Due to security reasons, web browsers cannot actually resolve DNS names to raw IP addresses. But because a few BSD sockets API functions and structures require IP addresses and cannot take in hostnames in strings, the internal BSD sockets support generates IP addresses on the fly, and internally maintains an IP->original domain name mapping table to work around the restriction that the API cannot express domain name strings.
Because of this mapping, the expectation is that every time you run, the gethostbyname calls always generate a running sequence of fixed IP addresses. See https://github.com/kripken/emscripten/blob/master/src/library.js#L3341 2017-02-17 7:57 GMT-08:00 Wilbert Jackson <wilbert.jack...@gmail.com>: > I have very simple C program that gets the ip addresses for a host name as > follows: > > #include<stdio.h> //printf > #include<string.h> //memset > #include<stdlib.h> //for exit(0); > #include<sys/socket.h> > #include<errno.h> //For errno - the error number > #include<netdb.h> //hostent > #include<arpa/inet.h> > > int hostname_to_ip(char * , char *); > > #include <sys/socket.h> > #include <netdb.h> > #include <string.h> > #include <netinet/in.h> > > int main(int argc , char *argv[]) > { > printf("In main\n"); > char *hostname = "www.google.com"; > char ip[100]; > > hostname_to_ip(hostname , ip); > printf("%s x resolved to %s" , hostname , ip); > } > /* > Get ip from domain name > */ > int hostname_to_ip(char * hostname , char* ip) > { > printf("hostname %s\n", hostname); > struct hostent *he; > struct in_addr **addr_list; > int i; > he = gethostbyname( hostname ); > printf("name %s\n", he->h_name); > printf("addrtype %d\n", he->h_addrtype); > > if ( (he = gethostbyname( hostname) ) == NULL) > { > printf("error"); > herror("gethostbyname"); > return 1; > } > addr_list = (struct in_addr **) he->h_addr_list; > for(i = 0; addr_list[i] != NULL; i++) > { > printf("address %s\n", inet_ntoa(*addr_list[i])); > } > return 1; > } > > On Ubuntu when I compile it with gcc as: gcc socket.c > -L/usr/lib/x86_64-linux-gnu -o socket -lpthread and run it produces > correct ip address. Output: > ./socket > In main > hostname www.google.com > name www.google.com > addrtype 2 > address 63.117.14.88 > address 63.117.14.86 > address 63.117.14.84 > address 63.117.14.90 > address 63.117.14.87 > address 63.117.14.89 > address 63.117.14.91 > address 63.117.14.85 > > When I compile the same program using the emsdk and emcc as: > emcc socket.c -g4 -v -s "BINARYEN_METHOD='interpret-binary'" > -L/usr/lib/x86_64-linux-gnu -o socket.html and run it with nodejs socket.js > or in a browser with emrun and socket.html it produces the output: > > In main > hostname www.google.com > name www.google.com > addrtype 2 > address 172.29.1.0 > > Clearly the ip address in bogus. In debugging socket.js I found the > __inet_pton4_raw (shown below) receives the correct host string ( > www.google.com) put generates address 172.29.1.0. This function generates > the same ip address not matter what host name is supplied. I have tried the > emsdk /test socket programs as well with the same results. They work when > compiled with gcc but not with emcc. Any help will be much appreciated. > > function __inet_pton4_raw(str) { > var b = str.split('.'); > for (var i = 0; i < 4; i++) { > var tmp = Number(b[i]); > if (isNaN(tmp)) return null; > b[i] = tmp; > } > return (b[0] | (b[1] << 8) | (b[2] << 16) | (b[3] << 24)) >>> 0; > } > > > > > > -- > You received this message because you are subscribed to the Google Groups > "emscripten-discuss" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to emscripten-discuss+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "emscripten-discuss" group. To unsubscribe from this group and stop receiving emails from it, send an email to emscripten-discuss+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
