1. TCP和UDP的区别
TCP(Transmission Control Protocol,传输控制协议)
UDP(User Datagram Protocol,用户数据报协议)
1.1 连接方式
- TCP 是面向连接的协议,它在数据传输前需要通过三次握手建立一个可靠的连接,确保双方都准备好进行通信,并维护连接状态直到连接被明确关闭(四次挥手)。
- UDP 是无连接的协议,它不建立正式的连接就可以直接发送数据包。发送端和接收端之间没有事先的握手过程,每个数据报都是独立发送的。
1.2 可靠性
- TCP 提供可靠的数据传输服务,确保数据包按序、无损地到达接收端。它通过序列号、确认应答、错误检测、重传机制和流量控制来保证数据的可靠性和顺序。
- UDP 不提供这些保障,数据包可能丢失、重复或乱序到达,适用于对实时性要求高于数据完整性的应用。
1.3 速度与效率
- TCP 因其额外的控制信息和确认过程,相比UDP来说,传输效率较低,但提供了更高的可靠性。
- UDP 由于其简单、无连接的特性,传输速度快,延迟低,适合实时应用。
1.4 数据包处理
- TCP 将数据视为字节流,可以拆分和重组数据包,适合传输大量或连续的数据。
- UDP 保留了数据报的边界,作为独立的数据单元传输,适合一次性传输小块或具有明确界限的数据。
1.5 应用场景
- TCP 适用于需要高度可靠传输的应用,如Web浏览、电子邮件、文件传输(FTP)等。
- UDP 适用于实时性要求高、可以容忍一定数据丢失的应用,如在线游戏、语音通话、视频流、DNS查询等。
1.6 资源消耗与复杂性
- TCP 需要更多的系统资源来维护连接状态和执行复杂的错误恢复机制。
- UDP 相对轻量,对系统资源的需求较少,程序实现也更为简单
2. TCP接口函数
2.1 socket
socket(AF_INET, SOCK_STREAM, 0);
2.2 connect
int connect(int sockfd, const struct sockaddr *addr,
socklen_t addrlen);
功能:
向接收端发送三次握手链接请求
参数:
sockfd:文件描述符
addr:接收方地址空间首地址
addrlen:接收方地址的大小
返回值:
成功返回0
失败返回-1
2.3 send (发的太块会阻塞)
ssize_t send(int sockfd, const void *buf, size_t len, int flags);
功能:
发送数据
参数:
sockfd:文件描述符
buf:存放数据空间首地址
len:发送数据长度
flags:属性 默认为0
返回值:
成功返回发送字节数
失败返回-1
2.4 recv
ssize_t recv(int sockfd, void *buf, size_t len, int flags);
功能:
接收数据
参数:
sockfd:文件描述符
buf:存放数据空间首地址
len:最多接收数据大小
flags:属性 默认为0
返回值:
成功返回实际接收字节数
失败返回-1
对方关闭套接字返回0
2.5 listen
int listen(int sockfd, int backlog);
功能:
监听链接请求
参数:
sockfd:文件描述符
backlog:允许最多等待链接的个数
返回值:
成功返回0
失败返回-1
2.6 accept(返回通信套接字)
int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen);
功能:
处理等待队列中第一个链接
参数:
sockfd:文件描述符
addr:存放链接对方地址信息空间首地址
addrlen:想要接收地址大小变量空间首地址
返回值:
成功返回与发送端建立的新文件描述符(通信套接字)
失败返回-1
2.7 inet_addr
in_addr_t inet_addr(const char *cp);
功能:
将字符串IP地址转换为二进制IP地址
参数:
cp:字符串IP地址空间首地址
返回值:
成功返回二进制IP地址
2.8 htons
uint16_t htons(uint16_t hostshort);
功能:
将本地字节序(小端)转换为网络字节序(大端)
参数:
hostshort:本地端口号
返回值:
返回网络字节序端口号
uint16_t ntohs(uint16_t netshort);
功能:
将网络字节序(大端)转换为本地字节序(小端)
2.9 bind
int bind(int sockfd, const struct sockaddr *addr,
socklen_t addrlen);
功能:
将套接字与IP地址端口绑定在一起
参数:
sockfd:文件描述符
addr:结构体空间首地址
addrlen:信息的长度
返回值:
成功返回0
失败返回-1
2.10 示例程序
(1)TCP单向通信
1. 头文件
#ifndef _HEAD_H_
#define _HEAD_H_#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <arpa/inet.h>
#include <time.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <pthread.h>#endif
2. makefile
all:send recvsend:send.cgcc $^ -o $@
recv:recv.cgcc $^ -o $@
3. recv.c
#include "head.h"int main(int argc, char const *argv[])
