1 use std::u64;
2 
3 /// A `Body` size hint
4 ///
5 /// The default implementation returns:
6 ///
7 /// * 0 for `lower`
8 /// * `None` for `upper`.
9 #[derive(Debug, Default, Clone)]
10 pub struct SizeHint {
11     lower: u64,
12     upper: Option<u64>,
13 }
14 
15 impl SizeHint {
16     /// Returns a new `SizeHint` with default values
17     #[inline]
new() -> SizeHint18     pub fn new() -> SizeHint {
19         SizeHint::default()
20     }
21 
22     /// Returns a new `SizeHint` with both upper and lower bounds set to the
23     /// given value.
24     #[inline]
with_exact(value: u64) -> SizeHint25     pub fn with_exact(value: u64) -> SizeHint {
26         SizeHint {
27             lower: value,
28             upper: Some(value),
29         }
30     }
31 
32     /// Returns the lower bound of data that the `Body` will yield before
33     /// completing.
34     #[inline]
lower(&self) -> u6435     pub fn lower(&self) -> u64 {
36         self.lower
37     }
38 
39     /// Set the value of the `lower` hint.
40     ///
41     /// # Panics
42     ///
43     /// The function panics if `value` is greater than `upper`.
44     #[inline]
set_lower(&mut self, value: u64)45     pub fn set_lower(&mut self, value: u64) {
46         assert!(value <= self.upper.unwrap_or(u64::MAX));
47         self.lower = value;
48     }
49 
50     /// Returns the upper bound of data the `Body` will yield before
51     /// completing, or `None` if the value is unknown.
52     #[inline]
upper(&self) -> Option<u64>53     pub fn upper(&self) -> Option<u64> {
54         self.upper
55     }
56 
57     /// Set the value of the `upper` hint value.
58     ///
59     /// # Panics
60     ///
61     /// This function panics if `value` is less than `lower`.
62     #[inline]
set_upper(&mut self, value: u64)63     pub fn set_upper(&mut self, value: u64) {
64         assert!(value >= self.lower, "`value` is less than than `lower`");
65 
66         self.upper = Some(value);
67     }
68 
69     /// Returns the exact size of data that will be yielded **if** the
70     /// `lower` and `upper` bounds are equal.
71     #[inline]
exact(&self) -> Option<u64>72     pub fn exact(&self) -> Option<u64> {
73         if Some(self.lower) == self.upper {
74             self.upper
75         } else {
76             None
77         }
78     }
79 
80     /// Set the value of the `lower` and `upper` bounds to exactly the same.
81     #[inline]
set_exact(&mut self, value: u64)82     pub fn set_exact(&mut self, value: u64) {
83         self.lower = value;
84         self.upper = Some(value);
85     }
86 }
87