servo/components/script/dom/bindings/structuredclone.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/. */

//! This module implements structured cloning, as defined by [HTML]
//! (https://html.spec.whatwg.org/multipage/#safe-passing-of-structured-data).

use dom::bindings::conversions::root_from_handleobject;
use dom::bindings::error::{Error, Fallible};
use dom::bindings::reflector::DomObject;
use dom::bindings::root::DomRoot;
use dom::blob::{Blob, BlobImpl};
use dom::globalscope::GlobalScope;
use js::glue::CopyJSStructuredCloneData;
use js::glue::DeleteJSAutoStructuredCloneBuffer;
use js::glue::GetLengthOfJSStructuredCloneData;
use js::glue::NewJSAutoStructuredCloneBuffer;
use js::glue::WriteBytesToJSStructuredCloneData;
use js::jsapi::{JSAutoCompartment, JSContext};
use js::jsapi::{JSStructuredCloneCallbacks, JSStructuredCloneReader, JSStructuredCloneWriter};
use js::jsapi::{JS_ClearPendingException, JSObject};
use js::jsapi::{JS_ReadBytes, JS_WriteBytes};
use js::jsapi::{JS_ReadUint32Pair, JS_WriteUint32Pair};
use js::jsapi::CloneDataPolicy;
use js::jsapi::HandleObject as RawHandleObject;
use js::jsapi::JS_STRUCTURED_CLONE_VERSION;
use js::jsapi::MutableHandleObject as RawMutableHandleObject;
use js::jsapi::StructuredCloneScope;
use js::jsapi::TransferableOwnership;
use js::rust::{Handle, HandleValue, MutableHandleValue};
use js::rust::wrappers::{JS_WriteStructuredClone, JS_ReadStructuredClone};
use libc::size_t;
use std::os::raw;
use std::ptr;
use std::slice;

// TODO: Should we add Min and Max const to https://github.com/servo/rust-mozjs/blob/master/src/consts.rs?
// TODO: Determine for sure which value Min and Max should have.
// NOTE: Current values found at https://dxr.mozilla.org/mozilla-central/
// rev/ff04d410e74b69acfab17ef7e73e7397602d5a68/js/public/StructuredClone.h#323
#[repr(u32)]
enum StructuredCloneTags {
    /// To support additional types, add new tags with values incremented from the last one before Max.
    Min = 0xFFFF8000,
    DomBlob = 0xFFFF8001,
    Max = 0xFFFFFFFF,
}

#[cfg(target_pointer_width = "64")]
unsafe fn write_length(w: *mut JSStructuredCloneWriter, length: usize) {
    let high: u32 = (length >> 32) as u32;
    let low: u32 = length as u32;
    assert!(JS_WriteUint32Pair(w, high, low));
}

#[cfg(target_pointer_width = "32")]
unsafe fn write_length(w: *mut JSStructuredCloneWriter, length: usize) {
    assert!(JS_WriteUint32Pair(w, length as u32, 0));
}

#[cfg(target_pointer_width = "64")]
unsafe fn read_length(r: *mut JSStructuredCloneReader) -> usize {
    let mut high: u32 = 0;
    let mut low: u32 = 0;
    assert!(JS_ReadUint32Pair(
        r,
        &mut high as *mut u32,
        &mut low as *mut u32
    ));
    return (low << high) as usize;
}

#[cfg(target_pointer_width = "32")]
unsafe fn read_length(r: *mut JSStructuredCloneReader) -> usize {
    let mut length: u32 = 0;
    let mut zero: u32 = 0;
    assert!(JS_ReadUint32Pair(
        r,
        &mut length as *mut u32,
        &mut zero as *mut u32
    ));
    return length as usize;
}

struct StructuredCloneWriter {
    w: *mut JSStructuredCloneWriter,
}

impl StructuredCloneWriter {
    unsafe fn write_slice(&self, v: &[u8]) {
        let type_length = v.len();
        write_length(self.w, type_length);
        assert!(JS_WriteBytes(
            self.w,
            v.as_ptr() as *const raw::c_void,
            type_length
        ));
    }
    unsafe fn write_str(&self, s: &str) {
        self.write_slice(s.as_bytes());
    }
}