{int confd = 0;int listfd = 0;int ret_connect = 0;int ret_bind = 0;int ret_listen = 0;struct sockaddr_in recvaddr;struct sockaddr_in sendaddr;socklen_t addrlen = sizeof(sendaddr);ssize_t ret_send = 0;ssize_t ret_recv = 0;listfd = socket(AF_INET, SOCK_STREAM, 0);if (-1 == listfd){perror("socket error!\n");return -1;}bzero(&recvaddr,sizeof(recvaddr));bzero(&sendaddr,sizeof(sendaddr));recvaddr.sin_family = AF_INET;recvaddr.sin_port = htons(50000);recvaddr.sin_addr.s_addr = inet_addr("192.168.0.109");ret_bind = bind(listfd, (struct sockaddr *)&recvaddr, sizeof(recvaddr));if (-1 == ret_bind){perror("bind error!\n");return -1;}ret_listen = listen(listfd, 3);if (-1 == ret_listen){perror("listen error!\n");return -1; }confd = accept(listfd, (struct sockaddr *)&sendaddr, &addrlen);if (-1 == confd){perror("accept error!\n");return -1; }while (1){char buf[256] = {0};ret_recv = recv(confd, buf, sizeof(buf), 0);if (ret_recv <= 0){break;}time_t tm;time(&tm);sprintf(buf, "%s %s", buf, ctime(&tm));ret_send = send(confd, buf, strlen(buf), 0);if (-1 == ret_send){perror("send error!\n");return -1; } }close(confd);close(listfd);return 0;
}
4. send.c
#include "head.h"int main(int argc, char const *argv[])
{int confd = 0;int ret_connect = 0;struct sockaddr_in recvaddr;socklen_t addrlen = 0;ssize_t ret_send = 0;ssize_t ret_recv = 0;confd = socket(AF_INET, SOCK_STREAM, 0);if (-1 == confd){perror("socket error!\n");return -1;}bzero(&recvaddr, sizeof(recvaddr));recvaddr.sin_family = AF_INET;recvaddr.sin_port = htons(50000);recvaddr.sin_addr.s_addr = inet_addr("192.168.0.109");ret_connect = connect(confd, (struct sockaddr *)&recvaddr, sizeof(recvaddr));if (-1 == ret_connect){perror("connect error!\n");return -1; }while (1){char buf[256] = {"supercarrydoinb"};ret_send = send(confd, buf, strlen(buf), 0);if (-1 == ret_connect){perror("send error!\n");return -1; } ret_recv = recv(confd, buf, sizeof(buf), 0);if (ret_recv <= 0){break;}printf("%s", buf);sleep(1);}close(confd);return 0;
}
(2) TCP实现多线程双机聊天(chat)——注意:!!线程编译gcc要加后缀 -lpthread
1. 头文件
#ifndef _HEAD_H_
#define _HEAD_H_#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <arpa/inet.h>
#include <time.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <pthread.h>#endif
2. makefile
all:send recvsend:send.cgcc $^ -o $@ -lpthread
recv:recv.cgcc $^ -o $@ -lpthread
3. send.c
#include "head.h"struct sockaddr_in sendaddr;
struct sockaddr_in recvaddr;void *th1(void *arg)
{int confd = *(int *)arg;ssize_t ret_recv = 0;while (1){char buf[256] = {0};ret_recv = recv(confd, buf, sizeof(buf), 0);if (-1 == ret_recv){perror("recv error!\n");}printf("from recv: %s\n", buf);}
}void *th2(void *arg)
{int confd = *(int *)arg;ssize_t ret_send = 0;while (1){printf("to recv:");char buf[256] = {0};fgets(buf, sizeof(buf), stdin);buf[strlen(buf)-1] = '\0';ret_send= send(confd, buf, strlen(buf), 0);if (-1 == ret_send){perror("send error!\n");}}
}int main(int argc, char const *argv[])
