1 use std::u32;
2 
3 /// A stream identifier, as described in [Section 5.1.1] of RFC 7540.
4 ///
5 /// Streams are identified with an unsigned 31-bit integer. Streams
6 /// initiated by a client MUST use odd-numbered stream identifiers; those
7 /// initiated by the server MUST use even-numbered stream identifiers.  A
8 /// stream identifier of zero (0x0) is used for connection control
9 /// messages; the stream identifier of zero cannot be used to establish a
10 /// new stream.
11 ///
12 /// [Section 5.1.1]: https://tools.ietf.org/html/rfc7540#section-5.1.1
13 #[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
14 pub struct StreamId(u32);
15 
16 #[derive(Debug, Copy, Clone)]
17 pub struct StreamIdOverflow;
18 
19 const STREAM_ID_MASK: u32 = 1 << 31;
20 
21 impl StreamId {
22     /// Stream ID 0.
23     pub const ZERO: StreamId = StreamId(0);
24 
25     /// The maximum allowed stream ID.
26     pub const MAX: StreamId = StreamId(u32::MAX >> 1);
27 
28     /// Parse the stream ID
29     #[inline]
parse(buf: &[u8]) -> (StreamId, bool)30     pub fn parse(buf: &[u8]) -> (StreamId, bool) {
31         let mut ubuf = [0; 4];
32         ubuf.copy_from_slice(&buf[0..4]);
33         let unpacked = u32::from_be_bytes(ubuf);
34         let flag = unpacked & STREAM_ID_MASK == STREAM_ID_MASK;
35 
36         // Now clear the most significant bit, as that is reserved and MUST be
37         // ignored when received.
38         (StreamId(unpacked & !STREAM_ID_MASK), flag)
39     }
40 
41     /// Returns true if this stream ID corresponds to a stream that
42     /// was initiated by the client.
is_client_initiated(&self) -> bool43     pub fn is_client_initiated(&self) -> bool {
44         let id = self.0;
45         id != 0 && id % 2 == 1
46     }
47 
48     /// Returns true if this stream ID corresponds to a stream that
49     /// was initiated by the server.
is_server_initiated(&self) -> bool50     pub fn is_server_initiated(&self) -> bool {
51         let id = self.0;
52         id != 0 && id % 2 == 0
53     }
54 
55     /// Return a new `StreamId` for stream 0.
56     #[inline]
zero() -> StreamId57     pub fn zero() -> StreamId {
58         StreamId::ZERO
59     }
60 
61     /// Returns true if this stream ID is zero.
is_zero(&self) -> bool62     pub fn is_zero(&self) -> bool {
63         self.0 == 0
64     }
65 
66     /// Returns the next stream ID initiated by the same peer as this stream
67     /// ID, or an error if incrementing this stream ID would overflow the
68     /// maximum.
next_id(&self) -> Result<StreamId, StreamIdOverflow>69     pub fn next_id(&self) -> Result<StreamId, StreamIdOverflow> {
70         let next = self.0 + 2;
71         if next > StreamId::MAX.0 {
72             Err(StreamIdOverflow)
73         } else {
74             Ok(StreamId(next))
75         }
76     }
77 }
78 
79 impl From<u32> for StreamId {
from(src: u32) -> Self80     fn from(src: u32) -> Self {
81         assert_eq!(src & STREAM_ID_MASK, 0, "invalid stream ID -- MSB is set");
82         StreamId(src)
83     }
84 }
85 
86 impl From<StreamId> for u32 {
from(src: StreamId) -> Self87     fn from(src: StreamId) -> Self {
88         src.0
89     }
90 }
91 
92 impl PartialEq<u32> for StreamId {
eq(&self, other: &u32) -> bool93     fn eq(&self, other: &u32) -> bool {
94         self.0 == *other
95     }
96 }
97