Implement proper timestamp validation for Twitch messages

.gitmodules

@@ -28,3 +28,6 @@
 [submodule "deps/libusb"]
 	path = deps/libusb
 	url = https://github.com/libusb/libusb.git
+[submodule "deps/date"]
+	path = deps/date
+	url = https://github.com/HowardHinnant/date.git

deps/date

@@ -0,0 +1 @@
+Subproject commit 5bdb7e6f31fac909c090a46dbd9fea27b6e609a4

plugins/twitch/CMakeLists.txt

@@ -30,6 +30,31 @@ if(NOT ZLIB_FOUND)
   return()
 endif()
 
+set(DATE_LIB_DIR "${ADVSS_SOURCE_DIR}/deps/date")
+if(EXISTS "${DATE_LIB_DIR}/CMakeLists.txt")
+  set(BUILD_TZ_LIB ON)
+  if(OS_WINDOWS)
+    if(CURL_FOUND AND TARGET CURL::libcurl)
+      get_target_property(CURL_INCLUDE_DIR CURL::libcurl
+                          INTERFACE_INCLUDE_DIRECTORIES)
+      add_subdirectory("${DATE_LIB_DIR}" "${DATE_LIB_DIR}/build"
+                       EXCLUDE_FROM_ALL)
+      target_include_directories(date-tz PRIVATE "${CURL_INCLUDE_DIR}")
+      set(VERIFY_TWITCH_TIMESTAMPS ON)
+    else()
+      message(WARNING "CURL not found - not verifying Twitch timestamps")
+    endif()
+  else()
+    add_subdirectory("${DATE_LIB_DIR}" "${DATE_LIB_DIR}/build" EXCLUDE_FROM_ALL)
+    target_compile_options(date-tz PUBLIC -Wno-error=conversion
+                                          -Wno-error=shadow)
+    set(VERIFY_TWITCH_TIMESTAMPS ON)
+  endif()
+else()
+  message(WARNING "date lib not found in \"${DATE_LIB_DIR}\"!\n"
+                  "Twitch timestamps will not be checked!")
+endif()
+
 # --- End of section ---
 
 add_library(${PROJECT_NAME} MODULE)
@@ -76,6 +101,14 @@ set_target_properties(${PROJECT_NAME} PROPERTIES PREFIX "")
 target_include_directories(${PROJECT_NAME} PRIVATE "${CPP_HTTPLIB_DIR}/"
                                                    "${OPENSSL_INCLUDE_DIR}")
 target_link_libraries(${PROJECT_NAME} PRIVATE ${OPENSSL_LIBRARIES} ZLIB::ZLIB)
+if(DEFINED VERIFY_TWITCH_TIMESTAMPS)
+  target_compile_definitions(${PROJECT_NAME} PRIVATE VERIFY_TIMESTAMPS=1)
+  target_link_libraries(${PROJECT_NAME} PRIVATE date::date-tz)
+  if(OS_WINDOWS)
+    target_link_libraries(${PROJECT_NAME} PRIVATE CURL::libcurl)
+  endif()
+endif()
+
 install_advss_plugin(${PROJECT_NAME})
 if(OS_WINDOWS)
   # Couldn't really find a better way to install runtime dependencies for

plugins/twitch/event-sub.cpp

@@ -4,6 +4,10 @@
 
 #include <log-helper.hpp>
 
+#ifdef VERIFY_TIMESTAMPS
+#include "date/tz.h"
+#endif
+
 namespace advss {
 
 using websocketpp::lib::placeholders::_1;
@@ -237,15 +241,43 @@ void EventSub::OnOpen(connection_hdl)
 
 static bool isValidTimestamp(const std::string &timestamp)
 {
-	std::tm tm = {};
-	std::istringstream ss(timestamp);
-	ss >> std::get_time(&tm, "%Y-%m-%dT%H:%M:%S.%fZ");
-	auto tp = std::chrono::system_clock::from_time_t(std::mktime(&tm));
-	tp += std::chrono::hours(1); // UTC
-	std::chrono::system_clock::time_point currentTime =
-		std::chrono::system_clock::now();
-	auto diff = currentTime - tp;
-	return diff <= std::chrono::minutes(10);
+#ifdef VERIFY_TIMESTAMPS
+	// Example input: 2023-07-19T14:56:51.634234626Z
+	try {
+		// Discard the nanosecond part
+		static constexpr size_t dotPos = 19;
+		std::string trimmed = timestamp.substr(0, dotPos);
+		auto tzStart = timestamp.find_first_of("Z+-", dotPos);
+		trimmed = timestamp.substr(0, dotPos);
+		if (tzStart != std::string::npos) {
+			trimmed += timestamp.substr(tzStart);
+		}
+
+		std::istringstream in(trimmed);
+		date::sys_time<std::chrono::seconds> parsedTime;
+		in >> date::parse("%FT%TZ", parsedTime);
+		if (in.fail()) {
+			blog(LOG_WARNING, "failed to parse timestamp %s",
+			     timestamp.c_str());
+			return false;
+		}
+
+		auto now = date::zoned_time{date::current_zone(),
+					    std::chrono::system_clock::now()}
+				   .get_sys_time();
+
+		auto duration = now - parsedTime;
+		// Clocks might be off by a bit, so allow negative values also
+		return duration <= std::chrono::minutes(10) &&
+		       duration >= std::chrono::minutes(-1);
+	} catch (const std::exception &e) {
+		blog(LOG_WARNING, "%s: %s", __func__, e.what());
+		return false;
+	}
+#else
+	// Just assume timestamps are always valid
+	return true;
+#endif
 }
 
 bool EventSub::IsValidMessageID(const std::string &id)
@@ -288,7 +320,8 @@ void EventSub::OnMessage(connection_hdl, EventSubWSClient::message_ptr message)
 		obs_data_get_string(metadata, "message_timestamp");
 	if (!isValidTimestamp(timestamp)) {
 		blog(LOG_WARNING,
-		     "Discarding Twitch EventSub with invalid timestamp");
+		     "Discarding Twitch EventSub with invalid timestamp %s",
+		     timestamp.c_str());
 		return;
 	}
 	std::string id = obs_data_get_string(metadata, "message_id");