struct StructuredCloneReader {
    r: *mut JSStructuredCloneReader,
}

impl StructuredCloneReader {
    unsafe fn read_bytes(&self) -> Vec<u8> {
        let mut bytes = vec![0u8; read_length(self.r)];
        let blob_length = bytes.len();
        assert!(JS_ReadBytes(
            self.r,
            bytes.as_mut_ptr() as *mut raw::c_void,
            blob_length
        ));
        return bytes;
    }
    unsafe fn read_str(&self) -> String {
        let str_buffer = self.read_bytes();
        return String::from_utf8_unchecked(str_buffer);
    }
}

unsafe fn read_blob(
    cx: *mut JSContext,
    r: *mut JSStructuredCloneReader,
    sc_holder: &mut StructuredCloneHolder,
) -> *mut JSObject {
    let structured_reader = StructuredCloneReader { r: r };
    let blob_buffer = structured_reader.read_bytes();
    let type_str = structured_reader.read_str();
    let target_global = GlobalScope::from_context(cx);
    let blob = Blob::new(
        &target_global,
        BlobImpl::new_from_bytes(blob_buffer),
        type_str,
    );
    let js_object = blob.reflector().get_jsobject().get();
    sc_holder.blob = Some(blob);
    js_object
}

unsafe fn write_blob(blob: DomRoot<Blob>, w: *mut JSStructuredCloneWriter) -> Result<(), ()> {
    let structured_writer = StructuredCloneWriter { w: w };
    let blob_vec = blob.get_bytes()?;
    assert!(JS_WriteUint32Pair(
        w,
        StructuredCloneTags::DomBlob as u32,
        0
    ));
    structured_writer.write_slice(&blob_vec);
    structured_writer.write_str(&blob.type_string());
    return Ok(());
}

unsafe extern "C" fn read_callback(
    cx: *mut JSContext,
    r: *mut JSStructuredCloneReader,
    tag: u32,
    _data: u32,
    closure: *mut raw::c_void,
) -> *mut JSObject {
    assert!(
        tag < StructuredCloneTags::Max as u32,
        "tag should be lower than StructuredCloneTags::Max"
    );
    assert!(
        tag > StructuredCloneTags::Min as u32,
        "tag should be higher than StructuredCloneTags::Min"
    );
    if tag == StructuredCloneTags::DomBlob as u32 {
        return read_blob(cx, r, &mut *(closure as *mut StructuredCloneHolder));
    }
    return ptr::null_mut();
}

unsafe extern "C" fn write_callback(
    _cx: *mut JSContext,
    w: *mut JSStructuredCloneWriter,
    obj: RawHandleObject,
    _closure: *mut raw::c_void,
) -> bool {
    if let Ok(blob) = root_from_handleobject::<Blob>(Handle::from_raw(obj)) {
        return write_blob(blob, w).is_ok();
    }
    return false;
}

unsafe extern "C" fn read_transfer_callback(
    _cx: *mut JSContext,
    _r: *mut JSStructuredCloneReader,
    _tag: u32,
    _content: *mut raw::c_void,
    _extra_data: u64,
    _closure: *mut raw::c_void,
    _return_object: RawMutableHandleObject,
) -> bool {
    false
}

unsafe extern "C" fn write_transfer_callback(
    _cx: *mut JSContext,
    _obj: RawHandleObject,
    _closure: *mut raw::c_void,
    _tag: *mut u32,
    _ownership: *mut TransferableOwnership,
    _content: *mut *mut raw::c_void,
    _extra_data: *mut u64,
) -> bool {
    false
}

unsafe extern "C" fn free_transfer_callback(
    _tag: u32,
    _ownership: TransferableOwnership,
    _content: *mut raw::c_void,
    _extra_data: u64,
    _closure: *mut raw::c_void,
) {
}

unsafe extern "C" fn report_error_callback(_cx: *mut JSContext, _errorid: u32) {}

static STRUCTURED_CLONE_CALLBACKS: JSStructuredCloneCallbacks = JSStructuredCloneCallbacks {
    read: Some(read_callback),
    write: Some(write_callback),
    reportError: Some(report_error_callback),
    readTransfer: Some(read_transfer_callback),
    writeTransfer: Some(write_transfer_callback),
    freeTransfer: Some(free_transfer_callback),
};

