Android DNS 代码分析

时间：2014-12-02 22:47:18

关键字： Android DNS 代码 ADDR

[导读] Android DNS 代码都在bionic/libc/netbsd中(虽然netbsd 是个废弃的项目，但dns功能部分代码被 Android用上了)netbsd 代码晦涩难懂，只有一边写程序，一边打log验证照抄了一

Android DNS 代码都在bionic/libc/netbsd中

(虽然netbsd 是个废弃的项目，但dns功能部分代码被 Android用上了)

netbsd 代码晦涩难懂，只有一边写程序，一边打log验证

照抄了一个简单程序，在android 下面用 mmm 编译可以得到 py_getaddr 可执行文件，用adb 登陆到 devices 再到 system/bin 下去执行

payne@payne-desktop:~/njb/getaddr$ cat py_getaddr.c 
#include <stdio.h>
#include <stdlib.h>
#include <sys socket.h="">
#include <netinet in.h="">
#include <netdb.h>
#include <string.h>
int main(int argc, char **argv)
{
if (argc != 2) {
fprintf(stderr, "Usage: %s hostnamen",
argv[1]);
exit(1);   
}
 
struct addrinfo *answer, hint, *curr;
char ipstr[16];   
bzero(&hint, sizeof(hint));
hint.ai_family = AF_INET;
hint.ai_socktype = SOCK_STREAM;
 
int ret = getaddrinfo(argv[1], NULL, &hint, &answer);
if (ret != 0) {
fprintf(stderr,"getaddrinfo: &sn",
gai_strerror(ret));
exit(1);
}
 
for (curr = answer; curr != NULL; curr = curr->ai_next) {
inet_ntop(AF_INET,
&(((struct sockaddr_in  *)(curr->ai_addr))->sin_addr),
ipstr, 16);
printf("%sn", ipstr);
}
 
freeaddrinfo(answer);
exit(0);
}</string.h></netdb.h></netinet></sys></stdlib.h></stdio.h>

cat Android.mk 
LOCAL_PATH:= $(call my-dir)
 
include $(CLEAR_VARS)
 
LOCAL_SRC_FILES:= py_getaddr.c
LOCAL_MODULE := py_getaddr
LOCAL_STATIC_LIBRARIES := libcutils libc
include  $(BUILD_EXECUTABLE)

到运行 py_getadd sohu.com 的时候，调用过程如下

_files_getaddrinfo 是读取/system/etc/hosts 检索<喎�"http://www.2cto.com/kf/ware/vc/" target="_blank" class="keylink">vcD4KPHA+X2Ruc19nZXRhZGRyaW5mbyDKx7fDzspkbnMgc2VydmVyPC9wPgo8cD7U2rfDzsq5udTsIGRucyC3w87KtcTKsbryo6zI57rO1dK1vSBkbnMgc2VydmVyLCDUrcC01NogX19yZXNfZ2V0X3N0YXRlICC199PDt7W72CBfX3Jlc19zdGF0ZSAgKNXiuPa4tNTTtcS94bm5tqjS5dTaICBiaW9uaWMvbGliYy9wcml2YXRlL3Jlc29sdl9wcml2YXRlLmgjX19yZXNfc3RhdGUgKTwvcD4KPHA+1Nq199PDuf2zzNbQIF9fcmVzX3Zpbml0IMq508PBy8+1zbPJ6NbDtcQgOC44LjguOCBuYW1lc2VydmVyIKOoamVhbGx5YmVhbiC0+sLr1NpiaW9uaWMvbGliYy9uZXRic2QvcmVzb2x2L3Jlc19pbml0LmMjMzM5o6k8L3A+CjxwPjxicj4KPC9wPgo8cD7WrrrzcmVzX3F1ZXJ5TiDTwyByZXNfbm1rcXVlcnkgubnU7GRucyCy6dGvo6yyotPDIHJlc19uc2VuZCC3osvNsunRr6OssqK1w7W9t7W72L3hufuhozwvcD4KPHA+PGltZyBzcmM9"http://www.2cto.com/uploadfile/Collfiles/20141126/20141126084453260.png" alt="">

运行程序和 log 的打印结果如下：

py_getaddr sohu.com

======================= _files_getaddrinfo

======================= _dns_getaddrinfo

=========== getaddrinfo cp 8.8.8.8, subf 53

================ res_searchN sohu.com

================ res_querydomainN name sohu.com, domain (null)

================ res_queryN sohu.com

;; res_nmkquery(QUERY, sohu.com, IN, A)

================getanswer sohu.com

220.181.90.240

123.125.116.19