《Linux C/C++服务器开发实践》之第4章 TCP服务器编程

4.1 套接字的基本概念

套接字是TCP/IP网络编程中的基本操作单元，不同主机的进程之间的相互通信的端点。
socket是在应用层和传输层之间的一个抽象层，它把TCP/IC层复杂的操作抽象为几个简单的接口，供应用层调用已实现进程在网络中通信。

4.2 网络程序的架构

B/S（Browser/Server，浏览器/服务器）架构，用户只需要浏览器就行，主要逻辑在服务器完成，减轻了客户端的升级和维护的工作量。

C/S（Client/Server，客户机/服务器）架构，客户端和服务端安装不同应用软件，客户端软件安装或升级比较复杂，维护成本大，可以充分利用两端的硬件能力，较为合理的分配任务。

客户机和服务器间的通信过程：
（1）客户机向服务器提出一个请求。
（2）服务器收到客户机的请求，进行分析处理。
（3）服务器将处理的结果返回给客户机。

4.3 IP地址的格式转换

#include <arpa/inet.h>
//字符串IP地址转换为网络字节序存储在addr中，并返回该网络字节序表示的无符号整数。
//失败：返回0
int inet_aton(const char *IP, struct in_addr *addr);//返回网络字节序
//uint32，失败-1
in_addr_t inet_addr(const char* cp);//及时复制返回的字符串
char *inet_ntoa(struct in_addr in);

#include <arpa/inet.h>
#include <stdlib.h>
#include <iostream>int main()
{char IP[] = "159.12.8.109";in_addr address;int number = inet_aton(IP, &address);//将点分十进制的IP地址转化为二进制的网络字节序if(number == 0){std::cerr<<"error IP!";exit(1);}std::cout << number << std::endl;std::cout << inet_ntoa(address) << std::endl;//将网络字节序地址转化为点分十进制表示形式return 0;
}

4.1.c

#include <stdio.h>
#include <arpa/inet.h>int main()
{in_addr_t dwIP = inet_addr("172.16.2.6");struct in_addr ia;ia.s_addr = dwIP;printf("ia.s_addr = %#x\n", ia.s_addr);printf("real_ip = %s\n", inet_ntoa(ia));return 0;
}

4.4 套接字的类型

（1）流套接字（SOCK_STREAM）
用于提供面向连接的、可靠的数据传输服务，无数据边界（收发次数不一致），可保证数据能够无差别、无重复发送，并按顺序接收（因为使用了传输控制协议即TCP）。

（2）数据报套接字（SOCK_DGRAM）
提供无连接的服务，不保证数据传输的可靠性，有数据边界（数据报收发次数一致），数据传输过程中可能丢失或重复，且无法保证接收数据有序。（使用UDP传输）

（3）原始套接字（SOCK_RAW）
允许对较低层次的协议（IP、ICMP等）直接访问，常用于检验新的协议实现，或者访问现有服务中配置的新设备。
能够控制网络底层传输机制，所以可以应用原始套接字操纵网络层和传输层应用。接收ICMP、IGMP协议包，接收TCP/IP栈不能处理的IP包，发送自定义报头或自定义协议的IP包。
能够读写内核没有处理的IP数据报。

4.5 套接字地址

包含IP地址和端口信息，识别主机及进程。

4.5.1 通用socket地址

表示大多数网络地址，用于socket API函数中。

struct sockaddr{sa_family_t sa_family;char sa_data[14];
};

sa_family_t：地址族或协议族类型

• PF_UNIX: UNIX本地域协议族
• PF_INET: IPv4协议族
• PF_INET6: IPv6协议族
• AF_UNIX: UNIX本地域地址族
• AF_INET: IPv4地址族
• AF_INET: IPv6地址族

sa_data：存放具体的地址数据（IP和端口）

协议族	地址的含义和长度
PF_INET	32位IPV4地址和16位端口号，共6字节
PF_INET6	128位IPv6地址、16位端口号、32位流标识和32位范围ID，共26字节
PF_UNIX	文件全路劲名，最大长度可达108字节

4.5.2 专用socket地址

不同协议族定义的不同socket地址结构体，各个信息用不同字段表示。
一般强制转换为通用地址结构使用。

/* Structure describing an Internet socket address.  */
struct sockaddr_in{__SOCKADDR_COMMON (sin_);in_port_t sin_port;			/* Port number.  */struct in_addr sin_addr;		/* Internet address.  *//* Pad to size of `struct sockaddr'.  */unsigned char sin_zero[sizeof (struct sockaddr)- __SOCKADDR_COMMON_SIZE- sizeof (in_port_t)- sizeof (struct in_addr)];};/* Internet address.  */
typedef uint32_t in_addr_t;
struct in_addr{in_addr_t s_addr;};

