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/*
* Copyright 2021 Google Inc. All rights reserved.
*
* 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.
*/
import Foundation
@frozen
public struct ByteBuffer {
/// Storage is a container that would hold the memory pointer to solve the issue of
/// deallocating the memory that was held by (memory: UnsafeMutableRawPointer)
@usableFromInline
final class Storage {
// This storage doesn't own the memory, therefore, we won't deallocate on deinit.
private let unowned: Bool
/// pointer to the start of the buffer object in memory
var memory: UnsafeMutableRawPointer
/// Capacity of UInt8 the buffer can hold
var capacity: Int
@usableFromInline
init(count: Int, alignment: Int) {
memory = UnsafeMutableRawPointer.allocate(byteCount: count, alignment: alignment)
capacity = count
unowned = false
}
@usableFromInline
init(memory: UnsafeMutableRawPointer, capacity: Int, unowned: Bool) {
self.memory = memory
self.capacity = capacity
self.unowned = unowned
}
deinit {
if !unowned {
memory.deallocate()
}
}
@usableFromInline
func copy(from ptr: UnsafeRawPointer, count: Int) {
assert(
!unowned,
"copy should NOT be called on a buffer that is built by assumingMemoryBound")
memory.copyMemory(from: ptr, byteCount: count)
}
@usableFromInline
func initialize(for size: Int) {
assert(
!unowned,
"initalize should NOT be called on a buffer that is built by assumingMemoryBound")
memset(memory, 0, size)
}
/// Reallocates the buffer incase the object to be written doesnt fit in the current buffer
/// - Parameter size: Size of the current object
@usableFromInline
internal func reallocate(_ size: Int, writerSize: Int, alignment: Int) {
let currentWritingIndex = capacity &- writerSize
while capacity <= writerSize &+ size {
capacity = capacity << 1
}
/// solution take from Apple-NIO
capacity = capacity.convertToPowerofTwo
let newData = UnsafeMutableRawPointer.allocate(byteCount: capacity, alignment: alignment)
memset(newData, 0, capacity &- writerSize)
memcpy(
newData.advanced(by: capacity &- writerSize),
memory.advanced(by: currentWritingIndex),
writerSize)
memory.deallocate()
memory = newData
}
}
@usableFromInline var _storage: Storage
/// The size of the elements written to the buffer + their paddings
private var _writerSize: Int = 0
/// Aliginment of the current memory being written to the buffer
internal var alignment = 1
/// Current Index which is being used to write to the buffer, it is written from the end to the start of the buffer
internal var writerIndex: Int { _storage.capacity &- _writerSize }
/// Reader is the position of the current Writer Index (capacity - size)
public var reader: Int { writerIndex }
/// Current size of the buffer
public var size: UOffset { UOffset(_writerSize) }
/// Public Pointer to the buffer object in memory. This should NOT be modified for any reason
public var memory: UnsafeMutableRawPointer { _storage.memory }
/// Current capacity for the buffer
public var capacity: Int { _storage.capacity }
/// Constructor that creates a Flatbuffer object from a UInt8
/// - Parameter bytes: Array of UInt8
public init(bytes: [UInt8]) {
var b = bytes
_storage = Storage(count: bytes.count, alignment: alignment)
_writerSize = _storage.capacity
b.withUnsafeMutableBytes { bufferPointer in
self._storage.copy(from: bufferPointer.baseAddress!, count: bytes.count)
}
}
/// Constructor that creates a Flatbuffer from the Swift Data type object
/// - Parameter data: Swift data Object
public init(data: Data) {
var b = data
_storage = Storage(count: data.count, alignment: alignment)
_writerSize = _storage.capacity
b.withUnsafeMutableBytes { bufferPointer in
self._storage.copy(from: bufferPointer.baseAddress!, count: data.count)
}
}
/// Constructor that creates a Flatbuffer instance with a size
/// - Parameter size: Length of the buffer
init(initialSize size: Int) {
let size = size.convertToPowerofTwo
_storage = Storage(count: size, alignment: alignment)
_storage.initialize(for: size)
}
#if swift(>=5.0)
/// Constructor that creates a Flatbuffer object from a ContiguousBytes
/// - Parameters:
/// - contiguousBytes: Binary stripe to use as the buffer
/// - count: amount of readable bytes
public init<Bytes: ContiguousBytes>(
contiguousBytes: Bytes,
count: Int)
{
_storage = Storage(count: count, alignment: alignment)
_writerSize = _storage.capacity
contiguousBytes.withUnsafeBytes { buf in
_storage.copy(from: buf.baseAddress!, count: buf.count)
}
}
#endif
/// Constructor that creates a Flatbuffer from unsafe memory region without copying
/// - Parameter assumingMemoryBound: The unsafe memory region
/// - Parameter capacity: The size of the given memory region
public init(assumingMemoryBound memory: UnsafeMutableRawPointer, capacity: Int) {
_storage = Storage(memory: memory, capacity: capacity, unowned: true)
_writerSize = capacity
}
/// Creates a copy of the buffer that's being built by calling sizedBuffer
/// - Parameters:
/// - memory: Current memory of the buffer
/// - count: count of bytes
internal init(memory: UnsafeMutableRawPointer, count: Int) {
_storage = Storage(count: count, alignment: alignment)
_storage.copy(from: memory, count: count)
_writerSize = _storage.capacity
}
/// Creates a copy of the existing flatbuffer, by copying it to a different memory.
