rustls/msgs/
fragmenter.rs

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1use crate::enums::ContentType;
2use crate::enums::ProtocolVersion;
3use crate::msgs::message::{BorrowedPlainMessage, PlainMessage};
4use crate::Error;
5pub const MAX_FRAGMENT_LEN: usize = 16384;
6pub const PACKET_OVERHEAD: usize = 1 + 2 + 2;
7pub const MAX_FRAGMENT_SIZE: usize = MAX_FRAGMENT_LEN + PACKET_OVERHEAD;
8
9pub struct MessageFragmenter {
10    max_frag: usize,
11}
12
13impl Default for MessageFragmenter {
14    fn default() -> Self {
15        Self {
16            max_frag: MAX_FRAGMENT_LEN,
17        }
18    }
19}
20
21impl MessageFragmenter {
22    /// Take the Message `msg` and re-fragment it into new
23    /// messages whose fragment is no more than max_frag.
24    /// Return an iterator across those messages.
25    /// Payloads are borrowed.
26    pub fn fragment_message<'a>(
27        &self,
28        msg: &'a PlainMessage,
29    ) -> impl Iterator<Item = BorrowedPlainMessage<'a>> + 'a {
30        self.fragment_slice(msg.typ, msg.version, &msg.payload.0)
31    }
32
33    /// Enqueue borrowed fragments of (version, typ, payload) which
34    /// are no longer than max_frag onto the `out` deque.
35    pub fn fragment_slice<'a>(
36        &self,
37        typ: ContentType,
38        version: ProtocolVersion,
39        payload: &'a [u8],
40    ) -> impl Iterator<Item = BorrowedPlainMessage<'a>> + 'a {
41        payload
42            .chunks(self.max_frag)
43            .map(move |c| BorrowedPlainMessage {
44                typ,
45                version,
46                payload: c,
47            })
48    }
49
50    /// Set the maximum fragment size that will be produced.
51    ///
52    /// This includes overhead. A `max_fragment_size` of 10 will produce TLS fragments
53    /// up to 10 bytes long.
54    ///
55    /// A `max_fragment_size` of `None` sets the highest allowable fragment size.
56    ///
57    /// Returns BadMaxFragmentSize if the size is smaller than 32 or larger than 16389.
58    pub fn set_max_fragment_size(&mut self, max_fragment_size: Option<usize>) -> Result<(), Error> {
59        self.max_frag = match max_fragment_size {
60            Some(sz @ 32..=MAX_FRAGMENT_SIZE) => sz - PACKET_OVERHEAD,
61            None => MAX_FRAGMENT_LEN,
62            _ => return Err(Error::BadMaxFragmentSize),
63        };
64        Ok(())
65    }
66}
67
68#[cfg(test)]
69mod tests {
70    use super::{MessageFragmenter, PACKET_OVERHEAD};
71    use crate::enums::ContentType;
72    use crate::enums::ProtocolVersion;
73    use crate::msgs::base::Payload;
74    use crate::msgs::message::{BorrowedPlainMessage, PlainMessage};
75
76    fn msg_eq(
77        m: &BorrowedPlainMessage,
78        total_len: usize,
79        typ: &ContentType,
80        version: &ProtocolVersion,
81        bytes: &[u8],
82    ) {
83        assert_eq!(&m.typ, typ);
84        assert_eq!(&m.version, version);
85        assert_eq!(m.payload, bytes);
86
87        let buf = m.to_unencrypted_opaque().encode();
88
89        assert_eq!(total_len, buf.len());
90    }
91
92    #[test]
93    fn smoke() {
94        let typ = ContentType::Handshake;
95        let version = ProtocolVersion::TLSv1_2;
96        let data: Vec<u8> = (1..70u8).collect();
97        let m = PlainMessage {
98            typ,
99            version,
100            payload: Payload::new(data),
101        };
102
103        let mut frag = MessageFragmenter::default();
104        frag.set_max_fragment_size(Some(32))
105            .unwrap();
106        let q = frag
107            .fragment_message(&m)
108            .collect::<Vec<_>>();
109        assert_eq!(q.len(), 3);
110        msg_eq(
111            &q[0],
112            32,
113            &typ,
114            &version,
115            &[
116                1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
117                24, 25, 26, 27,
118            ],
119        );
120        msg_eq(
121            &q[1],
122            32,
123            &typ,
124            &version,
125            &[
126                28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48,
127                49, 50, 51, 52, 53, 54,
128            ],
129        );
130        msg_eq(
131            &q[2],
132            20,
133            &typ,
134            &version,
135            &[55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69],
136        );
137    }
138
139    #[test]
140    fn non_fragment() {
141        let m = PlainMessage {
142            typ: ContentType::Handshake,
143            version: ProtocolVersion::TLSv1_2,
144            payload: Payload::new(b"\x01\x02\x03\x04\x05\x06\x07\x08".to_vec()),
145        };
146
147        let mut frag = MessageFragmenter::default();
148        frag.set_max_fragment_size(Some(32))
149            .unwrap();
150        let q = frag
151            .fragment_message(&m)
152            .collect::<Vec<_>>();
153        assert_eq!(q.len(), 1);
154        msg_eq(
155            &q[0],
156            PACKET_OVERHEAD + 8,
157            &ContentType::Handshake,
158            &ProtocolVersion::TLSv1_2,
159            b"\x01\x02\x03\x04\x05\x06\x07\x08",
160        );
161    }
162}
rustls/msgs/fragmenter.rs

rustls/msgs/
fragmenter.rs