#if !__USE_KERNEL_IPV6_DEFS
/* Ditto, for IPv6.  */
struct sockaddr_in6{__SOCKADDR_COMMON (sin6_);in_port_t sin6_port;	/* Transport layer port # */uint32_t sin6_flowinfo;	/* IPv6 flow information */struct in6_addr sin6_addr;	/* IPv6 address */uint32_t sin6_scope_id;	/* IPv6 scope-id */};
#endif /* !__USE_KERNEL_IPV6_DEFS */#if !__USE_KERNEL_IPV6_DEFS
/* IPv6 address */
struct in6_addr{union{uint8_t	__u6_addr8[16];uint16_t __u6_addr16[8];uint32_t __u6_addr32[4];} __in6_u;
#define s6_addr			__in6_u.__u6_addr8
#ifdef __USE_MISC
# define s6_addr16		__in6_u.__u6_addr16
# define s6_addr32		__in6_u.__u6_addr32
#endif};
#endif /* !__USE_KERNEL_IPV6_DEFS */

4.5.3 获取套接字地址

#include <sys/socket.h>
int getsockname(int sockfd, struct sockaddr *localaddr, socklen_t *addrlen);
//成功0，失败-1
//socklen_t addrlen = sizeof(struct sockaddr_in);

getsockname获取本地套接字地址的情况：

• 本地套接字已bind地址
• 本地套接字已connet到远程，内核会分配地址

#include <sys/socket.h>
int getpeername(int sockfd, struct sockaddr *peeraddr, socklen_t *addrlen);
//成功0，失败-1
//socklen_t addrlen = sizeof(struct sockaddr_in);

4.2.c

#include <stdio.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <string.h>
#include <errno.h>int main()
{int sfp = socket(AF_INET, SOCK_STREAM, 0);if (-1 == sfp){printf("socket() fail!\n");return -1;}printf("socket() ok!\n");char on = 1;setsockopt(sfp, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));struct sockaddr_in serv = {0};int serv_len = sizeof(serv);printf("ip=%s, port=%d\n", inet_ntoa(serv.sin_addr), ntohs(serv.sin_port));getsockname(sfp, (struct sockaddr *)&serv, (socklen_t *)&serv_len);printf("ip=%s, port=%d\n", inet_ntoa(serv.sin_addr), ntohs(serv.sin_port));unsigned short portnum = 10051;struct sockaddr_in s_add;memset(&s_add, 0, sizeof(struct sockaddr_in));s_add.sin_family = AF_INET;s_add.sin_addr.s_addr = inet_addr("127.0.0.1");s_add.sin_port = htons(portnum);if (-1 == bind(sfp, (struct sockaddr *)(&s_add), sizeof(struct sockaddr))){printf("bind() fail: %d!\n", errno);return -1;}printf("bind() ok!\n");getsockname(sfp, (struct sockaddr *)&serv, (socklen_t *)&serv_len);printf("ip=%s, port=%d\n", inet_ntoa(serv.sin_addr), ntohs(serv.sin_port));return 0;
}

4.6 主机字节序和网络字节序

• 小端字节序Little Endian
  底地址存放低字节

大端字节序Big Endian（网络字节序）
底地址存放高字节

uint32_t主机字节序转网络字节序
htonl
uint16_t主机字节序转网络字节序
htonsuint32_t网络字节序转主机字节序
ntohl
uint16_t网络字节序转主机字节序
ntohs

4.3.c

#include <iostream>
using namespace std;int main()
{int nNum = 0x12345678;char *p = (char *)&nNum;if (*p == 0x12)cout << "This machine is big endian." << endl;elsecout << "This machine is small endian." << endl;return 0;
}

4.7 协议族和地址族

• 协议族
  不同协议的集合，宏以PF_开头，PROTOCOL FAMILY

• 地址族
  协议族所使用的地址集合（不同网络协议使用不同网络地址），宏以AF_开头，Address Family

地址族和协议族的值一样，都用来标识不同的一套协议。

4.8 TCP套接字编程的基本步骤

• 服务器编程步骤：
  一、创建套接字，socket函数
  二、绑定套接字到IP地址和端口，bind函数
  三、套接字设置为监听模式并等待连接请求，listen函数
  四、请求到来时，接受连接请求，返回对应连接的套接字，accept函数
  五、用该连接套接字同客户端通信，send或recv函数，通信结束关闭，closesocket函数
  六、监听套接字等待其他客户端的连接
  七、推出服务器程序，关闭监听套接字，closesocket函数

客户端编程步骤：
一、创建套接字，socket函数
二、向服务器发出请求连接，connect函数
三、同服务器端通信，send或recv函数，
四、通信结束关闭，closesocket函数

4.9 TCP套接字编程的相关函数

4.9.1 BSD socket的头文件

• <sys/socket.h>：核心函数和数据结构的声明
• <netinet/in.h>：地址族和协议族，IP地址和端口号等
• <bits/socket.h>：地址族和协议族的宏定义
• <arpa/inet.h>：IP地址相关函数
• <netdb.h>：协议名和主机名转化为数字的函数

