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/*
* Copyright 2017-2024 JetBrains s.r.o. and respective authors and developers.
* Use of this source code is governed by the Apache 2.0 license that can be found in the LICENCE file.
*/
/*
* Copyright (C) 2019 Square, Inc.
*
* 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.
*/
package kotlinx.io
import kotlin.contracts.ExperimentalContracts
import kotlin.contracts.InvocationKind.EXACTLY_ONCE
import kotlin.contracts.contract
import kotlinx.io.unsafe.UnsafeBufferOperations
import kotlin.jvm.JvmSynthetic
/**
* A collection of bytes in memory.
*
* The buffer can be viewed as an unbound queue whose size grows with the data being written
* and shrinks with data being consumed. Internally, the buffer consists of data segments,
* and the buffer's capacity grows and shrinks in units of data segments instead of individual bytes.
*
* The buffer was designed to reduce memory allocations when possible. Instead of copying bytes
* from one place in memory to another, this class just changes ownership of the underlying data segments.
*
* To reduce allocations and speed up the buffer's extension, it may use data segments pooling.
*
* [Buffer] implements both [Source] and [Sink] and could be used as a source or a sink,
* but unlike regular sinks and sources its [close], [flush], [emit], [hintEmit]
* does not affect buffer's state and [exhausted] only indicates that a buffer is empty.
*/
public class Buffer : Source, Sink {
@PublishedApi
@get:JvmSynthetic
@set:JvmSynthetic
internal var head: Segment? = null
@PublishedApi
@get:JvmSynthetic
@set:JvmSynthetic
internal var tail: Segment? = null
/**
* The number of bytes accessible for read from this buffer.
*/
public val size: Long
get() = sizeMut
@PublishedApi
@get:JvmSynthetic
@set:JvmSynthetic
internal var sizeMut: Long = 0L
/**
* Returns the buffer itself.
*/
@InternalIoApi
override val buffer: Buffer get() = this
override fun exhausted(): Boolean = size == 0L
override fun require(byteCount: Long) {
require(byteCount >= 0) { "byteCount: $byteCount" }
if (size < byteCount) {
throw EOFException("Buffer doesn't contain required number of bytes (size: $size, required: $byteCount)")
}
}
override fun request(byteCount: Long): Boolean {
require(byteCount >= 0) { "byteCount: $byteCount < 0" }
return size >= byteCount
}
override fun readByte(): Byte {
val segment = head ?: throwEof(1)
val segmentSize = segment.size
if (segmentSize == 0) {
recycleHead()
return readByte()
}
val v = segment.readByte()
sizeMut -= 1L
if (segmentSize == 1) {
recycleHead()
}
return v
}
override fun readShort(): Short {
val segment = head ?: throwEof(2)
val segmentSize = segment.size
if (segmentSize < 2) {
// If the short is split across multiple segments, delegate to readByte().
require(2)
if (segmentSize == 0) {
recycleHead()
return readShort()
}
return (readByte() and 0xff shl 8 or (readByte() and 0xff)).toShort()
}
val v = segment.readShort()
sizeMut -= 2L
if (segmentSize == 2) {
recycleHead()
}
return v
}
override fun readInt(): Int {
val segment = head ?: throwEof(4)
val segmentSize = segment.size
if (segmentSize < 4) {
// If the short is split across multiple segments, delegate to readShort().
require(4)
if (segmentSize == 0) {
recycleHead()
return readInt()
}
return (readShort().toInt() shl 16 or (readShort().toInt() and 0xffff))
}
val v = segment.readInt()
sizeMut -= 4L
if (segmentSize == 4) {
recycleHead()
}
return v
}
override fun readLong(): Long {
val segment = head ?: throwEof(8)
val segmentSize = segment.size
if (segmentSize < 8) {
// If the short is split across multiple segments, delegate to readInt().
require(8)
if (segmentSize == 0) {
recycleHead()
return readLong()
}
return (readInt().toLong() shl 32 or (readInt().toLong() and 0xffffffffL))
}
val v = segment.readLong()
sizeMut -= 8L
if (segmentSize == 8) {
recycleHead()
}
return v
}
private fun throwEof(byteCount: Long): Nothing {
throw EOFException("Buffer doesn't contain required number of bytes (size: $size, required: $byteCount)")
}
/**
* This method does not affect the buffer's content as there is no upstream to write data to.
