标签：ber foo cas inf 使用 exist link 地址 window
socket API原本是为网络通讯设计的，但后来在socket的框架上发展出一种IPC机
制，就是UNIX Domain Socket。虽然网络socket也可用于同一台主机的进程间通讯（通过
loopback地址127.0.0.1），但是UNIX Domain Socket用于IPC更有效率：不需要经过网络协
议栈，不需要打包拆包、计算校验和、维护序号和应答等，只是将应用层数据从一个进程拷
贝到另一个进程。这是因为，IPC机制本质上是可靠的通讯，而网络协议是为不可靠的通讯
设计的。UNIX Domain Socket也提供面向流和面向数据包两种API接口，类似于TCP和UDP，
但是面向消息的UNIX Domain Socket也是可靠的，消息既不会丢失也不会顺序错乱。
UNIX Domain Socket是全双工的，API接口语义丰富，相比其它IPC机制有明显的优越
性，目前已成为使用最广泛的IPC机制，比如X Window服务器和GUI程序之间就是通过UNIX
Domain Socket通讯的。
使用UNIX Domain Socket的过程和网络socket十分相似，也要先调用socket()创
建一个socket文件描述符，address family指定为AF_UNIX，type可以选择SOCK_DGRAM或
SOCK_STREAM，protocol参数仍然指定为0即可。
UNIX Domain Socket与网络socket编程最明显的不同在于地址格式不同，用结构体
sockaddr_un表示，网络编程的socket地址是IP地址加端口号，而UNIX Domain Socket的地
址是一个socket类型的文件在文件系统中的路径，这个socket文件由bind()调用创建，如果
调用bind()时该文件已存在，则bind()错误返回。
以下程序将UNIX Domain socket绑定到一个地址。
size = offsetof(struct sockaddr_un, sun_path) + strlen(un.sun_path); #define offsetof(TYPE, MEMBER) ((int)&((TYPE *)0)->MEMBER)
server
#include <stdlib.h> #include <stdio.h> #include <stddef.h> #include <sys/socket.h> #include <sys/un.h> #include <sys/types.h> #include <sys/stat.h> #include <unistd.h> #include <errno.h> #define QLEN 10 /* * Create a server endpoint of a connection. * Returns fd if all OK, <0 on error. */ int serv_listen(const char *name) { int fd, len, err, rval; struct sockaddr_un un; /* create a UNIX domain stream socket */ if ((fd = socket(AF_UNIX, SOCK_STREAM, 0)) < 0) return(-1); unlink(name); /* in case it already exists 否则bind的时候会出错*/ /* fill in socket address structure */ memset(&un, 0, sizeof(un)); un.sun_family = AF_UNIX; strcpy(un.sun_path, name); len = offsetof(struct sockaddr_un, sun_path) + strlen(name); /* bind the name to the descriptor 会创建name*/ if (bind(fd, (struct sockaddr *)&un, len) < 0) { rval = -2; goto errout; } if (listen(fd, QLEN) < 0) { /* tell kernel we‘re a server */ rval = -3; goto errout; } return(fd); errout: err = errno; close(fd); errno = err; return(rval); } int serv_accept(int listenfd, uid_t *uidptr) { int clifd, len, err, rval; time_t staletime; struct sockaddr_un un; struct stat statbuf; len = sizeof(un); if ((clifd = accept(listenfd, (struct sockaddr *)&un, &len)) < 0) return(-1); /* often errno=EINTR, if signal caught */ /* obtain the client‘s uid from its calling address */ len -= offsetof(struct sockaddr_un, sun_path); /* len of pathname */ un.sun_path[len] = 0; /* null terminate */ if (stat(un.sun_path, &statbuf) < 0) { rval = -2; goto errout; } if (S_ISSOCK(statbuf.st_mode) == 0) { rval = -3; /* not a socket */ goto errout; } if (uidptr != NULL) *uidptr = statbuf.st_uid; /* return uid of caller */ unlink(un.sun_path); /* we‘re done with pathname now */ return(clifd); errout: err = errno; close(clifd); errno = err; return(rval); } int main(void) { int lfd, cfd, n, i; uid_t cuid; char buf[1024]; lfd = serv_listen("foo.socket"); if (lfd < 0) { switch (lfd) { case -3:perror("listen"); break; case -2:perror("bind"); break; case -1:perror("socket"); break; } exit(-1); } cfd = serv_accept(lfd, &cuid); if (cfd < 0) { switch (cfd) { case -3:perror("not a socket"); break; case -2:perror("a bad filename"); break; case -1:perror("accept"); break; } exit(-1); } while (1) { r_again: n = read(cfd, buf, 1024); if (n == -1) { if (errno == EINTR) goto r_again; } else if (n == 0) { printf("the other side has been closed.\n"); break; } for (i = 0; i < n; i++) buf[i] = toupper(buf[i]); write(cfd, buf, n); } close(cfd); close(lfd); return 0; }
client
#include <stdio.h> #include <stdlib.h> #include <stddef.h> #include <sys/stat.h> #include <fcntl.h> #include <unistd.h> #include <sys/socket.h> #include <sys/un.h> #include <errno.h> #define CLI_PATH "/var/tmp/" /* +5 for pid = 14 chars */ /* * Create a client endpoint and connect to a server. * Returns fd if all OK, <0 on error. */ int cli_conn(const char *name) { int fd, len, err, rval; struct sockaddr_un un; /* create a UNIX domain stream socket */ if ((fd = socket(AF_UNIX, SOCK_STREAM, 0)) < 0) return(-1); /* fill socket address structure with our address */ memset(&un, 0, sizeof(un)); un.sun_family = AF_UNIX; sprintf(un.sun_path, "%s%05d", CLI_PATH, getpid()); len = offsetof(struct sockaddr_un, sun_path) + strlen(un.sun_path); unlink(un.sun_path); /* in case it already exists */ if (bind(fd, (struct sockaddr *)&un, len) < 0) { rval = -2; goto errout; } /* fill socket address structure with server‘s address */ memset(&un, 0, sizeof(un)); un.sun_family = AF_UNIX; strcpy(un.sun_path, name); len = offsetof(struct sockaddr_un, sun_path) + strlen(name); if (connect(fd, (struct sockaddr *)&un, len) < 0) { rval = -4; goto errout; } return(fd); errout: err = errno; close(fd); errno = err; return(rval); } int main(void) { int fd, n; char buf[1024]; fd = cli_conn("foo.socket"); if (fd < 0) { switch (fd) { case -4:perror("connect"); break; case -3:perror("listen"); break; case -2:perror("bind"); break; case -1:perror("socket"); break; } exit(-1); } while (fgets(buf, sizeof(buf), stdin) != NULL) { write(fd, buf, strlen(buf)); n = read(fd, buf, sizeof(buf)); write(STDOUT_FILENO, buf, n); } close(fd); return 0; }
标签：ber foo cas inf 使用 exist link 地址 window
原文地址：https://www.cnblogs.com/xiangtingshen/p/10923350.html