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>

4.9.2 socket函数

创建套接字，并分配系统资源

int socket(int domain, int type, int protocol);
//AF_INET
//SOCK_STREAM, SOCK_DGRAM, SOCK_RAW
//IPPROTO_TCP, IPPROTO_UDP, 0
//默认都是阻塞

4.9.3 bind函数

本地地址信息关联到套接字上。

int bind(int sockfd, const struct* addr, socklen_t addrlen);
//成功0，失败-1，errno获取错误码

sockaddr_in in;
in_addr_t ip = inet_addr("192.168.13.25");
if(ip != -1)in.sin_addr.s_addr  = ip;//#define INADDR_ANY ((in_addr_t) 0x00000000)
in.sin_addr.s_addr = htonl(INADDR_ANY);//errno，98，端口占用、未释放或程序未正常结束

4.9.4 listen函数

套接字处于监听状态。

int listen(int sockfd, int backlog);
//成功0，失败-1

4.9.5 accept函数

从监听套接字的客户连接请求队列获取客户端请求，并创建新的套接字来和客户端通信。

int accept(int sockfd, struct sockaddr *addr, socklen_t * addrlen);
//失败-1

4.9.6 connect函数

请求与监听套接字建立连接。

int connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen);
//成功0，失败-1

非阻塞时，可设置连接超时时间，通过error中EINRPOCESS（Operation now in progress）判断。

4.9.7 send函数

发送数据，复制到套接字的发送缓冲区。

ssize_t send(int sockfd, const void *buf, size_t len, int flags);
//成功返回发送拷贝字节数，对方关闭返回0，错误-1

TCP有发送缓冲区，UDP无发送缓冲区。

非阻塞，可利用error变量EAGAIN

send用于有连接的套接字。

sendto和sendmsg用于有或无连接的套接字。

4.9.8 recv函数

接收数据.

ssize_t recv(int sockfd, const void *buf, size_t len, int flags);
//成功返回接收字节数，对方关闭返回0，错误-1，errno是EINTR、EWOULDBLOCK或EAGAIN时连接正常

recvfrom也能接收数据。

4.9.9 close函数

关闭套接字

#include <unistd.h>
int close(int fd);
//成功0，失败-1

4.10 简单的TCP套接字编程

4.4.server.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>int main()
{int sockSrv = socket(AF_INET, SOCK_STREAM, 0);char on = 1;setsockopt(sockSrv, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));struct sockaddr_in addrSrv;memset(&addrSrv, 0, sizeof(struct sockaddr_in));addrSrv.sin_addr.s_addr = inet_addr("127.0.0.1");addrSrv.sin_family = AF_INET;addrSrv.sin_port = htons(8000);if (-1 == bind(sockSrv, (struct sockaddr *)&addrSrv, sizeof(struct sockaddr))){printf("bind() fail: %d!\n", errno);return -1;}const int len = sizeof(struct sockaddr_in);struct sockaddr_in serv;getsockname(sockSrv, (struct sockaddr *)&serv, (socklen_t *)&len);printf("server has started, ip=%s, port=%d\n", inet_ntoa(serv.sin_addr), ntohs(serv.sin_port));listen(sockSrv, 5);struct sockaddr_in addrClient;while (1){printf("--------wait for client-----------\n");int sockConn = accept(sockSrv, (struct sockaddr *)&addrClient, (socklen_t *)&len);char sendBuf[100];sprintf(sendBuf, "Welcome client(%s: %d) to Server!", inet_ntoa(addrClient.sin_addr), ntohs(addrClient.sin_port));send(sockConn, sendBuf, strlen(sendBuf) + 1, 0);char recvBuf[100];recv(sockConn, recvBuf, 100, 0);printf("Receive client's msg: %s\n", recvBuf);close(sockConn);/*puts("continue to listen?(y/n)");char ch[2];scanf("%s", ch, 2);if (ch[0] != 'y')break;*/}close(sockSrv);return 0;
}

4.4.client.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>int main()
{int sockClient = socket(AF_INET, SOCK_STREAM, 0);struct sockaddr_in addrSrv;addrSrv.sin_addr.s_addr = inet_addr("127.0.0.1");addrSrv.sin_family = AF_INET;addrSrv.sin_port = htons(8000);int err = connect(sockClient, (struct sockaddr *)&addrSrv, sizeof(struct sockaddr));if (-1 == err){printf("Failed to connect to the server.Please check whether the server is started\n");return 0;}char recvBuf[100] = {0};recv(sockClient, recvBuf, 100, 0);printf("receive server's msg: %s\n", recvBuf);char msg[] = "hi,server";send(sockClient, msg, strlen(msg) + 1, 0);close(sockClient);return 0;
}