{int confd = 0;int ret_connect = 0;socklen_t addrlen = sizeof(sendaddr);ssize_t ret_recv = 0;ssize_t ret_send = 0;pthread_t tid1;pthread_t tid2;char buf[256] = {0};confd = socket(AF_INET, SOCK_STREAM, 0);if (-1 == confd){perror("socket error!\n");return -1;}bzero(&recvaddr, sizeof(recvaddr));bzero(&sendaddr, sizeof(sendaddr));recvaddr.sin_family = AF_INET;recvaddr.sin_port = htons(50000);recvaddr.sin_addr.s_addr = inet_addr("192.168.0.109");ret_connect = connect(confd, (struct sockaddr *)&recvaddr, sizeof(recvaddr));if (-1 == ret_connect){perror("connect error!\n");return -1;}#if 0ret_recv = recv(confd, buf, sizeof(buf), 0);if (-1 == ret_recv){perror("recv error!\n");return -1;}
#endifpthread_create(&tid1, NULL, th1, &confd);pthread_create(&tid2, NULL, th2, &confd);pthread_join(tid1, NULL);pthread_join(tid1, NULL);return 0;
}
4. recv.c
#include "head.h"struct sockaddr_in sendaddr;
struct sockaddr_in recvaddr;void *th1(void *arg)
{int confd = *(int *)arg;ssize_t ret_recv = 0;while (1){char buf[256] = {0};ret_recv = recv(confd, buf, sizeof(buf), 0);if (-1 == ret_recv){perror("recv error!\n");}printf("from send: %s\n", buf);}
}void *th2(void *arg)
{int confd = *(int *)arg;ssize_t ret_send = 0;while (1){printf("to send:");char buf[256] = {0};fgets(buf, sizeof(buf), stdin);buf[strlen(buf)-1] = '\0';ret_send = send(confd, buf, strlen(buf), 0);if (-1 == ret_send){perror("send error!\n");}}
}int main(int argc, char const *argv[])
{int listfd = 0;int confd = 0;int ret_bind = 0;int ret_listen = 0;socklen_t addrlen = sizeof(sendaddr);ssize_t ret_recv = 0;ssize_t ret_send = 0;pthread_t tid1;pthread_t tid2;char buf[256] = {0};listfd = socket(AF_INET, SOCK_STREAM, 0);if (-1 == listfd){perror("socket error!\n");return -1;}bzero(&recvaddr, sizeof(recvaddr));bzero(&sendaddr, sizeof(sendaddr));recvaddr.sin_family = AF_INET;recvaddr.sin_port = htons(50000);recvaddr.sin_addr.s_addr = inet_addr("192.168.0.109");ret_bind = bind(listfd, (struct sockaddr *)&recvaddr, sizeof(recvaddr));if (-1 == ret_bind){perror("bind error!\n");return -1;}ret_listen = listen(listfd, 3);if (-1 == ret_listen){perror("listen error!\n");return -1; }confd = accept(listfd, (struct sockaddr *)&sendaddr, &addrlen);if (-1 == confd){perror("accept error!\n");return -1; }#if 0ret_recv = recv(confd, buf, sizeof(buf), 0);if (-1 == ret_recv){perror("recv error!\n");return -1;}
#endifpthread_create(&tid1, NULL, th1, &confd);pthread_create(&tid2, NULL, th2, &confd);pthread_join(tid1, NULL);pthread_join(tid1, NULL);return 0;
}
(3) TCP实现文件的传输(结构体)
1. 头文件
#ifndef _HEAD_H_
#define _HEAD_H_#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <arpa/inet.h>
#include <time.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <pthread.h>#endif
2. makefile
all:send recvsend:send.cgcc $^ -o $@ -lpthread
recv:recv.cgcc $^ -o $@ -lpthread
3. send.c
#include "head.h"typedef struct
