evm_precompiles/

data.rs

// Copyright 2019-2021 PureStake Inc.
// This file is part of Moonbeam.

// Moonbeam is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Moonbeam is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Moonbeam. If not, see <http://www.gnu.org/licenses/>.

use super::{error, EvmResult};
use core::{any::type_name, ops::Range};
use primitive_types::{H160, H256, U256};
use std::{convert::TryInto, vec, vec::Vec};

/// The `address` type of Solidity.
/// H160 could represent 2 types of data (bytes20 and address) that are not encoded the same way.
/// To avoid issues writing H160 is thus not supported.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct Address(pub H160);

impl From<H160> for Address {
    fn from(a: H160) -> Address {
        Address(a)
    }
}

impl From<Address> for H160 {
    fn from(a: Address) -> H160 {
        a.0
    }
}

/// Wrapper around an EVM input slice, helping to parse it.
/// Provide functions to parse common types.
#[derive(Clone, Copy, Debug)]
pub struct EvmDataReader<'a> {
    input: &'a [u8],
    cursor: usize,
}

impl<'a> EvmDataReader<'a> {
    /// Create a new input parser.
    pub fn new(input: &'a [u8]) -> Self {
        Self { input, cursor: 0 }
    }

    /// Check the input has at least the correct amount of arguments before the end (32 bytes values).
    pub fn expect_arguments(&self, args: usize) -> EvmResult {
        if self.input.len() >= self.cursor + args * 32 {
            Ok(())
        } else {
            Err(error("input doesn't match expected length"))
        }
    }

    /// Read data from the input.
    pub fn read<T: EvmData>(&mut self) -> EvmResult<T> {
        T::read(self)
    }

    /// Read raw bytes from the input.
    /// Doesn't handle any alignement checks, prefer using `read` instead of possible.
    /// Returns an error if trying to parse out of bounds.
    pub fn read_raw_bytes(&mut self, len: usize) -> EvmResult<&[u8]> {
        let range = self.move_cursor(len)?;

        let data = self
            .input
            .get(range)
            .ok_or_else(|| error("tried to parse raw bytes out of bounds"))?;

        Ok(data)
    }

    /// Parse (4 bytes) selector.
    /// Returns an error if trying to parse out of bounds.
    pub fn read_selector<T>(&mut self) -> EvmResult<T>
    where
        T: num_enum::TryFromPrimitive<Primitive = u32>,
    {
        let mut buffer = [0u8; 4];
        buffer.copy_from_slice(
            self.read_raw_bytes(4)
                .map_err(|_| error("tried to parse selector out of bounds"))?,
        );
        T::try_from_primitive(u32::from_be_bytes(buffer)).map_err(|_| {
            log::trace!(
                target: "precompile",
                "Failed to match function selector for {}",
                type_name::<T>()
            );
            error("unknown selector")
        })
    }

    /// Move the reading cursor with provided length, and return a range from the previous cursor
    /// location to the new one.
    /// Checks cursor overflows.
    fn move_cursor(&mut self, len: usize) -> EvmResult<Range<usize>> {
        let start = self.cursor;
        let end = self
            .cursor
            .checked_add(len)
            .ok_or_else(|| error("data reading cursor overflow"))?;

        self.cursor = end;

        Ok(start..end)
    }
}

/// Help build an EVM input/output data.
#[derive(Clone, Debug)]
pub struct EvmDataWriter {
    pub(crate) data: Vec<u8>,
    arrays: Vec<Array>,
}

#[derive(Clone, Debug)]
struct Array {
    offset_position: usize,
    data: Vec<u8>,
    inner_arrays: Vec<Array>,
}

impl EvmDataWriter {
    /// Creates a new empty output builder.
    pub fn new() -> Self {
        Self {
            data: vec![],
            arrays: vec![],
        }
    }

    /// Return the built data.
    pub fn build(mut self) -> Vec<u8> {
        Self::build_arrays(&mut self.data, self.arrays, 0);

        self.data
    }

    /// Build the array into data.
    /// `global_offset` represents the start of the frame we are modifying.
    /// While the main data will have a `global_offset` of 0, inner arrays will have a
    /// `global_offset` corresponding to the start its parent array size data.
    fn build_arrays(output: &mut Vec<u8>, arrays: Vec<Array>, global_offset: usize) {
        for mut array in arrays {
            let offset_position = array.offset_position;
            let offset_position_end = offset_position + 32;
            let free_space_offset = output.len() + global_offset;

            // Override dummy offset to the offset it will be in the final output.
            U256::from(free_space_offset)
                .to_big_endian(&mut output[offset_position..offset_position_end]);

            // Build inner arrays if any.
            Self::build_arrays(&mut array.data, array.inner_arrays, free_space_offset);

            // Append this data at the end of the current output.
            output.append(&mut array.data);
        }
    }

    /// Write arbitrary bytes.
    /// Doesn't handle any alignement checks, prefer using `write` instead if possible.
    pub fn write_raw_bytes(mut self, value: &[u8]) -> Self {
        self.data.extend_from_slice(value);
        self
    }

    /// Write a selector.
    /// The provided type must impl `Into<u32>`.
    /// Doesn't handle any alignement checks, should be used only when adding the initial
    /// selector of a Solidity call data.
    pub fn write_selector<T: Into<u32>>(self, value: T) -> Self {
        self.write_raw_bytes(&value.into().to_be_bytes())
    }

