一、TCP实现
传输控制协议(TCP，Transmission Control Protocol) 是为了在不可靠的互联网络上提供可靠的端到端字节流而专门设计的一个传输协议。TCP是因特网中的传输层协议，使用三次握手协议建立连接。当主动方发出SYN连接请求后，等待对方回答SYN+ACK，并最终对对方的 SYN 执行 ACK 确认。这种建立连接的方法可以防止产生错误的连接，TCP使用的流量控制协议是可变大小的滑动窗口协议。
1.服务端
基于TCP协议的socket的server端程序编程步骤：
1、建立socket ，使用socket()
2、绑定socket ，使用bind()
3、打开listening socket,使用listen()
4、等待client连接请求，使用accept()
5、收到连接请求，确定连接成功后，使用输入，输出函数recv(),send()与client端互传信息
6、关闭socket,使用close()
服务端代码server.c
/*server.c*/
#include<netinet/in.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define SERVER_PORT 5678 //端口号
#define LENGTH_OF_LISTEN_QUEUE 20
#define BUFFER_SIZE 1024
#define FILE_NAME_MAX_SIZE 512
int main(int argc, char **argv)
{
// 设置一个socket地址结构server_addr,代表服务器ip地址和端口
struct sockaddr_in server_addr;
bzero(&server_addr, sizeof(server_addr));
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = htons(INADDR_ANY);
server_addr.sin_port = htons(SERVER_PORT);
// 创建用于流协议(TCP)socket，用server_socket代表服务器向客户端提供服务的接口
int server_socket = socket(PF_INET, SOCK_STREAM, 0);
if (server_socket < 0)
{
printf("Create Socket Failed!\n");
exit(1);
}
else
printf("Create Socket Success.\n");
// 把socket和socket地址结构绑定
if (bind(server_socket, (struct sockaddr*)&server_addr, sizeof(server_addr)))
{
printf("Server Bind Port: %d Failed!\n", SERVER_PORT);
exit(1);
}
else
printf("Client Bind Port Success.\n");
// server_socket用于监听
if (listen(server_socket, LENGTH_OF_LISTEN_QUEUE))
{
printf("Server Listen Failed!\n");
exit(1);
}
else
printf("Listening....\n");
// 服务器始终监听
while(1)
{
// 定义客户端的socket地址结构client_addr，当收到来自客户端的请求后，调用accept
// 接受此请求，同时将client端的地址和端口等信息写入client_addr中
struct sockaddr_in client_addr;
socklen_t length = sizeof(client_addr);
// 接受一个从client端到达server端的连接请求,将客户端的信息保存在client_addr中
// 如果没有连接请求，则一直等待直到有连接请求为止，这是accept函数的特性
// accpet返回一个新的socket,这个socket用来与此次连接到server的client进行通信
// 这里的new_server_socket代表了这个通信通道
int new_server_socket = accept(server_socket, (struct sockaddr*)&client_addr, &length);
if (new_server_socket < 0)
{
printf("Server Accept Failed!\n");
break;
}
else
printf("Server Accept Success.\n");
char buffer[BUFFER_SIZE];
bzero(buffer, sizeof(buffer));
length = recv(new_server_socket, buffer, BUFFER_SIZE, 0);
if (length < 0)
{
printf("Server Recieve Data Failed!\n");
break;
}
else
printf("Server Recieve Data Success.\n");
char file_name[FILE_NAME_MAX_SIZE + 1];
bzero(file_name, sizeof(file_name));
strncpy(file_name, buffer,
strlen(buffer) > FILE_NAME_MAX_SIZE ? FILE_NAME_MAX_SIZE : strlen(buffer));
FILE *fp = fopen(file_name, "r"); //获取文件操作符
if (fp == NULL)
{
printf("File:\t%s Not Found!\n", file_name);
}
else
{
bzero(buffer, BUFFER_SIZE);
int file_block_length = 0;
while( (file_block_length = fread(buffer, sizeof(char), BUFFER_SIZE, fp)) > 0)
{
// 发送buffer中的字符串到new_server_socket,实际上就是发送给客户端
if (send(new_server_socket, buffer, file_block_length, 0) < 0)
{
printf("Send File:\t%s Failed!\n", file_name);
break;
}
bzero(buffer, sizeof(buffer));
}