/// - Parameters:
/// - memory: Current memory of the buffer
/// - count: count of bytes
/// - removeBytes: Removes a number of bytes from the current size
internal init(memory: UnsafeMutableRawPointer, count: Int, removing removeBytes: Int) {
_storage = Storage(count: count, alignment: alignment)
_storage.copy(from: memory, count: count)
_writerSize = removeBytes
}
/// Fills the buffer with padding by adding to the writersize
/// - Parameter padding: Amount of padding between two to be serialized objects
@usableFromInline
mutating func fill(padding: Int) {
assert(padding >= 0, "Fill should be larger than or equal to zero")
ensureSpace(size: padding)
_writerSize = _writerSize &+ (MemoryLayout<UInt8>.size &* padding)
}
/// Adds an array of type Scalar to the buffer memory
/// - Parameter elements: An array of Scalars
@usableFromInline
mutating func push<T: Scalar>(elements: [T]) {
let size = elements.count &* MemoryLayout<T>.size
ensureSpace(size: size)
elements.reversed().forEach { s in
push(value: s, len: MemoryLayout.size(ofValue: s))
}
}
/// Adds an object of type NativeStruct into the buffer
/// - Parameters:
/// - value: Object that will be written to the buffer
/// - size: size to subtract from the WriterIndex
@inline(__always)
mutating func push<T: NativeStruct>(struct value: T, size: Int) {
ensureSpace(size: size)
var v = value
memcpy(_storage.memory.advanced(by: writerIndex &- size), &v, size)
_writerSize = _writerSize &+ size
}
/// Adds an object of type Scalar into the buffer
/// - Parameters:
/// - value: Object that will be written to the buffer
/// - len: Offset to subtract from the WriterIndex
@usableFromInline
mutating func push<T: Scalar>(value: T, len: Int) {
ensureSpace(size: len)
var v = value
memcpy(_storage.memory.advanced(by: writerIndex &- len), &v, len)
_writerSize = _writerSize &+ len
}
/// Adds a string to the buffer using swift.utf8 object
/// - Parameter str: String that will be added to the buffer
/// - Parameter len: length of the string
@usableFromInline
mutating func push(string str: String, len: Int) {
ensureSpace(size: len)
if str.utf8.withContiguousStorageIfAvailable({ self.push(bytes: $0, len: len) }) != nil {
} else {
let utf8View = str.utf8
for c in utf8View.reversed() {
push(value: c, len: 1)
}
}
}
/// Writes a string to Bytebuffer using UTF8View
/// - Parameters:
/// - bytes: Pointer to the view
/// - len: Size of string
@inline(__always)
mutating internal func push(
bytes: UnsafeBufferPointer<String.UTF8View.Element>,
len: Int) -> Bool
{
memcpy(
_storage.memory.advanced(by: writerIndex &- len),
UnsafeRawPointer(bytes.baseAddress!),
len)
_writerSize = _writerSize &+ len
return true
}
/// Write stores an object into the buffer directly or indirectly.
