rusqlite/util/
small_cstr.rs

1use smallvec::{smallvec, SmallVec};
2use std::ffi::{CStr, CString, NulError};
3
4/// Similar to `std::ffi::CString`, but avoids heap allocating if the string is
5/// small enough. Also guarantees it's input is UTF-8 -- used for cases where we
6/// need to pass a NUL-terminated string to SQLite, and we have a `&str`.
7#[derive(Clone, PartialEq, Eq, PartialOrd, Ord)]
8pub struct SmallCString(SmallVec<[u8; 16]>);
9
10impl SmallCString {
11    #[inline]
12    pub fn new(s: &str) -> Result<Self, NulError> {
13        if s.as_bytes().contains(&0_u8) {
14            return Err(Self::fabricate_nul_error(s));
15        }
16        let mut buf = SmallVec::with_capacity(s.len() + 1);
17        buf.extend_from_slice(s.as_bytes());
18        buf.push(0);
19        let res = Self(buf);
20        res.debug_checks();
21        Ok(res)
22    }
23
24    #[inline]
25    pub fn as_str(&self) -> &str {
26        self.debug_checks();
27        // Constructor takes a &str so this is safe.
28        unsafe { std::str::from_utf8_unchecked(self.as_bytes_without_nul()) }
29    }
30
31    /// Get the bytes not including the NUL terminator. E.g. the bytes which
32    /// make up our `str`:
33    /// - `SmallCString::new("foo").as_bytes_without_nul() == b"foo"`
34    /// - `SmallCString::new("foo").as_bytes_with_nul() == b"foo\0"`
35    #[inline]
36    pub fn as_bytes_without_nul(&self) -> &[u8] {
37        self.debug_checks();
38        &self.0[..self.len()]
39    }
40
41    /// Get the bytes behind this str *including* the NUL terminator. This
42    /// should never return an empty slice.
43    #[inline]
44    pub fn as_bytes_with_nul(&self) -> &[u8] {
45        self.debug_checks();
46        &self.0
47    }
48
49    #[inline]
50    #[cfg(debug_assertions)]
51    fn debug_checks(&self) {
52        debug_assert_ne!(self.0.len(), 0);
53        debug_assert_eq!(self.0[self.0.len() - 1], 0);
54        let strbytes = &self.0[..(self.0.len() - 1)];
55        debug_assert!(!strbytes.contains(&0));
56        debug_assert!(std::str::from_utf8(strbytes).is_ok());
57    }
58
59    #[inline]
60    #[cfg(not(debug_assertions))]
61    fn debug_checks(&self) {}
62
63    #[inline]
64    pub fn len(&self) -> usize {
65        debug_assert_ne!(self.0.len(), 0);
66        self.0.len() - 1
67    }
68
69    #[inline]
70    #[allow(unused)] // clippy wants this function.
71    pub fn is_empty(&self) -> bool {
72        self.len() == 0
73    }
74
75    #[inline]
76    pub fn as_cstr(&self) -> &CStr {
77        let bytes = self.as_bytes_with_nul();
78        debug_assert!(CStr::from_bytes_with_nul(bytes).is_ok());
79        unsafe { CStr::from_bytes_with_nul_unchecked(bytes) }
80    }
81
82    #[cold]
83    fn fabricate_nul_error(b: &str) -> NulError {
84        CString::new(b).unwrap_err()
85    }
86}
87
88impl Default for SmallCString {
89    #[inline]
90    fn default() -> Self {
91        Self(smallvec![0])
92    }
93}
94
95impl std::fmt::Debug for SmallCString {
96    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
97        f.debug_tuple("SmallCString").field(&self.as_str()).finish()
98    }
99}
100
101impl std::ops::Deref for SmallCString {
102    type Target = CStr;
103
104    #[inline]
105    fn deref(&self) -> &CStr {
106        self.as_cstr()
107    }
108}
109
110impl std::borrow::Borrow<str> for SmallCString {
111    #[inline]
112    fn borrow(&self) -> &str {
113        self.as_str()
114    }
115}
116
117#[cfg(test)]
118mod test {
119    use super::*;
120
121    #[test]
122    fn test_small_cstring() {
123        // We don't go through the normal machinery for default, so make sure
124        // things work.
125        assert_eq!(SmallCString::default().0, SmallCString::new("").unwrap().0);
126        assert_eq!(SmallCString::new("foo").unwrap().len(), 3);
127        assert_eq!(
128            SmallCString::new("foo").unwrap().as_bytes_with_nul(),
129            b"foo\0"
130        );
131        assert_eq!(
132            SmallCString::new("foo").unwrap().as_bytes_without_nul(),
133            b"foo",
134        );
135
136        assert_eq!(SmallCString::new("😀").unwrap().len(), 4);
137        assert_eq!(
138            SmallCString::new("😀").unwrap().0.as_slice(),
139            b"\xf0\x9f\x98\x80\0",
140        );
141        assert_eq!(
142            SmallCString::new("😀").unwrap().as_bytes_without_nul(),
143            b"\xf0\x9f\x98\x80",
144        );
145
146        assert_eq!(SmallCString::new("").unwrap().len(), 0);
147        assert!(SmallCString::new("").unwrap().is_empty());
148
149        assert_eq!(SmallCString::new("").unwrap().0.as_slice(), b"\0");
150        assert_eq!(SmallCString::new("").unwrap().as_bytes_without_nul(), b"");
151
152        SmallCString::new("\0").unwrap_err();
153        SmallCString::new("\0abc").unwrap_err();
154        SmallCString::new("abc\0").unwrap_err();
155    }
156}
rusqlite/util/small_cstr.rs

rusqlite/util/
small_cstr.rs
