servo/components/style/gecko_string_cache/mod.rs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#![allow(unsafe_code)]

//! A drop-in replacement for string_cache, but backed by Gecko `nsAtom`s.

use gecko_bindings::bindings::Gecko_AddRefAtom;
use gecko_bindings::bindings::Gecko_Atomize;
use gecko_bindings::bindings::Gecko_Atomize16;
use gecko_bindings::bindings::Gecko_ReleaseAtom;
use gecko_bindings::structs::{nsAtom, nsAtom_AtomKind, nsDynamicAtom, nsStaticAtom};
use nsstring::{nsAString, nsStr};
use precomputed_hash::PrecomputedHash;
use std::{mem, slice, str};
use std::borrow::{Borrow, Cow};
use std::char::{self, DecodeUtf16};
use std::fmt::{self, Write};
use std::hash::{Hash, Hasher};
use std::iter::Cloned;
use std::ops::Deref;
use style_traits::SpecifiedValueInfo;

#[macro_use]
#[allow(improper_ctypes, non_camel_case_types, missing_docs)]
pub mod atom_macro {
    include!(concat!(env!("OUT_DIR"), "/gecko/atom_macro.rs"));
}

#[macro_use]
pub mod namespace;

pub use self::namespace::{Namespace, WeakNamespace};

macro_rules! local_name {
    ($s:tt) => {
        atom!($s)
    };
}

/// A strong reference to a Gecko atom.
#[derive(Eq, PartialEq)]
pub struct Atom(*mut WeakAtom);

/// An atom *without* a strong reference.
///
/// Only usable as `&'a WeakAtom`,
/// where `'a` is the lifetime of something that holds a strong reference to that atom.
pub struct WeakAtom(nsAtom);

/// A BorrowedAtom for Gecko is just a weak reference to a `nsAtom`, that
/// hasn't been bumped.
pub type BorrowedAtom<'a> = &'a WeakAtom;

impl Deref for Atom {
    type Target = WeakAtom;

    #[inline]
    fn deref(&self) -> &WeakAtom {
        unsafe { &*self.0 }
    }
}

impl PrecomputedHash for Atom {
    #[inline]
    fn precomputed_hash(&self) -> u32 {
        self.get_hash()
    }
}

impl Borrow<WeakAtom> for Atom {
    #[inline]
    fn borrow(&self) -> &WeakAtom {
        self
    }
}

impl Eq for WeakAtom {}
impl PartialEq for WeakAtom {
    #[inline]
    fn eq(&self, other: &Self) -> bool {
        let weak: *const WeakAtom = self;
        let other: *const WeakAtom = other;
        weak == other
    }
}

unsafe impl Send for Atom {}
unsafe impl Sync for Atom {}
unsafe impl Sync for WeakAtom {}

impl WeakAtom {
    /// Construct a `WeakAtom` from a raw `nsAtom`.
    #[inline]
    pub unsafe fn new<'a>(atom: *const nsAtom) -> &'a mut Self {
        &mut *(atom as *mut WeakAtom)
    }

    /// Clone this atom, bumping the refcount if the atom is not static.
    #[inline]
    pub fn clone(&self) -> Atom {
        unsafe { Atom::from_raw(self.as_ptr()) }
    }

    /// Get the atom hash.
    #[inline]
    pub fn get_hash(&self) -> u32 {
        self.0.mHash
    }

    /// Get the atom as a slice of utf-16 chars.
    #[inline]
    pub fn as_slice(&self) -> &[u16] {
        let string = if self.is_static() {
            let atom_ptr = self.as_ptr() as *const nsStaticAtom;
            let string_offset = unsafe { (*atom_ptr).mStringOffset };
            let string_offset = -(string_offset as isize);
            let u8_ptr = atom_ptr as *const u8;
            // It is safe to use offset() here because both addresses are within
            // the same struct, e.g. mozilla::detail::gGkAtoms.
            unsafe { u8_ptr.offset(string_offset) as *const u16 }
        } else {
            let atom_ptr = self.as_ptr() as *const nsDynamicAtom;
            // Dynamic atom chars are stored at the end of the object.
            unsafe { atom_ptr.offset(1) as *const u16 }
        };
        unsafe { slice::from_raw_parts(string, self.len() as usize) }
    }

