名字與地址轉換getservbyname 與 getservbyport函數

服務也通常靠名字來標志，getservbyname函數用于根據給定名字查找相應服務。

#include
struct????servent *getservbyname( const char *servname, const char *protoname );
成功：返回servent類型非空指針；
失敗：空指針；
本函數返回非空指針

struct????servent
{
??????char??????*s_name;??????????//????服務的正是名字
??????char??????**s_aliases;??????//????別名列表
??????int???????s_port;???????????//????服務端口號
??????char??????*s_proto;?????????//????使用的協議
};

服務名參數servname必須指定。如果同時指定了協議（即protoname參數為非空指針），那么指定的服務必須有匹配的協議。有些因特網服務既用于TCP也用于UDP提供（如DNS）。如果protoname沒有指定而servname指定服務支持多個協議，那么返回那個端口號取決于實現。一般來說，支持多個協議的服務旺旺使用相同的TCP端口號和UDP端口號。

servent結構中關心的主要是端口號。
注意：該端口號是以網絡字節的順序返回的，因此把它存放到套接口地質結構時絕對不能調用htons。

函數getservbyport用于根據給定端口號和可選協議查找相應的服務。
#include
struct????servent *getservbyport( int port, const char *protoname );
成功：返回servent類型非空指針；
失敗：空指針；
注意： port的值必須為網絡字節序，如：
ptr = getservbyport( htons(53), "udp");?????// DNS using UDP

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示例代碼：

int main(int argc, char** argv)
{
????int sockFd,n;
????char recvLine[MAXLINE + 1], addrStr[128],str[INET_ADDRSTRLEN];;
????char **charpptr;
????struct sockaddr_in servAddr;
????struct in_addr **pptr;
????struct in_addr *inetAddrP[2];
????struct in_addr inetAddr;
????struct hostent *hptr;
????struct servent *sptr;

????if(argc != 3)
????{
????????ReportError("Usage : GetService ");
????????exit(1);
????}
????if((hptr = gethostbyname(argv[1])) == NULL)
????{
????????if(inet_aton(argv[1], &inetAddr) == 0)
????????{
????????????ReportError("hostName error for %s : %s",argv[1],hstrerror(h_errno));
????????????exit(1);
????????}
????????else
????????{
????????????inetAddrP[0] = &inetAddr;
????????????inetAddrP[1] = NULL;
????????????pptr = inetAddrP;
????????}
????}
????else?//先打印host信息
????{
????????printf("Official hostname : %s\n",hptr->h_name);
????????for(charpptr=hptr->h_aliases; *charpptr!=NULL; ++charpptr)
????????????printf("\tAlias : %s\n",*charpptr);
????????switch(hptr->h_addrtype)
????????{
????????????case AF_INET:
????????????????for(charpptr = hptr->h_addr_list; *charpptr!=NULL; ++charpptr)
????????????????????printf("\tAddress : %s\n",
???????????????????????????inet_ntop(hptr->h_addrtype, *charpptr, str, sizeof(str)));
????????????????break;
????????}

????????pptr = (struct in_addr**)hptr->h_addr_list;
????}

????if( (sptr = getservbyname(argv[2], "tcp")) == NULL)
????{
????????ReportError("getservbyname error for %s",argv[2]);
????????exit(1);
????}
????printf("Official service name : %s\n",sptr->s_name);//打印service信息
????for(charpptr=sptr->s_aliases; *charpptr!=NULL; ++charpptr)
????????printf("\tAlias : %s\n",*charpptr);
????printf("\tPort number : %d\n",sptr->s_port);
????printf("\tprotocol : %s\n",sptr->s_proto);

????for(; *pptr != NULL; ++pptr)
????{
????????if((sockFd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
????????{
????????????ReportError("socket error");
????????????exit(1);
????????}
????????bzero(&servAddr, sizeof(servAddr));
????????servAddr.sin_family = AF_INET;
????????servAddr.sin_port = sptr->s_port;//根據獲取的服務信息設置端口號
????????memcpy(&servAddr.sin_addr, *pptr, sizeof(struct in_addr));//根據hostname信息設置IP
????????inet_ntop(AF_INET, (struct sockaddr*)&servAddr, addrStr,sizeof(servAddr));
????????printf("trying %s : %d\n", addrStr, servAddr.sin_port);

