Allow calling Response::send multiple times: copy the buffer before async_write

server_http.hpp

@@ -89,9 +89,17 @@ namespace SimpleWeb {
 
       /// Use this function if you need to recursively send parts of a longer message
       void send(const std::function<void(const error_code &)> &callback = nullptr) noexcept {
+        // Take a snapshot of the stream buffer. Otherwise async_write may not
+        // have consumed the buffer before the next call, in which case the
+        // data from the first call may be sent twice. Use a captured shared
+        // pointer to keep the snapshot alive during the async call.
+        auto stream_snapshot = std::make_shared<asio::streambuf>();
+        std::ostream snapshot_writer(stream_snapshot.get());
+        snapshot_writer << &streambuf;
+
         session->connection->set_timeout(timeout_content);
         auto self = this->shared_from_this(); // Keep Response instance alive through the following async_write
-        asio::async_write(*session->connection->socket, streambuf, [self, callback](const error_code &ec, std::size_t /*bytes_transferred*/) {
+        asio::async_write(*session->connection->socket, *stream_snapshot, [self, callback, stream_snapshot](const error_code &ec, std::size_t /*bytes_transferred*/) {
           self->session->connection->cancel_timeout();
           auto lock = self->session->connection->handler_runner->continue_lock();
           if(!lock)

tests/io_test.cpp

@@ -69,6 +69,20 @@ int main() {
     assert(request->remote_endpoint_port() != 0);
   };
 
+  server.resource["^/string/dup$"]["POST"] = [](shared_ptr<HttpServer::Response> response, shared_ptr<HttpServer::Request> request) {
+    auto content = request->content.string();
+
+    // Send content twice, before it has a chance to be written to the socket.
+    *response << "HTTP/1.1 200 OK\r\nContent-Length: " << (content.length() * 2) << "\r\n\r\n"
+              << content;
+    response->send();
+    *response << content;
+    response->send();
+
+    assert(!request->remote_endpoint_address().empty());
+    assert(request->remote_endpoint_port() != 0);
+  };
+
   server.resource["^/string2$"]["POST"] = [](shared_ptr<HttpServer::Response> response, shared_ptr<HttpServer::Request> request) {
     response->write(request->content.string());
   };
@@ -202,6 +216,15 @@ int main() {
       assert(output.str() == "A string");
     }
 
+    {
+      // Test rapid calls to Response::send
+      stringstream output;
+      stringstream content("A string\n");
+      auto r = client.request("POST", "/string/dup", content);
+      output << r->content.rdbuf();
+      assert(output.str() == "A string\nA string\n");
+    }
+
     {
       stringstream output;
       auto r = client.request("GET", "/info", "", {{"Test Parameter", "test value"}});