strftime/format/
utils.rs

1//! Some useful types.
2
3use super::write::Write;
4use crate::Error;
5
6/// A `Cursor` contains a slice of a buffer.
7#[derive(Debug, Clone)]
8pub(crate) struct Cursor<'a> {
9    /// Slice representing the remaining data to be read.
10    remaining: &'a [u8],
11}
12
13impl<'a> Cursor<'a> {
14    /// Construct a new `Cursor` from remaining data.
15    pub(crate) fn new(remaining: &'a [u8]) -> Self {
16        Self { remaining }
17    }
18
19    /// Returns remaining data.
20    pub(crate) fn remaining(&self) -> &'a [u8] {
21        self.remaining
22    }
23
24    /// Returns the next byte.
25    pub(crate) fn next(&mut self) -> Option<u8> {
26        let (&first, tail) = self.remaining.split_first()?;
27        self.remaining = tail;
28        Some(first)
29    }
30
31    /// Read bytes if the remaining data is prefixed by the provided tag.
32    pub(crate) fn read_optional_tag(&mut self, tag: &[u8]) -> bool {
33        if self.remaining.starts_with(tag) {
34            self.read_exact(tag.len());
35            true
36        } else {
37            false
38        }
39    }
40
41    /// Read bytes as long as the provided predicate is true.
42    pub(crate) fn read_while<F: Fn(&u8) -> bool>(&mut self, f: F) -> &'a [u8] {
43        match self.remaining.iter().position(|x| !f(x)) {
44            None => self.read_exact(self.remaining.len()),
45            Some(position) => self.read_exact(position),
46        }
47    }
48
49    /// Read bytes until the provided predicate is true.
50    pub(crate) fn read_until<F: Fn(&u8) -> bool>(&mut self, f: F) -> &'a [u8] {
51        match self.remaining.iter().position(f) {
52            None => self.read_exact(self.remaining.len()),
53            Some(position) => self.read_exact(position),
54        }
55    }
56
57    /// Read exactly `count` bytes.
58    fn read_exact(&mut self, count: usize) -> &'a [u8] {
59        let (result, remaining) = self.remaining.split_at(count);
60        self.remaining = remaining;
61        result
62    }
63}
64
65/// A `SizeLimiter` limits the maximum amount a writer can write.
66pub(crate) struct SizeLimiter<'a> {
67    /// Inner writer.
68    inner: &'a mut dyn Write,
69    /// Size limit.
70    size_limit: usize,
71    /// Current write count.
72    count: usize,
73}
74
75impl<'a> SizeLimiter<'a> {
76    /// Construct a new `SizeLimiter`.
77    pub(crate) fn new(inner: &'a mut dyn Write, size_limit: usize) -> Self {
78        Self {
79            inner,
80            size_limit,
81            count: 0,
82        }
83    }
84
85    /// Pad with the specified character.
86    pub(crate) fn pad(&mut self, c: u8, n: usize) -> Result<(), Error> {
87        if self.count.saturating_add(n) > self.size_limit {
88            return Err(Error::FormattedStringTooLarge);
89        }
90
91        let buffer = [c; 1024];
92        let mut remaining = n;
93
94        while remaining > 0 {
95            let size = remaining.min(1024);
96            self.inner.write_all(&buffer[..size])?;
97            remaining -= size;
98        }
99
100        self.count += n;
101
102        Ok(())
103    }
104}
105
106impl Write for SizeLimiter<'_> {
107    fn write(&mut self, data: &[u8]) -> Result<usize, Error> {
108        if self.count.saturating_add(data.len()) > self.size_limit {
109            return Err(Error::FormattedStringTooLarge);
110        }
111
112        let written = self.inner.write(data)?;
113        self.count += written;
114        Ok(written)
115    }
116}
117
118#[cfg(test)]
119mod tests {
120    #[cfg(feature = "alloc")]
121    #[test]
122    fn test_cursor_debug_is_non_empty() {
123        use alloc::format;
124
125        use super::Cursor;
126
127        assert!(!format!("{:?}", Cursor::new(&[])).is_empty());
128    }
129}
strftime/format/utils.rs

strftime/format/
utils.rs
