1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186

use std::net::{Ipv4Addr, SocketAddr};
use crate::message::{DNSQuestion, DNSHeader, questions_to_bytes, Direction, ResponseCode, QType, QClass, ResourceRecord, records_to_bytes, ARdata, TXTRdata, RData};
use crate::RequestError;

pub const MESSAGE_SIZE: usize = 512;

/// A DNS message which can be used as either a request or response based on its direction and composition
#[derive(Debug)]
pub struct DNSMessage {
    /// Status/request codes, counts for other collections
    pub header: DNSHeader,
    /// Hostname queries, should be the same in both requests and responses
    pub questions: Vec<DNSQuestion>,
    /// Responses for [`DNSMessage::questions`], has similar structure with varying data field based on query type
    pub answer_records: Vec<ResourceRecord>,
    pub authority_records: Vec<ResourceRecord>,
    pub additional_records: Vec<ResourceRecord>,
    /// IP and socket address of the client which sent this message/client to send message to
    pub peer: SocketAddr
}

impl DNSMessage {

    /// Transform a message into a network transmissable byte sequence
    pub fn to_bytes(& self) -> Vec<u8>
    {
        let mut header_bytes = self.header.to_bytes().to_vec();
        let mut body_bytes = questions_to_bytes(&self.questions);
        let mut answer_bytes = records_to_bytes(&self.answer_records);
        let mut authority_bytes = records_to_bytes(&self.authority_records);
        let mut additional_bytes = records_to_bytes(&self.additional_records);

        header_bytes.append(&mut body_bytes);
        header_bytes.append(&mut answer_bytes);
        header_bytes.append(&mut authority_bytes);
        header_bytes.append(&mut additional_bytes);

        return header_bytes
    }

    /// Helper function for getting a DNS request for the IPv4 of a single hostname
    pub fn req_from_hostname(peer: SocketAddr, id: u16, hostname: String) -> DNSMessage
    {
        DNSMessage {
            header: DNSHeader::new_request(id, None),
            questions: vec![
                DNSQuestion {
                    qname: hostname,
                    qtype: QType::A,
                    qclass: QClass::Internet
                }
            ],
            answer_records: vec![],
            authority_records: vec![],
            additional_records: vec![],
            peer
        }
    }

    /// Helper function to get a DNS request for the IPv4s of multiple hostnames
    pub fn reqs_from_hostnames(peer: SocketAddr, id: u16, hostnames: Vec<String>) -> DNSMessage
    {
        DNSMessage {
            header: DNSHeader::new_request(id, Some(hostnames.len() as u16)),
            questions: hostnames
                .into_iter()
                .map(|n|
                    DNSQuestion {
                        qname: n,
                        qclass: QClass::Internet,
                        qtype: QType::A
                    })
                .collect(),
            answer_records: vec![],
            authority_records: vec![],
            additional_records: vec![],
            peer
        }
    }

    pub fn a_resp_from_request(&self, ip: impl Fn(&DNSQuestion) -> Ipv4Addr) -> DNSMessage
    {
        let mut response = DNSMessage{
            header: self.header.clone(),
            questions: self.questions.clone(),
            answer_records: vec![],
            authority_records: vec![],
            additional_records: vec![],
            peer: self.peer
        };

        response.answer_records = self.questions
            .iter()
            .map(|x|
                ResourceRecord::from_query(x,
                                           12,
                                           Box::new(ARdata::from(ip(x))),
                                           None))
            .collect();

        response.header.direction = Direction::Response;
        response.header.response = ResponseCode::NoError;
        response.header.answer_record_count = response.answer_records.len() as u16;
        response.header.authority_record_count = 0;
        response.header.additional_record_count = 0;

        if response.header.recursion_desired {
            response.header.recursion_available = true;
        }

        response
    }

    pub fn dumb_resp_from_request(&self) -> DNSMessage
    {
        let mut response = DNSMessage{
            header: self.header.clone(),
            questions: self.questions.clone(),
            answer_records: vec![],
            authority_records: vec![],
            additional_records: vec![],
            peer: self.peer
        };

        response.header.direction = Direction::Response;
        response.header.response = ResponseCode::NotImplemented;
        response.header.answer_record_count = 0;
        response.header.authority_record_count = 0;
        response.header.additional_record_count = 0;

        response
    }

    pub fn empty_resp_from_request(&self) -> DNSMessage
    {
        let mut response = DNSMessage{
            header: self.header.clone(),
            questions: self.questions.clone(),
            answer_records: vec![],
            authority_records: vec![],
            additional_records: vec![],
            peer: self.peer
        };

        response.header.direction = Direction::Response;
        response.header.response = ResponseCode::NoError;
        response.header.answer_record_count = 0;
        response.header.authority_record_count = 0;
        response.header.additional_record_count = 0;

        if response.header.recursion_desired {
            response.header.recursion_available = true;
        }

        response
    }

    pub fn protocol_error_from_request(&self, _error_code: RequestError) -> DNSMessage
    {
        let txt = Box::new(TXTRdata::from(String::new()));

        let mut response = DNSMessage{
            header: self.header.clone(),
            questions: self.questions.clone(),
            answer_records: vec![ResourceRecord {
                name_offset: 12,
                answer_type: QType::TXT,
                class: QClass::Internet,
                ttl: 0,
                rd_length: txt.to_bytes().len() as u16,
                r_data: txt
            }],
            authority_records: vec![],
            additional_records: vec![],
            peer: self.peer
        };

        response.header.direction = Direction::Response;
        response.header.response = ResponseCode::ServerFailure;
        response.header.answer_record_count = 1;
        response.header.authority_record_count = 0;
        response.header.additional_record_count = 0;

        response
    }
}