Boost.Asio实战：C++网络编程Cookbook

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"Boost.Asio C++ Network Programming Cookbook 原版pdf by Radchuk" 本书专注于使用Boost.Asio库进行C++网络编程，旨在帮助开发者构建强大且高效的跨平台分布式应用程序。Boost.Asio库是C++中一个强大的工具，它通过引入类型系统和利用面向对象的方法减少了网络编程的复杂性，提高了代码的可重用性，从而缩短了开发时间。此外，由于该库是跨平台的，所以使用Boost.Asio开发的应用可以在多种操作系统上构建，进一步增强了软件的兼容性和降低了成本。书中包含超过30个实战食谱，即针对网络编程中常见（以及不那么常见的）任务的逐步解决方案。每个食谱都充分利用了Boost.Asio库提供的功能，展示了如何最好地应用该库来执行典型任务和解决各种问题，涵盖了网络通信的可靠性、效率和性能优化等方面。作者Dmytro Radchuk通过这些精心设计的实例，让读者能够掌握网络编程的关键技术和最佳实践。内容可能涉及TCP和UDP套接字的使用，异步编程，多线程和并发处理，错误处理，以及高级网络协议的实现等。书中的每个食谱都是为了帮助读者解决实际遇到的问题，提升网络应用的健壮性和性能。书中的例子覆盖了从基础的连接建立、数据传输到复杂的网络服务和协议实现，读者可以通过这些实例学习如何有效地管理网络连接，实现高效的数据交换，以及如何在不同平台上确保程序的一致性。无论是对于初学者还是有经验的开发者，这本书都是深入理解和运用Boost.Asio进行C++网络编程的宝贵资源。虽然书中明确声明对任何因使用书中信息而造成的直接或间接损害，作者、出版商及其经销商和分销商均不承担法律责任，但这并不削弱本书作为学习和参考的价值。它提供了丰富的信息和实用的指导，有助于读者在实际项目中避免常见错误，提高代码质量。 "Boost.Asio C++ Network Programming Cookbook"是一本深入实践的指南，涵盖了C++网络编程的多个方面，借助Boost.Asio的强大功能，帮助读者构建可靠、高效和跨平台的网络应用程序。

Chapter 1

Network programming is inherently complex and doing it with a low-level C-style socket API

makes it even more complex and error prone. Boost.Asio is an O-O C++ library that is, just like

raw Sockets API, built around the concept of a socket. Roughly speaking, Boost.Asio wraps

raw Sockets API and provides the developer with O-O interface to it. It is intended to simplify

network programming in several ways as follows:

f It hides the raw C-style API and providing a user with an object-oriented API

f It provides a rich-type system, which makes code more readable and allows it to

catch many errors at compilation time

f As Boost.Asio is a cross-platform library, it simplies development of cross-platform

distributed applications

f It provides auxiliary functionality such as scatter-gather I/O operations, stream-based

I/O, exception-based error handling, and others

f The library is designed so that it can be relatively easily extended to add new

custom functionality

This chapter introduces essential Boost.Asio classes and demonstrates how to perform basic

operations with them.

Creating an endpoint

A typical client application, before it can communicate with a server application to consume

its services, must obtain the IP address of the host on which the server application is running

and the protocol port number associated with it. A pair of values consisting of an IP address

and a protocol port number that uniquely identies a particular application running on a

particular host in a computer network is called an endpoint.

The client application will usually obtain the IP address and the port number identifying the

server application either from the user directly through the application UI or as command-line

arguments or will read it from the application's conguration le.

The IP address can be represented as a string containing an address in dot-decimal notation

if it is an IPv4 address (for example, 192.168.10.112) or in hexadecimal notation if it is

an IPv6 address (for example, FE36::0404:C3FA:EF1E:3829). Besides, the server IP

address can be provided to the client application in an indirect form, as a string containing a

DNS name (for example, localhost or www.google.com). Another way to represent an IP

address is an integer value. The IPv4 address is represented as a 32-bit integer and IPv6 as a

64-bit integer. However, due to poor readability and memorability this representation is used

extremely rarely.

