Fix server crash caused due to regex complexity while matching headers. (#632)

* Fix parsing to parse query string with single space char.

When passed ' ' as a query string, the server crashes cause of illegal memory access done in httplib::detail::split. Have added checks to make sure the split function has a valid string with length > 0.

* Fix parsing to parse query string with single space char.

* Fix server crash caused due to regex complexity while matching headers.

While parsing content-type header in multipart form request the server crashes due to the exhaustion of max iterations performed while matching the input string with content-type regex.
Have removed the regex which might use backtracking while matching and replaced it with manual string processing. Have added tests as well.

* Remove magic number

Co-authored-by: Ivan Fefer <fefer.ivan@gmail.com>

Co-authored-by: yhirose <yhirose@users.noreply.github.com>
Co-authored-by: Ivan Fefer <fefer.ivan@gmail.com>

httplib.h

@@ -1452,6 +1452,13 @@ inline std::pair<int, int> trim(const char *b, const char *e, int left,
   return std::make_pair(left, right);
 }
 
+inline void trim(std::string &s) {
+  auto is_not_space = [](int ch) { return !std::isspace(ch); };
+  s.erase(s.begin(), std::find_if(s.begin(), s.end(), is_not_space));
+  s.erase(std::find_if(s.rbegin(), s.rend(), is_not_space).base(), s.end());
+}
+
+
 template <class Fn> void split(const char *b, const char *e, char d, Fn fn) {
   int i = 0;
   int beg = 0;
@@ -2828,6 +2835,18 @@ inline bool redirect(T &cli, const Request &req, Response &res,
   return ret;
 }
 
+inline bool contains_header(const std::string &header, const std::string &name) {
+  if (header.length() >= name.length()) {
+    for (int i = 0; i < name.length(); ++i) {
+      if (std::tolower(header[i]) != std::tolower(name[i])) {
+        return false;
+      }
+    }
+    return true;
+  }
+  return false;
+}
+
 inline std::string params_to_query_str(const Params &params) {
   std::string query;
 
@@ -2914,8 +2933,6 @@ public:
 
   template <typename T, typename U>
   bool parse(const char *buf, size_t n, T content_callback, U header_callback) {
-    static const std::regex re_content_type(R"(^Content-Type:\s*(.*?)\s*$)",
-                                            std::regex_constants::icase);
 
     static const std::regex re_content_disposition(
         "^Content-Disposition:\\s*form-data;\\s*name=\"(.*?)\"(?:;\\s*filename="
@@ -2961,8 +2978,11 @@ public:
           auto header = buf_.substr(0, pos);
           {
             std::smatch m;
-            if (std::regex_match(header, m, re_content_type)) {
+            const std::string header_name = "content-type:";
-              file_.content_type = m[1];
+            if (contains_header(header, header_name)) {
+              header.erase(header.begin(), header.begin() + header_name.size());
+              trim(header);
+              file_.content_type = header;
             } else if (std::regex_match(header, m, re_content_disposition)) {
               file_.name = m[1];
               file_.filename = m[2];

test/test.cc

@@ -43,6 +43,23 @@ TEST(StartupTest, WSAStartup) {
   ASSERT_EQ(0, ret);
 }
 #endif
+TEST(TrimTests, TrimStringTests) {
+  {
+    std::string s = "abc";
+    detail::trim(s);
+    EXPECT_EQ("abc", s);
+  }
+  {
+    std::string s = "  abc  ";
+    detail::trim(s);
+    EXPECT_EQ("abc", s);
+  }
+  {
+    std::string s = "";
+    detail::trim(s);
+    EXPECT_TRUE( s.empty() );
+  }
+}
 
 TEST(SplitTest, ParseQueryString) {
   string s = "key1=val1&key2=val2&key3=val3";
@@ -1082,7 +1099,7 @@ protected:
               })
         .Post("/multipart",
               [&](const Request &req, Response & /*res*/) {
-                EXPECT_EQ(5u, req.files.size());
+                EXPECT_EQ(6u, req.files.size());
                 ASSERT_TRUE(!req.has_file("???"));
                 ASSERT_TRUE(req.body.empty());
 
@@ -1111,6 +1128,13 @@ protected:
                   EXPECT_EQ("application/octet-stream", file.content_type);
                   EXPECT_EQ(0u, file.content.size());
                 }
+
+                {
+                  const auto &file = req.get_file_value("file4");
+                  EXPECT_TRUE(file.filename.empty());
+                  EXPECT_EQ(0u, file.content.size());
+                  EXPECT_EQ("application/json  tmp-string", file.content_type);
+                }
               })
         .Post("/empty",
               [&](const Request &req, Response &res) {
@@ -1803,6 +1827,7 @@ TEST_F(ServerTest, MultipartFormData) {
       {"file1", "h\ne\n\nl\nl\no\n", "hello.txt", "text/plain"},
       {"file2", "{\n  \"world\", true\n}\n", "world.json", "application/json"},
       {"file3", "", "", "application/octet-stream"},
+      {"file4", "", "", "   application/json  tmp-string    "}
   };
 
   auto res = cli_.Post("/multipart", items);