feat: add cors example to demonstrate cross-origin support in drogon

examples/CMakeLists.txt

@@ -34,6 +34,8 @@ add_executable(redis_chat redis_chat/main.cc
 add_executable(async_stream async_stream/main.cc
                             async_stream/RequestStreamExampleCtrl.cc)
 
+add_executable(cors cors/main.cc)
+
 set(example_targets
     benchmark
     client
@@ -45,7 +47,8 @@ set(example_targets
     jsonstore
     redis_simple
     redis_chat
-    async_stream)
+    async_stream
+    cors)
 
 # Add warnings for our example targets--some warnings (such as -Wunused-parameter) only appear
 # when the templated functions are instantiated at their point of use.

examples/README.md

@@ -16,6 +16,7 @@ proxy with a simple round robin
 11. [redis_cache](https://github.com/drogonframework/drogon/tree/master/examples/redis_cache) - An example for using coroutines of Redis clients
 12. [redis_chat](https://github.com/drogonframework/drogon/tree/master/examples/redis_chat) - A chatroom server built with websocket and Redis pub/sub service
 13. [prometheus_example](https://github.com/drogonframework/drogon/tree/master/examples/prometheus_example) - An example of how to use the Prometheus exporter in Drogon
+14. [cors](https://github.com/drogonframework/drogon/tree/master/examples/cors) - An example demonstrating how to implement CORS (Cross-Origin Resource Sharing) support in Drogon
 
 ### [TechEmpower Framework Benchmarks](https://github.com/TechEmpower/FrameworkBenchmarks) test suite
 

examples/cors/main.cc

@@ -0,0 +1,153 @@
+#include <drogon/HttpAppFramework.h>
+#include <drogon/HttpResponse.h>
+#include <drogon/drogon.h>
+#include "trantor/utils/Logger.h"
+
+using namespace drogon;
+
+/// Configure Cross-Origin Resource Sharing (CORS) support.
+///
+///  This function registers both synchronous pre-processing advice for handling
+///  OPTIONS preflight requests and post-handling advice to inject CORS headers
+///  into all responses dynamically based on the incoming request headers.
+void setupCors()
+{
+    // Register sync advice to handle CORS preflight (OPTIONS) requests
+    drogon::app().registerSyncAdvice([](const drogon::HttpRequestPtr &req)
+                                         -> drogon::HttpResponsePtr {
+        if (req->method() == drogon::HttpMethod::Options)
+        {
+            auto resp = drogon::HttpResponse::newHttpResponse();
+
+            // Set Access-Control-Allow-Origin header based on the Origin
+            // request header
+            const auto &origin = req->getHeader("Origin");
+            if (!origin.empty())
+            {
+                resp->addHeader("Access-Control-Allow-Origin", origin);
+            }
+
+            // Set Access-Control-Allow-Methods based on the requested method
+            const auto &requestMethod =
+                req->getHeader("Access-Control-Request-Method");
+            if (!requestMethod.empty())
+            {
+                resp->addHeader("Access-Control-Allow-Methods", requestMethod);
+            }
+
+            // Allow credentials to be included in cross-origin requests
+            resp->addHeader("Access-Control-Allow-Credentials", "true");
+
+            // Set allowed headers from the Access-Control-Request-Headers
+            // header
+            const auto &requestHeaders =
+                req->getHeader("Access-Control-Request-Headers");
+            if (!requestHeaders.empty())
+            {
+                resp->addHeader("Access-Control-Allow-Headers", requestHeaders);
+            }
+
+            return std::move(resp);
+        }
+        return {};
+    });
+
+    // Register post-handling advice to add CORS headers to all responses
+    drogon::app().registerPostHandlingAdvice(
+        [](const drogon::HttpRequestPtr &req,
+           const drogon::HttpResponsePtr &resp) -> void {
+            // Set Access-Control-Allow-Origin based on the Origin request
+            // header
+            const auto &origin = req->getHeader("Origin");
+            if (!origin.empty())
+            {
+                resp->addHeader("Access-Control-Allow-Origin", origin);
+            }
+
+            // Reflect the requested Access-Control-Request-Method back in the
+            // response
+            const auto &requestMethod =
+                req->getHeader("Access-Control-Request-Method");
+            if (!requestMethod.empty())
+            {
+                resp->addHeader("Access-Control-Allow-Methods", requestMethod);
+            }
+
+            // Allow credentials to be included in cross-origin requests
+            resp->addHeader("Access-Control-Allow-Credentials", "true");
+
+            // Reflect the requested Access-Control-Request-Headers back
+            const auto &requestHeaders =
+                req->getHeader("Access-Control-Request-Headers");
+            if (!requestHeaders.empty())
+            {
+                resp->addHeader("Access-Control-Allow-Headers", requestHeaders);
+            }
+        });
+}
+
+/**
+ * Main function to start the Drogon application with CORS-enabled routes.
+ * This example includes:
+ * - A simple GET endpoint `/hello` that returns a greeting message.
+ * - A POST endpoint `/echo` that echoes back the request body.
+ *  You can test with curl to test the CORS support:
+ *
+```
+    curl -i -X OPTIONS http://localhost:8000/echo \
+        -H "Origin: http://localhost:3000" \
+        -H "Access-Control-Request-Method: POST" \
+        -H "Access-Control-Request-Headers: Content-Type"
+```
+or
+```
+    curl -i -X POST http://localhost:8000/echo \
+        -H "Origin: http://localhost:3000" \
+        -H "Content-Type: application/json" \
+        -d '{"key":"value"}'
+```
+ */
+int main()
+{
+    // Listen on port 8000 for all interfaces
+    app().addListener("0.0.0.0", 8000);
+
+    // Setup CORS support
+    setupCors();
+
+    // Register /hello route for GET and OPTIONS methods
+    app().registerHandler(
+        "/hello",
+        [](const HttpRequestPtr &req,
+           std::function<void(const HttpResponsePtr &)> &&callback) {
+            auto resp = HttpResponse::newHttpResponse();
+            resp->setBody("Hello from Drogon!");
+
+            // Log client IP address
+            LOG_INFO << "Request to /hello from " << req->getPeerAddr().toIp();
+
+            callback(resp);
+        },
+        {Get, Options});
+
+    // Register /echo route for POST and OPTIONS methods
+    app().registerHandler(
+        "/echo",
+        [](const HttpRequestPtr &req,
+           std::function<void(const HttpResponsePtr &)> &&callback) {
+            auto resp = HttpResponse::newHttpResponse();
+            resp->setBody(std::string("Echo: ").append(req->getBody()));
+
+            // Log client IP and request body
+            LOG_INFO << "Request to /echo from " << req->getPeerAddr().toIp();
+            LOG_INFO << "Echo content: " << req->getBody();
+
+            callback(resp);
+        },
+        {Post, Options});
+
+    // Start the application main loop
+    app().run();
+
+    return 0;
+}