fclose(fp);
printf("File:\t%s Transfer Finished!\n", file_name);
}
close(new_server_socket);
}
close(server_socket);
return 0;
}
2.客户端
基于TCP协议的socket的Client程序编程步骤：
1、建立socket，使用socket()
2、通知server请求连接，使用connect()
3、若连接成功，就使用输入输出函数recv(),send()与server互传信息
4、关闭socket，使用close()
客户端代码client.c
/*client.c*/
#include<netinet/in.h> // for sockaddr_in
#include<sys/types.h> // for socket
#include<sys/socket.h> // for socket
#include<stdio.h> // for printf
#include<stdlib.h> // for exit
#include<string.h> // for bzero
#define SERVER_PORT 5678
#define BUFFER_SIZE 1024
#define FILE_NAME_MAX_SIZE 512
int main(int argc, char **argv)
{
if (argc != 2) //判断有没有输入服务器ip
{
printf("Usage: ./%s ServerIPAddress\n", argv[0]);
exit(1);
}
// 设置一个socket地址结构client_addr, 代表客户机的ip地址和端口
struct sockaddr_in client_addr;
bzero(&client_addr, sizeof(client_addr));
client_addr.sin_family = AF_INET; // internet协议族IPv4
client_addr.sin_addr.s_addr = htons(INADDR_ANY); // INADDR_ANY表示自动获取本机地址
client_addr.sin_port = htons(0); // auto allocated, 让系统自动分配一个空闲端口
// 创建用于internet的流协议(TCP)类型socket，用client_socket代表客户端socket
int client_socket = socket(AF_INET, SOCK_STREAM, 0);
if (client_socket < 0)
{
printf("Create Socket Failed!\n");
exit(1);
}
else
printf("Create Socket Success.\n");
// 把客户端的socket和客户端的socket地址结构绑定
if (bind(client_socket, (struct sockaddr*)&client_addr, sizeof(client_addr)))
{
printf("Client Bind Port Failed!\n");
exit(1);
}
else
printf("Client Bind Port Success.\n");
// 设置一个socket地址结构server_addr,代表服务器的internet地址和端口
struct sockaddr_in server_addr;
bzero(&server_addr, sizeof(server_addr));
server_addr.sin_family = AF_INET;
// 服务器的IP地址来自程序的参数
if (inet_aton(argv[1], &server_addr.sin_addr) == 0)
{
printf("Server IP Address Error!\n");
exit(1);
}
server_addr.sin_port = htons(SERVER_PORT);
int server_addr_length = sizeof(server_addr);
// 向服务器发起连接请求，连接成功后client_socket代表客户端和服务器端的一个socket连接
if (connect(client_socket, (struct sockaddr*)&server_addr, server_addr_length) < 0)
{
printf("Can Not Connect To %s!\n", argv[1]);
exit(1);
}
else
printf("Alreadly Connect To %s.\n", argv[1]);
char file_name[FILE_NAME_MAX_SIZE + 1];
bzero(file_name, sizeof(file_name));
printf("Please Input File Name On Server: ");
scanf("%s", file_name);
char buffer[BUFFER_SIZE];//缓存区
bzero(buffer, sizeof(buffer));
strncpy(buffer, file_name, strlen(file_name) > BUFFER_SIZE ? BUFFER_SIZE : strlen(file_name));
// 向服务器发送buffer中的数据，此时buffer中存放的是客户端需要接收的文件的名字
send(client_socket, buffer, BUFFER_SIZE, 0);
// send , sendto(), recv(),recvfrom()
FILE *fp = fopen(file_name, "w");
if (fp == NULL)
{
printf("File: %s Can Not Open To Write!\n", file_name);
exit(1);
}
// 从服务器端接收数据到buffer中
bzero(buffer, sizeof(buffer));
int length = 0;
while(length = recv(client_socket, buffer, BUFFER_SIZE, 0))
{
if (length < 0)
{
printf("Recieve Data From Server %s Failed!\n", argv[1]);
break;
}
int write_length = fwrite(buffer, sizeof(char), length, fp);
if (write_length < length)
{
