DnsResponse

pub const DnsResponse = struct {
    bytes: []const u8,
    bytes_index: u32,
    answers_remaining: u16,

    pub const Answer = struct {
        rr: DnsRecord,
        packet: []const u8,
        data_off: u32,
        data_len: u16,
    };

    pub const Error = error{InvalidDnsPacket};

    pub fn init(r: []const u8) Error!DnsResponse {
        if (r.len < 12) return error.InvalidDnsPacket;
        if ((r[3] & 15) != 0) return .{ .bytes = r, .bytes_index = 3, .answers_remaining = 0 };
        var i: u32 = 12;
        var query_count = std.mem.readInt(u16, r[4..6], .big);
        while (query_count != 0) : (query_count -= 1) {
            while (i < r.len and r[i] -% 1 < 127) i += 1;
            if (r.len - i < 6) return error.InvalidDnsPacket;
            i = i + 5 + @intFromBool(r[i] != 0);
        }
        return .{
            .bytes = r,
            .bytes_index = i,
            .answers_remaining = std.mem.readInt(u16, r[6..8], .big),
        };
    }

    pub fn next(dr: *DnsResponse) Error!?Answer {
        if (dr.answers_remaining == 0) return null;
        dr.answers_remaining -= 1;
        const r = dr.bytes;
        var i = dr.bytes_index;
        while (i < r.len and r[i] -% 1 < 127) i += 1;
        if (r.len - i < 12) return error.InvalidDnsPacket;
        i = i + 1 + @intFromBool(r[i] != 0);
        const len = std.mem.readInt(u16, r[i + 8 ..][0..2], .big);
        if (i + 10 + len > r.len) return error.InvalidDnsPacket;
        defer dr.bytes_index = i + 10 + len;
        return .{
            .rr = @fromBackingInt(@intCast(r[i + 1])),
            .packet = r,
            .data_off = i + 10,
            .data_len = len,
        };
    }
}