4.5.c

#include <stdio.h>
#include <assert.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>#define BUFFER_SIZE 512unsigned long GetTickCount()
{struct timeval tv;if (gettimeofday(&tv, NULL) != 0)return 0;return (tv.tv_sec * 1000) + (tv.tv_usec / 1000);
}int main()
{struct sockaddr_in server_address;memset(&server_address, 0, sizeof(server_address));server_address.sin_family = AF_INET;server_address.sin_addr.s_addr = inet_addr("192.168.0.88");server_address.sin_port = htons(13334);int sock = socket(PF_INET, SOCK_STREAM, 0);assert(sock >= 0);long t1 = GetTickCount();int ret = connect(sock, (struct sockaddr *)&server_address, sizeof(server_address));if (ret == -1){long t2 = GetTickCount();printf("connect() failed: %d\n", ret);printf("time used: %ldms\n", t2 - t1);if (errno == EINPROGRESS)printf("unblock mode ret code...\n");}elseprintf("ret code is: %d\n", ret);close(sock);return 0;
}

4.11 深入理解TCP编程

4.11.1 数据发送和接收涉及的缓冲区

应用缓冲区和TCP套接字缓冲区（内核缓冲区）。

4.11.2 TCP数据传输的特点

一、字节流，无消息边界。
二、send后并不立即发送数据，内核控制。
三、数据发送速度，网络状态决定。
四、控制数据真实发送，网络状态决定。
五、recv时并不知道真实已接收多少数据。

4.11.3 数据发送的六种情形

假设调用两次send，发送数据A和数据B。（send(A)，send(B)），真实发送情况：
一、网络情况良好，未受发送窗口、拥塞窗口和TCP最大传输单元影响，A、B变成两个数据段发送。
二、网络不好，发送A被延迟，A、B数据合并，且长度未超过窗口大小和最大传输单元。AB合并发送一次。
三、网络不好，发送A被延迟，A、B数据合并，且长度超过窗口大小或最大传输单元。AB合并发送（AB1、B2）。
四、网络不好，发送A被延迟，A、B数据合并，且长度超过窗口大小或最大传输单元。AB合并发送（A1、A2B）。
五、接收窗口小，AB分成多份发送。
六、发送错误，失败。

4.11.4 数据接收时的情形

1. 接收到本次达到接收端的全部数据
2. 接收到达到接收端的部分数据
3. 没有收到数据

send与实际发送次数无关，send与recv次数无关。

4.11.5 一次请求响应的数据接收

接收到全部数据后断开连接，通过recv返回0判断发送方数据发送完毕。

4.6.server.c

#include <stdio.h>
#include <assert.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>#define BUF_LEN 300typedef struct sockaddr_in SOCKADDR_IN;
typedef struct sockaddr SOCKADDR;int main()
{int sockSrv = socket(AF_INET, SOCK_STREAM, 0);assert(sockSrv >= 0);char on = 1;setsockopt(sockSrv, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));SOCKADDR_IN addrSrv;addrSrv.sin_addr.s_addr = inet_addr("127.0.0.1");addrSrv.sin_family = AF_INET;addrSrv.sin_port = htons(8000);bind(sockSrv, (SOCKADDR *)&addrSrv, sizeof(SOCKADDR));listen(sockSrv, 5);const int len = sizeof(SOCKADDR);SOCKADDR_IN addrClient;while (1){printf("--------wait for client-----------\n");int sockConn = accept(sockSrv, (SOCKADDR *)&addrClient, (socklen_t *)&len);char sendBuf[100] = "";for (int i = 0; i < 10; i++){memset(sendBuf, 0, sizeof(sendBuf));sprintf(sendBuf, "N0.%d Welcome to the server. What is 1 + 1 = ? (client IP: %s, client Port: %d)\n", i + 1, inet_ntoa(addrClient.sin_addr), ntohs(addrClient.sin_port));send(sockConn, sendBuf, strlen(sendBuf), 0);}int iRes = shutdown(sockConn, SHUT_WR);if (iRes == -1){printf("shutdown failed with error: %d\n", errno);close(sockConn);return 1;}char recvBuf[BUF_LEN];do{iRes = recv(sockConn, recvBuf, BUF_LEN, 0);if (iRes > 0){printf("Recv %d bytes.\n", iRes);for (int i = 0; i < iRes; i++)printf("%c", recvBuf[i]);printf("\n");}else if (iRes == 0){printf("The client has closed the connection.\n");}else{printf("recv failed with error: %d\n", errno);close(sockConn);return 1;}} while (iRes > 0);close(sockConn);/*puts("Continue monitoring?(y/n)");char ch[2];scanf("%s", ch, 2);if (ch[0] != 'y')break;*/}close(sockSrv);return 0;
}