    // NOTE: don't expose this, since it's slow, and easy to be misused.
    fn chars(&self) -> DecodeUtf16<Cloned<slice::Iter<u16>>> {
        char::decode_utf16(self.as_slice().iter().cloned())
    }

    /// Execute `cb` with the string that this atom represents.
    ///
    /// Find alternatives to this function when possible, please, since it's
    /// pretty slow.
    pub fn with_str<F, Output>(&self, cb: F) -> Output
    where
        F: FnOnce(&str) -> Output,
    {
        let mut buffer: [u8; 64] = unsafe { mem::uninitialized() };

        // The total string length in utf16 is going to be less than or equal
        // the slice length (each utf16 character is going to take at least one
        // and at most 2 items in the utf16 slice).
        //
        // Each of those characters will take at most four bytes in the utf8
        // one. Thus if the slice is less than 64 / 4 (16) we can guarantee that
        // we'll decode it in place.
        let owned_string;
        let len = self.len();
        let utf8_slice = if len <= 16 {
            let mut total_len = 0;

            for c in self.chars() {
                let c = c.unwrap_or(char::REPLACEMENT_CHARACTER);
                let utf8_len = c.encode_utf8(&mut buffer[total_len..]).len();
                total_len += utf8_len;
            }

            let slice = unsafe { str::from_utf8_unchecked(&buffer[..total_len]) };
            debug_assert_eq!(slice, String::from_utf16_lossy(self.as_slice()));
            slice
        } else {
            owned_string = String::from_utf16_lossy(self.as_slice());
            &*owned_string
        };

        cb(utf8_slice)
    }

    /// Returns whether this atom is static.
    #[inline]
    pub fn is_static(&self) -> bool {
        unsafe { (*self.as_ptr()).mKind() == nsAtom_AtomKind::Static as u32 }
    }

    /// Returns the length of the atom string.
    #[inline]
    pub fn len(&self) -> u32 {
        unsafe { (*self.as_ptr()).mLength() }
    }

    /// Returns whether this atom is the empty string.
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }

    /// Returns the atom as a mutable pointer.
    #[inline]
    pub fn as_ptr(&self) -> *mut nsAtom {
        let const_ptr: *const nsAtom = &self.0;
        const_ptr as *mut nsAtom
    }

    /// Convert this atom to ASCII lower-case
    pub fn to_ascii_lowercase(&self) -> Atom {
        let slice = self.as_slice();
        match slice
            .iter()
            .position(|&char16| (b'A' as u16) <= char16 && char16 <= (b'Z' as u16))
        {
            None => self.clone(),
            Some(i) => {
                let mut buffer: [u16; 64] = unsafe { mem::uninitialized() };
                let mut vec;
                let mutable_slice = if let Some(buffer_prefix) = buffer.get_mut(..slice.len()) {
                    buffer_prefix.copy_from_slice(slice);
                    buffer_prefix
                } else {
                    vec = slice.to_vec();
                    &mut vec
                };
                for char16 in &mut mutable_slice[i..] {
                    if *char16 <= 0x7F {
                        *char16 = (*char16 as u8).to_ascii_lowercase() as u16
                    }
                }
                Atom::from(&*mutable_slice)
            },
        }
    }

    /// Return whether two atoms are ASCII-case-insensitive matches
    pub fn eq_ignore_ascii_case(&self, other: &Self) -> bool {
        if self == other {
            return true;
        }

        let a = self.as_slice();
        let b = other.as_slice();
        a.len() == b.len() && a.iter().zip(b).all(|(&a16, &b16)| {
            if a16 <= 0x7F && b16 <= 0x7F {
                (a16 as u8).eq_ignore_ascii_case(&(b16 as u8))
            } else {
                a16 == b16
            }
        })
    }

    /// Return whether this atom is an ASCII-case-insensitive match for the given string
    pub fn eq_str_ignore_ascii_case(&self, other: &str) -> bool {
        self.chars()
            .map(|r| r.map(|c: char| c.to_ascii_lowercase()))
            .eq(other.chars().map(|c: char| Ok(c.to_ascii_lowercase())))
    }
}

impl fmt::Debug for WeakAtom {
    fn fmt(&self, w: &mut fmt::Formatter) -> fmt::Result {
        write!(w, "Gecko WeakAtom({:p}, {})", self, self)
    }
}

impl fmt::Display for WeakAtom {
    fn fmt(&self, w: &mut fmt::Formatter) -> fmt::Result {
        for c in self.chars() {
            w.write_char(c.unwrap_or(char::REPLACEMENT_CHARACTER))?
        }
        Ok(())
    }
}

impl Atom {
    /// Execute a callback with the atom represented by `ptr`.
    pub unsafe fn with<F, R>(ptr: *mut nsAtom, callback: F) -> R
    where
        F: FnOnce(&Atom) -> R,
    {
        let atom = Atom(WeakAtom::new(ptr));
        let ret = callback(&atom);
        mem::forget(atom);
        ret
    }

