Support backup and restore of special files on POSIX style systems

Special files are device nodes and named pipes. The necessity of the
former is clear, the latter is debatable.
In order to preserve backward compatibility, the device number is
encoded in the StartChunk/StartOffset fields of the entry.

src/duplicacy_backupmanager.go

@@ -797,6 +797,21 @@ func (manager *BackupManager) Restore(top string, revision int, inPlace bool, qu
 			}
 			remoteEntry.RestoreEarlyDirFlags(fullPath)
 			directoryEntries = append(directoryEntries, remoteEntry)
+		} else if remoteEntry.IsSpecial() {
+			if stat, _ := os.Lstat(fullPath); stat != nil {
+				if !overwrite {
+					LOG_WERROR(allowFailures, "DOWNLOAD_OVERWRITE",
+						"File %s already exists.  Please specify the -overwrite option to overwrite", remoteEntry.Path)
+					continue
+				}
+				os.Remove(fullPath)
+			}
+
+			if err := remoteEntry.RestoreSpecial(fullPath); err != nil {
+				LOG_ERROR("RESTORE_SPECIAL", "Unable to restore special file %s: %v", remoteEntry.Path, err)
+				return 0
+			}
+			remoteEntry.RestoreMetadata(fullPath, nil, setOwner)
 		} else {
 			if remoteEntry.IsHardlinkRoot() {
 				hardLinkTable[len(hardLinkTable)-1] = hardLinkEntry{remoteEntry, true}

src/duplicacy_entry.go

@@ -509,6 +509,10 @@ func (entry *Entry) IsLink() bool {
 	return entry.Mode&uint32(os.ModeSymlink) != 0
 }
 
+func (entry *Entry) IsSpecial() bool {
+	return entry.Mode&uint32(os.ModeNamedPipe|os.ModeDevice|os.ModeCharDevice) != 0
+}
+
 func (entry *Entry) IsComplete() bool {
 	return entry.Size >= 0
 }
@@ -815,12 +819,15 @@ func ListEntries(top string, path string, patterns []string, nobackupFile string
 				}
 				entry = newEntry
 			}
-		}
-
-		if f.Mode()&(os.ModeNamedPipe|os.ModeSocket|os.ModeDevice) != 0 {
-			LOG_WARN("LIST_SKIP", "Skipped non-regular file %s", entry.Path)
-			skippedFiles = append(skippedFiles, entry.Path)
+		} else if entry.Mode & uint32(os.ModeSocket) != 0 {
+			// no reason to issue a warning for what should always be a transient file anyways
 			continue
+		} else if entry.IsSpecial() {
+			if !entry.ReadSpecial(f) {
+				LOG_WARN("LIST_DEV", "Failed to save device node %s", entry.Path)
+				skippedFiles = append(skippedFiles, entry.Path)
+				continue
+			}
 		}
 
 		var linkKey *listEntryLinkKey

src/duplicacy_entrylist.go

@@ -111,12 +111,12 @@ func (entryList *EntryList)createOnDiskFile() error {
 // Add an entry to the entry list
 func (entryList *EntryList)AddEntry(entry *Entry) error {
 
-	if !entry.IsDir() && !entry.IsLink() {
+	if entry.IsFile() {
 		entryList.NumberOfEntries++
 	}
 
 	if !entry.IsComplete() {
-		if entry.IsDir() || entry.IsLink() {
+		if !entry.IsFile() {
 			entry.Size = 0
 		} else {
 			modifiedEntry := ModifiedEntry {

src/duplicacy_utils_linux.go

@@ -48,6 +48,9 @@ func ioctl(f *os.File, request uintptr, attrp *uint32) error {
 }
 
 func (entry *Entry) ReadFileFlags(f *os.File) error {
+	if entry.IsSpecial() {
+		return nil
+	}
 	var flags uint32
 	if err := ioctl(f, linux_FS_IOC_GETFLAGS, &flags); err != nil {
 		return err

src/duplicacy_utils_others.go

@@ -49,7 +49,7 @@ func SetOwner(fullPath string, entry *Entry, fileInfo *os.FileInfo) bool {
 
 func (entry *Entry) ReadAttributes(top string) {
 	fullPath := filepath.Join(top, entry.Path)
-	f, err := os.OpenFile(fullPath, os.O_RDONLY|syscall.O_NOFOLLOW, 0)
+	f, err := os.OpenFile(fullPath, os.O_RDONLY|syscall.O_NOFOLLOW|syscall.O_NONBLOCK, 0)
 	if err != nil {
 		return
 	}
@@ -101,6 +101,37 @@ func (entry *Entry) SetAttributesToFile(fullPath string) {
 	f.Close()
 }
 
+func (entry *Entry) ReadSpecial(fileInfo os.FileInfo) bool {
+	if fileInfo.Mode() & (os.ModeDevice | os.ModeCharDevice) == 0 {
+		return true
+	}
+	stat, ok := fileInfo.Sys().(*syscall.Stat_t)
+	if !ok || stat == nil {
+		return false
+	}
+	entry.Size = 0
+	rdev := uint64(stat.Rdev)
+	entry.StartChunk = int(rdev & 0xFFFFFFFF)
+	entry.StartOffset = int(rdev >> 32)
+	return true
+}
+
+func (entry *Entry) RestoreSpecial(fullPath string) error {
+	if entry.Mode & uint32(os.ModeDevice | os.ModeCharDevice) != 0 {
+		mode := entry.Mode & uint32(fileModeMask)
+		if entry.Mode & uint32(os.ModeCharDevice) != 0 {
+			mode |= syscall.S_IFCHR
+		} else {
+			mode |= syscall.S_IFBLK
+		}
+		rdev := uint64(entry.StartChunk) | uint64(entry.StartOffset) << 32
+		return syscall.Mknod(fullPath, mode, int(rdev))
+	} else if entry.Mode & uint32(os.ModeNamedPipe) != 0 {
+		return syscall.Mkfifo(fullPath, uint32(entry.Mode))
+	}
+	return nil
+}
+
 func joinPath(components ...string) string {
 	return path.Join(components...)
 }

src/duplicacy_utils_windows.go

@@ -117,6 +117,14 @@ func (entry *Entry) SetAttributesToFile(fullPath string) {
 
 }
 
+func (entry *Entry) ReadDeviceNode(fileInfo os.FileInfo) bool {
+	return nil
+}
+
+func (entry *Entry) RestoreSpecial(fullPath string) error {
+	return nil
+}
+
 func joinPath(components ...string) string {
 
 	combinedPath := `\\?\` + filepath.Join(components...)