DoH proxy for OpenWRT and uhttpd-mod-ucode

doh.uc

#!/usr/bin/env ucode
import { fdopen } from "fs";
import { create, AF_INET6, SOCK_DGRAM, SOL_SOCKET, SO_RCVTIMEO } from "socket";

const MAXLEN = 4096;
const TIMEOUT = 10000;

function b64url_decode(s) {
  if (!s) return null;
  s = replace(s, "-", "+");
  s = replace(s, "_", "/");
  const pad = length(s) % 4;
  if (pad == 2) s += "==";
  else if (pad == 3) s += "=";
  else if (pad == 1) return null;
  return b64dec(s);
}

function read_body(len) {
  return len ? fdopen(0, "r").read(len) : "";
}

const method = getenv("REQUEST_METHOD") ?? "";
const qs = getenv("QUERY_STRING") ?? "";
const accept = lc(getenv("HTTP_ACCEPT") ?? "");
const clen = int(getenv("CONTENT_LENGTH") ?? 0);

let wire_query = null;

if (method == "GET") {
  let b64 = null;
  let parts = split(qs, "&");
  for (let i = 0; i < length(parts); i++)
    if (substr(parts[i], 0, 4) == "dns=") {
      b64 = substr(parts[i], 4);
      break;
    }
  wire_query = b64url_decode(b64);
} else if (method == "POST") {
  wire_query = read_body(clen);
} else {
  print("Status: 405 Method Not Allowed\r\n\r\n");
  exit(0);
}

if (!wire_query || length(wire_query) == 0 || length(wire_query) > MAXLEN) {
  print("Status: 400 Bad Request\r\n\r\n");
  exit(0);
}

const sock = create(AF_INET6, SOCK_DGRAM);
sock.setopt(SOL_SOCKET, SO_RCVTIMEO, {
  tv_sec: TIMEOUT / 1000,
  tv_usec: (TIMEOUT % 1000) * 1000,
});
sock.send(wire_query, 0, { address: "::1", port: 53 });
const reply = sock.recv(MAXLEN);
sock.close();

if (!reply || length(reply) == 0) {
  print("Status: 504 Gateway Timeout\r\n\r\n");
  exit(0);
}

print("Content-Type: application/dns-message\r\n");
print("Cache-Control: no-store\r\n");
print("Content-Length: ", length(reply), "\r\n\r\n");
print(reply);