diff options
Diffstat (limited to 'c/nslookup.c')
| -rw-r--r-- | c/nslookup.c | 83 |
1 files changed, 9 insertions, 74 deletions
diff --git a/c/nslookup.c b/c/nslookup.c index 020a1c1..6a531b8 100644 --- a/c/nslookup.c +++ b/c/nslookup.c @@ -1,88 +1,23 @@ -#include "sock.h" +#include "resolve.h" /* nslookup HOST - resolve a hostname to an IPv4 address via DNS over UDP. - The kernel owns UDP; this program just builds the DNS query and parses the - answer. Queries 1.1.1.1:53 (reachable through the bridge NAT). */ + All the DNS logic lives in resolve.h (shared with wget). */ -/* buf is first and large so 'name' lands past the arg string at 0xA000 */ -static unsigned char buf[200]; -static unsigned char name[64]; -static unsigned char dnssrv[4]; +static unsigned char namebuf[64]; /* first so it lands past the arg at 0xA000 */ static unsigned char ip[4]; -/* build a DNS A-record query for 'host' into buf; return total length */ -static unsigned char build_query(unsigned char *host) { - unsigned char i = 0, p = 12, lblpos, len; - buf[0] = 0x12; buf[1] = 0x34; /* id */ - buf[2] = 0x01; buf[3] = 0x00; /* flags: recursion desired */ - buf[4] = 0; buf[5] = 1; /* qdcount = 1 */ - buf[6] = 0; buf[7] = 0; buf[8] = 0; buf[9] = 0; buf[10] = 0; buf[11] = 0; - while (host[i]) { - lblpos = p++; len = 0; - while (host[i] && host[i] != '.') { buf[p++] = host[i]; i++; len++; } - buf[lblpos] = len; - if (host[i] == '.') i++; - } - buf[p++] = 0; /* root label */ - buf[p++] = 0; buf[p++] = 1; /* QTYPE = A */ - buf[p++] = 0; buf[p++] = 1; /* QCLASS = IN */ - return p; -} - -/* advance past a DNS name at offset p (handles 0xC0 compression pointers) */ -static unsigned int skip_name(unsigned int p) { - for (;;) { - if (buf[p] == 0) return p + 1; - if ((buf[p] & 0xC0) == 0xC0) return p + 2; - p += buf[p] + 1; - } -} - -/* find the first A record in the response; fill ip[]; return 1 on success */ -static unsigned char parse_answer(void) { - unsigned int p, a, an, type, rdlen; - an = ((unsigned int)buf[6] << 8) | buf[7]; /* ancount */ - if (an == 0) return 0; - p = skip_name(12) + 4; /* skip question (QNAME+QT+QC) */ - for (a = 0; a < an; a++) { - p = skip_name(p); - type = ((unsigned int)buf[p] << 8) | buf[p + 1]; - p += 8; /* TYPE(2)+CLASS(2)+TTL(4) */ - rdlen = ((unsigned int)buf[p] << 8) | buf[p + 1]; - p += 2; - if (type == 1 && rdlen == 4) { - ip[0] = buf[p]; ip[1] = buf[p + 1]; ip[2] = buf[p + 2]; ip[3] = buf[p + 3]; - return 1; - } - p += rdlen; - } - return 0; -} - void main(void) { char *host; - unsigned char s, i, qlen, rlen; + unsigned char i; host = getargs(); if (!host || !*host) { puts("usage: nslookup HOST"); nl(); sexit(1); } - for (i = 0; host[i] && i < 63; i++) name[i] = host[i]; /* arg -> safe buf */ - name[i] = 0; - - dnssrv[0] = 1; dnssrv[1] = 1; dnssrv[2] = 1; dnssrv[3] = 1; /* 1.1.1.1 */ - s = net_socket(SOCK_UDP); - if (s == 0xFF) { puts("nslookup: no socket"); nl(); sexit(1); } - net_bind(s, 40000); - net_connect(s, dnssrv, 53); - - qlen = build_query(name); - net_send(s, buf, qlen); - rlen = net_recv(s, buf, sizeof(buf)); - if (rlen == 0xFF) { puts("nslookup: timeout"); nl(); net_close(s); sexit(1); } + for (i = 0; host[i] && i < 63; i++) namebuf[i] = (unsigned char)host[i]; + namebuf[i] = 0; - if (parse_answer()) { - puts((char *)name); puts(" -> "); + if (resolve((char *)namebuf, ip)) { + puts((char *)namebuf); puts(" -> "); for (i = 0; i < 4; i++) { putu(ip[i]); if (i < 3) putc('.'); } nl(); } else { - puts("nslookup: no A record"); nl(); + puts("nslookup: cannot resolve "); puts((char *)namebuf); nl(); } - net_close(s); } |