*/
@InternalIoApi
override fun hintEmit(): Unit = Unit
/**
* This method does not affect the buffer's content as there is no upstream to write data to.
*/
override fun emit(): Unit = Unit
/**
* This method does not affect the buffer's content as there is no upstream to write data to.
*/
override fun flush(): Unit = Unit
/**
* Copies bytes from this buffer's subrange starting at [startIndex] and ending at [endIndex], to [out] buffer.
* This method does not consume data from the buffer.
*
* @param out the destination buffer to copy data into.
* @param startIndex the index (inclusive) of the first byte of data in this buffer to copy,
* 0 by default.
* @param endIndex the index (exclusive) of the last byte of data in this buffer to copy, `buffer.size` by default.
*
* @throws IndexOutOfBoundsException when [startIndex] or [endIndex] is out of this buffer bounds
* (`[0..buffer.size)`).
* @throws IllegalArgumentException when `startIndex > endIndex`.
*
* @sample kotlinx.io.samples.KotlinxIoCoreCommonSamples.bufferCopy
*/
public fun copyTo(
out: Buffer,
startIndex: Long = 0L,
endIndex: Long = size
) {
checkBounds(size, startIndex, endIndex)
if (startIndex == endIndex) return
var currentOffset = startIndex
var remainingByteCount = endIndex - startIndex
out.sizeMut += remainingByteCount
// Skip segments that we aren't copying from.
var s = head
while (currentOffset >= s!!.limit - s.pos) {
currentOffset -= (s.limit - s.pos).toLong()
s = s.next
}
// Copy one segment at a time.
while (remainingByteCount > 0L) {
val copy = s!!.sharedCopy()
copy.pos += currentOffset.toInt()
copy.limit = minOf(copy.pos + remainingByteCount.toInt(), copy.limit)
out.pushSegment(copy)
remainingByteCount -= (copy.limit - copy.pos).toLong()
currentOffset = 0L
s = s.next
}
}
/**
* Returns the number of bytes in segments that are fully filled and are no longer writable.
*
* This is the number of bytes that can be flushed immediately to an underlying sink without harming throughput.
*/
internal fun completeSegmentByteCount(): Long {
var result = size
if (result == 0L) return 0L
// Omit the tail if it's still writable.
val tail = tail!!
if (tail.limit < Segment.SIZE && tail.owner) {
result -= (tail.limit - tail.pos).toLong()
}
return result
}
/**
* Returns the byte at [position].
*
* Use of this method may expose significant performance penalties and it's not recommended to use it
* for sequential access to a range of bytes within the buffer.
*
* @throws IndexOutOfBoundsException when [position] is negative or greater or equal to [Buffer.size].
*
* @sample kotlinx.io.samples.KotlinxIoCoreCommonSamples.bufferGetByte
*/
public operator fun get(position: Long): Byte {
if (position < 0 || position >= size) {
throw IndexOutOfBoundsException("position ($position) is not within the range [0..size($size))")
}
if (position == 0L) {
return head!!.getUnchecked(0)
}
seek(position) { s, offset ->
return s!!.getUnchecked((position - offset).toInt())
}
}
/**
* Discards all bytes in this buffer.
*
* Call to this method is equivalent to [skip] with `byteCount = size`.
*
* @sample kotlinx.io.samples.KotlinxIoCoreCommonSamples.bufferClear
*/
public fun clear(): Unit = skip(size)
/**
* Discards [byteCount] bytes from the head of this buffer.
*
* @throws IllegalArgumentException when [byteCount] is negative.
