Properly trim whitespace from headers

HTTP Whitespace and regex whitespace are not the same, so we can't use
\s in regexes when parsing HTTP headers. Instead, explicitly specify
what is considered whitespace in the regex.

test/test.cc

@@ -1766,6 +1766,52 @@ TEST_F(ServerTest, MultipartFormDataGzip) {
 }
 #endif
 
+TEST(ServerRequestParsingTest, TrimWhitespaceFromHeaderValues) {
+  Server svr;
+  std::string header_value;
+  svr.Get("/validate-ws-in-headers",
+          [&](const Request &req, Response &res) {
+            header_value = req.get_header_value("foo");
+            res.set_content("ok", "text/plain");
+          });
+
+  thread t = thread([&] { svr.listen(HOST, PORT); });
+  while (!svr.is_running()) {
+    msleep(1);
+  }
+
+  // Only space and horizontal tab are whitespace. Make sure other whitespace-
+  // like characters are not treated the same - use vertical tab and escape.
+  auto client_sock =
+      detail::create_client_socket(HOST, PORT, /*timeout_sec=*/5);
+  ASSERT_TRUE(client_sock != INVALID_SOCKET);
+  const std::string req =
+      "GET /validate-ws-in-headers HTTP/1.1\r\n"
+      "foo: \t \v bar \e\t \r\n"
+      "Connection: close\r\n"
+      "\r\n";
+
+  bool process_ok = detail::process_and_close_socket(
+      true, client_sock, 1, 5, 0,
+      [&](Stream& strm, bool /*last_connection*/,
+          bool &/*connection_close*/) -> bool {
+        if (req.size() !=
+            static_cast<size_t>(strm.write(req.data(), req.size()))) {
+          return false;
+        }
+
+        char buf[512];
+
+        detail::stream_line_reader line_reader(strm, buf, sizeof(buf));
+        while (line_reader.getline()) {}
+        return true;
+      });
+  ASSERT_TRUE(process_ok);
+  svr.stop();
+  t.join();
+  EXPECT_EQ(header_value, "\v bar \e");
+}
+
 class ServerTestWithAI_PASSIVE : public ::testing::Test {
 protected:
   ServerTestWithAI_PASSIVE()