struct StructuredCloneHolder {
    blob: Option<DomRoot<Blob>>,
}

/// A buffer for a structured clone.
pub enum StructuredCloneData {
    /// A non-serializable (default) variant
    Struct(*mut u64, size_t),
    /// A variant that can be serialized
    Vector(Vec<u8>),
}

impl StructuredCloneData {
    // TODO: should this be unsafe?
    /// Writes a structured clone. Returns a `DataClone` error if that fails.
    pub fn write(cx: *mut JSContext, message: HandleValue) -> Fallible<StructuredCloneData> {
        unsafe {
            let scbuf = NewJSAutoStructuredCloneBuffer(
                StructuredCloneScope::DifferentProcess,
                &STRUCTURED_CLONE_CALLBACKS,
            );
            let scdata = &mut ((*scbuf).data_);
            let policy = CloneDataPolicy {
                // TODO: SAB?
                sharedArrayBuffer_: false,
            };
            let result = JS_WriteStructuredClone(
                cx,
                message,
                scdata,
                StructuredCloneScope::DifferentProcess,
                policy,
                &STRUCTURED_CLONE_CALLBACKS,
                ptr::null_mut(),
                HandleValue::undefined(),
            );
            if !result {
                JS_ClearPendingException(cx);
                return Err(Error::DataClone);
            }

            let nbytes = GetLengthOfJSStructuredCloneData(scdata);
            let mut data = Vec::with_capacity(nbytes);
            CopyJSStructuredCloneData(scdata, data.as_mut_ptr());
            data.set_len(nbytes);

            DeleteJSAutoStructuredCloneBuffer(scbuf);

            Ok(StructuredCloneData::Vector(data))
        }
    }

    /// Converts a StructuredCloneData to Vec<u8> for inter-thread sharing
    pub fn move_to_arraybuffer(self) -> Vec<u8> {
        match self {
            StructuredCloneData::Struct(data, nbytes) => unsafe {
                slice::from_raw_parts(data as *mut u8, nbytes).to_vec()
            },
            StructuredCloneData::Vector(msg) => msg,
        }
    }

    /// Reads a structured clone.
    ///
    /// Panics if `JS_ReadStructuredClone` fails.
    fn read_clone(global: &GlobalScope, data: *mut u64, nbytes: size_t, rval: MutableHandleValue) {
        let cx = global.get_cx();
        let globalhandle = global.reflector().get_jsobject();
        let _ac = JSAutoCompartment::new(cx, globalhandle.get());
        let mut sc_holder = StructuredCloneHolder { blob: None };
        let sc_holder_ptr = &mut sc_holder as *mut _;
        unsafe {
            let scbuf = NewJSAutoStructuredCloneBuffer(
                StructuredCloneScope::DifferentProcess,
                &STRUCTURED_CLONE_CALLBACKS,
            );
            let scdata = &mut ((*scbuf).data_);

            WriteBytesToJSStructuredCloneData(data as *const u8, nbytes, scdata);

            assert!(JS_ReadStructuredClone(
                cx,
                scdata,
                JS_STRUCTURED_CLONE_VERSION,
                StructuredCloneScope::DifferentProcess,
                rval,
                &STRUCTURED_CLONE_CALLBACKS,
                sc_holder_ptr as *mut raw::c_void
            ));

            DeleteJSAutoStructuredCloneBuffer(scbuf);
        }
    }

    /// Thunk for the actual `read_clone` method. Resolves proper variant for read_clone.
    pub fn read(self, global: &GlobalScope, rval: MutableHandleValue) {
        match self {
            StructuredCloneData::Vector(mut vec_msg) => {
                let nbytes = vec_msg.len();
                let data = vec_msg.as_mut_ptr() as *mut u64;
                StructuredCloneData::read_clone(global, data, nbytes, rval);
            },
            StructuredCloneData::Struct(data, nbytes) => {
                StructuredCloneData::read_clone(global, data, nbytes, rval)
            },
        }
    }
}

unsafe impl Send for StructuredCloneData {}