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/* Copyright 2018 Mozilla Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
use crate::{
BinaryReader, BinaryReaderError, ConstExpr, Result, SectionIteratorLimited, SectionReader,
SectionWithLimitedItems,
};
use std::ops::Range;
/// Represents a data segment in a core WebAssembly module.
#[derive(Debug, Clone)]
pub struct Data<'a> {
/// The kind of data segment.
pub kind: DataKind<'a>,
/// The data of the data segment.
pub data: &'a [u8],
/// The range of the data segment.
pub range: Range<usize>,
}
/// The kind of data segment.
#[derive(Debug, Copy, Clone)]
pub enum DataKind<'a> {
/// The data segment is passive.
Passive,
/// The data segment is active.
Active {
/// The memory index for the data segment.
memory_index: u32,
/// The initialization expression for the data segment.
offset_expr: ConstExpr<'a>,
},
}
/// A reader for the data section of a WebAssembly module.
#[derive(Clone)]
pub struct DataSectionReader<'a> {
reader: BinaryReader<'a>,
count: u32,
}
impl<'a> DataSectionReader<'a> {
/// Constructs a new `DataSectionReader` for the given data and offset.
pub fn new(data: &'a [u8], offset: usize) -> Result<DataSectionReader<'a>> {
let mut reader = BinaryReader::new_with_offset(data, offset);
let count = reader.read_var_u32()?;
Ok(DataSectionReader { reader, count })
}
/// Gets the original position of the section reader.
pub fn original_position(&self) -> usize {
self.reader.original_position()
}
/// Gets the count of items in the section.
pub fn get_count(&self) -> u32 {
self.count
}
fn verify_data_end(&self, end: usize) -> Result<()> {
if self.reader.buffer.len() < end {
return Err(BinaryReaderError::new(
"unexpected end of section or function: data segment extends past end of the data section",
self.reader.original_offset + self.reader.buffer.len(),
));
}
Ok(())
}
/// Reads content of the data section.
///
/// # Examples
/// ```
/// use wasmparser::{DataSectionReader, DataKind};
/// # let data: &[u8] = &[
/// # 0x01, 0x00, 0x41, 0x80, 0x08, 0x0b, 0x04, 0x00, 0x00, 0x00, 0x00];
/// let mut data_reader = DataSectionReader::new(data, 0).unwrap();
/// for _ in 0..data_reader.get_count() {
/// let data = data_reader.read().expect("data");
/// println!("Data: {:?}", data);
/// if let DataKind::Active { offset_expr, .. } = data.kind {
/// let mut offset_expr_reader = offset_expr.get_binary_reader();
/// let op = offset_expr_reader.read_operator().expect("op");
/// println!("offset expression: {:?}", op);
/// }
/// }
/// ```
pub fn read<'b>(&mut self) -> Result<Data<'b>>
where
'a: 'b,
{
let segment_start = self.reader.original_position();
// The current handling of the flags is largely specified in the `bulk-memory` proposal,
// which at the time this commend is written has been merged to the main specification
// draft.
//
// Notably, this proposal allows multiple different encodings of the memory index 0. `00`
// and `02 00` are both valid ways to specify the 0-th memory. However it also makes
// another encoding of the 0-th memory `80 00` no longer valid.
//
// We, however maintain this by parsing `flags` as a LEB128 integer. In that case, `80 00`
// encoding is parsed out as `0` and is therefore assigned a `memidx` 0, even though the
// current specification draft does not allow for this.
//
// See also https://github.com/WebAssembly/spec/issues/1439
let flags = self.reader.read_var_u32()?;
let kind = match flags {
1 => DataKind::Passive,
0 | 2 => {
let memory_index = if flags == 0 {
0
} else {
self.reader.read_var_u32()?
};
let offset_expr = {
let expr_offset = self.reader.position;
self.reader.skip_const_expr()?;
let data = &self.reader.buffer[expr_offset..self.reader.position];
ConstExpr::new(data, self.reader.original_offset + expr_offset)
};
DataKind::Active {
memory_index,
offset_expr,
}
}
_ => {
return Err(BinaryReaderError::new(
"invalid flags byte in data segment",
self.reader.original_position() - 1,
));
}
};
let data_len = self.reader.read_var_u32()? as usize;
let data_end = self.reader.position + data_len;
self.verify_data_end(data_end)?;
let data = &self.reader.buffer[self.reader.position..data_end];
self.reader.skip_to(data_end);
let segment_end = self.reader.original_position();
let range = segment_start..segment_end;
Ok(Data { kind, data, range })
}
}
impl<'a> SectionReader for DataSectionReader<'a> {
type Item = Data<'a>;
fn read(&mut self) -> Result<Self::Item> {
DataSectionReader::read(self)
}
fn eof(&self) -> bool {
self.reader.eof()
}
fn original_position(&self) -> usize {
DataSectionReader::original_position(self)
}
fn range(&self) -> Range<usize> {
self.reader.range()
}
}
impl<'a> SectionWithLimitedItems for DataSectionReader<'a> {
fn get_count(&self) -> u32 {
DataSectionReader::get_count(self)
}
}
impl<'a> IntoIterator for DataSectionReader<'a> {
type Item = Result<Data<'a>>;
type IntoIter = SectionIteratorLimited<DataSectionReader<'a>>;
fn into_iter(self) -> Self::IntoIter {
SectionIteratorLimited::new(self)
}
}