printf("File:\t%s Write Failed!\n", file_name);
break;
}
bzero(buffer, BUFFER_SIZE);
}
printf("Recieve File: %s From Server[%s] Finished!\n", file_name, argv[1]);
// 传输完毕，关闭socket
fclose(fp);
close(client_socket);
return 0;
}
如图，客户端（左）从服务端（右）下载文件/图片：
二、UDP实现
UDP(User Datagram Protocol) 全称是用户数据报协议,是一种非面向连接的协议,这种协议并不能保证我们的网络程序的连接是可靠的。
1.服务端
基于UDP协议的socket的server编程步骤：
1、建立socket,使用socket()
2、绑定socket,使用bind()
3、以recvfrom()函数接收发送端传来的数据（使用recvfrom函数 时需设置非阻塞，以免程序卡在此处）
4、关闭socket，使用close()
/*server.c*/
#include<netinet/in.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define SERVER_PORT 5678 //端口号
#define LENGTH_OF_LISTEN_QUEUE 20
#define BUFFER_SIZE 1024
#define FILE_NAME_MAX_SIZE 512
int main(int argc, char **argv)
{
// 设置一个socket地址结构server_addr,代表服务器internet的地址和端口
struct sockaddr_in server_addr;
bzero(&server_addr, sizeof(server_addr));
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = htons(INADDR_ANY);
server_addr.sin_port = htons(SERVER_PORT);
// create a stream socket
// 创建用于internet的流协议(UDP)socket，用server_socket代表服务器向客户端提供服务的接口
int server_socket = socket(PF_INET, SOCK_DGRAM, 0);
if (server_socket < 0)
{
printf("Create Socket Failed!\n");
exit(1);
}
else
printf("Create Socket Success.\n");
// 把socket和socket地址结构绑定
if (bind(server_socket, (struct sockaddr*)&server_addr, sizeof(server_addr)))
{
printf("Server Bind Port: %d Failed!\n", SERVER_PORT);
exit(1);
}
else
printf("Server Bind Port Success.\n");
printf("Waiting......\n");
// 服务器端一直运行用以持续为客户端提供服务
while(1)
{
// 接受此请求，同时将client端的地址和端口等信息写入client_addr中
struct sockaddr_in client_addr;
int length = 0;
int addrlen = sizeof(client_addr);
char buffer[BUFFER_SIZE];
bzero(buffer, sizeof(buffer));
length = recvfrom(server_socket, buffer, BUFFER_SIZE, 0,(struct sockaddr *)&client_addr,&addrlen);
if (length < 0)
{
printf("Server Recieve Data Failed!\n");
break;
}
char file_name[FILE_NAME_MAX_SIZE + 1];
bzero(file_name, sizeof(file_name));
strncpy(file_name, buffer,
strlen(buffer) > FILE_NAME_MAX_SIZE ? FILE_NAME_MAX_SIZE : strlen(buffer));
FILE *fp = fopen(file_name, "r");
if (fp == NULL)
{
printf("File:\t%s Not Found!\n", file_name);
}
else
{
bzero(buffer, BUFFER_SIZE);
int file_block_length = 0;
while( (file_block_length = fread(buffer, sizeof(char), BUFFER_SIZE, fp)) > 0)
{
// 发送buffer中的字符串到server_socket,实际上就是发送给客户端
if (sendto(server_socket, buffer, BUFFER_SIZE, 0,(struct sockaddr *)&client_addr,addrlen) < 0)
{
printf("Send File:\t%s Failed!\n", file_name);
break;
}
bzero(buffer, sizeof(buffer));
}
fclose(fp);
printf("File:\t%s Transfer Finished!\n", file_name);
}
}
close(server_socket);
return 0;
}
2.客户端
基于UDP协议的socket的client端编程步骤：
1、建立Socket，使socket()
2、用sendto()函数向接收端发送数据。
3、关闭socket，使用close()函数
/*client.c*/
#include<netinet/in.h> // for sockaddr_in
#include<sys/types.h> // for socket
#include<sys/socket.h> // for socket
#include<stdio.h> // for printf
#include<stdlib.h> // for exit
#include<string.h> // for bzero
#include <fcntl.h>
