Add FNV-1a content hash to detect same-size changesHEADmain

4 files changed, 44 insertions, 3 deletions

diff --git a/cmd_linux.go b/cmd_linux.go
index 305b7d1..70ee2fb 100644
--- a/cmd_linux.go
+++ b/cmd_linux.go
@@ -194,13 +194,15 @@ func syncFromManifest(remote *Manifest, stack *GitignoreStack) {
 
 		if localMeta, exists := localManifest.Files[relPath]; exists {
 			if localMeta.Size == remoteMeta.Size &&
-				localMeta.Symlink == remoteMeta.Symlink {
+				localMeta.Symlink == remoteMeta.Symlink &&
+				(remoteMeta.Hash == 0 || localMeta.Hash == remoteMeta.Hash) {
 				continue
 			}
 			if debugShown < 5 {
-				logDebug("mismatch %s: size=%d/%d symlink=%q/%q",
+				logDebug("mismatch %s: size=%d/%d hash=%d/%d symlink=%q/%q",
 					relPath,
 					localMeta.Size, remoteMeta.Size,
+					localMeta.Hash, remoteMeta.Hash,
 					localMeta.Symlink, remoteMeta.Symlink)
 				debugShown++
 			}
@@ -310,11 +312,17 @@ func scanLocalDirectory(root string) *Manifest {
 			linkTarget, _ = os.Readlink(path)
 		}
 
+		var hash uint64
+		if !info.IsDir() && linkTarget == "" {
+			hash = hashFile(path)
+		}
+
 		manifest.Files[relPath] = FileMeta{
 			Size:    info.Size(),
 			Mode:    info.Mode(),
 			ModTime: info.ModTime(),
 			Symlink: linkTarget,
+			Hash:    hash,
 		}
 
 		return nil
diff --git a/cmd_windows.go b/cmd_windows.go
index f76d95d..2557803 100644
--- a/cmd_windows.go
+++ b/cmd_windows.go
@@ -317,11 +317,17 @@ func scanDirectory(root string, stack *GitignoreStack) *Manifest {
 			linkTarget, _ = os.Readlink(path)
 		}
 
+		var hash uint64
+		if !info.IsDir() && linkTarget == "" {
+			hash = hashFile(path)
+		}
+
 		manifest.Files[relPath] = FileMeta{
 			Size:    info.Size(),
 			Mode:    info.Mode(),
 			ModTime: info.ModTime(),
 			Symlink: linkTarget,
+			Hash:    hash,
 		}
 
 		return nil
diff --git a/types.go b/types.go
index bf5dd00..60e1ea9 100644
--- a/types.go
+++ b/types.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"encoding/json"
+	"hash/fnv"
 	"os"
 	"time"
 )
@@ -17,6 +18,7 @@ type FileMeta struct {
 	Mode    os.FileMode
 	ModTime time.Time
 	Symlink string
+	Hash    uint64
 }
 
 type FileMetaJSON struct {
@@ -24,6 +26,7 @@ type FileMetaJSON struct {
 	Mode    uint32 `json:"mode"`
 	ModTime string `json:"modtime"`
 	Symlink string `json:"symlink,omitempty"`
+	Hash    uint64 `json:"hash,omitempty"`
 }
 
 type Manifest struct {
@@ -45,6 +48,7 @@ func (m *Manifest) ToJSON() map[string]FileMetaJSON {
 			Mode:    uint32(v.Mode),
 			ModTime: v.ModTime.UTC().Format(time.RFC3339Nano),
 			Symlink: v.Symlink,
+			Hash:    v.Hash,
 		}
 	}
 	return files
@@ -59,6 +63,7 @@ func ManifestFromJSON(files map[string]FileMetaJSON) *Manifest {
 			Mode:    os.FileMode(v.Mode),
 			ModTime: t,
 			Symlink: v.Symlink,
+			Hash:    v.Hash,
 		}
 	}
 	return m
@@ -75,3 +80,23 @@ func DecodeMessage(data []byte) (*ProtocolMessage, error) {
 func EncodeMessage(msg *ProtocolMessage) ([]byte, error) {
 	return json.Marshal(msg)
 }
+
+func hashFile(path string) uint64 {
+	f, err := os.Open(path)
+	if err != nil {
+		return 0
+	}
+	defer f.Close()
+	h := fnv.New64a()
+	buf := make([]byte, 32*1024)
+	for {
+		n, err := f.Read(buf)
+		if n > 0 {
+			h.Write(buf[:n])
+		}
+		if err != nil {
+			break
+		}
+	}
+	return h.Sum64()
+}
diff --git a/watcher.go b/watcher.go
index 137bb36..284c3fa 100644
--- a/watcher.go
+++ b/watcher.go
@@ -99,7 +99,8 @@ func syncWrite(srcPath, destPath, relPath string, manifest *Manifest, dryRun boo
 	}
 
 	meta, exists := manifest.Files[relPath]
-	if exists && meta.Size == info.Size() && meta.Symlink == linkTarget {
+	srcHash := hashFile(srcPath)
+	if exists && meta.Size == info.Size() && meta.Symlink == linkTarget && (srcHash == 0 || meta.Hash == srcHash) {
 		return
 	}
 
@@ -108,6 +109,7 @@ func syncWrite(srcPath, destPath, relPath string, manifest *Manifest, dryRun boo
 		Mode:    info.Mode(),
 		ModTime: info.ModTime(),
 		Symlink: linkTarget,
+		Hash:    srcHash,
 	}
 
 	if dryRun {