Add symlink support (fixes #873)

internal/model/puller.go

@@ -20,6 +20,7 @@ import (
 	"crypto/sha256"
 	"errors"
 	"fmt"
+	"io/ioutil"
 	"os"
 	"path/filepath"
 	"sync"
@@ -32,6 +33,7 @@ import (
 	"github.com/syncthing/syncthing/internal/osutil"
 	"github.com/syncthing/syncthing/internal/protocol"
 	"github.com/syncthing/syncthing/internal/scanner"
+	"github.com/syncthing/syncthing/internal/symlinks"
 	"github.com/syncthing/syncthing/internal/versioner"
 )
 
@@ -314,14 +316,15 @@ func (p *Puller) pullerIteration(ncopiers, npullers, nfinishers int, checksum bo
 
 		switch {
 		case file.IsDeleted():
-			// A deleted file or directory
+			// A deleted file, directory or symlink
 			deletions = append(deletions, file)
-		case file.IsDirectory():
+		case file.IsDirectory() && !file.IsSymlink():
 			// A new or changed directory
 			p.handleDir(file)
 		default:
-			// A new or changed file. This is the only case where we do stuff
-			// in the background; the other three are done synchronously.
+			// A new or changed file or symlink. This is the only case where we
+			// do stuff in the background; the other three are done
+			// synchronously.
 			p.handleFile(file, copyChan, finisherChan)
 		}
 
@@ -459,24 +462,21 @@ func (p *Puller) deleteFile(file protocol.FileInfo) {
 func (p *Puller) handleFile(file protocol.FileInfo, copyChan chan<- copyBlocksState, finisherChan chan<- *sharedPullerState) {
 	curFile := p.model.CurrentFolderFile(p.folder, file.Name)
 
-	if len(curFile.Blocks) == len(file.Blocks) {
-		for i := range file.Blocks {
-			if !bytes.Equal(curFile.Blocks[i].Hash, file.Blocks[i].Hash) {
-				goto FilesAreDifferent
-			}
-		}
+	if len(curFile.Blocks) == len(file.Blocks) && scanner.BlocksEqual(curFile.Blocks, file.Blocks) {
 		// We are supposed to copy the entire file, and then fetch nothing. We
 		// are only updating metadata, so we don't actually *need* to make the
 		// copy.
 		if debug {
 			l.Debugln(p, "taking shortcut on", file.Name)
 		}
-		p.shortcutFile(file)
+		if file.IsSymlink() {
+			p.shortcutSymlink(curFile, file)
+		} else {
+			p.shortcutFile(file)
+		}
 		return
 	}
 
-FilesAreDifferent:
-
 	scanner.PopulateOffsets(file.Blocks)
 
 	// Figure out the absolute filenames we need once and for all
@@ -571,6 +571,17 @@ func (p *Puller) shortcutFile(file protocol.FileInfo) {
 	p.model.updateLocal(p.folder, file)
 }
 
+// shortcutSymlink changes the symlinks type if necessery.
+func (p *Puller) shortcutSymlink(curFile, file protocol.FileInfo) {
+	err := symlinks.ChangeType(filepath.Join(p.dir, file.Name), file.Flags)
+	if err != nil {
+		l.Infof("Puller (folder %q, file %q): symlink shortcut: %v", p.folder, file.Name, err)
+		return
+	}
+
+	p.model.updateLocal(p.folder, file)
+}
+
 // copierRoutine reads copierStates until the in channel closes and performs
 // the relevant copies when possible, or passes it to the puller routine.
 func (p *Puller) copierRoutine(in <-chan copyBlocksState, pullChan chan<- pullBlockState, out chan<- *sharedPullerState, checksum bool) {
@@ -791,6 +802,25 @@ func (p *Puller) finisherRoutine(in <-chan *sharedPullerState) {
 				continue
 			}
 
+			// If it's a symlink, the target of the symlink is inside the file.
+			if state.file.IsSymlink() {
+				content, err := ioutil.ReadFile(state.realName)
+				if err != nil {
+					l.Warnln("puller: final: reading symlink:", err)
+					continue
+				}
+
+				// Remove the file, and replace it with a symlink.
+				err = osutil.InWritableDir(func(path string) error {
+					os.Remove(path)
+					return symlinks.Create(path, string(content), state.file.Flags)
+				}, state.realName)
+				if err != nil {
+					l.Warnln("puller: final: creating symlink:", err)
+					continue
+				}
+			}
+
 			// Record the updated file in the index
 			p.model.updateLocal(p.folder, state.file)
 		}