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C++ Networking with Asio: Building a Client-Server Framework (Part 1)
0:00:03 Introduction: The video series will explore implementing networking in C++ using the Asio library for asynchronous input/output. It will focus on building a framework to support a server-client system, addressing common networking challenges.
0:01:03 Asio Library: C++ networking is traditionally tricky due to a lack of standardization, Asio offers a solution. The goal is for Asio to become part of the C++ standard, it's important to know that Asio uses Modern C++.
0:01:53 Part 1 Overview: This part covers acquiring and installing Asio, basic (non-asynchronous) usage examples, revealing networking difficulties, outlining the framework's architecture, and starting development on core components.
0:02:20 Acquiring Asio: Asio can be downloaded from think-async.com. It originated as part of the Boost framework, but a standalone (non-Boost) version is available.
0:03:10 Asio Installation: Installation involves extracting the downloaded folder (containing header files) to your SDKs directory. It's header-based, requiring no library linking or building.
0:03:47 Visual Studio Setup: A Visual Studio project is created, and the Asio include directory is added to the project properties.
0:05:12 Core Asio Includes:asio.hpp, asio/buffer.hpp, and asio/internet.hpp are included for basic networking functionality. #define ASIO_STANDALONE is used to indicate the non-Boost version.
0:06:01 Windows-Specific Issue: A Windows-specific warning (WIN32_WINNT) is addressed by defining the target Windows version.
0:07:05 Asio Error Handling: Asio provides descriptive error handling, demonstrated using an asio::error_code variable.
0:07:17 Asio Context: An asio::io_context object is essential; it's the space where Asio performs operations and hides platform-specific details.
0:07:35 Endpoints: Endpoints represent connectable entities (not just network addresses). A tcp::endpoint is created using an IP address and port.
0:08:28 Sockets: A tcp::socket is the operating system's network interface, associated with the Asio context.
0:08:49 Connecting: The socket.connect() function attempts to establish a connection, and the error code indicates success or failure.
0:10:15 Sending and Receiving Data (Synchronous): A basic HTTP request is constructed as a string and sent using socket.write_some(). asio::buffer is used for data transfer. socket.available() checks for incoming data, and socket.read_some() reads it.
0:12:48 Problems with Synchronous Networking: The example highlights problems: uncertainty about when data will arrive (due to network latency) and unknown response size. Hard-coded delays (like std::this_thread::sleep_for()) are bad practice.
0:13:53 Asynchronous Operations: Asio's asynchronous capabilities are introduced to address these problems. async_read_some() is used to prime Asio with a read instruction, executed when data arrives. A lambda function handles the received data.
0:18:11 Asynchronous Challenges: Thinking asynchronously requires understanding that operations may not happen in the expected order. The program must not exit prematurely.
0:18:50 Running Context in a Thread: The asio::io_context can run in its own thread (std::thread) using context.run(), preventing blocking of the main program.
0:19:43 Preventing Context Exit: "Fake work" can be created for the context to prevent it from exiting if no other instructions are pending.
0:21:26 Benefits of Asynchronous Approach: Asynchronous operation avoids blocking and handles variable data sizes more efficiently.
0:22:11 Framework Design: The goal is to create a user-friendly framework that simplifies message passing between clients and servers, abstracting away Asio's complexity.
0:23:34 Message Structure: Messages will have a header (ID and size) and a body (payload). The ID will be an enum class for compile-time type safety, allowing users to define their own message types.
0:26:34 Project Setup: A new "static library" project (net_common) is added to the solution to contain framework headers.
0:27:37 Message Header Implementation: The net_message.h file defines the message_header struct, templated on the user-defined enum class. It includes an ID and size (uint32_t).
0:29:37 Message Implementation: The message struct contains a message_header and a std::vector<uint8_t> for the body. Utility functions (like size()) are added.
0:30:53 Operator Overloads: Overloads for << (output stream) and data pushing/popping are implemented. The latter uses std::is_standard_layout to ensure data is trivially serializable. This allows for easy message construction (e.g., message << x << y;).
0:35:55 Stack-like Body Access: Data is added to and removed from the end of the body vector (like a stack) to avoid unnecessary reallocations.
0:36:09 Example Usage: An example enum class (custom_message_types) is created, and a message is constructed and manipulated using the overloaded operators.
0:40:37 Server-Client Architecture: The client and server both have message queues. Clients have one connection to the server; servers have multiple connections to clients. The server has a single input queue.
0:43:11 Framework Components: Key components are identified: queue, connection, client_interface, and server.
0:44:11 Thread-Safe Queue Implementation: A net_threadsafe_queue.h file defines a queue class, templated on the data type. It uses a std::mutex and std::lock_guard to ensure thread-safe access to a std::deque.
0:47:46 Owned Message: An owned_message struct is added, containing a regular message and a std::shared_ptr to the connection it originated from.
0:49:14 Connection Implementation:net_connection.h defines the connection class, which includes an Asio socket, io_context reference, and queues for outgoing and incoming messages.
0:51:28 Client Interface Implementation:net_client.h defines the client_interface class, which manages Asio, the connection, and provides an interface for the application. It includes a queue for incoming messages, an Asio context, a thread, and a socket.
0:53:23 Partial Implementation: Some functions (like is_connected(), connect(), and disconnect()) are partially implemented, with details to be filled in later. connect() will use an Asio resolver to handle URLs.
0:55:24 Example Client Application: A simplified example of how a user would interact with the framework is shown. The user defines an enum class for message types, derives from client_interface, and can then easily send messages.
0:56:57 Next Steps: Part 2 will fully implement the connection, client, and server, demonstrating message exchange. Future topics include handling timing, connection robustness, network failures, and potentially a login system. Part 3 aims to create a simple networked game.