1use 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)]
10pub struct SizeHint {
11 lower: u64,
12 upper: Option<u64>,
13}
14
15impl SizeHint {
16 /// Returns a new `SizeHint` with default values
17 #[inline]
18 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]
25 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]
35 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]
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]
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]
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]
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]
82 pub fn set_exact(&mut self, value: u64) {
83 self.lower = value;
84 self.upper = Some(value);
85 }
86}
87