#include <unistd.h>
#include <sys/time.h>
#define SERVER_PORT 5678
#define BUFFER_SIZE 1024
#define FILE_NAME_MAX_SIZE 512
int main(int argc, char **argv)
{
if (argc != 2)
{
printf("Usage: ./%s ServerIPAddress\n", argv[0]);
exit(1);
}
// 设置一个socket地址结构client_addr, 代表客户机的internet地址和端口
struct sockaddr_in client_addr;
bzero(&client_addr, sizeof(client_addr));
client_addr.sin_family = AF_INET; // internet协议族
client_addr.sin_addr.s_addr = htons(INADDR_ANY); // INADDR_ANY表示自动获取本机地址
client_addr.sin_port = htons(0); // auto allocated, 让系统自动分配一个空闲端口
// 创建用于internet的流协议(TCP)类型socket，用client_socket代表客户端socket
int client_socket = socket(AF_INET, SOCK_DGRAM, 0);
if (client_socket < 0)
{
printf("Create Socket Failed!\n");
exit(1);
}
// 设置超时，防止recvfrom（）函数阻塞
struct timeval timeout;
timeout.tv_sec = 1;//秒
timeout.tv_usec = 0;//微秒
if (setsockopt(client_socket, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout)) == -1) {
perror("setsockopt failed:");
}
// 把客户端的socket和客户端的socket地址结构绑定
if (bind(client_socket, (struct sockaddr*)&client_addr, sizeof(client_addr)))
{
printf("Client Bind Port Failed!\n");
exit(1);
}
// 设置一个socket地址结构server_addr,代表服务器的internet地址和端口
struct sockaddr_in server_addr;
bzero(&server_addr, sizeof(server_addr));
server_addr.sin_family = AF_INET;
// 服务器的IP地址来自程序的参数
if (inet_aton(argv[1], &server_addr.sin_addr) == 0)
{
printf("Server IP Address Error!\n");
exit(1);
}
server_addr.sin_port = htons(SERVER_PORT);
int server_addr_length = sizeof(server_addr);
char file_name[FILE_NAME_MAX_SIZE + 1];
bzero(file_name, sizeof(file_name));
printf("Please Input File Name On Server: ");
scanf("%s", file_name);
char buffer[BUFFER_SIZE];
bzero(buffer, sizeof(buffer));
strncpy(buffer, file_name, strlen(file_name) > BUFFER_SIZE ? BUFFER_SIZE : strlen(file_name));
// 向服务器发送buffer中的数据，此时buffer中存放的是客户端需要接收的文件的名字
if( sendto(client_socket, buffer, BUFFER_SIZE, 0,(struct sockaddr *)&server_addr,server_addr_length) )
printf("Waiting receive %s from server....\n",file_name);
FILE *fp = fopen(file_name, "w");
if (fp == NULL)
{
printf("File:\t%s Can Not Open To Write!\n", file_name);
exit(1);
}
// 从服务器端接收数据到buffer中
bzero(buffer, sizeof(buffer));
int length = 0;
//length = recvfrom(client_socket, buffer, BUFFER_SIZE, 0, (struct sockaddr*)&server_addr, &server_addr_length)//非阻塞
while( length = recvfrom(client_socket, buffer, BUFFER_SIZE, 0, (struct sockaddr*)&server_addr, &server_addr_length))
{
if (length < 0)
{
//printf("Recieve Data From Server %s Failed!\n", argv[1]);
break;
}
int write_length = fwrite(buffer, sizeof(char), length, fp);
if (write_length < length)
{
printf("File: %s Write Failed!\n", file_name);
break;
}
bzero(buffer, BUFFER_SIZE);
}
printf("Receive File: %s From Server[%s] Finished!\n", file_name, argv[1]);
// 传输完毕，关闭socket
fclose(fp);
close(client_socket);
return 0;
}
如图，客户端（左）从服务端（右）下载文件/图片：
注：使用recvfrom函数 时需设置非阻塞，以免程序卡住。
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