4.6.client.c

#include <stdio.h>
#include <assert.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>#define BUF_LEN 300typedef struct sockaddr_in SOCKADDR_IN;
typedef struct sockaddr SOCKADDR;int main()
{int sockClient = socket(AF_INET, SOCK_STREAM, 0);SOCKADDR_IN addrSrv;addrSrv.sin_addr.s_addr = inet_addr("127.0.0.1");addrSrv.sin_family = AF_INET;addrSrv.sin_port = htons(8000);int err = connect(sockClient, (SOCKADDR *)&addrSrv, sizeof(SOCKADDR));if (-1 == err){printf("Failed to connect to the server. Please check whether the server is started\n");return 0;}char recvBuf[BUF_LEN];int iRes;do{iRes = recv(sockClient, recvBuf, BUF_LEN, 0);if (iRes > 0){printf("\nRecv %d bytes:", iRes);for (int i = 0; i < iRes; i++)printf("%c", recvBuf[i]);printf("\n");}else if (iRes == 0){puts("The server has closed the send connection.\n");}else{printf("recv failed:%d\n", errno);close(sockClient);return 1;}} while (iRes > 0);char sendBuf[100];for (int i = 0; i < 10; i++){memset(sendBuf, 0, sizeof(sendBuf));sprintf(sendBuf, "N0.%d I'm the client, 1+1=2\n", i + 1);send(sockClient, sendBuf, strlen(sendBuf) + 1, 0);}puts("Sending data to the server is completed.");close(sockClient);return 0;
}

4.11.6 多次请求响应的数据接收

1. 定长数据的接收

4.7.server.c

#include <stdio.h>
#include <assert.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>#define BUF_LEN 300typedef struct sockaddr_in SOCKADDR_IN;
typedef struct sockaddr SOCKADDR;int main()
{int sockSrv = socket(AF_INET, SOCK_STREAM, 0);assert(sockSrv >= 0);char on = 1;setsockopt(sockSrv, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));SOCKADDR_IN addrSrv;addrSrv.sin_addr.s_addr = inet_addr("127.0.0.1");addrSrv.sin_family = AF_INET;addrSrv.sin_port = htons(8000);bind(sockSrv, (SOCKADDR *)&addrSrv, sizeof(SOCKADDR));listen(sockSrv, 5);const int len = sizeof(SOCKADDR);SOCKADDR_IN addrClient;char sendBuf[111];char recvBuf[BUF_LEN];while (1){printf("--------wait for client-----------\n");int sockConn = accept(sockSrv, (SOCKADDR *)&addrClient, (socklen_t *)&len);printf("--------client comes-----------\n");memset(sendBuf, 'a', 111);for (int cn = 0; cn < 50; cn++){if (cn == 49)sendBuf[110] = 'b';send(sockConn, sendBuf, 111, 0);}int iRes;do{iRes = recv(sockConn, recvBuf, BUF_LEN, 0);if (iRes > 0){printf("\nRecv %d bytes:", iRes);for (int i = 0; i < iRes; i++)printf("%c", recvBuf[i]);printf("\n");}else if (iRes == 0){printf("The client closes the connection.\n");}else{printf("recv failed with error: %d\n", errno);close(sockConn);return 1;}} while (iRes > 0);close(sockConn);/*puts("Continue monitoring?(y/n)");char ch[2];scanf("%s", ch, 2);if (ch[0] != 'y')break;*/}close(sockSrv);return 0;
}

4.7.client.c

#include <stdio.h>
#include <assert.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>#define BUF_LEN 250typedef struct sockaddr_in SOCKADDR_IN;
typedef struct sockaddr SOCKADDR;int main()
{int sockClient = socket(AF_INET, SOCK_STREAM, 0);SOCKADDR_IN addrSrv;addrSrv.sin_addr.s_addr = inet_addr("127.0.0.1");addrSrv.sin_family = AF_INET;addrSrv.sin_port = htons(8000);int err = connect(sockClient, (SOCKADDR *)&addrSrv, sizeof(SOCKADDR));if (-1 == err){printf("Failed to connect to the server:%d\n", errno);return 0;}char recvBuf[BUF_LEN];int iRes;int cn = 1;for (int leftlen = 50 * 111; leftlen > 0; leftlen -= iRes){iRes = recv(sockClient, recvBuf, BUF_LEN, 0);if (iRes > 0){printf("\nNo.%d: Recv %d bytes: ", cn++, iRes);for (int i = 0; i < iRes; i++)printf("%c", recvBuf[i]);printf("\n");}else if (iRes == 0){puts("\nThe server has closed the send connection.\n");}else{printf("recv failed: %d\n", errno);close(sockClient);return -1;}}/*int leftlen = 50 * 111;while (leftlen > BUF_LEN){iRes = recv(sockClient, recvBuf, BUF_LEN, 0);if (iRes > 0){printf("\nNo.%d: Recv %d bytes: ", cn++, iRes);for (int i = 0; i < iRes; i++)printf("%c", recvBuf[i]);printf("\n");}else if (iRes == 0){puts("\nThe server has closed the send connection.\n");}else{printf("recv failed: %d\n", errno);close(sockClient);return -1;}leftlen -= iRes;}if (leftlen > 0){iRes = recv(sockClient, recvBuf, leftlen, 0);if (iRes > 0){printf("\nNo.%d: Recv %d bytes: ", cn++, iRes);for (int i = 0; i < iRes; i++)printf("%c", recvBuf[i]);printf("\n");}else if (iRes == 0){puts("\nThe server has closed the send connection.\n");}else{printf("recv failed: %d\n", errno);close(sockClient);return -1;}leftlen -= iRes;}
*/char sendBuf[100];memset(sendBuf, 0, sizeof(sendBuf));sprintf(sendBuf, "Hi, Server, I've finished receiving the data.");send(sockClient, sendBuf, strlen(sendBuf) + 1, 0);puts("Sending data to the server is completed");close(sockClient);return 0;
}

