Fix not transferring files that don't differ in size - fixes #911

Due to a logic error files stored on remotes which support modtime but
not hashes weren't being transferred when updating with a file of the
same size but different modtime.  Instead the modtime of the remote
file was being set to that of the local file.

In practice this affected crypt with all remotes except Amazon Drive
and Dropbox.

fs/operations.go

@@ -12,7 +12,6 @@ import (
 	"strings"
 	"sync"
 	"sync/atomic"
-	"time"
 
 	"github.com/pkg/errors"
 	"github.com/spf13/pflag"
@@ -121,34 +120,53 @@ func Equal(src, dst Object) bool {
 		return true
 	}
 
-	var srcModTime time.Time
+	// Assert: Size is equal or being ignored
-	if !Config.CheckSum {
+
+	// If checking checksum and not modtime
+	if Config.CheckSum {
+		// Check the hash
+		same, hash, _ := CheckHashes(src, dst)
+		if !same {
+			Debug(src, "%v differ", hash)
+			return false
+		}
+		if hash == HashNone {
+			Debug(src, "Size of src and dst objects identical")
+		} else {
+			Debug(src, "Size and %v of src and dst objects identical", hash)
+		}
+		return true
+	}
+
+	// Sizes the same so check the mtime
 	if Config.ModifyWindow == ModTimeNotSupported {
 		Debug(src, "Sizes identical")
 		return true
 	}
-		// Size the same so check the mtime
+	srcModTime := src.ModTime()
-		srcModTime = src.ModTime()
 	dstModTime := dst.ModTime()
 	dt := dstModTime.Sub(srcModTime)
 	ModifyWindow := Config.ModifyWindow
-		if dt >= ModifyWindow || dt <= -ModifyWindow {
+	if dt < ModifyWindow && dt > -ModifyWindow {
-			Debug(src, "Modification times differ by %s: %v, %v", dt, srcModTime, dstModTime)
-		} else {
 		Debug(src, "Size and modification time the same (differ by %s, within tolerance %s)", dt, ModifyWindow)
 		return true
 	}
-	}
 
-	// mtime is unreadable or different but size is the same so
+	Debug(src, "Modification times differ by %s: %v, %v", dt, srcModTime, dstModTime)
-	// check the hash
+
+	// Check if the hashes are the same
 	same, hash, _ := CheckHashes(src, dst)
 	if !same {
-		Debug(src, "Hash differ")
+		Debug(src, "%v differ", hash)
+		return false
+	}
+	if hash == HashNone {
+		// if couldn't check hash, return that they differ
 		return false
 	}
 
-	if !(Config.CheckSum || Config.NoUpdateModTime) {
+	// mod time differs but hash is the same to reset mod time if required
+	if !Config.NoUpdateModTime {
 		// Size and hash the same but mtime different so update the
 		// mtime of the dst object here
 		err := dst.SetModTime(srcModTime)
@@ -157,14 +175,10 @@ func Equal(src, dst Object) bool {
 			return false
 		} else if err != nil {
 			Stats.Error()
-			ErrorLog(dst, "Failed to read set modification time: %v", err)
+			ErrorLog(dst, "Failed to set modification time: %v", err)
-		}
-	}
-
-	if hash == HashNone {
-		Debug(src, "Size of src and dst objects identical")
 		} else {
-		Debug(src, "Size and %v of src and dst objects identical", hash)
+			Debug(src, "Updated modification time in destination")
+		}
 	}
 	return true
 }

fs/sync_test.go

@@ -336,6 +336,30 @@ func TestSyncAfterChangingModtimeOnlyWithNoUpdateModTime(t *testing.T) {
 	fstest.CheckItems(t, r.fremote, file2)
 }
 
+func TestSyncDoesntUpdateModtime(t *testing.T) {
+	if fs.Config.ModifyWindow == fs.ModTimeNotSupported {
+		t.Skip("Can't run this test on fs which doesn't support mod time")
+	}
+	r := NewRun(t)
+	defer r.Finalise()
+
+	file1 := r.WriteFile("foo", "foo", t2)
+	file2 := r.WriteObject("foo", "bar", t1)
+
+	fstest.CheckItems(t, r.flocal, file1)
+	fstest.CheckItems(t, r.fremote, file2)
+
+	fs.Stats.ResetCounters()
+	err := fs.Sync(r.fremote, r.flocal)
+	require.NoError(t, err)
+
+	fstest.CheckItems(t, r.flocal, file1)
+	fstest.CheckItems(t, r.fremote, file1)
+
+	// We should have transferred exactly one file, not set the mod time
+	assert.Equal(t, int64(1), fs.Stats.GetTransfers())
+}
+
 func TestSyncAfterAddingAFile(t *testing.T) {
 	r := NewRun(t)
 	defer r.Finalise()