Refuse a ':' in a path a mount point serves on Windows (#2643)

On NTFS a ':' in a path names a stream of the file, so /dir/test.html::$DATA opened the default stream of dir/test.html and passed a set_pre_routing_handler() guard on /dir/test.html, and /setup.exe:Zone.Identifier served the stream Windows attaches to downloaded files. is_valid_path() now refuses a ':' on Windows.

Elsewhere a ':' is an ordinary file name character, so it is still served: a file such as 2024-01-01T10:00:00.log would otherwise answer 404. The test pins both sides.

README.md

@@ -409,7 +409,7 @@ ret = svr.remove_mount_point("/");
 ret = svr.remove_mount_point("/public");
 ```
 
-A mount point serves a path only when it has no `.`, `..` or empty segment other than a trailing `/`, and no segment ending in `.` or a space, so a check on `req.path` in `set_pre_routing_handler()` sees the path of the file that is served. A path ending in `/`, and the mount point itself such as `/public`, serve the `index.html` in that directory. The file system can still give a file other names: another case on a case-insensitive file system, such as the default ones on macOS and Windows, and on Windows an 8.3 short name such as `PRIVAT~1`. Compare paths without regard to case on such a file system, and on Windows keep files that need a guard out of mounted directories.
+A mount point serves a path only when it has no `.`, `..` or empty segment other than a trailing `/`, no segment ending in `.` or a space and, on Windows, no `:` (it names an NTFS stream), so a check on `req.path` in `set_pre_routing_handler()` sees the path of the file that is served. A path ending in `/`, and the mount point itself such as `/public`, serve the `index.html` in that directory. The file system can still give a file other names: another case on a case-insensitive file system, such as the default ones on macOS and Windows, and on Windows an 8.3 short name such as `PRIVAT~1`. Compare paths without regard to case on such a file system, and on Windows keep files that need a guard out of mounted directories.
 
 ```cpp
 // User defined file extension and MIME type mappings

httplib.h

@@ -6007,9 +6007,10 @@ inline bool is_valid_close_payload(const std::string &payload) {
 namespace detail {
 
 // A path a mount point serves: absolute, with no empty segment except a
-// trailing '/' and no segment ending in '.' or a space (which covers "." and
+// trailing '/', no segment ending in '.' or a space (which covers "." and
-// ".." and names Windows trims into another file's name), so the file served
+// ".." and names Windows trims into another file's name) and, on Windows, no
-// is the one that req.path names to the handlers that ran before it.
+// ':' (which names an NTFS stream, so "a.txt::$DATA" is a.txt), so the file
+// served is the one that req.path names to the handlers that ran before it.
 inline bool is_valid_path(const std::string &path) {
   if (path.empty() || path[0] != '/') { return false; }
 
@@ -6017,6 +6018,9 @@ inline bool is_valid_path(const std::string &path) {
   for (auto i = beg; i <= path.size(); i++) {
     if (i < path.size() && path[i] != '/') {
       if (path[i] == '\0' || path[i] == '\\') { return false; }
+#ifdef _WIN32
+      if (path[i] == ':') { return false; }
+#endif
       continue;
     }
     auto len = i - beg;

test/test.cc

@@ -707,6 +707,18 @@ TEST(IsValidPathTest, RejectsSegmentsEndingInDotOrSpace) {
   }
 }
 
+// ':' names an NTFS stream on Windows and is an ordinary character in a file
+// name anywhere else.
+TEST(IsValidPathTest, ColonIsRejectedOnlyOnWindows) {
+  for (auto path : {"/a.txt::$DATA", "/a.txt:Zone.Identifier", "/dir:x/a"}) {
+#ifdef _WIN32
+    EXPECT_FALSE(detail::is_valid_path(path)) << path;
+#else
+    EXPECT_TRUE(detail::is_valid_path(path)) << path;
+#endif
+  }
+}
+
 TEST(CanCompressContentTypeTest, ComparesWholeTypes) {
   EXPECT_TRUE(detail::can_compress_content_type("application/json"));
   EXPECT_TRUE(detail::can_compress_content_type("text/plain; charset=utf-8"));
@@ -12760,7 +12772,8 @@ TEST(MountTest, AliasedPathDoesNotPassPreRoutingGuard) {
   for (auto path :
        {"/./dir/test.html", "/dir/./test.html", "//dir/test.html",
         "/dir//test.html", "/dir/../dir/test.html", "/%2e/dir/test.html",
-        "/dir/test.html.", "/dir/test.html%20"}) {
+        "/dir/test.html.", "/dir/test.html%20", "/dir/test.html::$DATA",
+        "/dir/test.html%3A%3A$DATA"}) {
     SCOPED_TRACE(path);
     auto res = cli.Get(path);
     ASSERT_TRUE(res) << "Error: " << to_string(res.error());