0x01 緣由

一直在從事linux c/c++相關網絡開發，現在想進一步深入到核心，了解更多的東西，以支撐上層應用的開發。在linux上寫個c/s 通訊過程很簡單，如何寫得高并發、穩定才是真正的難點。

0x02 linux c服務端和用戶端代碼

服務端：

#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/shm.h>

#define MYPORT  8887
#define QUEUE   20
#define BUFFER_SIZE 1024

int main()
{
	int server_sockfd = socket(AF_INET,SOCK_STREAM, 0);

	struct sockaddr_in server_sockaddr;
	server_sockaddr.sin_family = AF_INET;
	server_sockaddr.sin_port = htons(MYPORT);
	server_sockaddr.sin_addr.s_addr = htonl(INADDR_ANY);

	if(bind(server_sockfd,(struct sockaddr *)&server_sockaddr,sizeof(server_sockaddr))==-1)
	{
		perror("bind");
		exit(1);
	}

	if(listen(server_sockfd,QUEUE) == -1)
	{
		perror("listen");
		exit(1);
	}

	char buffer[BUFFER_SIZE];
	char client_ip[16];
	int client_port;
	struct sockaddr_in client_addr;
	socklen_t length = sizeof(client_addr);

	int conn = accept(server_sockfd, (struct sockaddr*)&client_addr, &length);
	if(conn<0)
	{
		perror("connect");
		exit(1);
	}
	snprintf(client_ip, 16, "%s", inet_ntoa(client_addr.sin_addr));
	client_port = client_addr.sin_port;
	printf("client %s:%d\n", client_ip, client_port);

	while(1)
	{
		sleep(1);
		memset(buffer,0,sizeof(buffer));
		int len = recv(conn, buffer, sizeof(buffer),0);
		if(strcmp(buffer,"exit\n")==0)
			break;
		fputs(buffer, stdout);
		send(conn, buffer, len, 0);
	}
	close(conn);
	close(server_sockfd);
	return 0;
}

用戶端：

#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/shm.h>

#define MYPORT  8887
#define BUFFER_SIZE 1024

int main()
{
    int sock_cli = socket(AF_INET,SOCK_STREAM, 0);

    struct sockaddr_in servaddr;
    memset(&servaddr, 0, sizeof(servaddr));
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(MYPORT); 
    servaddr.sin_addr.s_addr = inet_addr("172.16.3.162");

    if (connect(sock_cli, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0)
    {
        perror("connect");
        exit(1);
    }

    char sendbuf[BUFFER_SIZE];
    char recvbuf[BUFFER_SIZE];
    while (fgets(sendbuf, sizeof(sendbuf), stdin) != NULL)
    {
        send(sock_cli, sendbuf, strlen(sendbuf),0);
        if(strcmp(sendbuf,"exit\n")==0)
            break;
        recv(sock_cli, recvbuf, sizeof(recvbuf),0);
        fputs(recvbuf, stdout);

        memset(sendbuf, 0, sizeof(sendbuf));
        memset(recvbuf, 0, sizeof(recvbuf));
    }

    close(sock_cli);
    return 0;
}

0x03 開始調試

結合上篇文章的調試環境來開始核心之旅。 host 主機上：用eclipse開啟調試模式； guest主機上：編譯運作client/server端代碼；在eclipse中設定相關斷點：即可調試；

0x04 了解相關系統調用

系統調用圖：