tor_netdoc/util/
str.rs

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1//! String-manipulation utilities
2
3/// Return the position of one string slice within another.
4///
5/// If `needle` is indeed part of `haystack`, returns some offset
6/// `off`, such that `needle` is the same as
7/// `&haystack[off..needle.len()]`.
8///
9/// Returns None if `needle` is not a part of `haystack`.
10///
11/// Remember, offsets are in bytes, not in characters.
12///
13/// # Example
14/// ```ignore
15/// use tor_netdoc::util::str_offset;
16/// let quote = "A rose is a rose is a rose."; // -- Gertrude Stein
17/// assert_eq!(&quote[2..6], "rose");
18/// assert_eq!(str_offset(quote, &quote[2..6]).unwrap(), 2);
19/// assert_eq!(&quote[12..16], "rose");
20/// assert_eq!(str_offset(quote, &quote[12..16]).unwrap(), 12);
21/// assert_eq!(&quote[22..26], "rose");
22/// assert_eq!(str_offset(quote, &quote[22..26]).unwrap(), 22);
23///
24/// assert_eq!(str_offset(quote, "rose"), None);
25///
26/// assert_eq!(str_offset(&quote[1..], &quote[2..6]), Some(1));
27/// assert_eq!(str_offset(&quote[1..5], &quote[2..6]), None);
28/// ```
29pub(crate) fn str_offset(haystack: &str, needle: &str) -> Option<usize> {
30    let needle_start_u = needle.as_ptr() as usize;
31    let needle_end_u = needle_start_u + needle.len();
32    let haystack_start_u = haystack.as_ptr() as usize;
33    let haystack_end_u = haystack_start_u + haystack.len();
34    if haystack_start_u <= needle_start_u && needle_end_u <= haystack_end_u {
35        Some(needle_start_u - haystack_start_u)
36    } else {
37        None
38    }
39}
40
41/// An extent within a given string slice.
42///
43/// This whole type is probably naughty and shouldn't exist.  We use
44/// it only within this crate, to remember where it was that we found
45/// parsed objects within the strings we got them from.
46#[derive(Clone, Debug)]
47pub(crate) struct Extent {
48    /// At what position within the original string is this extent, in bytes?
49    offset: usize,
50    /// How long is this extend, in bytes?
51    length: usize,
52    /// What was the original string?
53    ///
54    /// If this doesn't match, there's been an error.
55    sliceptr: *const u8,
56    /// How long was the original string?
57    ///
58    /// If this doesn't match, there's been an error.
59    slicelen: usize,
60}
61
62impl Extent {
63    /// Construct a new extent to represent the position of `needle`
64    /// within `haystack`.
65    ///
66    /// Return None if `needle` is not in fact a slice of `haystack`.
67    pub(crate) fn new(haystack: &str, needle: &str) -> Option<Extent> {
68        str_offset(haystack, needle).map(|offset| Extent {
69            offset,
70            length: needle.len(),
71            sliceptr: haystack.as_ptr(),
72            slicelen: haystack.len(),
73        })
74    }
75    /// Reconstruct the original `needle` within `haystack`.
76    ///
77    /// Return None if we're sure that the haystack doesn't match the one
78    /// we were originally given.
79    ///
80    /// Note that it is possible for this to give a bogus result if
81    /// provided a new haystack that happens to be at the same
82    /// position in memory as the original one.
83    pub(crate) fn reconstruct<'a>(&self, haystack: &'a str) -> Option<&'a str> {
84        if self.sliceptr != haystack.as_ptr() || self.slicelen != haystack.len() {
85            None
86        } else {
87            haystack.get(self.offset..self.offset + self.length)
88        }
89    }
90}
91
92#[cfg(test)]
93mod test {
94    // @@ begin test lint list maintained by maint/add_warning @@
95    #![allow(clippy::bool_assert_comparison)]
96    #![allow(clippy::clone_on_copy)]
97    #![allow(clippy::dbg_macro)]
98    #![allow(clippy::mixed_attributes_style)]
99    #![allow(clippy::print_stderr)]
100    #![allow(clippy::print_stdout)]
101    #![allow(clippy::single_char_pattern)]
102    #![allow(clippy::unwrap_used)]
103    #![allow(clippy::unchecked_duration_subtraction)]
104    #![allow(clippy::useless_vec)]
105    #![allow(clippy::needless_pass_by_value)]
106    //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
107
108    #[test]
109    fn test_str_offset() {
110        use super::str_offset;
111        let quote = "A rose is a rose is a rose."; // -- Gertrude Stein
112        assert_eq!(&quote[2..6], "rose");
113        assert_eq!(str_offset(quote, &quote[2..6]).unwrap(), 2);
114        assert_eq!(&quote[12..16], "rose");
115        assert_eq!(str_offset(quote, &quote[12..16]).unwrap(), 12);
116        assert_eq!(&quote[22..26], "rose");
117        assert_eq!(str_offset(quote, &quote[22..26]).unwrap(), 22);
118
119        assert_eq!(str_offset(quote, "rose"), None);
120
121        assert_eq!(str_offset(&quote[1..], &quote[2..6]), Some(1));
122        assert_eq!(str_offset(&quote[1..5], &quote[2..6]), None);
123    }
124
125    #[test]
126    fn test_extent() {
127        use super::Extent;
128        let quote = "What is a winter wedding a winter wedding."; // -- ibid
129        assert_eq!(&quote[10..16], "winter");
130        let ex = Extent::new(quote, &quote[10..16]).unwrap();
131        let s = ex.reconstruct(quote).unwrap();
132        assert_eq!(s, "winter");
133
134        assert!(Extent::new(quote, "winter").is_none());
135        assert!(ex.reconstruct("Hello world").is_none());
136    }
137}
tor_netdoc/util/str.rs

tor_netdoc/util/
str.rs
