diff options
| author | user <user@clank> | 2026-07-17 13:11:53 +0200 |
|---|---|---|
| committer | user <user@clank> | 2026-07-17 13:11:53 +0200 |
| commit | a565bcd942efeb617f5424ae5a881211a7bd0216 (patch) | |
| tree | 518915e70d097ed8f8fee99422bc7161f9c53fc1 /c/resolve.h | |
| parent | net: TCP sockets in the kernel - a Game Boy fetches HTTP over real TCP (diff) | |
| download | gbos-a565bcd942efeb617f5424ae5a881211a7bd0216.tar.gz gbos-a565bcd942efeb617f5424ae5a881211a7bd0216.tar.xz gbos-a565bcd942efeb617f5424ae5a881211a7bd0216.zip | |
net: wget-by-hostname + shared DNS resolver (a Game Boy fetches example.com)
resolve.h: shared helper that turns a dotted-quad or a hostname into an IPv4
address (DNS A query over a UDP socket to 1.1.1.1). nslookup now uses it and
slims down; wget uses it so you can name a host directly.
wget HOST|IP now: resolve -> TCP connect -> "GET / HTTP/1.0" with the real
Host header -> stream the body to the LCD/console until EOF. One command does
DNS + TCP + HTTP, all on the kernel socket layer.
Verified over tunbridge's NAT against the real internet:
/# wget example.com
connecting 172.66.147.243
HTTP/1.1 200 OK
Server: cloudflare
<!doctype html><html lang="en"><head><title>Example Domain</title>...
</body></html>
[eof]
The full HTML page arrives across many TCP segments and is reassembled and
printed - real DNS, real TCP, real HTTP, fetched by a Game Boy by name.
(tunbridge.py already sets up + tears down the NAT, so the demo is a one-liner:
sudo python3 tools/tunbridge.py "wget example.com")
Diffstat (limited to 'c/resolve.h')
| -rw-r--r-- | c/resolve.h | 81 |
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 |