????????if(connect(sockFd, (struct sockaddr*)&servAddr, sizeof(servAddr)) == 0) //連接成功
????????????break;
????????ReportError("connect error");
????????close(sockFd);
????}
????if(*pptr == NULL)
????{
????????ReportError("unable to connet");
????????exit(1);
????}
????while( (n=read(sockFd, recvLine, MAXLINE)) > 0)
????{
????????recvLine[n] = 0;
????????fputs(recvLine, stdout);
????}
????return 0;
}

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連接被拒絕，不知道什么原因，難道是相應的服務沒開啟？

用service --status-all命令可以查看那當前運行的服務及其狀態

[root@localhost bin]# service --status-all
abrtd (pid??1979) 正在運行...
abrt-dump-oops (pid 1987) 正在運行...
acpid (pid??1801) 正在運行...
atd (pid??2006) 正在運行...
auditd (pid??1679) 正在運行...
avahi-daemon (pid??1775) 正在運行...
用法：/etc/init.d/bluetooth {start|stop}
Stopped
cgred 已停
cpuspeed 已停
crond (pid??1995) 正在運行...
dnsmasq 已停
用法：/etc/init.d/firstboot {start|stop}
hald (pid??1810) 正在運行...
httpd 已停
表格：filter
Chain INPUT (policy ACCEPT)
num??target?????prot opt source???????????????destination????????
1????ACCEPT?????all??????::/0?????????????????::/0????????????????state RELATED,ESTABLISHED
2????ACCEPT?????icmpv6????::/0?????????????????::/0???????????????
3????ACCEPT?????all??????::/0?????????????????::/0???????????????
4????ACCEPT?????tcp??????::/0?????????????????::/0????????????????state NEW tcp dpt:22
5????REJECT?????all??????::/0?????????????????::/0????????????????reject-with icmp6-adm-prohibited

Chain FORWARD (policy ACCEPT)
num??target?????prot opt source???????????????destination????????
1????REJECT?????all??????::/0?????????????????::/0????????????????reject-with icmp6-adm-prohibited

Chain OUTPUT (policy ACCEPT)
num??target?????prot opt source???????????????destination????????

表格：filter
Chain INPUT (policy ACCEPT)
num??target?????prot opt source???????????????destination????????
1????ACCEPT?????all??--??0.0.0.0/0????????????0.0.0.0/0???????????state RELATED,ESTABLISHED
2????ACCEPT?????icmp --??0.0.0.0/0????????????0.0.0.0/0??????????
3????ACCEPT?????all??--??0.0.0.0/0????????????0.0.0.0/0??????????
4????ACCEPT?????tcp??--??0.0.0.0/0????????????0.0.0.0/0???????????state NEW tcp dpt:22
5????REJECT?????all??--??0.0.0.0/0????????????0.0.0.0/0???????????reject-with icmp-host-prohibited

Chain FORWARD (policy ACCEPT)
num??target?????prot opt source???????????????destination????????
1????REJECT?????all??--??0.0.0.0/0????????????0.0.0.0/0???????????reject-with icmp-host-prohibited

Chain OUTPUT (policy ACCEPT)
num??target?????prot opt source???????????????destination????????

irqbalance 已停
Kdump is not operational
mdmonitor (pid??1733) 正在運行...
messagebus (pid??1752) 正在運行...
模塊 netconsole 未被加載
配置設備：
lo eth0
當前的活躍設備：
lo eth0
NetworkManager (pid??1763) 正在運行...
ntpd 已停
master (pid??1955) 正在運行...
進程記帳被禁用。
quota_nld 已停
rdisc 已停
restorecond (pid 2781) 正在運行...
rngd 已停
rsyslogd (pid??1695) 正在運行...
sandbox is stopped
saslauthd 已停
smartd 已停
openssh-daemon (pid??1879) 正在運行...
wpa_supplicant (pid??1812) 正在運行...

轉載于:https://www.cnblogs.com/rexienk/p/4856079.html

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