    /// Creates an atom from an static atom pointer without checking in release
    /// builds.
    ///
    /// Right now it's only used by the atom macro, and ideally it should keep
    /// that way, now we have sugar for is_static, creating atoms using
    /// Atom::from_raw should involve almost no overhead.
    #[inline]
    pub unsafe fn from_static(ptr: *mut nsStaticAtom) -> Self {
        let atom = Atom(ptr as *mut WeakAtom);
        debug_assert!(
            atom.is_static(),
            "Called from_static for a non-static atom!"
        );
        atom
    }

    /// Creates an atom from an atom pointer.
    #[inline(always)]
    pub unsafe fn from_raw(ptr: *mut nsAtom) -> Self {
        let atom = Atom(ptr as *mut WeakAtom);
        if !atom.is_static() {
            Gecko_AddRefAtom(ptr);
        }
        atom
    }

    /// Creates an atom from a dynamic atom pointer that has already had AddRef
    /// called on it.
    #[inline]
    pub unsafe fn from_addrefed(ptr: *mut nsAtom) -> Self {
        assert!(!ptr.is_null());
        Atom(WeakAtom::new(ptr))
    }

    /// Convert this atom into an addrefed nsAtom pointer.
    #[inline]
    pub fn into_addrefed(self) -> *mut nsAtom {
        let ptr = self.as_ptr();
        mem::forget(self);
        ptr
    }
}

impl Hash for Atom {
    fn hash<H>(&self, state: &mut H)
    where
        H: Hasher,
    {
        state.write_u32(self.get_hash());
    }
}

impl Hash for WeakAtom {
    fn hash<H>(&self, state: &mut H)
    where
        H: Hasher,
    {
        state.write_u32(self.get_hash());
    }
}

impl Clone for Atom {
    #[inline(always)]
    fn clone(&self) -> Atom {
        unsafe { Atom::from_raw(self.as_ptr()) }
    }
}

impl Drop for Atom {
    #[inline]
    fn drop(&mut self) {
        if !self.is_static() {
            unsafe {
                Gecko_ReleaseAtom(self.as_ptr());
            }
        }
    }
}

impl Default for Atom {
    #[inline]
    fn default() -> Self {
        atom!("")
    }
}

impl fmt::Debug for Atom {
    fn fmt(&self, w: &mut fmt::Formatter) -> fmt::Result {
        write!(w, "Gecko Atom({:p}, {})", self.0, self)
    }
}

impl fmt::Display for Atom {
    fn fmt(&self, w: &mut fmt::Formatter) -> fmt::Result {
        unsafe { (&*self.0).fmt(w) }
    }
}

impl<'a> From<&'a str> for Atom {
    #[inline]
    fn from(string: &str) -> Atom {
        debug_assert!(string.len() <= u32::max_value() as usize);
        unsafe {
            Atom(WeakAtom::new(Gecko_Atomize(
                string.as_ptr() as *const _,
                string.len() as u32,
            )))
        }
    }
}

impl<'a> From<&'a [u16]> for Atom {
    #[inline]
    fn from(slice: &[u16]) -> Atom {
        Atom::from(&*nsStr::from(slice))
    }
}

impl<'a> From<&'a nsAString> for Atom {
    #[inline]
    fn from(string: &nsAString) -> Atom {
        unsafe { Atom(WeakAtom::new(Gecko_Atomize16(string))) }
    }
}

impl<'a> From<Cow<'a, str>> for Atom {
    #[inline]
    fn from(string: Cow<'a, str>) -> Atom {
        Atom::from(&*string)
    }
}

impl From<String> for Atom {
    #[inline]
    fn from(string: String) -> Atom {
        Atom::from(&*string)
    }
}

malloc_size_of_is_0!(Atom);

impl SpecifiedValueInfo for Atom {}