add FILE_SHARE_DELETE flag when opening file

Author: florindragos

tail.go

@@ -104,7 +104,7 @@ func TailFile(filename string, config Config) (*Tail, error) {
 
 	if t.MustExist {
 		var err error
-		t.file, err = os.Open(t.Filename)
+		t.file, err = OpenFile(t.Filename)
 		if err != nil {
 			return nil, err
 		}
@@ -149,7 +149,7 @@ func (tail *Tail) reopen() error {
 	}
 	for {
 		var err error
-		tail.file, err = os.Open(tail.Filename)
+		tail.file, err = OpenFile(tail.Filename)
 		if err != nil {
 			if os.IsNotExist(err) {
 				tail.Logger.Printf("Waiting for %s to appear...", tail.Filename)

tail_linux.go

@@ -0,0 +1,11 @@
+// +build linux
+
+package tail
+
+import (
+	"os"
+)
+
+func OpenFile(name string) (file *os.File, err error) {
+	return os.Open(name)
+}

tail_windows.go

@@ -0,0 +1,12 @@
+// +build windows
+
+package tail
+
+import (
+	"github.com/ActiveState/tail/winfile"
+	"os"
+)
+
+func OpenFile(name string) (file *os.File, err error) {
+	return winfile.OpenFile(name, os.O_RDONLY, 0)
+}

watch/polling.go

@@ -51,6 +51,8 @@ func (fw *PollingFileWatcher) ChangeEvents(t *tomb.Tomb, origFi os.FileInfo) *Fi
 	go func() {
 		defer changes.Close()
 
+		var retry int = 0
+
 		prevSize := fw.Size
 		for {
 			select {
@@ -67,6 +69,11 @@ func (fw *PollingFileWatcher) ChangeEvents(t *tomb.Tomb, origFi os.FileInfo) *Fi
 					changes.NotifyDeleted()
 					return
 				}
+
+				if permissionErrorRetry(err, &retry) {
+					continue
+				}
+
 				// XXX: report this error back to the user
 				util.Fatal("Failed to stat file %v: %v", fw.Filename, err)
 			}

watch/polling_linux.go

@@ -0,0 +1,9 @@
+// Copyright (c) 2013 ActiveState Software Inc. All rights reserved.
+// +build linux
+
+package watch
+
+func permissionErrorRetry(err error, retry *int) bool {
+	// No need for this on linux, don't retry
+	return false
+}

watch/polling_windows.go

@@ -0,0 +1,18 @@
+// +build windows
+
+package watch
+
+import (
+	"os"
+)
+
+const permissionDeniedRetryCount int = 5
+
+func permissionErrorRetry(err error, retry *int) bool {
+	if os.IsPermission(err) && *retry < permissionDeniedRetryCount {
+		// While pooling a file that does not exist yet, but will be created by another process we can get Permission Denied
+		(*retry)++
+		return true
+	}
+	return false
+}

winfile/winfile.go

@@ -0,0 +1,92 @@
+// +build windows
+
+package winfile
+
+import (
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+// issue also described here
+//https://codereview.appspot.com/8203043/
+
+// https://github.com/jnwhiteh/golang/blob/master/src/pkg/syscall/syscall_windows.go#L218
+func Open(path string, mode int, perm uint32) (fd syscall.Handle, err error) {
+	if len(path) == 0 {
+		return syscall.InvalidHandle, syscall.ERROR_FILE_NOT_FOUND
+	}
+	pathp, err := syscall.UTF16PtrFromString(path)
+	if err != nil {
+		return syscall.InvalidHandle, err
+	}
+	var access uint32
+	switch mode & (syscall.O_RDONLY | syscall.O_WRONLY | syscall.O_RDWR) {
+	case syscall.O_RDONLY:
+		access = syscall.GENERIC_READ
+	case syscall.O_WRONLY:
+		access = syscall.GENERIC_WRITE
+	case syscall.O_RDWR:
+		access = syscall.GENERIC_READ | syscall.GENERIC_WRITE
+	}
+	if mode&syscall.O_CREAT != 0 {
+		access |= syscall.GENERIC_WRITE
+	}
+	if mode&syscall.O_APPEND != 0 {
+		access &^= syscall.GENERIC_WRITE
+		access |= syscall.FILE_APPEND_DATA
+	}
+	sharemode := uint32(syscall.FILE_SHARE_READ | syscall.FILE_SHARE_WRITE | syscall.FILE_SHARE_DELETE)
+	var sa *syscall.SecurityAttributes
+	if mode&syscall.O_CLOEXEC == 0 {
+		sa = makeInheritSa()
+	}
+	var createmode uint32
+	switch {
+	case mode&(syscall.O_CREAT|syscall.O_EXCL) == (syscall.O_CREAT | syscall.O_EXCL):
+		createmode = syscall.CREATE_NEW
+	case mode&(syscall.O_CREAT|syscall.O_TRUNC) == (syscall.O_CREAT | syscall.O_TRUNC):
+		createmode = syscall.CREATE_ALWAYS
+	case mode&syscall.O_CREAT == syscall.O_CREAT:
+		createmode = syscall.OPEN_ALWAYS
+	case mode&syscall.O_TRUNC == syscall.O_TRUNC:
+		createmode = syscall.TRUNCATE_EXISTING
+	default:
+		createmode = syscall.OPEN_EXISTING
+	}
+	h, e := syscall.CreateFile(pathp, access, sharemode, sa, createmode, syscall.FILE_ATTRIBUTE_NORMAL, 0)
+	return h, e
+}
+
+// https://github.com/jnwhiteh/golang/blob/master/src/pkg/syscall/syscall_windows.go#L211
+func makeInheritSa() *syscall.SecurityAttributes {
+	var sa syscall.SecurityAttributes
+	sa.Length = uint32(unsafe.Sizeof(sa))
+	sa.InheritHandle = 1
+	return &sa
+}
+
+// https://github.com/jnwhiteh/golang/blob/master/src/pkg/os/file_windows.go#L133
+func OpenFile(name string, flag int, perm os.FileMode) (file *os.File, err error) {
+	r, e := Open(name, flag|syscall.O_CLOEXEC, syscallMode(perm))
+	if e != nil {
+		return nil, e
+	}
+	return os.NewFile(uintptr(r), name), nil
+}
+
+// https://github.com/jnwhiteh/golang/blob/master/src/pkg/os/file_posix.go#L61
+func syscallMode(i os.FileMode) (o uint32) {
+	o |= uint32(i.Perm())
+	if i&os.ModeSetuid != 0 {
+		o |= syscall.S_ISUID
+	}
+	if i&os.ModeSetgid != 0 {
+		o |= syscall.S_ISGID
+	}
+	if i&os.ModeSticky != 0 {
+		o |= syscall.S_ISVTX
+	}
+	// No mapping for Go's ModeTemporary (plan9 only).
+	return
+}