2. 变长数据的接收
   数据报末尾加结束标识符
   变长消息体前加固定长度的报头，报头内加入消息体长度字段

struct MyData
{int nLen;char data[0];
};
struct MyData* p = (struct MyData*)malloc(sizeof(struct MyData)+strlen(str));

4.8.c

#include <cstdio>
#include <iostream>
#include <string.h>
using namespace std;struct MyData
{int nLen;char data[0];
};int main()
{cout << "Size of MyData: " << sizeof(MyData) << endl;char str[10] = "123456";int nLen = sizeof(str);MyData *myData = (MyData *)malloc(sizeof(MyData) + nLen);myData->nLen = nLen;memcpy(myData->data, str, nLen);cout << "myData's Data is: " << myData->data << endl;cout << "Size of MyData: " << sizeof(MyData) << endl;free(myData);return 0;
}

4.9.server.c

#include <cstdio>
#include <assert.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <malloc.h>#define BUF_LEN 300typedef struct sockaddr_in SOCKADDR_IN;
typedef struct sockaddr SOCKADDR;struct MyData
{int nLen;char data[0];
};int main()
{int sockSrv = socket(AF_INET, SOCK_STREAM, 0);SOCKADDR_IN addrSrv;addrSrv.sin_addr.s_addr = inet_addr("127.0.0.1");addrSrv.sin_family = AF_INET;addrSrv.sin_port = htons(8000);bind(sockSrv, (SOCKADDR *)&addrSrv, sizeof(SOCKADDR));listen(sockSrv, 5);SOCKADDR_IN addrClient;int len = sizeof(SOCKADDR);int cn = 5550;struct MyData *mydata;int iRes;char recvBuf[BUF_LEN];while (1){printf("--------wait for client-----------\n");int sockConn = accept(sockSrv, (SOCKADDR *)&addrClient, (socklen_t *)&len);printf("--------client comes-----------\n");mydata = (MyData *)malloc(sizeof(MyData) + cn);mydata->nLen = htonl(cn);memset(mydata->data, 'a', cn);mydata->data[cn - 1] = 'b';send(sockConn, (char *)mydata, sizeof(MyData) + cn, 0);free(mydata);do{iRes = recv(sockConn, recvBuf, BUF_LEN, 0);if (iRes > 0){printf("\nRecv %d bytes: ", iRes);for (int i = 0; i < iRes; i++)printf("%c", recvBuf[i]);printf("\n");}else if (iRes == 0){printf("\nThe client has closed the connection.\n");}else{printf("recv failed with error: %d\n", errno);close(sockConn);return 1;}} while (iRes > 0);close(sockConn);/*puts("Continue monitoring?(y/n)");char ch[2];scanf("%s", ch, 2);if (ch[0] != 'y')break;*/}close(sockSrv);return 0;
}

4.9.client.c

#include <stdio.h>
#include <assert.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <malloc.h>#define BUF_LEN 250typedef struct sockaddr_in SOCKADDR_IN;
typedef struct sockaddr SOCKADDR;int main()
{int sockClient = socket(AF_INET, SOCK_STREAM, 0);SOCKADDR_IN addrSrv;addrSrv.sin_addr.s_addr = inet_addr("127.0.0.1");addrSrv.sin_family = AF_INET;addrSrv.sin_port = htons(8000);int err = connect(sockClient, (SOCKADDR *)&addrSrv, sizeof(SOCKADDR));if (-1 == err){printf("Failed to connect to the server:%d\n", errno);return 0;}int leftlen;int iRes = recv(sockClient, (char *)&leftlen, sizeof(int), 0);leftlen = ntohl(leftlen);printf("Need to receive %d bytes data.\n", leftlen);char recvBuf[BUF_LEN];int cn = 1;for (; leftlen > 0; leftlen -= iRes){if (leftlen < BUF_LEN)iRes = recv(sockClient, recvBuf, leftlen, 0);elseiRes = recv(sockClient, recvBuf, BUF_LEN, 0);if (iRes > 0){printf("\nNo.%d: Recv %d bytes: ", cn++, iRes);for (int i = 0; i < iRes; i++)printf("%c", recvBuf[i]);printf("\n");}else if (iRes == 0){puts("\nThe server has closed the send connection.\n");}else{printf("recv failed: %d\n", errno);close(sockClient);return -1;}}/*while (leftlen > BUF_LEN){iRes = recv(sockClient, recvBuf, BUF_LEN, 0);if (iRes > 0){printf("\nNo.%d: Recv %d bytes: ", cn++, iRes);for (int i = 0; i < iRes; i++)printf("%c", recvBuf[i]);printf("\n");}else if (iRes == 0){puts("\nThe server has closed the send connection.\n");}else{printf("recv failed: %d\n", errno);close(sockClient);return -1;}leftlen -= iRes;}if (leftlen > 0){iRes = recv(sockClient, recvBuf, leftlen, 0);if (iRes > 0){printf("\nNo.%d: Recv %d bytes: ", cn++, iRes);for (int i = 0; i < iRes; i++)printf("%c", recvBuf[i]);printf("\n");}else if (iRes == 0){puts("\nThe server has closed the send connection.\n");}else{printf("recv failed: %d\n", errno);close(sockClient);return -1;}leftlen -= iRes;}*/char sendBuf[100];memset(sendBuf, 0, sizeof(sendBuf));sprintf(sendBuf, "I'm the client. I've finished receiving the data.");send(sockClient, sendBuf, strlen(sendBuf) + 1, 0);puts("Sending data to the server is completed");close(sockClient);return 0;
}

