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227 lines
4.5 KiB
Plaintext
Content-Type: text/x-zim-wiki
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Wiki-Format: zim 0.4
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Creation-Date: 2011-04-21T16:55:47+08:00
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====== getaddrinfo ======
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Created Thursday 21 April 2011
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http://blog168.chinaunix.net/space.php?uid=20196318&do=blog&id=172427
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getaddrinfo使用详解 (2011-03-15 15:25)
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标签: getaddrinfo 套接字 主机地址转换 服务端口转换 分类： Socket网络编程
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getaddrinfo是在gethostbyname系列函数不支持Ipv6的情况下逐渐催生的，其能够处理名字到地址以及服务到端口这两种转换，返回一个sockaddr结构的链表，这些sockaddr地址结构随后可有套接口函数（socket、bind、connect、listen等）直接调用，将协议相关性隐藏在该函数内部。应该尽量选择使用getaddrinfo函数代替之前的getxx函数族，就像应该使用inet_ntop(inet_pton)代替inet_aton, inet_addr等函数一样。
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#include <netdb.h>
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int getaddrinfo(const char* hostname, const char* service,
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const struct addinfo* hints, struct addrinfo** result);
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其中hostname可以是主机名后者地址串（Ipv4点分十进制数串或者Ipv6十六进制数串）；service参数是一个服务名或者十进制端口号数串。与getaddrinfo相关的系统配置文件包括/etc/hosts、/etc/services，用于处理主机名与地址串、服务名与端口号之间的转换。
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/etc/hosts存储地址与主机名的对应关系，如下例：
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127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
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10.0.1.73 fedora11
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/etc/services 则存储服务与端口号的对应关系，如下例：
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tcpmux 1/tcp # TCP port service multiplexer
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tcpmux 1/udp # TCP port service multiplexer
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rje 5/tcp # Remote Job Entry
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rje 5/udp # Remote Job Entry
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echo 7/tcp #TCP echo
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echo 7/udp #UDP echo
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如果你的应用程序需要使用主机名代替IP地址，或服务名代替端口号，你需要先把对应关系增加到对应的配置文件中，否则getaddrinfo会解析出错。
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有了getaddrinfo就可以很方便的构建服务器及客户端的应用程序，不用考虑数据尾端，地址转换等。tcp_listen根据host及service的信息获取sockaddr信息，创建套接字、绑定地址并监听。同样tcp_connect通过getaddrinfo返回的信息，连接服务器。创建udp的服务器与客户端与此类似。
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tcp_listen(const char* host, const char* serv)
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{
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int listenfd, n;
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const int on = 1;
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struct addrinfo hints, *res, *ressave;
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bzero(&hints, sizeof(struct addrinfo));
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hints.ai_flags = AI_PASSIVE;
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hints.ai_family = AF_INET;
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hints.ai_socktype = SOCK_STREAM;
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if((n = getaddrinfo(host, serv, &hints, &res)) != 0) {
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printf("tcp_listen error for %s, %s: %s\n",
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host, serv, gai_strerror(n));
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return -1;
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}
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ressave = res;
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do {
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listenfd = socket(res->ai_family, res->ai_socktype,
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res->ai_protocol);
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if(listenfd < 0) {
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continue;
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}
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setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));
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if(bind(listenfd, res->ai_addr, res->ai_addrlen) == 0) {
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break;
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}
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close(listenfd);
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}while((res = res->ai_next) != NULL);
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if(res == NULL) {
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printf("tcp_listen error for %s, %s: %s\n",
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host, serv, gai_strerror(n));
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return -1;
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}
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listen(listenfd, BACK_LOG);
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freeaddrinfo(ressave);
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return(listenfd);
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}
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int tcp_connect(const char* host, const char* serv)
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{
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int sockfd, n;
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struct addrinfo hints, *res, *ressave;
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bzero(&hints, sizeof(struct addrinfo));
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hints.ai_family = AF_INET;
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hints.ai_socktype = SOCK_STREAM;
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if((n = getaddrinfo(host, serv, &hints, &res)) != 0) {
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printf("tcp_connect error for %s, %s: %s\n",
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host, serv, gai_strerror(n));
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return -1;
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}
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ressave = res;
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do {
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sockfd = socket(res->ai_family, res->ai_socktype,
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res->ai_protocol);
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if(sockfd < 0) {
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continue;
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}
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if(connect(sockfd, res->ai_addr, res->ai_addrlen) == 0) {
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break;
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}
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close(sockfd);
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}while((res = res->ai_next) != NULL);
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if(res == NULL) {
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printf("tcp_connect error for %s, %s: %s\n",
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host, serv, gai_strerror(n));
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return -1;
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}
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freeaddrinfo(ressave);
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return(sockfd);
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}
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