linux socket进程通信

socket进程通信与网络通信使用的是统一套接口，只是地址结构与某些参数不同。

一。创建socket服务端的流程如下：

（1）创建socket，类型为AF_LOCAL或AF_UNIX，表示用于进程通信：

int server_fd;
int client_fd;//client file descriptor
struct sockaddr_un server_addr;
struct sockaddr_un client_addr;
size_t server_len,client_len;

//cteate server socket
//delete old socket file
unlink(SERVER_NAME);
if ((server_fd = socket(AF_UNIX,  SOCK_STREAM,  0)) == -1) {
    perror("socket");
    exit(1);
}

(2)命名socket。这里面有一个很关键的东西，socket进程通信命名方式有两种。 一是普通的命名，socket会根据此命名创建一个同名的socket文件，客户端连接的时候通过读取该socket文件连接到socket服务端。这种 方式的弊端是服务端必须对socket文件的路径具备写权限，客户端必须知道socket文件路径，且必须对该路径有读权限。另外一种命名方式是抽象命名 空间，这种方式不需要创建socket文件，只需要命名一个全局名字，即可让客户端根据此名字进行连接。后者的实现过程与前者的差别是，后者在对地址结构 成员sun_path数组赋值的时候，必须把第一个字节置0，即sun_path[0] = 0，下面用代码说明：

第一种方式：

      //name the server socket
server_addr.sun_family = AF_UNIX;
strcpy(server_addr.sun_path,SERVER_NAME);
server_len = sizeof(struct sockaddr_un);
client_len = server_len;

第二种方式：

//name the socket
server_addr.sun_family = AF_UNIX;
strcpy(server_addr.sun_path, SERVER_NAME);
server_addr.sun_path[0]=0;
//server_len = sizeof(server_addr);
server_len = strlen(SERVER_NAME)  + offsetof(struct sockaddr_un, sun_path);

其中，offsetof函数在#include 头文件中定义。因第二种方式的首字节置0，我们可以在命名字符串SERVER_NAME前添加一个占位字符串，例如:

#define SERVER_NAME @socket_server

前面的@符号就表示占位符，不算为实际名称。

或者可以把第二种方式的实现封装成一个函数：

int makeAddr(const char* name, struct sockaddr_un* pAddr, socklen_t* pSockLen)
{
    int nameLen = strlen(name);
    if (nameLen >= (int) sizeof(pAddr->sun_path) -1)  /* too long? */
        return -1;
    pAddr->sun_path[0] = '\0';  /* abstract namespace */
    strcpy(pAddr->sun_path+1, name);
    pAddr->sun_family = AF_UNIX;
    *pSockLen = 1 + nameLen + offsetof(struct sockaddr_un, sun_path);
    return 0;
}

像下面这样使用这个函数：

makeAddr("server_socket", &server_addr, &server_len);

提示：客户端连接服务器的时候，必须与服务端的命名方式相同，即如果服务端是普通命名方式，客户端的地址也必须是普通命名方式；如果服务端是抽象命名方式，客户端的地址也必须是抽象命名方式。

（3）绑定并侦听

bind(server_sockfd, (struct sockaddr *)&server_addr, server_len);

//listen the server
listen(server_sockfd, 5);

（4）等待客户端连接，并读写数据。

while(1){
printf("server waiting...\n");

//accept client connect
client_len = sizeof(client_addr);
client_sockfd = accept(server_sockfd,(struct sockaddr*)&client_addr, &client_len);

//read  data from client socket
read(client_sockfd, &ch, 1);
printf("read from client %d: %c",client_sockfd,ch);
ch ++;
write(client_sockfd, &ch, 1);
close(client_sockfd);
usleep(100);//1000 miliseconds = 1 second
  }

二 socket客户端创建流程

（1）创建socket

（2）命名socket

（3）连接到服务端：

//connect to server
    result = connect(sockfd, (struct sockaddr*)&address, len);

（4）与服务端进行通信

//communicate with server socket
while(1)
{
    printf("set send content:");
    scanf("%c",&ch);
    write(sockfd, &ch, 1);
    printf("send to server:%c \n",ch);
    read(sockfd, &ch, 1);
    printf("read from server: %c\n", ch);