4.12 I/O控制命令

设置套接字的工作模式（阻塞或非阻塞），获取套接字I/O操作的参数信息。

#include <sys/ioctl.h>
int ioctl(int fd, int request, ...);
//成功0，失败-1，errno错误码

I/O控制命令request：

• FIONBIO
  阻塞
• FIONREAD
  流套接字，recv一次可读入数据量；数据报套接字，第一个数据报大小；缓冲区大小。
• FIOASYNC
  异步

int iMode = 0;
ioctl(m_socket, FIONBIO, &iMode); //阻塞模式int num = 0;
ioctl(0, FIONREAD, &iMode); //标准输入缓冲区字节数

4.10.c

#include <stdio.h>
#include <assert.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/ioctl.h>unsigned long GetTickCount()
{struct timeval tv;if (gettimeofday(&tv, NULL) != 0)return 0;return (tv.tv_sec * 1000) + (tv.tv_usec / 1000);
}int main()
{char ip[] = "192.168.0.88";in_addr_t dwIP = inet_addr(ip);int port = 13334;struct sockaddr_in server_address;memset(&server_address, 0, sizeof(server_address));server_address.sin_family = AF_INET;server_address.sin_addr.s_addr = dwIP;server_address.sin_port = htons(port);int sock = socket(PF_INET, SOCK_STREAM, 0);assert(sock >= 0);long t1 = GetTickCount();int ret = connect(sock, (struct sockaddr *)&server_address, sizeof(server_address));printf("connect ret code is: %d\n", ret);if (ret == -1){long t2 = GetTickCount();printf("time used: %ldms\n", t2 - t1);printf("connect() failed...\n");if (errno == EINPROGRESS)printf("unblock mode ret code...\n");}elseprintf("ret code is: %d\n", ret);int argp = 1;int res = ioctl(sock, FIONBIO, &argp);if (-1 == res){printf("Error at ioctlsocket(): %d\n", errno);return -1;}puts("\nAfter setting non blocking mode:");/*memset(&server_address, 0, sizeof(server_address));server_address.sin_family = AF_INET;server_address.sin_addr.s_addr = dwIP;server_address.sin_port = htons(port);*/t1 = GetTickCount();ret = connect(sock, (struct sockaddr *)&server_address, sizeof(server_address));printf("connect ret code is: %d\n", ret);if (ret == -1){long t2 = GetTickCount();printf("time used: %ldms\n", t2 - t1);if (errno == EINPROGRESS)printf("unblock mode errno: %d\n", errno);}elseprintf("ret code is: %d\n", ret);close(sock);return 0;
}

4.13 套接字选项

4.13.1 基本概念

设置或获取套接字属性

4.13.2 选项的级别

适用范围或适用对象，有些选项针对特定协议，有些选项适用所有类型套接字。
SO_TYPE
SO_SNDBUF
SO_REUSEADDR
SO_RCVBUF
SO_ERROR
…

4.13.3 获取套接字选项

#include <sys/types.h>
#include <sys/socket.h>
int getsockopt(int sockfd, int level, int optname, void *optval, socklen_t *optlen);
//成功0，失败-1，errno错误码
//EBADF：sockfd不是有效文件描述符
//EFAULT：optlen太小或optval缓冲区非法
//EINVAL：level未知或非法
//ENOPROTOOPT：选项未知或不被指定协议族支持
//ENOTSOCK：sockfd不是套接字描述符

