refactor and add tests for percent encoding (#977)

* refactor: move AsciiSet related code to ascii_set.rs

Makes it a little easier to just look at the code related to the set rather than encoding

* Add tests for percent_encoding

percent_encoding/src/ascii_set.rs

@@ -0,0 +1,213 @@
+// Copyright 2013-2016 The rust-url developers.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use core::{mem, ops};
+
+/// Represents a set of characters or bytes in the ASCII range.
+///
+/// This is used in [`percent_encode`] and [`utf8_percent_encode`].
+/// This is similar to [percent-encode sets](https://url.spec.whatwg.org/#percent-encoded-bytes).
+///
+/// Use the `add` method of an existing set to define a new set. For example:
+///
+/// [`percent_encode`]: crate::percent_encode
+/// [`utf8_percent_encode`]: crate::utf8_percent_encode
+///
+/// ```
+/// use percent_encoding::{AsciiSet, CONTROLS};
+///
+/// /// https://url.spec.whatwg.org/#fragment-percent-encode-set
+/// const FRAGMENT: &AsciiSet = &CONTROLS.add(b' ').add(b'"').add(b'<').add(b'>').add(b'`');
+/// ```
+#[derive(Debug, PartialEq, Eq)]
+pub struct AsciiSet {
+    mask: [Chunk; ASCII_RANGE_LEN / BITS_PER_CHUNK],
+}
+
+type Chunk = u32;
+
+const ASCII_RANGE_LEN: usize = 0x80;
+
+const BITS_PER_CHUNK: usize = 8 * mem::size_of::<Chunk>();
+
+impl AsciiSet {
+    /// An empty set.
+    pub const EMPTY: AsciiSet = AsciiSet {
+        mask: [0; ASCII_RANGE_LEN / BITS_PER_CHUNK],
+    };
+
+    /// Called with UTF-8 bytes rather than code points.
+    /// Not used for non-ASCII bytes.
+    pub(crate) const fn contains(&self, byte: u8) -> bool {
+        let chunk = self.mask[byte as usize / BITS_PER_CHUNK];
+        let mask = 1 << (byte as usize % BITS_PER_CHUNK);
+        (chunk & mask) != 0
+    }
+
+    pub(crate) fn should_percent_encode(&self, byte: u8) -> bool {
+        !byte.is_ascii() || self.contains(byte)
+    }
+
+    pub const fn add(&self, byte: u8) -> Self {
+        let mut mask = self.mask;
+        mask[byte as usize / BITS_PER_CHUNK] |= 1 << (byte as usize % BITS_PER_CHUNK);
+        AsciiSet { mask }
+    }
+
+    pub const fn remove(&self, byte: u8) -> Self {
+        let mut mask = self.mask;
+        mask[byte as usize / BITS_PER_CHUNK] &= !(1 << (byte as usize % BITS_PER_CHUNK));
+        AsciiSet { mask }
+    }
+
+    /// Return the union of two sets.
+    pub const fn union(&self, other: Self) -> Self {
+        let mask = [
+            self.mask[0] | other.mask[0],
+            self.mask[1] | other.mask[1],
+            self.mask[2] | other.mask[2],
+            self.mask[3] | other.mask[3],
+        ];
+        AsciiSet { mask }
+    }
+
+    /// Return the negation of the set.
+    pub const fn complement(&self) -> Self {
+        let mask = [!self.mask[0], !self.mask[1], !self.mask[2], !self.mask[3]];
+        AsciiSet { mask }
+    }
+}
+
+impl ops::Add for AsciiSet {
+    type Output = Self;
+
+    fn add(self, other: Self) -> Self {
+        self.union(other)
+    }
+}
+
+impl ops::Not for AsciiSet {
+    type Output = Self;
+
+    fn not(self) -> Self {
+        self.complement()
+    }
+}
+
+/// The set of 0x00 to 0x1F (C0 controls), and 0x7F (DEL).
+///
+/// Note that this includes the newline and tab characters, but not the space 0x20.
+///
+/// <https://url.spec.whatwg.org/#c0-control-percent-encode-set>
+pub const CONTROLS: &AsciiSet = &AsciiSet {
+    mask: [
+        !0_u32, // C0: 0x00 to 0x1F (32 bits set)
+        0,
+        0,
+        1 << (0x7F_u32 % 32), // DEL: 0x7F (one bit set)
+    ],
+};
+
+macro_rules! static_assert {
+    ($( $bool: expr, )+) => {
+        fn _static_assert() {
+            $(
+                let _ = mem::transmute::<[u8; $bool as usize], u8>;
+            )+
+        }
+    }
+}
+
+static_assert! {
+    CONTROLS.contains(0x00),
+    CONTROLS.contains(0x1F),
+    !CONTROLS.contains(0x20),
+    !CONTROLS.contains(0x7E),
+    CONTROLS.contains(0x7F),
+}
+
+/// Everything that is not an ASCII letter or digit.
+///
+/// This is probably more eager than necessary in any context.
+pub const NON_ALPHANUMERIC: &AsciiSet = &CONTROLS
+    .add(b' ')
+    .add(b'!')
+    .add(b'"')
+    .add(b'#')
+    .add(b'$')
+    .add(b'%')
+    .add(b'&')
+    .add(b'\'')
+    .add(b'(')
+    .add(b')')
+    .add(b'*')
+    .add(b'+')
+    .add(b',')
+    .add(b'-')
+    .add(b'.')
+    .add(b'/')
+    .add(b':')
+    .add(b';')
+    .add(b'<')
+    .add(b'=')
+    .add(b'>')
+    .add(b'?')
+    .add(b'@')
+    .add(b'[')
+    .add(b'\\')
+    .add(b']')
+    .add(b'^')
+    .add(b'_')
+    .add(b'`')
+    .add(b'{')
+    .add(b'|')
+    .add(b'}')
+    .add(b'~');
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn add_op() {
+        let left = AsciiSet::EMPTY.add(b'A');
+        let right = AsciiSet::EMPTY.add(b'B');
+        let expected = AsciiSet::EMPTY.add(b'A').add(b'B');
+        assert_eq!(left + right, expected);
+    }
+
+    #[test]
+    fn not_op() {
+        let set = AsciiSet::EMPTY.add(b'A').add(b'B');
+        let not_set = !set;
+        assert!(!not_set.contains(b'A'));
+        assert!(not_set.contains(b'C'));
+    }
+
+    /// This test ensures that we can get the union of two sets as a constant value, which is
+    /// useful for defining sets in a modular way.
+    #[test]
+    fn union() {
+        const A: AsciiSet = AsciiSet::EMPTY.add(b'A');
+        const B: AsciiSet = AsciiSet::EMPTY.add(b'B');
+        const UNION: AsciiSet = A.union(B);
+        const EXPECTED: AsciiSet = AsciiSet::EMPTY.add(b'A').add(b'B');
+        assert_eq!(UNION, EXPECTED);
+    }
+
+    /// This test ensures that we can get the complement of a set as a constant value, which is
+    /// useful for defining sets in a modular way.
+    #[test]
+    fn complement() {
+        const BOTH: AsciiSet = AsciiSet::EMPTY.add(b'A').add(b'B');
+        const COMPLEMENT: AsciiSet = BOTH.complement();
+        assert!(!COMPLEMENT.contains(b'A'));
+        assert!(!COMPLEMENT.contains(b'B'));
+        assert!(COMPLEMENT.contains(b'C'));
+    }
+}