Socket编程

Socket编程很简单。因为不管用什么语言、什么环境编写，都是那几个固定的步骤。

Socket可以通过TCP\IP和UDP两种方式实现。

TCP\IP

　　tcp建立连接要进行“三次握手”，即交换三个分组。大致流程如下：

客户端向服务器发送一个SYN J
服务器向客户端响应一个SYN K，并对SYN J进行确认ACK J+1
客户端再想服务器发一个确认ACK K+1

　　当客户端调用connect时，触发了连接请求，向服务器发送了SYN J包，这时connect进入阻塞状态；服务器监听到连接请求，即收到SYN J包，调用accept函数接收请求向客户端发送SYN K ，ACK J+1，这时accept进入阻塞状态；客户端收到服务器的SYN K ，ACK J+1之后，这时connect返回，并对SYN K进行确认；服务器收到ACK K+1时，accept返回，至此三次握手完毕，连接建立。

Linux下实现，看下面的例子。windows下微软已经封装很好了，更简单一些，这里不赘述。

一、Server端。

View Code

#include <stdlib.h>
#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <fcntl.h>
#include <string.h>


int open_file(const char* filename)
{
        int fd;

        if ((fd = open(filename, O_CREAT | O_RDWR, 0666)) < 0) {
                printf("open error");
		return 0;
        }
        else {
        //        printf("Open file%d\n", fd);
        }

        return fd;
}

void write_file(int fd, char *buf, int len)
{
	lseek(fd, 0, SEEK_END);
        if (write(fd, buf, len) < 0) {
                printf("write error");
        }
        else {
        //        printf("Write: %s\n", buf);
        }
}

void read_file(int fd, int len)
{
        char buff[len + 1];

        lseek(fd, 0, SEEK_SET);
        if (read(fd, buff, len) < 0) {
                printf("read error");
        }
        else {
                buff[len] = '\0';
          //      printf("read from file: %s\n", buff);
        }
}

void close_file(int fd)
{
        if (close(fd) < 0) {
                printf("close error");
        }
        else 
	{//do nothing, close file right
        }
}

int main(int argc, char *argv[])
{
    // Get Port option
    if (argc < 2)
    {
        fprintf(stderr, "ERROR, no port provided\n");
        exit(1);
    }
    int port_no = atoi(argv[1]);

    // Get socket
    int socket_fd = socket(AF_INET, SOCK_STREAM, 0);

    // Bind
    struct sockaddr_in server_addr;
    bzero((char *) &server_addr, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = INADDR_ANY;
    server_addr.sin_port = htons(port_no);
    bind(socket_fd, (struct sockaddr *) &server_addr, sizeof(server_addr));

    // Listen
    listen(socket_fd, 5);

    while (1) {

        // Accept
        struct sockaddr_in client_addr;
        socklen_t client_addr_length = sizeof(client_addr);
        int socket_to_client = accept(socket_fd, (struct sockaddr *) &client_addr, &client_addr_length);

        // Read the buffer from the socket
        char buffer[1024*10240];
        bzero(buffer, sizeof(buffer));
        read(socket_to_client, buffer, sizeof(buffer) - 1);
　　　　//上面这个函数可以用下面的这个代替
　　　　//recv(socket_toclient, buffer, sizeof(buffer)-1, 0);
       //printf("Here is the message: %s\n", buffer);
	//write the string into the file
	int fd = open_file("server.log");
	if(fd > 0)
	{
		int len = strlen(buffer);
		write_file(fd, buffer, len);
		close_file(fd);
	}

        // Write
        const char *data = "I got your message.";
        write(socket_to_client, data, strlen(data));

        // Close
        close(socket_to_client);
    }

    close(socket_fd);

    return 0;
}

二、Client端。

View Code
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <string.h>
#include <netdb.h> // bcopy
#include <stdlib.h>

int main(int argc, char *argv[])
{
　　// Get options
　　if (argc < 3)
　　{
　　　　fprintf(stderr, "Usage: %s <hostname> <port>\n", argv[0]);
　　　　exit(1);
　　}
　　struct hostent *server_host = gethostbyname(argv[1]);
　　int server_port = atoi(argv[2]);

　　// Get socket
　　int socket_fd = socket(AF_INET, SOCK_STREAM, 0);

