Merge branch 'kuguma-use_exception_ptr'

Author: yhirose

README.md

@@ -212,15 +212,23 @@ svr.set_error_handler([](const auto& req, auto& res) {
 The exception handler gets called if a user routing handler throws an error.
 
 ```cpp
-svr.set_exception_handler([](const auto& req, auto& res, std::exception &e) {
-  res.status = 500;
+svr.set_exception_handler([](const auto& req, auto& res, std::exception_ptr ep) {
   auto fmt = "<h1>Error 500</h1><p>%s</p>";
   char buf[BUFSIZ];
-  snprintf(buf, sizeof(buf), fmt, e.what());
+  try {
+    std::rethrow_exception(ep);
+  } catch (std::exception &e) {
+    snprintf(buf, sizeof(buf), fmt, e.what());
+  } catch (...) { // See the following NOTE
+    snprintf(buf, sizeof(buf), fmt, "Unknown Exception");
+  }
   res.set_content(buf, "text/html");
+  res.status = 500;
 });
 ```
 
+NOTE: if you don't provide the `catch (...)` block for a rethrown exception pointer, an uncaught exception will end up causing the server crash. Be careful!
+
 ### Pre routing handler
 
 ```cpp

httplib.h

@@ -614,7 +614,7 @@ class Server {
   using Handler = std::function<void(const Request &, Response &)>;
 
   using ExceptionHandler =
-      std::function<void(const Request &, Response &, std::exception &e)>;
+      std::function<void(const Request &, Response &, std::exception_ptr ep)>;
 
   enum class HandlerResponse {
     Handled,
@@ -5721,15 +5721,22 @@ Server::process_request(Stream &strm, bool close_connection,
     routed = routing(req, res, strm);
   } catch (std::exception &e) {
     if (exception_handler_) {
-      exception_handler_(req, res, e);
+      auto ep = std::current_exception();
+      exception_handler_(req, res, ep);
       routed = true;
     } else {
       res.status = 500;
       res.set_header("EXCEPTION_WHAT", e.what());
     }
   } catch (...) {
-    res.status = 500;
-    res.set_header("EXCEPTION_WHAT", "UNKNOWN");
+    if (exception_handler_) {
+      auto ep = std::current_exception();
+      exception_handler_(req, res, ep);
+      routed = true;
+    } else {
+      res.status = 500;
+      res.set_header("EXCEPTION_WHAT", "UNKNOWN");
+    }
   }
 #endif
 

test/test.cc

@@ -1249,8 +1249,11 @@ TEST(ExceptionHandlerTest, ContentLength) {
   Server svr;
 
   svr.set_exception_handler([](const Request & /*req*/, Response &res,
-                               std::exception &e) {
-    EXPECT_EQ("abc", std::string(e.what()));
+                               std::exception_ptr ep) {
+    EXPECT_FALSE(ep == nullptr);
+    try {
+      std::rethrow_exception(ep);
+    } catch (std::exception &e) { EXPECT_EQ("abc", std::string(e.what())); }
     res.status = 500;
     res.set_content("abcdefghijklmnopqrstuvwxyz",
                     "text/html"); // <= Content-Length still 13 at this point