tool_doswin: Support for literal path prefix \\?\

For example something like --output \\?\C:\foo

src/tool_doswin.c

@@ -150,9 +150,8 @@ SANITIZEcode sanitize_file_name(char **const sanitized, const char *file_name,
 
   if((flags & SANITIZE_ALLOW_PATH)) {
 #ifndef MSDOS
-    if((flags & SANITIZE_ALLOW_PATH) &&
-       file_name[0] == '\\' && file_name[1] == '\\')
-      /* UNC prefixed path, eg \\?\C:\foo */
+    if(file_name[0] == '\\' && file_name[1] == '\\')
+      /* UNC prefixed path \\ (eg \\?\C:\foo) */
       max_sanitized_len = 32767-1;
     else
 #endif
@@ -180,8 +179,16 @@ SANITIZEcode sanitize_file_name(char **const sanitized, const char *file_name,
   strncpy(target, file_name, len);
   target[len] = '\0';
 
+#ifndef MSDOS
+  if((flags & SANITIZE_ALLOW_PATH) && !strncmp(target, "\\\\?\\", 4))
+    /* Skip the literal path prefix \\?\ */
+    p = target + 4;
+  else
+#endif
+    p = target;
+
   /* replace control characters and other banned characters */
-  for(p = target; *p; ++p) {
+  for(; *p; ++p) {
     const char *banned;
 
     if((1 <= *p && *p <= 31) ||

tests/unit/unit1604.c

@@ -110,6 +110,14 @@ UNITTEST_START
     { "f:/foo", SANITIZE_ALLOW_PATH,
       "f:/foo", SANITIZE_ERR_OK
     },
+#ifndef MSDOS
+    { "\\\\?\\C:\\foo", SANITIZE_ALLOW_PATH,
+      "\\\\?\\C:\\foo", SANITIZE_ERR_OK
+    },
+    { "\\\\?\\C:\\foo", 0,
+      "____C__foo", SANITIZE_ERR_OK
+    },
+#endif
     { "foo:bar", 0,
       "foo_bar", SANITIZE_ERR_OK
     },
@@ -164,6 +172,17 @@ UNITTEST_START
     { "com1:\\com1", SANITIZE_ALLOW_RESERVED,
       "com1__com1", SANITIZE_ERR_OK
     },
+#ifndef MSDOS
+    { "\\com1", SANITIZE_ALLOW_PATH,
+      "\\_com1", SANITIZE_ERR_OK
+    },
+    { "\\\\com1", SANITIZE_ALLOW_PATH,
+      "\\\\com1", SANITIZE_ERR_OK
+    },
+    { "\\\\?\\C:\\com1", SANITIZE_ALLOW_PATH,
+      "\\\\?\\C:\\com1", SANITIZE_ERR_OK
+    },
+#endif
     { "CoM1", 0,
       "_CoM1", SANITIZE_ERR_OK
     },