The Basics

If the client application is provided with a DNS name before it can communicate with

the server application, it must resolve the DNS name to obtain the actual IP address of the

host running the server application. Sometimes, the DNS name may map to multiple IP

addresses, in which case the client may want to try addresses one by one until it nds the

one that works. We'll consider a recipe describing how to resolve DNS names with Boost.Asio

later in this chapter.

The server application needs to deal with endpoints too. It uses the endpoint to specify to the

operating system on which the IP address and protocol port it wants to listen for incoming

messages from the clients. If the host running the server application has only one network

interface and a single IP address assigned to it, the server application has only one option

as to on which address to listen. However, sometimes the host might have more than one

network interface and correspondingly more than one IP address. In this situation, the server

application encounters a difcult problem of selecting an appropriate IP address on which to

listen for incoming messages. The problem is that the application knows nothing about details

such as underlying IP protocol settings, packet routing rules, DNS names which are mapped

to the corresponding IP addresses, and so on. Therefore, it is quite a complex task (and

sometimes even not solvable) for the server application to foresee through which IP

address the messages sent by clients will be delivered to the host.

If the server application chooses only one IP address to listen for incoming messages, it may

miss messages routed to other IP addresses of the host. Therefore, the server application

usually wants to listen on all IP addresses available on the host. This guarantees that the

server application will receive all messages arriving at any IP address and the particular

protocol port.

To sum up, the endpoints serve two goals:

f The client application uses an endpoint to designate a particular server application it

wants to communicate with.

f The server application uses an endpoint to specify a local IP address and a port

number on which it wants to receive incoming messages from clients. If there is more

than one IP address on the host, the server application will want to create a special

endpoint representing all IP addresses at once.

This recipe explains how to create endpoints in Boost.Asio both in client and

server applications.

Getting ready

Before creating the endpoint, the client application must obtain the raw IP address and the

protocol port number designating the server it will communicate with. The server application

on the other hand, as it usually listens for incoming messages on all IP addresses, only needs

to obtain a port number on which to listen.

Chapter 1

Here, we don't consider how the application obtains a raw IP address or a port number. In

the following recipes, we assume that the IP address and the port number have already been

obtained by the application and are available at the beginning of the corresponding algorithm.

How to do it…

The following algorithms and corresponding code samples demonstrate two common

scenarios of creating an endpoint. The rst one demonstrates how the client application

can create an endpoint to specify the server it wants to communicate with. The second

one demonstrates how the server application creates an endpoint to specify on which IP

addresses and port it wants to listen for incoming messages from clients.

Creating an endpoint in the client to designate the server

The following algorithm describes steps required to perform in the client application to create

an endpoint designating a server application the client wants to communicate with. Initially,

the IP address is represented as a string in the dot-decimal notation if this is an IPv4 address

or in hexadecimal notation if this is an IPv6 address:

1. Obtain the server application's IP address and port number. The IP address should be

specied as a string in the dot-decimal (IPv4) or hexadecimal (IPv6) notation.

2. Represent the raw IP address as an object of the asio::ip::address class.

3. Instantiate the object of the asio::ip::tcp::endpoint class from the address

object created in step 2 and a port number.

4. The endpoint is ready to be used to designate the server application in Boost.Asio

communication related methods.

The following code sample demonstrates possible implementation of the algorithm:

#include <boost/asio.hpp>

#include <iostream>

using namespace boost;

int main()

{

// Step 1. Assume that the client application has already

// obtained the IP-address and the protocol port number.

std::string raw_ip_address = "127.0.0.1";

unsigned short port_num = 3333;

// Used to store information about error that happens

// while parsing the raw IP-address.

boost::system::error_code ec;

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