{char buf[1024];char filename[32];int rd_ret;int total;
}MSG;int main(int argc, char const *argv[])
{int ret_connect = 0;int ret_stat = 0;int confd = 0;int openfd = 0;ssize_t ret_recv = 0;ssize_t ret_send = 0;struct sockaddr_in recvaddr;MSG msg;struct stat st;confd = socket(AF_INET, SOCK_STREAM, 0);if (-1 == confd){perror("socket error!\n");return -1;}bzero(&recvaddr, sizeof(recvaddr));bzero(&msg, sizeof(msg));recvaddr.sin_family = AF_INET;recvaddr.sin_port = htons(50000);recvaddr.sin_addr.s_addr = inet_addr("192.168.0.109");ret_connect = connect(confd, (struct sockaddr *)&recvaddr, sizeof(recvaddr));if (-1 == ret_connect){perror("connetc error!\n");return -1;}openfd = open("./1.png", O_RDONLY);if (-1 == openfd){perror("open error!\n");return -1;}strcpy(msg.filename, "2.png");ret_stat = stat("./1.png", &st);if (-1 == ret_stat){perror("stat error!\n");return -1;}msg.total = st.st_size;while (1){bzero(msg.buf, sizeof(msg.buf));msg.rd_ret = read(openfd, msg.buf, sizeof(msg.buf));send(confd, &msg, sizeof(msg), 0);if (msg.rd_ret <= 0){break;}char buf[256] = {0};ret_recv = recv(confd, buf, sizeof(buf), 0);if (ret_recv <= 0){break;}usleep(1000 * 200);}close(confd);close(openfd);return 0;
}
4. recv.c
#include "head.h"typedef struct
{char buf[1024];char filename[32];int rd_ret;int total;
}MSG;int main(int argc, char const *argv[])
{int listfd = 0;int ret_bind = 0;int ret_listen = 0;int confd = 0;ssize_t ret_recv = 0;ssize_t ret_send = 0;struct sockaddr_in recvaddr;struct sockaddr_in sendaddr;socklen_t addrlen = sizeof(sendaddr);MSG msg;listfd = socket(AF_INET, SOCK_STREAM, 0);if (-1 == listfd){perror("socket error!\n");return -1;}bzero(&recvaddr, sizeof(recvaddr));bzero(&sendaddr, sizeof(sendaddr));bzero(&msg, sizeof(msg));recvaddr.sin_family = AF_INET;recvaddr.sin_port = htons(50000);recvaddr.sin_addr.s_addr = inet_addr("192.168.0.109");ret_bind = bind(listfd, (struct sockaddr *)&recvaddr, sizeof(recvaddr));if (-1 == ret_bind){perror("bind error!\n");return -1;}ret_listen = listen(listfd, 3);if (-1 == ret_listen){perror("listen error!\n");return -1;}confd = accept(listfd, (struct sockaddr *)&sendaddr, &addrlen);if (-1 == confd){perror("accept error!\n");return -1;}int openfd = 0;int flag = 0;int total = 0;int current_size = 0;while (1){ret_recv = recv(confd, &msg, sizeof(msg), 0);if (ret_recv <= 0){break;}if (0 == msg.rd_ret){printf("file upload end\n");return -1;}if (0 == flag)//拿到文件总大小{openfd = open(msg.filename, O_WRONLY | O_CREAT | O_TRUNC, 0666);if (-1 == openfd){perror("open error!\n");return -1;}flag = 1;total = msg.total;}write(openfd, msg.buf, msg.rd_ret);current_size += msg.rd_ret;printf("%d / %d\n", current_size, total);char buf[256] = "go on";send(confd, buf, strlen(buf), 0);}close(confd);close(openfd);close(listfd);return 0;
}