}

完整代码如下：

（1）服务端server.c：

#include
#include
#include
#include
#include
#include
#include

#define SERVER_NAME "@server_socket"
/*
 * Create a UNIX-domain socket address in the Linux "abstract namespace".
 *
 * The socket code doesn't require null termination on the filename, but
 * we do it anyway so string functions work.
 */
int makeAddr(const char* name, struct sockaddr_un* pAddr, socklen_t* pSockLen)
{
    int nameLen = strlen(name);
    if (nameLen >= (int) sizeof(pAddr->sun_path) -1)  /* too long? */
        return -1;
    pAddr->sun_path[0] = '\0';  /* abstract namespace */
    strcpy(pAddr->sun_path+1, name);
    pAddr->sun_family = AF_UNIX;
    *pSockLen = 1 + nameLen + offsetof(struct sockaddr_un, sun_path);
    return 0;
}

int main()

{
    int server_sockfd, client_sockfd;
    socklen_t server_len, client_len;
    struct sockaddr_un server_addr;
    struct sockaddr_un client_addr;
    char ch;
    int nread;

    //delete the old server socket
    //unlink("server_socket");
    //create socket
    server_sockfd = socket(AF_UNIX, SOCK_STREAM, 0);

    //name the socket
    server_addr.sun_family = AF_UNIX;
    strcpy(server_addr.sun_path, SERVER_NAME);
    server_addr.sun_path[0]=0;
    //server_len = sizeof(server_addr);
    server_len = strlen(SERVER_NAME)  + offsetof(struct sockaddr_un, sun_path);
    //makeAddr("server_socket", &server_addr, &server_len);
    bind(server_sockfd, (struct sockaddr *)&server_addr, server_len);

    //listen the server
    listen(server_sockfd, 5);
    client_sockfd = -1;
    client_len = sizeof(client_addr);
    while(1){
        printf("server waiting...\n");
        //accept client connect
        if(client_sockfd == -1){
            client_sockfd = accept(server_sockfd,(struct sockaddr*)&client_addr, &client_len);
        }

        //read  data from client socket
        nread = read(client_sockfd, &ch, 1);
        if(nread == 0){//client disconnected
            printf("client %d disconnected\n",client_sockfd);
            client_sockfd = -1;
        }
        else{
            printf("read from client %d: %c\n",client_sockfd,ch);
            ch ++;
            write(client_sockfd, &ch, 1);
        }
        usleep(100);//1000 miliseconds = 1 second
    }

    return 0;

}

（2）客户端client.c

#include
#include
#include
#include
#include
#include
#include
#define SERVER_NAME "@server_socket"
/*
 * Create a UNIX-domain socket address in the Linux "abstract namespace".
 *
 * The socket code doesn't require null termination on the filename, but
 * we do it anyway so string functions work.
 */
int makeAddr(const char* name, struct sockaddr_un* pAddr, socklen_t* pSockLen)
{
    int nameLen = strlen(name);
    if (nameLen >= (int) sizeof(pAddr->sun_path) -1)  /* too long? */
        return -1;
    pAddr->sun_path[0] = '\0';  /* abstract namespace */
    strcpy(pAddr->sun_path+1, name);
    pAddr->sun_family = AF_UNIX;
    *pSockLen = 1 + nameLen + offsetof(struct sockaddr_un, sun_path);
    return 0;
}


int main()
{
    int sockfd;
    socklen_t len;
    struct sockaddr_un address;
    int result;
    char ch = 'A';

    //create socket
    sockfd = socket(AF_UNIX, SOCK_STREAM, 0);
    //name the server socket
    //makeAddr("server_socket", &address, &len);
    address.sun_family = AF_UNIX;
    strcpy(address.sun_path, SERVER_NAME);
    address.sun_path[0]=0;
    //len = sizeof(address);
    len =  strlen(SERVER_NAME)  + offsetof(struct sockaddr_un, sun_path);
    //connect to server
    result = connect(sockfd, (struct sockaddr*)&address, len);
    if(result == -1)
    {
        perror("opps:client1");
        exit(1);
    }
    //communicate with server socket
    while(1)
    {
        printf("set send content:");
        scanf("%c",&ch);
        write(sockfd, &ch, 1);
        printf("send to server:%c \n",ch);
        read(sockfd, &ch, 1);
        printf("read from server: %c\n", ch);


    }
    exit(0);

}