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 https://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 crate::compartments::enter_realm;
use crate::dom::bindings::conversions::{root_from_object, ToJSValConvertible};
use crate::dom::bindings::error::{Error, Fallible};
use crate::dom::bindings::reflector::DomObject;
use crate::dom::bindings::root::DomRoot;
use crate::dom::bindings::transferable::Transferable;
use crate::dom::blob::{Blob, BlobImpl};
use crate::dom::globalscope::GlobalScope;
use crate::dom::messageport::MessagePort;
use crate::script_runtime::JSContext as SafeJSContext;
use js::glue::CopyJSStructuredCloneData;
use js::glue::DeleteJSAutoStructuredCloneBuffer;
use js::glue::GetLengthOfJSStructuredCloneData;
use js::glue::NewJSAutoStructuredCloneBuffer;
use js::glue::WriteBytesToJSStructuredCloneData;
use js::jsapi::CloneDataPolicy;
use js::jsapi::HandleObject as RawHandleObject;
use js::jsapi::JSContext;
use js::jsapi::MutableHandleObject as RawMutableHandleObject;
use js::jsapi::StructuredCloneScope;
use js::jsapi::TransferableOwnership;
use js::jsapi::JS_STRUCTURED_CLONE_VERSION;
use js::jsapi::{JSObject, JS_ClearPendingException};
use js::jsapi::{JSStructuredCloneCallbacks, JSStructuredCloneReader, JSStructuredCloneWriter};
use js::jsapi::{JS_ReadBytes, JS_WriteBytes};
use js::jsapi::{JS_ReadUint32Pair, JS_WriteUint32Pair};
use js::jsval::UndefinedValue;
use js::rust::wrappers::{JS_ReadStructuredClone, JS_WriteStructuredClone};
use js::rust::{CustomAutoRooterGuard, HandleValue, MutableHandleValue};
use msg::constellation_msg::MessagePortId;
use script_traits::transferable::MessagePortImpl;
use script_traits::StructuredSerializedData;
use std::collections::HashMap;
use std::os::raw;
use std::ptr;

// 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,
    MessagePort = 0xFFFF8002,
    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 StructuredDataHolder,
) -> *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 read_blob = Blob::new(
        &target_global,
        BlobImpl::new_from_bytes(blob_buffer),
        type_str,
    );
    let js_object = read_blob.reflector().get_jsobject().get();
    match sc_holder {
        StructuredDataHolder::Read { blob, .. } => {
            *blob = Some(read_blob);
        },
        _ => panic!("Unexpected variant of StructuredDataHolder"),
    }
    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 StructuredDataHolder));
    }
    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_object::<Blob>(*obj, cx) {
        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 {
    if tag == StructuredCloneTags::MessagePort as u32 {
        let mut sc_holder = &mut *(closure as *mut StructuredDataHolder);
        let owner = GlobalScope::from_context(cx);
        if let Ok(_) = <MessagePort as Transferable>::transfer_receive(
            &owner,
            &mut sc_holder,
            extra_data,
            return_object,
        ) {
            return true;
        }
    }
    false
}

/// <https://html.spec.whatwg.org/multipage/#structuredserializewithtransfer>
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 {
    if let Ok(port) = root_from_object::<MessagePort>(*obj, cx) {
        *tag = StructuredCloneTags::MessagePort as u32;
        *ownership = TransferableOwnership::SCTAG_TMO_CUSTOM;
        let mut sc_holder = &mut *(closure as *mut StructuredDataHolder);
        if let Ok(data) = port.transfer(&mut sc_holder) {
            *extra_data = data;
            return true;
        }
    }
    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 can_transfer_callback(
    cx: *mut JSContext,
    obj: RawHandleObject,
    _closure: *mut raw::c_void,
) -> bool {
    if let Ok(_port) = root_from_object::<MessagePort>(*obj, cx) {
        return true;
    }
    false
}

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),
    canTransfer: Some(can_transfer_callback),
};

/// A data holder for results from, and inputs to, structured-data read/write operations.
/// https://html.spec.whatwg.org/multipage/#safe-passing-of-structured-data
pub enum StructuredDataHolder {
    Read {
        /// A deserialized blob, stored temporarily here to keep it rooted.
        blob: Option<DomRoot<Blob>>,
        /// A vec of transfer-received DOM ports,
        /// to be made available to script through a message event.
        message_ports: Option<Vec<DomRoot<MessagePort>>>,
        /// A map of port implementations,
        /// used as part of the "transfer-receiving" steps of ports,
        /// to produce the DOM ports stored in `message_ports` above.
        port_impls: Option<HashMap<MessagePortId, MessagePortImpl>>,
    },
    /// A data holder into which transferred ports
    /// can be written as part of their transfer steps.
    Write(Option<HashMap<MessagePortId, MessagePortImpl>>),
}

/// Writes a structured clone. Returns a `DataClone` error if that fails.
pub fn write(
    cx: SafeJSContext,
    message: HandleValue,
    transfer: Option<CustomAutoRooterGuard<Vec<*mut JSObject>>>,
) -> Fallible<StructuredSerializedData> {
    unsafe {
        rooted!(in(*cx) let mut val = UndefinedValue());
        if let Some(transfer) = transfer {
            transfer.to_jsval(*cx, val.handle_mut());
        }

        let mut sc_holder = StructuredDataHolder::Write(None);
        let sc_holder_ptr = &mut sc_holder as *mut _;

        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,
            sc_holder_ptr as *mut raw::c_void,
            val.handle(),
        );
        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);

        let mut port_impls = match sc_holder {
            StructuredDataHolder::Write(port_impls) => port_impls,
            _ => panic!("Unexpected variant of StructuredDataHolder"),
        };

        let data = StructuredSerializedData {
            serialized: data,
            ports: port_impls.take(),
        };

        Ok(data)
    }
}

/// Read structured serialized data, possibly containing transferred objects.
/// Returns a vec of rooted transfer-received ports, or an error.
pub fn read(
    global: &GlobalScope,
    mut data: StructuredSerializedData,
    rval: MutableHandleValue,
) -> Result<Vec<DomRoot<MessagePort>>, ()> {
    let cx = global.get_cx();
    let _ac = enter_realm(&*global);
    let mut sc_holder = StructuredDataHolder::Read {
        blob: None,
        message_ports: None,
        port_impls: data.ports.take(),
    };
    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.serialized.as_mut_ptr() as *const u8,
            data.serialized.len(),
            scdata,
        );

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

        DeleteJSAutoStructuredCloneBuffer(scbuf);

        if result {
            let (mut message_ports, port_impls) = match sc_holder {
                StructuredDataHolder::Read {
                    message_ports,
                    port_impls,
                    ..
                } => (message_ports, port_impls),
                _ => panic!("Unexpected variant of StructuredDataHolder"),
            };

            // Any transfer-received port-impls should have been taken out.
            assert!(port_impls.is_none());

            match message_ports.take() {
                Some(ports) => return Ok(ports),
                None => return Ok(Vec::with_capacity(0)),
            }
        }
        Err(())
    }
}