core: Verify MD5 sums after each transfer

fs/operations.go

@@ -97,6 +97,18 @@ func Equal(src, dst Object) bool {
 	return true
 }
 
+// Used to remove a failed copy
+func removeFailedCopy(dst Object) {
+	if dst != nil {
+		Debug(dst, "Removing failed copy")
+		removeErr := dst.Remove()
+		if removeErr != nil {
+			Stats.Error()
+			Log(dst, "Failed to remove failed copy: %s", removeErr)
+		}
+	}
+}
+
 // Copy src object to dst or f if nil
 //
 // If dst is nil then the object must not exist already.  If you do
@@ -126,16 +138,29 @@ func Copy(f Fs, dst, src Object) {
 	if err != nil {
 		Stats.Error()
 		Log(src, "Failed to copy: %s", err)
-		if dst != nil {
+		removeFailedCopy(dst)
-			Debug(dst, "Removing failed copy")
-			removeErr := dst.Remove()
-			if removeErr != nil {
-				Stats.Error()
-				Log(dst, "Failed to remove failed copy: %s", removeErr)
-			}
-		}
 		return
 	}
+
+	// Verify md5sums are the same after transfer - ignoring blank md5sums
+	srcMd5sum, md5sumErr := src.Md5sum()
+	if md5sumErr != nil {
+		Stats.Error()
+		Log(src, "Failed to read md5sum: %s", md5sumErr)
+	} else if srcMd5sum != "" {
+		dstMd5sum, md5sumErr := dst.Md5sum()
+		if md5sumErr != nil {
+			Stats.Error()
+			Log(dst, "Failed to read md5sum: %s", md5sumErr)
+		} else if dstMd5sum != "" && srcMd5sum != dstMd5sum {
+			Stats.Error()
+			err = fmt.Errorf("Corrupted on transfer: md5sums differ %q vs %q", srcMd5sum, dstMd5sum)
+			Log(dst, "%s", err)
+			removeFailedCopy(dst)
+			return
+		}
+	}
+
 	Debug(src, actionTaken)
 }