lookupDns

fn lookupDns(
    t: *Threaded,
    lookup_canon_name: []const u8,
    rc: *const HostName.ResolvConf,
    resolved: *Io.Queue(HostName.LookupResult),
    options: HostName.LookupOptions,
) (HostName.LookupError || Io.QueueClosedError)!void

File

Code

fn lookupDns(
    t: *Threaded,
    lookup_canon_name: []const u8,
    rc: *const HostName.ResolvConf,
    resolved: *Io.Queue(HostName.LookupResult),
    options: HostName.LookupOptions,
) (HostName.LookupError || Io.QueueClosedError)!void {
    const t_io = io(t);
    const family_records: [2]struct { af: IpAddress.Family, rr: HostName.DnsRecord } = .{
        .{ .af = .ip6, .rr = .A },
        .{ .af = .ip4, .rr = .AAAA },
    };
    var query_buffers: [2][280]u8 = undefined;
    var answer_buffer: [2 * 512]u8 = undefined;
    var queries_buffer: [2][]const u8 = undefined;
    var answers_buffer: [2][]const u8 = undefined;
    var nq: usize = 0;
    var answer_buffer_i: usize = 0;

    for (family_records) |fr| {
        if (options.family != fr.af) {
            var entropy: [2]u8 = undefined;
            random(t, &entropy);
            const len = writeResolutionQuery(&query_buffers[nq], 0, lookup_canon_name, 1, fr.rr, entropy);
            queries_buffer[nq] = query_buffers[nq][0..len];
            nq += 1;
        }
    }

    var ip4_mapped_buffer: [HostName.ResolvConf.max_nameservers]IpAddress = undefined;
    const ip4_mapped = ip4_mapped_buffer[0..rc.nameservers_len];
    var any_ip6 = false;
    for (rc.nameservers(), ip4_mapped) |*ns, *m| {
        m.* = .{ .ip6 = .fromAny(ns.*) };
        any_ip6 = any_ip6 or ns.* == .ip6;
    }
    var socket = s: {
        if (any_ip6) ip6: {
            const ip6_addr: IpAddress = .{ .ip6 = .unspecified(0) };
            const socket = ip6_addr.bind(t_io, .{ .ip6_only = false, .mode = .dgram }) catch |err| switch (err) {
                error.AddressFamilyUnsupported => break :ip6,
                else => |e| return e,
            };
            break :s socket;
        }
        any_ip6 = false;
        const ip4_addr: IpAddress = .{ .ip4 = .unspecified(0) };
        const socket = try ip4_addr.bind(t_io, .{ .mode = .dgram });
        break :s socket;
    };
    defer socket.close(t_io);

    const mapped_nameservers = if (any_ip6) ip4_mapped else rc.nameservers();
    const queries = queries_buffer[0..nq];
    const answers = answers_buffer[0..queries.len];
    var answers_remaining = answers.len;
    for (answers) |*answer| answer.len = 0;

    // boot clock is chosen because time the computer is suspended should count
    // against time spent waiting for external messages to arrive.
    const clock: Io.Clock = .boot;
    var now_ts = clock.now(t_io);
    const final_ts = now_ts.addDuration(.fromSeconds(rc.timeout_seconds));
    const attempt_duration: Io.Duration = .{
        .nanoseconds = (std.time.ns_per_s / rc.attempts) * @as(i96, rc.timeout_seconds),
    };

    send: while (now_ts.nanoseconds < final_ts.nanoseconds) : (now_ts = clock.now(t_io)) {
        const max_messages = queries_buffer.len * HostName.ResolvConf.max_nameservers;
        {
            var message_buffer: [max_messages]net.OutgoingMessage = undefined;
            var message_i: usize = 0;
            for (queries, answers) |query, *answer| {
                if (answer.len != 0) continue;
                for (mapped_nameservers) |*ns| {
                    message_buffer[message_i] = .{
                        .address = ns,
                        .data_ptr = query.ptr,
                        .data_len = query.len,
                    };
                    message_i += 1;
                }
            }
            _ = netSendPosix(t, socket.handle, message_buffer[0..message_i], .{});
        }

