1 files changed, 45 insertions, 14 deletions

diff --git a/generic/tclIOUtil.c b/generic/tclIOUtil.c
index fe398fc..f4e3bc4 100644
--- a/generic/tclIOUtil.c
+++ b/generic/tclIOUtil.c
@@ -1390,31 +1390,62 @@ TclFSNormalizeToUniquePath(
 {
     FilesystemRecord *fsRecPtr, *firstFsRecPtr;
 
+    int i;
+    int isVfsPath = 0;
+    char *path;
+
     /*
-     * Call each of the "normalise path" functions in succession. This is a
-     * special case, in which if we have a native filesystem handler, we call
-     * it first. This is because the root of Tcl's filesystem is always a
-     * native filesystem (i.e., '/' on unix is native).
+     * Paths starting with a UNC prefix whose final character is a colon
+     * are reserved for VFS use.  These names can not conflict with real
+     * UNC paths per https://msdn.microsoft.com/en-us/library/gg465305.aspx
+     * and rfc3986's definition of reg-name.
+     *
+     * We check these first to avoid useless calls to the native filesystem's
+     * normalizePathProc.
      */
+    path = Tcl_GetStringFromObj(pathPtr, &i);
+
+    if ( (i >= 3) && ( (path[0] == '/' && path[1] == '/')
+		    || (path[0] == '\\' && path[1] == '\\') ) ) {
+	for ( i = 2; ; i++) {
+	    if (path[i] == '\0') break;
+	    if (path[i] == path[0]) break;
+	}
+	--i;
+	if (path[i] == ':') isVfsPath = 1;
+    }
 
+    /*
+     * Call each of the "normalise path" functions in succession.
+     */
     firstFsRecPtr = FsGetFirstFilesystem();
 
     Claim();
-    for (fsRecPtr=firstFsRecPtr; fsRecPtr!=NULL; fsRecPtr=fsRecPtr->nextPtr) {
-	if (fsRecPtr->fsPtr != &tclNativeFilesystem) {
-	    continue;
-	}
+
+    if (!isVfsPath) {
 
 	/*
-	 * TODO: Assume that we always find the native file system; it should
-	 * always be there...
+	 * If we have a native filesystem handler, we call it first.  This is
+	 * because the root of Tcl's filesystem is always a native filesystem
+	 * (i.e., '/' on unix is native).
 	 */
 
-	if (fsRecPtr->fsPtr->normalizePathProc != NULL) {
-	    startAt = fsRecPtr->fsPtr->normalizePathProc(interp, pathPtr,
-		    startAt);
+	for (fsRecPtr=firstFsRecPtr; fsRecPtr!=NULL; fsRecPtr=fsRecPtr->nextPtr) {
+	    if (fsRecPtr->fsPtr != &tclNativeFilesystem) {
+		continue;
+	    }
+
+	    /*
+	     * TODO: Assume that we always find the native file system; it should
+	     * always be there...
+	     */
+
+	    if (fsRecPtr->fsPtr->normalizePathProc != NULL) {
+		startAt = fsRecPtr->fsPtr->normalizePathProc(interp, pathPtr,
+			startAt);
+	    }
+	    break;
 	}
-	break;
     }
 
     for (fsRecPtr=firstFsRecPtr; fsRecPtr!=NULL; fsRecPtr=fsRecPtr->nextPtr) {