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DynamicBuffer.sol
96 lines (85 loc) · 3.76 KB
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DynamicBuffer.sol
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// SPDX-License-Identifier: MIT
// Copyright (c) 2021 the ethier authors (github.com/divergencetech/ethier)
pragma solidity >=0.8.0;
/// @title DynamicBuffer
/// @author David Huber (@cxkoda) and Simon Fremaux (@dievardump). See also
/// https://raw.githubusercontent.com/dievardump/solidity-dynamic-buffer
/// @notice This library is used to allocate a big amount of container memory
// which will be subsequently filled without needing to reallocate
/// memory.
/// @dev First, allocate memory.
/// Then use `buffer.appendUnchecked(theBytes)` or `appendSafe()` if
/// bounds checking is required.
library DynamicBuffer {
/// @notice Allocates container space for the DynamicBuffer
/// @param capacity The intended max amount of bytes in the buffer
/// @return buffer The memory location of the buffer
/// @dev Allocates `capacity + 0x60` bytes of space
/// The buffer array starts at the first container data position,
/// (i.e. `buffer = container + 0x20`)
function allocate(uint256 capacity) internal pure returns (bytes memory buffer) {
assembly {
// Get next-free memory address
let container := mload(0x40)
// Allocate memory by setting a new next-free address
{
// Add 2 x 32 bytes in size for the two length fields
// Add 32 bytes safety space for 32B chunked copy
let size := add(capacity, 0x60)
let newNextFree := add(container, size)
mstore(0x40, newNextFree)
}
// Set the correct container length
{
let length := add(capacity, 0x40)
mstore(container, length)
}
// The buffer starts at idx 1 in the container (0 is length)
buffer := add(container, 0x20)
// Init content with length 0
mstore(buffer, 0)
}
return buffer;
}
/// @notice Appends data to buffer, and update buffer length
/// @param buffer the buffer to append the data to
/// @param data the data to append
/// @dev Does not perform out-of-bound checks (container capacity)
/// for efficiency.
function appendUnchecked(bytes memory buffer, bytes memory data) internal pure {
assembly {
let length := mload(data)
for {
data := add(data, 0x20)
let dataEnd := add(data, length)
let copyTo := add(buffer, add(mload(buffer), 0x20))
} lt(data, dataEnd) {
data := add(data, 0x20)
copyTo := add(copyTo, 0x20)
} {
// Copy 32B chunks from data to buffer.
// This may read over data array boundaries and copy invalid
// bytes, which doesn't matter in the end since we will
// later set the correct buffer length, and have allocated an
// additional word to avoid buffer overflow.
mstore(copyTo, mload(data))
}
// Update buffer length
mstore(buffer, add(mload(buffer), length))
}
}
/// @notice Appends data to buffer, and update buffer length
/// @param buffer the buffer to append the data to
/// @param data the data to append
/// @dev Performs out-of-bound checks and calls `appendUnchecked`.
function appendSafe(bytes memory buffer, bytes memory data) internal pure {
uint256 capacity;
uint256 length;
assembly {
capacity := sub(mload(sub(buffer, 0x20)), 0x40)
length := mload(buffer)
}
require(length + data.length <= capacity, "DynamicBuffer: Appending out of bounds.");
appendUnchecked(buffer, data);
}
}