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218 lines
5.0 KiB
218 lines
5.0 KiB
package autofile
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import (
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"context"
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"errors"
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"fmt"
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"os"
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"os/signal"
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"path/filepath"
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"sync"
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"syscall"
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"time"
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tmrand "github.com/tendermint/tendermint/libs/rand"
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)
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/* AutoFile usage
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// Create/Append to ./autofile_test
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af, err := OpenAutoFile("autofile_test")
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if err != nil {
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panic(err)
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}
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// Stream of writes.
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// During this time, the file may be moved e.g. by logRotate.
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for i := 0; i < 60; i++ {
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af.Write([]byte(Fmt("LOOP(%v)", i)))
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time.Sleep(time.Second)
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}
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// Close the AutoFile
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err = af.Close()
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if err != nil {
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panic(err)
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}
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*/
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const (
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autoFileClosePeriod = 1000 * time.Millisecond
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autoFilePerms = os.FileMode(0600)
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)
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// ErrAutoFileClosed is reported when operations attempt to use an autofile
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// after it has been closed.
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var ErrAutoFileClosed = errors.New("autofile is closed")
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// AutoFile automatically closes and re-opens file for writing. The file is
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// automatically setup to close itself every 1s and upon receiving SIGHUP.
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//
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// This is useful for using a log file with the logrotate tool.
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type AutoFile struct {
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ID string
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Path string
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closeTicker *time.Ticker // signals periodic close
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cancel func() // cancels the lifecycle context
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mtx sync.Mutex // guards the fields below
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closed bool // true when the the autofile is no longer usable
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file *os.File // the underlying file (may be nil)
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}
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// OpenAutoFile creates an AutoFile in the path (with random ID). If there is
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// an error, it will be of type *PathError or *ErrPermissionsChanged (if file's
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// permissions got changed (should be 0600)).
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func OpenAutoFile(ctx context.Context, path string) (*AutoFile, error) {
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var err error
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path, err = filepath.Abs(path)
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if err != nil {
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return nil, err
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}
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ctx, cancel := context.WithCancel(ctx)
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af := &AutoFile{
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ID: tmrand.Str(12) + ":" + path,
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Path: path,
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closeTicker: time.NewTicker(autoFileClosePeriod),
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cancel: cancel,
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}
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if err := af.openFile(); err != nil {
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af.Close()
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return nil, err
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}
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// Set up a SIGHUP handler to forcibly flush and close the filehandle.
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// This forces the next operation to re-open the underlying path.
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hupc := make(chan os.Signal, 1)
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signal.Notify(hupc, syscall.SIGHUP)
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go func() {
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defer close(hupc)
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for {
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select {
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case <-hupc:
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_ = af.closeFile()
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case <-ctx.Done():
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return
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}
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}
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}()
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go af.closeFileRoutine(ctx)
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return af, nil
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}
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// Close shuts down the service goroutine and marks af as invalid. Operations
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// on af after Close will report an error.
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func (af *AutoFile) Close() error {
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return af.withLock(func() error {
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af.cancel() // signal the close service to stop
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af.closed = true // mark the file as invalid
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return af.unsyncCloseFile()
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})
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}
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func (af *AutoFile) closeFileRoutine(ctx context.Context) {
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for {
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select {
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case <-ctx.Done():
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_ = af.Close()
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return
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case <-af.closeTicker.C:
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_ = af.closeFile()
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}
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}
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}
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func (af *AutoFile) closeFile() (err error) {
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return af.withLock(af.unsyncCloseFile)
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}
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// unsyncCloseFile closes the underlying filehandle if one is open, and reports
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// any error it returns. The caller must hold af.mtx exclusively.
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func (af *AutoFile) unsyncCloseFile() error {
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if fp := af.file; fp != nil {
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af.file = nil
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return fp.Close()
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}
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return nil
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}
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// withLock runs f while holding af.mtx, and reports any error it returns.
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func (af *AutoFile) withLock(f func() error) error {
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af.mtx.Lock()
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defer af.mtx.Unlock()
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return f()
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}
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// Write writes len(b) bytes to the AutoFile. It returns the number of bytes
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// written and an error, if any. Write returns a non-nil error when n !=
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// len(b).
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// Opens AutoFile if needed.
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func (af *AutoFile) Write(b []byte) (n int, err error) {
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af.mtx.Lock()
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defer af.mtx.Unlock()
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if af.closed {
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return 0, fmt.Errorf("write: %w", ErrAutoFileClosed)
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}
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if af.file == nil {
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if err = af.openFile(); err != nil {
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return
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}
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}
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n, err = af.file.Write(b)
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return
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}
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// Sync commits the current contents of the file to stable storage. Typically,
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// this means flushing the file system's in-memory copy of recently written
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// data to disk.
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func (af *AutoFile) Sync() error {
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return af.withLock(func() error {
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if af.closed {
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return fmt.Errorf("sync: %w", ErrAutoFileClosed)
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} else if af.file == nil {
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return nil // nothing to sync
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}
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return af.file.Sync()
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})
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}
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// openFile unconditionally replaces af.file with a new filehandle on the path.
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// The caller must hold af.mtx exclusively.
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func (af *AutoFile) openFile() error {
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file, err := os.OpenFile(af.Path, os.O_RDWR|os.O_CREATE|os.O_APPEND, autoFilePerms)
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if err != nil {
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return err
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}
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af.file = file
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return nil
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}
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// Size returns the size of the AutoFile. It returns -1 and an error if fails
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// get stats or open file.
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// Opens AutoFile if needed.
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func (af *AutoFile) Size() (int64, error) {
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af.mtx.Lock()
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defer af.mtx.Unlock()
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if af.closed {
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return 0, fmt.Errorf("size: %w", ErrAutoFileClosed)
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}
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if af.file == nil {
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if err := af.openFile(); err != nil {
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return -1, err
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}
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}
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stat, err := af.file.Stat()
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if err != nil {
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return -1, err
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}
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return stat.Size(), nil
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}
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