[Original]socket communication for domain name resolution

//extern unsigned char gsntpserverip[20];intGetntptime (unsignedChar*ntpserverip,unsignedintntpport,unsignedint*data) {      intSockfd=0; Charntpservername[ -];                Stnp_header H_NTP; H_NTP. Livnmode=0x1b;//LI (2bit) VN (3bit version) mode (3bit client mode)H_NTP. Stratum =stratum; H_NTP. Poll=POLL; H_NTP. Precision=PREC; memset (Ntpservername,0,sizeof(Ntpservername)); sprintf (Ntpservername,"%s", Ntpserverip); Nf_log (Debug_k,"@[email protected],sync time from%S,H_NTP. stratum=%d\n", NTPSERVERNAME,H_NTP.     Stratum); #if0//how the domain name cannot be resolved    structsockaddr_in server; Server.sin_family=af_inet; Server.sin_addr.s_addr= Gethostipbyname ((Const Char*) ntpservername); Server.sin_port=htons (Ntpport); if(-1== (int) {Nf_log (server.sin_addr.s_addr) {error_l,"[%s,%d]s_addr error...\n", __function__,__line__); return-1; } SOCKFD= Socket (Af_inet, SOCK_DGRAM,0); if(sockfd<0) {Nf_log (error_l,"[%s,%d]socket error...\n", __function__,__line__); return-1; }    #endif        #if1//how getaddrinfo can parse a domain name    intRC; Addrinfo hints,*res = null,*cur=NULL; memset (&hints,0,sizeof(hints)); Hints.ai_family=Af_unspec; Hints.ai_socktype=Sock_dgram; Hints.ai_protocol=ipproto_udp; Charport[Ten]; memset (Port,0,sizeof(port)); sprintf (Port,"%d", Ntpport); RC= Getaddrinfo ((Const Char*) Ntpservername, port, &hints, &res); if(RC! =0) {Nf_log (error_l,"[%s,%d]getaddrinfo error...rc=%s\n", __function__,__line__,gai_strerror (RC)); return-1; }    structSOCKADDR_IN *addr; Charm_ipaddr[ -]; memset (M_IPADDR,0,sizeof(M_IPADDR));  for(cur = res; cur! = NULL; cur = cur->Ai_next) {Addr= (structsockaddr_in *) cur->ai_addr; Inet_pton (Af_inet, m_ipaddr, (void*) addr); Inet_ntop (Af_inet, (void*) &addr, M_IPADDR, -);//Inverse Conversionprintf"@[email protected]:P arse ip:%s\n", M_IPADDR); } SOCKFD= Socket (res->ai_family, Res->ai_socktype, res->Ai_protocol); if(SOCKFD <0) {Nf_log (error_l,"[%s,%d]socket error...\n", __function__,__line__); return-1; }    #endif    //if (SendTo (SOCKFD, (void*) &h_ntp, sizeof (Stnp_header), 0, (struct sockaddr*) &server, sizeof (server)) <0 )      if(SendTo (SOCKFD, (void*) &AMP;H_NTP,sizeof(Stnp_header),0, RES-&GT;AI_ADDR, Res->ai_addrlen) <0) {Nf_log (error_l,"[%s,%d]sendto error...\n", __function__,__line__); return-1;      } fd_set R; Fd_zero (&R); Fd_set (SOCKFD,&R); structtimeval timeout; Timeout.tv_sec=Ten; Timeout.tv_usec=0; if(1!=Select(sockfd+1, &r, NULL, NULL, &timeout)) {Nf_log (error_l,"[%s,%d] Select error...\n", __function__,__line__); return-1; }        if(Recv (SOCKFD, (void*) data, -,0) <0)//48 follow-up to define macro{nf_log (error_l,"[%s,%d]recv error...\n", __function__,__line__); return-1;      } close (SOCKFD); return 0; }  

getaddrinfo function

Use of the structure of the body to understand
Addrinfo
Sockaddr_in

/* Internet address.   */

typedef __U16 IN_PORT_T;
typedef __U32 in_addr_t;

structin_addr {in_addr_t s_addr; };/*Structure describing an Internet socket address. */structsockaddr_in {__sockaddr_common (sin_);            in_port_t Sin_port; /*Port number. */    structIN_ADDR sin_addr;/*Internet address. */    /*Pad to size of ' struct sockaddr '. */unsignedCharsin_zero[sizeof(structSOCKADDR)-__sockaddr_common_size-sizeof(in_port_t)-sizeof(structin_addr)]; };

Print the address of the sockaddr_in format in dotted decimal mode:

struct sockaddr_in *addr;
Char m_ipaddr[16];
memset (m_ipaddr,0,sizeof (M_IPADDR));

for (cur = res; cur = NULL; cur = cur->= (struct sockaddr_in *) cur->Ai_addr;inet_pton (AF _inet, M_ipaddr, (void *) addr) inet_ntop (Af_inet, (void); // Reverse Convert printf ("@[email protected]:P arse ip:%s\n", m_ipaddr);}

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The differences between these structures need to be differentiated

Sockaddr_in is used for IPV4 network Internet ip/port, so its struct member sin_family must be filled in af_inet??

 struct   sockaddr_in server;      server.sin_family  = af_inet; Server.sin_addr.s_addr  = Gethostipbyname ((const       char  * = htons (Ntpport);  if  (-1  = = ( int  ) server.sin_addr.s_addr) {Nf_log (error_l,   "
     [%s,%d]s_addr error...\n   " ,__function__,__line__);  return -1       ; }

Addrinfo

Addrinfo hints, *res = null,*cur=NULL; memset (&hints,0,sizeof(hints)); Hints.ai_family=Af_unspec; Hints.ai_socktype=Sock_dgram; Hints.ai_protocol=ipproto_udp; Charport[Ten]; memset (Port,0,sizeof(port)); sprintf (Port,"%d", Ntpport); RC= Getaddrinfo ((Const Char*) Ntpservername, port, &hints, &res);

Information obtained from the Address field is stored in the Res

operation Res Gets the address and port information to link and send data: SOCKFD= Socket (res->ai_family, Res->ai_socktype, res->Ai_protocol); if(SOCKFD <0) {Nf_log (error_l,"[%s,%d]socket error...\n", __function__,__line__); return-1; }if(SendTo (SOCKFD, (void*) &AMP;H_NTP,sizeof(Ntp_header),0, RES-&GT;AI_ADDR, Res->ai_addrlen) <0) {Nf_log (error_l,"[%s,%d]sendto error...\n", __function__,__line__); return-1; } 

Getaddrinfo can get multiple IP addresses, here you can go to bind and try to see which one can be optimized:

8591729

Pending confirmation:
Gethostipbyname cannot resolve address domain??? The reason why this was not resolved was because no DNS server was added to the resolv.conf

[Original]socket communication for domain name resolution