嵌入式学习——网络编程（TCP）——day31

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;
}

嵌入式学习——网络编程（TCP）——day31

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