1/// A `Body` size hint
2///
3/// The default implementation returns:
4///
5/// * 0 for `lower`
6/// * `None` for `upper`.
7#[derive(Debug, Default, Clone)]
8pub struct SizeHint {
9 lower: u64,
10 upper: Option<u64>,
11}
12
13impl SizeHint {
14 /// Returns a new `SizeHint` with default values
15 #[inline]
16 pub fn new() -> SizeHint {
17 SizeHint::default()
18 }
19
20 /// Returns a new `SizeHint` with both upper and lower bounds set to the
21 /// given value.
22 #[inline]
23 pub fn with_exact(value: u64) -> SizeHint {
24 SizeHint {
25 lower: value,
26 upper: Some(value),
27 }
28 }
29
30 /// Returns the lower bound of data that the `Body` will yield before
31 /// completing.
32 #[inline]
33 pub fn lower(&self) -> u64 {
34 self.lower
35 }
36
37 /// Set the value of the `lower` hint.
38 ///
39 /// # Panics
40 ///
41 /// The function panics if `value` is greater than `upper`.
42 #[inline]
43 pub fn set_lower(&mut self, value: u64) {
44 assert!(value <= self.upper.unwrap_or(u64::MAX));
45 self.lower = value;
46 }
47
48 /// Returns the upper bound of data the `Body` will yield before
49 /// completing, or `None` if the value is unknown.
50 #[inline]
51 pub fn upper(&self) -> Option<u64> {
52 self.upper
53 }
54
55 /// Set the value of the `upper` hint value.
56 ///
57 /// # Panics
58 ///
59 /// This function panics if `value` is less than `lower`.
60 #[inline]
61 pub fn set_upper(&mut self, value: u64) {
62 assert!(value >= self.lower, "`value` is less than than `lower`");
63
64 self.upper = Some(value);
65 }
66
67 /// Returns the exact size of data that will be yielded **if** the
68 /// `lower` and `upper` bounds are equal.
69 #[inline]
70 pub fn exact(&self) -> Option<u64> {
71 if Some(self.lower) == self.upper {
72 self.upper
73 } else {
74 None
75 }
76 }
77
78 /// Set the value of the `lower` and `upper` bounds to exactly the same.
79 #[inline]
80 pub fn set_exact(&mut self, value: u64) {
81 self.lower = value;
82 self.upper = Some(value);
83 }
84}
85