dns_parser/
builder.rs

1use byteorder::{ByteOrder, BigEndian, WriteBytesExt};
2
3use {Opcode, ResponseCode, Header, QueryType, QueryClass};
4
5/// Allows to build a DNS packet
6///
7/// Both query and answer packets may be built with this interface, although,
8/// much of functionality is not implemented yet.
9#[derive(Debug)]
10pub struct Builder {
11    buf: Vec<u8>,
12}
13
14impl Builder {
15    /// Creates a new query
16    ///
17    /// Initially all sections are empty. You're expected to fill
18    /// the questions section with `add_question`
19    pub fn new_query(id: u16, recursion: bool) -> Builder {
20        let mut buf = Vec::with_capacity(512);
21        let head = Header {
22            id: id,
23            query: true,
24            opcode: Opcode::StandardQuery,
25            authoritative: false,
26            truncated: false,
27            recursion_desired: recursion,
28            recursion_available: false,
29            authenticated_data: false,
30            checking_disabled: false,
31            response_code: ResponseCode::NoError,
32            questions: 0,
33            answers: 0,
34            nameservers: 0,
35            additional: 0,
36        };
37        buf.extend([0u8; 12].iter());
38        head.write(&mut buf[..12]);
39        Builder { buf: buf }
40    }
41    /// Adds a question to the packet
42    ///
43    /// # Panics
44    ///
45    /// * Answers, nameservers or additional section has already been written
46    /// * There are already 65535 questions in the buffer.
47    /// * When name is invalid
48    pub fn add_question(&mut self, qname: &str, prefer_unicast: bool,
49        qtype: QueryType, qclass: QueryClass)
50        -> &mut Builder
51    {
52        if &self.buf[6..12] != b"\x00\x00\x00\x00\x00\x00" {
53            panic!("Too late to add a question");
54        }
55        self.write_name(qname);
56        self.buf.write_u16::<BigEndian>(qtype as u16).unwrap();
57        let prefer_unicast: u16 = if prefer_unicast { 0x8000 } else { 0x0000 };
58        self.buf.write_u16::<BigEndian>(qclass as u16 | prefer_unicast).unwrap();
59        let oldq = BigEndian::read_u16(&self.buf[4..6]);
60        if oldq == 65535 {
61            panic!("Too many questions");
62        }
63        BigEndian::write_u16(&mut self.buf[4..6], oldq+1);
64        self
65    }
66    fn write_name(&mut self, name: &str) {
67        for part in name.split('.') {
68            assert!(part.len() < 63);
69            let ln = part.len() as u8;
70            self.buf.push(ln);
71            self.buf.extend(part.as_bytes());
72        }
73        self.buf.push(0);
74    }
75    /// Returns the final packet
76    ///
77    /// When packet is not truncated method returns `Ok(packet)`. If
78    /// packet is truncated the method returns `Err(packet)`. In both
79    /// cases the packet is fully valid.
80    ///
81    /// In the server implementation you may use
82    /// `x.build().unwrap_or_else(|x| x)`.
83    ///
84    /// In the client implementation it's probably unwise to send truncated
85    /// packet, as it doesn't make sense. Even panicking may be more
86    /// appropriate.
87    // TODO(tailhook) does the truncation make sense for TCP, and how
88    // to treat it for EDNS0?
89    pub fn build(mut self) -> Result<Vec<u8>,Vec<u8>> {
90        // TODO(tailhook) optimize labels
91        if self.buf.len() > 512 {
92            Header::set_truncated(&mut self.buf[..12]);
93            Err(self.buf)
94        } else {
95            Ok(self.buf)
96        }
97    }
98}
99
100#[cfg(test)]
101mod test {
102    use QueryType as QT;
103    use QueryClass as QC;
104    use super::Builder;
105
106    #[test]
107    fn build_query() {
108        let mut bld = Builder::new_query(1573, true);
109        bld.add_question("example.com", false, QT::A, QC::IN);
110        let result = b"\x06%\x01\x00\x00\x01\x00\x00\x00\x00\x00\x00\
111                      \x07example\x03com\x00\x00\x01\x00\x01";
112        assert_eq!(&bld.build().unwrap()[..], &result[..]);
113    }
114
115    #[test]
116    fn build_unicast_query() {
117        let mut bld = Builder::new_query(1573, true);
118        bld.add_question("example.com", true, QT::A, QC::IN);
119        let result = b"\x06%\x01\x00\x00\x01\x00\x00\x00\x00\x00\x00\
120                      \x07example\x03com\x00\x00\x01\x80\x01";
121        assert_eq!(&bld.build().unwrap()[..], &result[..]);
122    }
123
124    #[test]
125    fn build_srv_query() {
126        let mut bld = Builder::new_query(23513, true);
127        bld.add_question("_xmpp-server._tcp.gmail.com", false, QT::SRV, QC::IN);
128        let result = b"[\xd9\x01\x00\x00\x01\x00\x00\x00\x00\x00\x00\
129            \x0c_xmpp-server\x04_tcp\x05gmail\x03com\x00\x00!\x00\x01";
130        assert_eq!(&bld.build().unwrap()[..], &result[..]);
131    }
132}
dns_parser/builder.rs

dns_parser/
builder.rs
