Refuse to serve a path segment ending in a dot or a space

Windows trims a trailing '.' or space from a file name, so a mount
point there served a file under a path other than the one a pre-routing
handler checked. A mount point now serves no path with a segment
ending in '.' or a space, on every platform; "." and ".." are among
them. The README no longer lists such names among the ones the file
system can still alias.

README.md

@@ -406,7 +406,7 @@ 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 `/`, 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 a name with a trailing `.` or space, or 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 `/`, 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.
 
 ```cpp
 // User defined file extension and MIME type mappings

httplib.h

@@ -5988,9 +5988,10 @@ inline bool is_valid_close_payload(const std::string &payload) {
 
 namespace detail {
 
-// A path a mount point serves: absolute, with no ".", ".." or empty segment
-// except a trailing '/', so the file served is the one that req.path names to
-// the handlers that ran before it.
+// 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
+// ".." and names Windows trims into another file's name), 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; }
 
@@ -6001,8 +6002,8 @@ inline bool is_valid_path(const std::string &path) {
       continue;
     }
     auto len = i - beg;
-    if ((len == 0 && i < path.size()) || (len == 1 && path[beg] == '.') ||
-        (len == 2 && path[beg] == '.' && path[beg + 1] == '.')) {
+    if ((len == 0 && i < path.size()) ||
+        (len > 0 && (path[i - 1] == '.' || path[i - 1] == ' '))) {
       return false;
     }
     beg = i + 1;

test/test.cc

@@ -566,6 +566,7 @@ find_content_type(const std::string &path,
                   const std::string &default_content_type);
 bool can_compress_content_type(const std::string &content_type);
 bool is_prohibited_header_name(const std::string &name);
+bool is_valid_path(const std::string &path);
 #ifdef CPPHTTPLIB_SSL_ENABLED
 bool match_hostname(const std::string &pattern, const std::string &hostname);
 #endif
@@ -693,6 +694,12 @@ TEST(FindContentTypeTest, ComparesWholeExtensions) {
   EXPECT_EQ("", detail::find_content_type("/a.l5", {}, ""));
 }
 
+TEST(IsValidPathTest, RejectsSegmentsEndingInDotOrSpace) {
+  for (auto path : {"/a.", "/a ", "/dir./a", "/dir /a", "/..."}) {
+    EXPECT_FALSE(detail::is_valid_path(path)) << path;
+  }
+}
+
 TEST(CanCompressContentTypeTest, ComparesWholeTypes) {
   EXPECT_TRUE(detail::can_compress_content_type("application/json"));
   EXPECT_TRUE(detail::can_compress_content_type("text/plain; charset=utf-8"));
@@ -12607,8 +12614,9 @@ TEST(MountTest, MultibytesPathName) {
   EXPECT_EQ(U8("日本語コンテンツ"), res->body);
 }
 
-// A mount point serves no path with an empty, "." or ".." segment, so a guard
-// in the pre-routing handler sees the path of every file that is served
+// A mount point serves no path with an empty segment or one ending in '.' or
+// a space, so a guard in the pre-routing handler sees the path of every file
+// that is served
 TEST(MountTest, AliasedPathDoesNotPassPreRoutingGuard) {
   Server svr;
   ASSERT_TRUE(svr.set_mount_point("/", "./www"));
@@ -12633,7 +12641,8 @@ TEST(MountTest, AliasedPathDoesNotPassPreRoutingGuard) {
   Client cli(HOST, port);
   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/../dir/test.html", "/%2e/dir/test.html",
+        "/dir/test.html.", "/dir/test.html%20"}) {
     SCOPED_TRACE(path);
     auto res = cli.Get(path);
     ASSERT_TRUE(res) << "Error: " << to_string(res.error());