1 files changed, 81 insertions, 0 deletions
diff --git a/c/resolve.h b/c/resolve.h
new file mode 100644
index 0000000..9aaccc1
--- /dev/null
+++ b/c/resolve.h
@@ -0,0 +1,81 @@
+#ifndef RESOLVE_H
+#define RESOLVE_H
+/* resolve.h - turn a dotted-quad OR a hostname into an IPv4 address. Hostname
+   lookups go out as a DNS A query over a UDP socket to 1.1.1.1:53; the kernel
+   owns UDP, this owns DNS. Header-only (one copy per program). */
+#include "sock.h"
+
+static unsigned char _dnsbuf[200];
+static unsigned char _dnssrv[4];
+
+/* parse "A.B.C.D" into out[4]; return 1 on success */
+static unsigned char parse_ip(char *s, unsigned char *out) {
+    unsigned char i, v;
+    for (i = 0; i < 4; i++) {
+        if (*s < '0' || *s > '9') return 0;
+        v = 0;
+        while (*s >= '0' && *s <= '9') { v = (unsigned char)(v * 10 + (*s - '0')); s++; }
+        out[i] = v;
+        if (i < 3) { if (*s != '.') return 0; s++; }
+    }
+    return 1;
+}
+
+static unsigned char _dns_query(char *host) {
+    unsigned char i = 0, p = 12, lblpos, len;
+    _dnsbuf[0] = 0x12; _dnsbuf[1] = 0x34; _dnsbuf[2] = 0x01; _dnsbuf[3] = 0x00;
+    _dnsbuf[4] = 0; _dnsbuf[5] = 1;
+    _dnsbuf[6] = 0; _dnsbuf[7] = 0; _dnsbuf[8] = 0; _dnsbuf[9] = 0; _dnsbuf[10] = 0; _dnsbuf[11] = 0;
+    while (host[i]) {
+        lblpos = p++; len = 0;
+        while (host[i] && host[i] != '.') { _dnsbuf[p++] = host[i]; i++; len++; }
+        _dnsbuf[lblpos] = len;
+        if (host[i] == '.') i++;
+    }
+    _dnsbuf[p++] = 0; _dnsbuf[p++] = 0; _dnsbuf[p++] = 1; _dnsbuf[p++] = 0; _dnsbuf[p++] = 1;
+    return p;
+}
+static unsigned int _dns_skip(unsigned int p) {
+    for (;;) {
+        if (_dnsbuf[p] == 0) return p + 1;
+        if ((_dnsbuf[p] & 0xC0) == 0xC0) return p + 2;
+        p += _dnsbuf[p] + 1;
+    }
+}
+static unsigned char _dns_answer(unsigned char *ip) {
+    unsigned int p, a, an, type, rdlen;
+    an = ((unsigned int)_dnsbuf[6] << 8) | _dnsbuf[7];
+    if (an == 0) return 0;
+    p = _dns_skip(12) + 4;
+    for (a = 0; a < an; a++) {
+        p = _dns_skip(p);
+        type = ((unsigned int)_dnsbuf[p] << 8) | _dnsbuf[p + 1];
+        p += 8;
+        rdlen = ((unsigned int)_dnsbuf[p] << 8) | _dnsbuf[p + 1];
+        p += 2;
+        if (type == 1 && rdlen == 4) {
+            ip[0] = _dnsbuf[p]; ip[1] = _dnsbuf[p + 1]; ip[2] = _dnsbuf[p + 2]; ip[3] = _dnsbuf[p + 3];
+            return 1;
+        }
+        p += rdlen;
+    }
+    return 0;
+}
+
+/* resolve a dotted-quad or hostname into ip[4]; return 1 on success */
+static unsigned char resolve(char *host, unsigned char *ip) {
+    unsigned char s, n;
+    if (parse_ip(host, ip)) return 1;                 /* already an address */
+    _dnssrv[0] = 1; _dnssrv[1] = 1; _dnssrv[2] = 1; _dnssrv[3] = 1;
+    s = net_socket(SOCK_UDP);
+    if (s == 0xFF) return 0;
+    net_bind(s, 40000);
+    net_connect(s, _dnssrv, 53);
+    n = _dns_query(host);
+    net_send(s, _dnsbuf, n);
+    n = net_recv(s, _dnsbuf, 200);
+    net_close(s);
+    if (n == 0xFF) return 0;
+    return _dns_answer(ip);
+}
+#endif