h2/frame/
stream_id.rs

1/// A stream identifier, as described in [Section 5.1.1] of RFC 7540.
2///
3/// Streams are identified with an unsigned 31-bit integer. Streams
4/// initiated by a client MUST use odd-numbered stream identifiers; those
5/// initiated by the server MUST use even-numbered stream identifiers.  A
6/// stream identifier of zero (0x0) is used for connection control
7/// messages; the stream identifier of zero cannot be used to establish a
8/// new stream.
9///
10/// [Section 5.1.1]: https://tools.ietf.org/html/rfc7540#section-5.1.1
11#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
12pub struct StreamId(u32);
13
14#[derive(Debug, Copy, Clone)]
15pub struct StreamIdOverflow;
16
17const STREAM_ID_MASK: u32 = 1 << 31;
18
19impl StreamId {
20    /// Stream ID 0.
21    pub const ZERO: StreamId = StreamId(0);
22
23    /// The maximum allowed stream ID.
24    pub const MAX: StreamId = StreamId(u32::MAX >> 1);
25
26    /// Parse the stream ID
27    #[inline]
28    pub fn parse(buf: &[u8]) -> (StreamId, bool) {
29        let mut ubuf = [0; 4];
30        ubuf.copy_from_slice(&buf[0..4]);
31        let unpacked = u32::from_be_bytes(ubuf);
32        let flag = unpacked & STREAM_ID_MASK == STREAM_ID_MASK;
33
34        // Now clear the most significant bit, as that is reserved and MUST be
35        // ignored when received.
36        (StreamId(unpacked & !STREAM_ID_MASK), flag)
37    }
38
39    /// Returns true if this stream ID corresponds to a stream that
40    /// was initiated by the client.
41    pub fn is_client_initiated(&self) -> bool {
42        let id = self.0;
43        id != 0 && id % 2 == 1
44    }
45
46    /// Returns true if this stream ID corresponds to a stream that
47    /// was initiated by the server.
48    pub fn is_server_initiated(&self) -> bool {
49        let id = self.0;
50        id != 0 && id % 2 == 0
51    }
52
53    /// Return a new `StreamId` for stream 0.
54    #[inline]
55    pub fn zero() -> StreamId {
56        StreamId::ZERO
57    }
58
59    /// Returns true if this stream ID is zero.
60    pub fn is_zero(&self) -> bool {
61        self.0 == 0
62    }
63
64    /// Returns the next stream ID initiated by the same peer as this stream
65    /// ID, or an error if incrementing this stream ID would overflow the
66    /// maximum.
67    pub fn next_id(&self) -> Result<StreamId, StreamIdOverflow> {
68        let next = self.0 + 2;
69        if next > StreamId::MAX.0 {
70            Err(StreamIdOverflow)
71        } else {
72            Ok(StreamId(next))
73        }
74    }
75}
76
77impl From<u32> for StreamId {
78    fn from(src: u32) -> Self {
79        assert_eq!(src & STREAM_ID_MASK, 0, "invalid stream ID -- MSB is set");
80        StreamId(src)
81    }
82}
83
84impl From<StreamId> for u32 {
85    fn from(src: StreamId) -> Self {
86        src.0
87    }
88}
89
90impl PartialEq<u32> for StreamId {
91    fn eq(&self, other: &u32) -> bool {
92        self.0 == *other
93    }
94}
h2/frame/stream_id.rs

h2/frame/
stream_id.rs