　　// Connect
　　struct sockaddr_in server_addr;
　　bzero((char *) &server_addr, sizeof(server_addr));
　　server_addr.sin_family = AF_INET;
　　bcopy((char *) server_host->h_addr, (char *) &server_addr.sin_addr.s_addr, server_host->h_length);
　　server_addr.sin_port = htons(server_port);
　　connect(socket_fd, (struct sockaddr *) &server_addr, sizeof(server_addr));

　　// Input
　　printf("Please enter the message: ");
　　char buffer[1024];
　　bzero(buffer, sizeof(buffer));
　　fgets(buffer, sizeof(buffer) - 1, stdin);

　　// Write
　　write(socket_fd, buffer, strlen(buffer));

　　// Read
　　bzero(buffer, sizeof(buffer));
　　read(socket_fd, buffer, sizeof(buffer) - 1);
　　printf("%s\n", buffer);

　　// Close
　　close(socket_fd);

　　return 0;
}

 1 #include <sys/socket.h>
 2 #include <netinet/in.h>
 3 #include <stdio.h>
 4 #include <string.h>
 5 #include <netdb.h> // bcopy
 6 #include <stdlib.h> 
 7 
 8 int main(int argc, char *argv[])
 9 {
10     // Get options
11     if (argc < 3)
12     {
13         fprintf(stderr, "Usage: %s <hostname> <port>\n", argv[0]);
14         exit(1);
15     }
16     struct hostent *server_host = gethostbyname(argv[1]);
17     int server_port = atoi(argv[2]);
18 
19     // Get socket
20     int socket_fd = socket(AF_INET, SOCK_STREAM, 0);
21 
22     // Connect
23     struct sockaddr_in server_addr;
24     bzero((char *) &server_addr, sizeof(server_addr));
25     server_addr.sin_family = AF_INET;
26     bcopy((char *) server_host->h_addr, (char *) &server_addr.sin_addr.s_addr, server_host->h_length);
27     server_addr.sin_port = htons(server_port);
28     connect(socket_fd, (struct sockaddr *) &server_addr, sizeof(server_addr));
29 
30     // Input
31     printf("Please enter the message: ");
32     char buffer[1024];
33     bzero(buffer, sizeof(buffer));
34     fgets(buffer, sizeof(buffer) - 1, stdin);
35 
36     // Write
37     write(socket_fd, buffer, strlen(buffer));
38 
39     // Read
40     bzero(buffer, sizeof(buffer));
41     read(socket_fd, buffer, sizeof(buffer) - 1);
42     printf("%s\n", buffer);
43 
44     // Close
45     close(socket_fd);
46 
47     return 0;
48 }

UDP

看例子代码。

Server端。

View Code

Client端。

View Code

 1 #include <sys/socket.h>
 2 #include <string.h>
 3 #include <netinet/in.h>
 4 #include <netdb.h>
 5 
 6 int main(int argc, char *argv[])
 7 {
 8     // Create socket
 9     int socket_fd = socket(AF_INET, SOCK_DGRAM, 0);
10 
11     // Initialize server address
12     struct hostent *server_host = gethostbyname(argv[1]);
13     struct sockaddr_in server_addr;
14     server_addr.sin_family = AF_INET; // socket internet family
15     bcopy((char *)server_host->h_addr, (char *)&server_addr.sin_addr.s_addr, server_host->h_length); // socket internet address
16     server_addr.sin_port = htons(atoi(argv[2])); // socket internet port
17 
18 // Send
19     char buffer[1024];
20     sendto(socket_fd, buffer, sizeof(buffer), 0, (const struct sockaddr *) &server_addr, sizeof(struct sockaddr_in));
21 
22     // Receive and write
23     struct sockaddr_in client_addr;
24     socklen_t client_addr_length = sizeof(client_addr);
25     int msg_recv_length = recvfrom(socket_fd, buffer, sizeof(buffer), 0, (struct sockaddr *) &client_addr, &client_addr_length);
26     const char *hint = "Got an ACK: ";
27     write(1, hint, strlen(hint));
28     write(1, buffer, msg_recv_length);
29 
30     // Close
31     close(socket_fd);
32 
33     return 0;
34 }

posted @ 2012-03-27 17:28 陈朋阅读(460) 评论(0) 编辑收藏举报

陈朋

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Socket编程

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