changelog/1.4.0: add 'Better error handling' section.

changelog/1.4.0.md

@@ -13,6 +13,7 @@ Contents:
 - [Remapper](#remapper)
 - [oatpp::web::mime::ContentMappers](#oatppwebmimecontentmappers)
 - [New OATPP_LOGx format](#new-oatpp_logx-format)
+- [Better error handling](#better-error-handling)
 - [Restructuring](#restructuring)
 
 
@@ -172,6 +173,66 @@ Instead of old formatting "%s", "%d", "%f" use "{}" for any variable type:
 OATPP_LOGd("MyController", "User: name={}, age={}", user->name, user->age)
 ```
 
+## Better error handling
+
+Fixed error handling in the `ApiController` and `ConnectionHandler`.
+
+The new recommended way to implement custom error handler:
+
+```cpp
+/**
+ * Extend the DefaultErrorHandling class by overriding the renderError() method instead of the handleError() method. 
+ * You can still override the handleError() method, but in most cases, it isn't necessary.
+ */
+class ErrorHandler : public oatpp::web::server::handler::DefaultErrorHandler {
+private:
+  /* mappers to map response according to 'Accept' header and available mappers */
+  std::shared_ptr<oatpp::web::mime::ContentMappers> m_mappers;
+public:
+
+  ErrorHandler(const std::shared_ptr<oatpp::web::mime::ContentMappers>& mappers)
+    : m_mappers(mappers)
+  {}
+  
+  std::shared_ptr<OutgoingResponse> renderError(const HttpServerErrorStacktrace& stacktrace) override {
+    
+    /* create ErrorDto */
+    auto error = ErrorDto::createShared();
+    error->code = stacktrace.status.code;
+    error->stack = {}; // initialize stack as empty list
+
+    /* push all items of stacktrace */
+    for(auto& s : stacktrace.stack) {
+      error->stack->push_back(s);
+    }
+    
+    /* get all variants of acceptable mime-types from request */
+    std::vector<oatpp::String> acceptable;
+    if(stacktrace.request) {
+      acceptable = stacktrace.request->getHeaderValues("Accept");
+    }
+    
+    /* select mapper based on provided preferences */
+    auto mapper = m_mappers->selectMapper(acceptable);
+    if(!mapper) {
+      mapper = m_mappers->getDefaultMapper();
+    }
+    
+    /* create response object */
+    auto response = ResponseFactory::createResponse(stacktrace.status, error, mapper);
+    
+    /* put all error related headers */
+    for(const auto& pair : stacktrace.headers.getAll()) {
+      response->putHeader(pair.first.toString(), pair.second.toString());
+    }
+    
+    /* return response */
+    return response;
+    
+  }
+
+};
+```
 
 ## Restructuring