///
/// Direct: ignores the capacity of buffer which would mean we are referring to the direct point in memory
/// indirect: takes into respect the current capacity of the buffer (capacity - index), writing to the buffer from the end
/// - Parameters:
/// - value: Value that needs to be written to the buffer
/// - index: index to write to
/// - direct: Should take into consideration the capacity of the buffer
func write<T>(value: T, index: Int, direct: Bool = false) {
var index = index
if !direct {
index = _storage.capacity &- index
}
assert(index < _storage.capacity, "Write index is out of writing bound")
assert(index >= 0, "Writer index should be above zero")
_storage.memory.storeBytes(of: value, toByteOffset: index, as: T.self)
}
/// Makes sure that buffer has enouch space for each of the objects that will be written into it
/// - Parameter size: size of object
@discardableResult
@inline(__always)
mutating func ensureSpace(size: Int) -> Int {
if size &+ _writerSize > _storage.capacity {
_storage.reallocate(size, writerSize: _writerSize, alignment: alignment)
}
assert(size < FlatBufferMaxSize, "Buffer can't grow beyond 2 Gigabytes")
return size
}
/// pops the written VTable if it's already written into the buffer
/// - Parameter size: size of the `VTable`
@inline(__always)
mutating internal func pop(_ size: Int) {
assert((_writerSize &- size) > 0, "New size should NOT be a negative number")
memset(_storage.memory.advanced(by: writerIndex), 0, _writerSize &- size)
_writerSize = size
}
/// Clears the current size of the buffer
@inline(__always)
mutating public func clearSize() {
_writerSize = 0
}
/// Clears the current instance of the buffer, replacing it with new memory
@inline(__always)
mutating public func clear() {
_writerSize = 0
alignment = 1
_storage.initialize(for: _storage.capacity)
}
/// Reads an object from the buffer
/// - Parameters:
/// - def: Type of the object
/// - position: the index of the object in the buffer
public func read<T>(def: T.Type, position: Int) -> T {
assert(
position + MemoryLayout<T>.size <= _storage.capacity,
"Reading out of bounds is illegal")
return _storage.memory.advanced(by: position).load(as: T.self)
}
/// Reads a slice from the memory assuming a type of T
/// - Parameters:
/// - index: index of the object to be read from the buffer
/// - count: count of bytes in memory
@inline(__always)
public func readSlice<T>(
index: Int32,
count: Int32) -> [T]
{
let _index = Int(index)
let _count = Int(count)
assert(_index + _count <= _storage.capacity, "Reading out of bounds is illegal")
let start = _storage.memory.advanced(by: _index).assumingMemoryBound(to: T.self)
let array = UnsafeBufferPointer(start: start, count: _count)
return Array(array)
}
/// Reads a string from the buffer and encodes it to a swift string
/// - Parameters:
/// - index: index of the string in the buffer
/// - count: length of the string
/// - type: Encoding of the string
@inline(__always)
public func readString(
at index: Int32,
count: Int32,
type: String.Encoding = .utf8) -> String?
{
let _index = Int(index)
let _count = Int(count)
assert(_index + _count <= _storage.capacity, "Reading out of bounds is illegal")
let start = _storage.memory.advanced(by: _index).assumingMemoryBound(to: UInt8.self)
let bufprt = UnsafeBufferPointer(start: start, count: _count)
return String(bytes: Array(bufprt), encoding: type)
}
/// Creates a new Flatbuffer object that's duplicated from the current one
/// - Parameter removeBytes: the amount of bytes to remove from the current Size
public func duplicate(removing removeBytes: Int = 0) -> ByteBuffer {
assert(removeBytes > 0, "Can NOT remove negative bytes")
assert(removeBytes < _storage.capacity, "Can NOT remove more bytes than the ones allocated")
return ByteBuffer(
memory: _storage.memory,
count: _storage.capacity,
removing: _writerSize &- removeBytes)
}
}
extension ByteBuffer: CustomDebugStringConvertible {
public var debugDescription: String {
"""
buffer located at: \(_storage.memory), with capacity of \(_storage.capacity)
{ writerSize: \(_writerSize), readerSize: \(reader), writerIndex: \(writerIndex) }
"""
}
}