        const timeout: Io.Timeout = .{ .deadline = .{
            .raw = now_ts.addDuration(attempt_duration),
            .clock = clock,
        } };

        while (true) {
            var message_buffer: [max_messages]net.IncomingMessage = @splat(.init);
            const buf = answer_buffer[answer_buffer_i..];
            const recv_err, const recv_n = socket.receiveManyTimeout(t_io, &message_buffer, buf, .{}, timeout);
            for (message_buffer[0..recv_n]) |*received_message| {
                const reply = received_message.data;
                // Ignore non-identifiable packets.
                if (reply.len < 4) continue;

                // Ignore replies from addresses we didn't send to.
                const ns = for (mapped_nameservers) |*ns| {
                    if (received_message.from.eql(ns)) break ns;
                } else {
                    continue;
                };

                // Find which query this answer goes with, if any.
                const query, const answer = for (queries, answers) |query, *answer| {
                    if (reply[0] == query[0] and reply[1] == query[1]) break .{ query, answer };
                } else {
                    continue;
                };
                if (answer.len != 0) continue;

                // Only accept positive or negative responses; retry immediately on
                // server failure, and ignore all other codes such as refusal.
                switch (reply[3] & 15) {
                    0, 3 => {
                        answer.* = reply;
                        answer_buffer_i += reply.len;
                        answers_remaining -= 1;
                        if (answer_buffer.len - answer_buffer_i == 0) break :send;
                        if (answers_remaining == 0) break :send;
                    },
                    2 => {
                        var retry_message: net.OutgoingMessage = .{
                            .address = ns,
                            .data_ptr = query.ptr,
                            .data_len = query.len,
                        };
                        _ = netSendPosix(t, socket.handle, (&retry_message)[0..1], .{});
                        continue;
                    },
                    else => continue,
                }
            }
            if (recv_err) |err| switch (err) {
                error.Canceled => |e| return e,
                error.Timeout => continue :send,
                else => continue,
            };
        }
    } else {
        return error.NameServerFailure;
    }

    var addresses_len: usize = 0;
    var canonical_name: ?HostName = null;

    for (answers) |answer| {
        var it = HostName.DnsResponse.init(answer) catch {
            // Here we could potentially add diagnostics to the results queue.
            continue;
        };
        while (it.next() catch {
            // Here we could potentially add diagnostics to the results queue.
            continue;
        }) |record| switch (record.rr) {
            .A => {
                const data = record.packet[record.data_off..][0..record.data_len];
                if (data.len != 4) return error.InvalidDnsARecord;
                try resolved.putOne(t_io, .{ .address = .{ .ip4 = .{
                    .bytes = data[0..4].*,
                    .port = options.port,
                } } });
                addresses_len += 1;
            },
            .AAAA => {
                const data = record.packet[record.data_off..][0..record.data_len];
                if (data.len != 16) return error.InvalidDnsAAAARecord;
                try resolved.putOne(t_io, .{ .address = .{ .ip6 = .{
                    .bytes = data[0..16].*,
                    .port = options.port,
                } } });
                addresses_len += 1;
            },
            .CNAME => {
                if (options.canonical_name_buffer) |buf| {
                    _, canonical_name = HostName.expand(
                        record.packet,
                        record.data_off,
                        buf,
                    ) catch return error.InvalidDnsCnameRecord;
                }
            },
            _ => continue,
        };
    }

    if (options.canonical_name_buffer != null) {
        try resolved.putOne(t_io, .{
            .canonical_name = canonical_name orelse .{ .bytes = lookup_canon_name },
        });
    }
    if (addresses_len == 0) return error.NoAddressReturned;
}