 0 && len(line) > tail.MaxLineSize {
lines = partitionString(
string(line), tail.MaxLineSize)
}
for _, line := range lines {
tail.Lines <- &Line{line, now}
}
}
// partitionString partitions the string into chunks of given size,
// with the last chunk of variable size.
func partitionString(s string, chunkSize int) []string {
if chunkSize <= 0 {
panic("invalid chunkSize")
}
length := len(s)
chunks := 1 + length/chunkSize
start := 0
end := chunkSize
parts := make([]string, 0, chunks)
for {
if end > length {
end = length
}
parts = append(parts, s[start:end])
if end == length {
break
}
start, end = end, end+chunkSize
}
return parts
}