4.11.c

#include <stdio.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/ioctl.h>int main()
{int s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);if (s == -1){printf("Error at socket()\n");return -1;}int su = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);if (s == -1){printf("Error at socket()\n");return -1;}int optVal;int optLen = sizeof(optVal);if (getsockopt(s, SOL_SOCKET, SO_RCVBUF, (char *)&optVal, (socklen_t *)&optLen) == -1)printf("getsockopt failed: %d", errno);elseprintf("Size of stream socket receive buffer: %d bytes\n", optVal);if (getsockopt(s, SOL_SOCKET, SO_SNDBUF, (char *)&optVal, (socklen_t *)&optLen) == -1)printf("getsockopt failed: %d", errno);elseprintf("Size of streaming socket send buffer: %d bytes\n", optVal);if (getsockopt(su, SOL_SOCKET, SO_RCVBUF, (char *)&optVal, (socklen_t *)&optLen) == -1)printf("getsockopt failed: %d", errno);elseprintf("Size of datagram socket receive buffer: %d bytes\n", optVal);if (getsockopt(su, SOL_SOCKET, SO_SNDBUF, (char *)&optVal, (socklen_t *)&optLen) == -1)printf("getsockopt failed: %d", errno);elseprintf("Size of datagram socket send buffer: %d bytes\n", optVal);return 0;
}

4.12.c

#include <stdio.h>
#include <assert.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/ioctl.h>int main()
{int s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);if (s == -1){printf("Error at socket()\n");return -1;}int optVal;int optLen = sizeof(optVal);if (getsockopt(s, SOL_SOCKET, SO_TYPE, (char *)&optVal, (socklen_t *)&optLen) == -1)printf("getsockopt failed: %d", errno);else{if (SOCK_STREAM == optVal)printf("The current socket is a stream socket.\n");else if (SOCK_DGRAM == optVal)printf("The current socket is a datagram socket.\n");}int su = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);if (su == -1){printf("Error at socket()\n");return -1;}if (getsockopt(su, SOL_SOCKET, SO_TYPE, (char *)&optVal, (socklen_t *)&optLen) == -1)printf("getsockopt failed: %d", errno);else{if (SOCK_STREAM == optVal)printf("The current socket is a stream socket.\n");else if (SOCK_DGRAM == optVal)printf("The current socket is a datagram socket.\n");}return 0;
}

4.13.c

#include <stdio.h>
#include <assert.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/ioctl.h>typedef struct sockaddr SOCKADDR;int main()
{int s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);if (s == -1){printf("Error at socket()\n");return -1;}char on = 1;setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));char ip[] = "127.0.0.1";struct sockaddr_in service;service.sin_family = AF_INET;service.sin_addr.s_addr = inet_addr(ip);service.sin_port = htons(8000);if (bind(s, (SOCKADDR *)&service, sizeof(service)) == -1){printf("bind failed: %d\n", errno);return -1;}int optVal;int optLen = sizeof(optVal);if (getsockopt(s, SOL_SOCKET, SO_ACCEPTCONN, (char *)&optVal, (socklen_t *)&optLen) == -1)printf("getsockopt failed: %d", errno);elseprintf("Before listening, The value of SO_ACCEPTCONN: %d, The socket is not listening\n", optVal);if (listen(s, 100) == -1){printf("listen failed: %d\n", errno);return -1;}if (getsockopt(s, SOL_SOCKET, SO_ACCEPTCONN, (char *)&optVal, (socklen_t *)&optLen) == -1){printf("getsockopt failed: %d", errno);return -1;}elseprintf("After listening, The value of SO_ACCEPTCONN: %d, The socket is listening\n", optVal);return 0;
}

4.13.4 设置套接字选项

#include <sys/types.h>
#include <sys/socket.h>
int setsockopt(int sockfd, int level, int optname, const void *optval, socklen_t *optlen);
//成功0，失败-1，errno错误码

4.14.c

#include <stdio.h>
#include <assert.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/ioctl.h>typedef struct sockaddr SOCKADDR;int main()
{int s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);if (s == -1){printf("Error at socket()\n");return -1;}char on = 1;setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));char ip[] = "127.0.0.1";struct sockaddr_in service;service.sin_family = AF_INET;service.sin_addr.s_addr = inet_addr(ip);service.sin_port = htons(9900);if (bind(s, (SOCKADDR *)&service, sizeof(service)) == -1){printf("bind failed\n");return -1;}int optVal = 1;int optLen = sizeof(int);if (getsockopt(s, SOL_SOCKET, SO_KEEPALIVE, (char *)&optVal, (socklen_t *)&optLen) == -1){printf("getsockopt failed: %d", errno);return -1;}elseprintf("After bind, the value of SO_KEEPALIVE: %d\n", optVal);optVal = 1;if (setsockopt(s, SOL_SOCKET, SO_KEEPALIVE, (char *)&optVal, optLen) != -1)printf("Successful activation of keep alive mechanism.\n");if (getsockopt(s, SOL_SOCKET, SO_KEEPALIVE, (char *)&optVal, (socklen_t *)&optLen) == -1){printf("getsockopt failed: %d", errno);return -1;}elseprintf("After setting, the value of SO_KEEPALIVE: %d\n", optVal);return 0;
}