lookupDnsSearch

fn lookupDnsSearch(
    t: *Threaded,
    host_name: HostName,
    resolved: *Io.Queue(HostName.LookupResult),
    options: HostName.LookupOptions,
) (HostName.LookupError || Io.QueueClosedError)!void {
    const t_io = io(t);
    const rc = HostName.ResolvConf.init(t_io) catch return error.ResolvConfParseFailed;

    // Count dots, suppress search when >=ndots or name ends in
    // a dot, which is an explicit request for global scope.
    const dots = std.mem.countScalar(u8, host_name.bytes, '.');
    const search_len = if (dots >= rc.ndots or std.mem.endsWith(u8, host_name.bytes, ".")) 0 else rc.search_len;
    const search = rc.search_buffer[0..search_len];

    var canon_name = host_name.bytes;

    // Strip final dot for canon, fail if multiple trailing dots.
    if (std.mem.endsWith(u8, canon_name, ".")) canon_name.len -= 1;
    if (std.mem.endsWith(u8, canon_name, ".")) return error.UnknownHostName;

    // Name with search domain appended is set up in `canon_name`. This
    // both provides the desired default canonical name (if the requested
    // name is not a CNAME record) and serves as a buffer for passing the
    // full requested name to `lookupDns`.
    var local_buf: [HostName.max_len]u8 = undefined;
    const canon_buf = options.canonical_name_buffer orelse &local_buf;
    @memcpy(canon_buf[0..canon_name.len], canon_name);
    canon_buf[canon_name.len] = '.';
    var it = std.mem.tokenizeAny(u8, search, " \t");
    while (it.next()) |token| {
        @memcpy(canon_buf[canon_name.len + 1 ..][0..token.len], token);
        const lookup_canon_name = canon_buf[0 .. canon_name.len + 1 + token.len];
        if (t.lookupDns(lookup_canon_name, &rc, resolved, options)) |result| {
            return result;
        } else |err| switch (err) {
            error.UnknownHostName, error.NoAddressReturned => continue,
            else => |e| return e,
        }
    }

    const lookup_canon_name = canon_buf[0..canon_name.len];
    return t.lookupDns(lookup_canon_name, &rc, resolved, options);
}