socket API原本是為網(wǎng)絡(luò)通訊設(shè)計(jì)的，但后來在socket的框架上發(fā)展出一種IPC機(jī)
制，就是UNIX Domain Socket。雖然網(wǎng)絡(luò)socket也可用于同一臺(tái)主機(jī)的進(jìn)程間通訊（通過
loopback地址127.0.0.1），但是UNIX Domain Socket用于IPC更有效率：不需要經(jīng)過網(wǎng)絡(luò)協(xié)
議棧，不需要打包拆包、計(jì)算校驗(yàn)和、維護(hù)序號(hào)和應(yīng)答等，只是將應(yīng)用層數(shù)據(jù)從一個(gè)進(jìn)程拷
貝到另一個(gè)進(jìn)程。這是因?yàn)?#xff0c;IPC機(jī)制本質(zhì)上是可靠的通訊，而網(wǎng)絡(luò)協(xié)議是為不可靠的通訊
設(shè)計(jì)的。UNIX Domain Socket也提供面向流和面向數(shù)據(jù)包兩種API接口，類似于TCP和UDP，
但是面向消息的UNIX Domain Socket也是可靠的，消息既不會(huì)丟失也不會(huì)順序錯(cuò)亂。
UNIX Domain Socket是全雙工的，API接口語義豐富，相比其它IPC機(jī)制有明顯的優(yōu)越
性，目前已成為使用最廣泛的IPC機(jī)制，比如X Window服務(wù)器和GUI程序之間就是通過UNIX
Domain Socket通訊的。
使用UNIX Domain Socket的過程和網(wǎng)絡(luò)socket十分相似，也要先調(diào)用socket()創(chuàng)
建一個(gè)socket文件描述符，address family指定為AF_UNIX，type可以選擇SOCK_DGRAM或

SOCK_STREAM，protocol參數(shù)仍然指定為0即可。
UNIX Domain Socket與網(wǎng)絡(luò)socket編程最明顯的不同在于地址格式不同，用結(jié)構(gòu)體
sockaddr_un表示，網(wǎng)絡(luò)編程的socket地址是IP地址加端口號(hào)，而UNIX Domain Socket的地
址是一個(gè)socket類型的文件在文件系統(tǒng)中的路徑，這個(gè)socket文件由bind()調(diào)用創(chuàng)建，如果
調(diào)用bind()時(shí)該文件已存在，則bind()錯(cuò)誤返回。
以下程序?qū)NIX Domain socket綁定到一個(gè)地址。

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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 否則bind的時(shí)候會(huì)出錯(cuò)*/ /* 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 會(huì)創(chuàng)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; }

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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; }

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轉(zhuǎn)載于:https://www.cnblogs.com/xiangtingshen/p/10923350.html

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