new
diff --git a/src/libndb/dnsquery.c b/src/libndb/dnsquery.c
new file mode 100644
index 0000000..4cf8735
--- /dev/null
+++ b/src/libndb/dnsquery.c
@@ -0,0 +1,156 @@
+#include <u.h>
+#include <libc.h>
+#include <bio.h>
+#include <ndb.h>
+#include <ndbhf.h>
+
+static void nstrcpy(char*, char*, int);
+static void mkptrname(char*, char*, int);
+static Ndbtuple *doquery(int, char *dn, char *type);
+
+/*
+ * search for a tuple that has the given 'attr=val' and also 'rattr=x'.
+ * copy 'x' into 'buf' and return the whole tuple.
+ *
+ * return 0 if not found.
+ */
+Ndbtuple*
+dnsquery(char *net, char *val, char *type)
+{
+ char rip[128];
+ char *p;
+ Ndbtuple *t;
+ int fd;
+
+ /* if the address is V4 or V6 null address, give up early vwhoi*/
+ if(strcmp(val, "::") == 0 || strcmp(val, "0.0.0.0") == 0)
+ return nil;
+
+ if(net == nil)
+ net = "/net";
+ snprint(rip, sizeof(rip), "%s/dns", net);
+ fd = open(rip, ORDWR);
+ if(fd < 0){
+ if(strcmp(net, "/net") == 0)
+ snprint(rip, sizeof(rip), "/srv/dns");
+ else {
+ snprint(rip, sizeof(rip), "/srv/dns%s", net);
+ p = strrchr(rip, '/');
+ *p = '_';
+ }
+ fd = open(rip, ORDWR);
+ if(fd < 0)
+ return nil;
+ if(mount(fd, -1, net, MBEFORE, "") < 0){
+ close(fd);
+ return nil;
+ }
+ /* fd is now closed */
+ snprint(rip, sizeof(rip), "%s/dns", net);
+ fd = open(rip, ORDWR);
+ if(fd < 0)
+ return nil;
+ }
+
+ /* zero out the error string */
+ werrstr("");
+
+ /* if this is a reverse lookup, first lookup the domain name */
+ if(strcmp(type, "ptr") == 0){
+ mkptrname(val, rip, sizeof rip);
+ t = doquery(fd, rip, "ptr");
+ } else
+ t = doquery(fd, val, type);
+
+ close(fd);
+ return t;
+}
+
+/*
+ * convert address into a reverse lookup address
+ */
+static void
+mkptrname(char *ip, char *rip, int rlen)
+{
+ char buf[128];
+ char *p, *np;
+ int len;
+
+ if(strstr(ip, "in-addr.arpa") || strstr(ip, "IN-ADDR.ARPA")){
+ nstrcpy(rip, ip, rlen);
+ return;
+ }
+
+ nstrcpy(buf, ip, sizeof buf);
+ for(p = buf; *p; p++)
+ ;
+ *p = '.';
+ np = rip;
+ len = 0;
+ while(p >= buf){
+ len++;
+ p--;
+ if(*p == '.'){
+ memmove(np, p+1, len);
+ np += len;
+ len = 0;
+ }
+ }
+ memmove(np, p+1, len);
+ np += len;
+ strcpy(np, "in-addr.arpa");
+}
+
+static void
+nstrcpy(char *to, char *from, int len)
+{
+ strncpy(to, from, len);
+ to[len-1] = 0;
+}
+
+static Ndbtuple*
+doquery(int fd, char *dn, char *type)
+{
+ char buf[1024];
+ int n;
+ Ndbtuple *t, *first, *last;
+
+ seek(fd, 0, 0);
+ snprint(buf, sizeof(buf), "!%s %s", dn, type);
+ if(write(fd, buf, strlen(buf)) < 0)
+ return nil;
+
+ seek(fd, 0, 0);
+
+ first = last = nil;
+
+ for(;;){
+ n = read(fd, buf, sizeof(buf)-2);
+ if(n <= 0)
+ break;
+ if(buf[n-1] != '\n')
+ buf[n++] = '\n'; /* ndbparsline needs a trailing new line */
+ buf[n] = 0;
+
+ /* check for the error condition */
+ if(buf[0] == '!'){
+ werrstr("%s", buf+1);
+ return nil;
+ }
+
+ t = _ndbparseline(buf);
+ if(t != nil){
+ if(first)
+ last->entry = t;
+ else
+ first = t;
+ last = t;
+
+ while(last->entry)
+ last = last->entry;
+ }
+ }
+
+ setmalloctag(first, getcallerpc(&fd));
+ return first;
+}