    /// Write data of requested type.
    pub fn write<T: EvmData>(mut self, value: T) -> Self {
        T::write(&mut self, value);
        self
    }
}

impl Default for EvmDataWriter {
    fn default() -> Self {
        Self::new()
    }
}

/// Data that can be converted from and to EVM data types.
pub trait EvmData: Sized {
    fn read(reader: &mut EvmDataReader) -> EvmResult<Self>;
    fn write(writer: &mut EvmDataWriter, value: Self);
}

impl EvmData for H256 {
    fn read(reader: &mut EvmDataReader) -> EvmResult<Self> {
        let range = reader.move_cursor(32)?;

        let data = reader
            .input
            .get(range)
            .ok_or_else(|| error("tried to parse H256 out of bounds"))?;

        Ok(H256::from_slice(data))
    }

    fn write(writer: &mut EvmDataWriter, value: Self) {
        writer.data.extend_from_slice(value.as_bytes());
    }
}

impl EvmData for Address {
    fn read(reader: &mut EvmDataReader) -> EvmResult<Self> {
        let range = reader.move_cursor(32)?;

        let data = reader
            .input
            .get(range)
            .ok_or_else(|| error("tried to parse H160 out of bounds"))?;

        Ok(H160::from_slice(&data[12..32]).into())
    }

    fn write(writer: &mut EvmDataWriter, value: Self) {
        H256::write(writer, value.0.into());
    }
}

impl EvmData for U256 {
    fn read(reader: &mut EvmDataReader) -> EvmResult<Self> {
        let range = reader.move_cursor(32)?;

        let data = reader
            .input
            .get(range)
            .ok_or_else(|| error("tried to parse U256 out of bounds"))?;

        Ok(U256::from_big_endian(data))
    }

    fn write(writer: &mut EvmDataWriter, value: Self) {
        let mut buffer = [0u8; 32];
        value.to_big_endian(&mut buffer);
        writer.data.extend_from_slice(&buffer);
    }
}

macro_rules! impl_evmdata_for_uints {
    ($($uint:ty, )*) => {
        $(
            impl EvmData for $uint {
                fn read(reader: &mut EvmDataReader) -> EvmResult<Self> {
                    let range = reader.move_cursor(32)?;

                    let data = reader
                        .input
                        .get(range)
                        .ok_or_else(|| error(format!(
                            "tried to parse {} out of bounds", core::any::type_name::<Self>()
                        )))?;

                    let mut buffer = [0u8; core::mem::size_of::<Self>()];
                    buffer.copy_from_slice(&data[32 - core::mem::size_of::<Self>()..]);
                    Ok(Self::from_be_bytes(buffer))
                }

                fn write(writer: &mut EvmDataWriter, value: Self) {
                    let mut buffer = [0u8; 32];
                    buffer[32 - core::mem::size_of::<Self>()..].copy_from_slice(&value.to_be_bytes());
                    writer.data.extend_from_slice(&buffer);
                }
            }
        )*
    };
}
impl_evmdata_for_uints!(u16, u32, u64, u128,);

// The implementation for u8 is specific, for performance reasons.
impl EvmData for u8 {
    fn read(reader: &mut EvmDataReader) -> EvmResult<Self> {
        let range = reader.move_cursor(32)?;

        let data = reader
            .input
            .get(range)
            .ok_or_else(|| error("tried to parse u64 out of bounds"))?;

        Ok(data[31])
    }

    fn write(writer: &mut EvmDataWriter, value: Self) {
        let mut buffer = [0u8; 32];
        buffer[31] = value;

        writer.data.extend_from_slice(&buffer);
    }
}

impl EvmData for bool {
    fn read(reader: &mut EvmDataReader) -> EvmResult<Self> {
        let h256 = H256::read(reader).map_err(|_| error("tried to parse bool out of bounds"))?;

        Ok(!h256.is_zero())
    }

    fn write(writer: &mut EvmDataWriter, value: Self) {
        let mut buffer = [0u8; 32];
        if value {
            buffer[31] = 1;
        }

        writer.data.extend_from_slice(&buffer);
    }
}

impl<T: EvmData> EvmData for Vec<T> {
    fn read(reader: &mut EvmDataReader) -> EvmResult<Self> {
        let array_start: usize = reader
            .read::<U256>()
            .map_err(|_| error("tried to parse array offset out of bounds"))?
            .try_into()
            .map_err(|_| error("array offset is too large"))?;

        // We temporarily move the cursor to the offset, we'll set it back afterward.
        let original_cursor = reader.cursor;
        reader.cursor = array_start;

        let array_size: usize = reader
            .read::<U256>()
            .map_err(|_| error("tried to parse array length out of bounds"))?
            .try_into()
            .map_err(|_| error("array length is too large"))?;

        let mut array = vec![];

        for _ in 0..array_size {
            array.push(reader.read()?);
        }

        // We set back the cursor to its original location.
        reader.cursor = original_cursor;

        Ok(array)
    }

    fn write(writer: &mut EvmDataWriter, value: Self) {
        let offset_position = writer.data.len();
        H256::write(writer, H256::repeat_byte(0xff));
        // 0xff = When debugging it makes spoting offset values easier.

        let mut inner_writer = EvmDataWriter::new();

        // Write length.
        inner_writer = inner_writer.write(U256::from(value.len()));

        // Write elements of array.
        for inner in value {
            inner_writer = inner_writer.write(inner);
        }

        let array = Array {
            offset_position,
            data: inner_writer.data,
            inner_arrays: inner_writer.arrays,
        };

        writer.arrays.push(array);
    }
}