*/
override fun skip(byteCount: Long) {
checkByteCount(byteCount)
var remainingByteCount = byteCount
while (remainingByteCount > 0) {
val head = head ?: throw EOFException("Buffer exhausted before skipping $byteCount bytes.")
val toSkip = minOf(remainingByteCount, head.limit - head.pos).toInt()
sizeMut -= toSkip.toLong()
remainingByteCount -= toSkip.toLong()
head.pos += toSkip
if (head.pos == head.limit) {
recycleHead()
}
}
}
override fun readAtMostTo(sink: ByteArray, startIndex: Int, endIndex: Int): Int {
checkBounds(sink.size, startIndex, endIndex)
val s = this.head ?: return -1
val toCopy = minOf(endIndex - startIndex, s.size)
s.readTo(sink, startIndex, startIndex + toCopy)
sizeMut -= toCopy.toLong()
if (s.isEmpty()) {
recycleHead()
}
return toCopy
}
override fun readAtMostTo(sink: Buffer, byteCount: Long): Long {
checkByteCount(byteCount)
if (size == 0L) return -1L
val bytesWritten = if (byteCount > size) size else byteCount
sink.write(this, bytesWritten)
return bytesWritten
}
override fun readTo(sink: RawSink, byteCount: Long) {
checkByteCount(byteCount)
if (size < byteCount) {
sink.write(this, size) // Exhaust ourselves.
throw EOFException("Buffer exhausted before writing $byteCount bytes. Only $size bytes were written.")
}
sink.write(this, byteCount)
}
override fun transferTo(sink: RawSink): Long {
val byteCount = size
if (byteCount > 0L) {
sink.write(this, byteCount)
}
return byteCount
}
override fun peek(): Source = PeekSource(this).buffered()
/**
* Returns a tail segment that we can write at least `minimumCapacity`
* bytes to, creating it if necessary.
*/
@PublishedApi
@JvmSynthetic
internal fun writableSegment(minimumCapacity: Int): Segment {
require(minimumCapacity >= 1 && minimumCapacity <= Segment.SIZE) { "unexpected capacity" }
if (tail == null) {
val result = SegmentPool.take() // Acquire a first segment.
head = result
tail = result
return result
}
val t = tail!!
if (t.limit + minimumCapacity > Segment.SIZE || !t.owner) {
val newTail = t.push(SegmentPool.take()) // Append a new empty segment to fill up.
tail = newTail
return newTail
}
return t
}
override fun write(source: ByteArray, startIndex: Int, endIndex: Int) {
checkBounds(source.size, startIndex, endIndex)
var currentOffset = startIndex
while (currentOffset < endIndex) {
val tail = writableSegment(1)
val toCopy = minOf(endIndex - currentOffset, tail.remainingCapacity)
tail.write(source, currentOffset, currentOffset + toCopy)
currentOffset += toCopy
}
sizeMut += endIndex - startIndex
}
override fun write(source: RawSource, byteCount: Long) {
checkByteCount(byteCount)
var remainingByteCount = byteCount
while (remainingByteCount > 0L) {
val read = source.readAtMostTo(this, remainingByteCount)
if (read == -1L) {
throw EOFException(
"Source exhausted before reading $byteCount bytes. " +
"Only ${byteCount - remainingByteCount} were read."
)
}
remainingByteCount -= read
}
}
override fun write(source: Buffer, byteCount: Long) {
// Move bytes from the head of the source buffer to the tail of this buffer
// while balancing two conflicting goals: don't waste CPU and don't waste
// memory.
//
//
// Don't waste CPU (ie. don't copy data around).
//
// Copying large amounts of data is expensive. Instead, we prefer to
// reassign entire segments from one buffer to the other.
//
//
// Don't waste memory.
//
// As an invariant, adjacent pairs of segments in a buffer should be at
// least 50% full, except for the head segment and the tail segment.
//
// The head segment cannot maintain the invariant because the application is
// consuming bytes from this segment, decreasing its level.
//
// The tail segment cannot maintain the invariant because the application is
// producing bytes, which may require new nearly-empty tail segments to be
// appended.
//
//
// Moving segments between buffers
//
// When writing one buffer to another, we prefer to reassign entire segments
// over copying bytes into their most compact form. Suppose we have a buffer
// with these segment levels [91%, 61%]. If we append a buffer with a
// single [72%] segment, that yields [91%, 61%, 72%]. No bytes are copied.
//
// Or suppose we have a buffer with these segment levels: [100%, 2%], and we
// want to append it to a buffer with these segment levels [99%, 3%]. This
// operation will yield the following segments: [100%, 2%, 99%, 3%]. That
// is, we do not spend time copying bytes around to achieve more efficient
// memory use like [100%, 100%, 4%].
//
// When combining buffers, we will compact adjacent buffers when their
// combined level doesn't exceed 100%. For example, when we start with
// [100%, 40%] and append [30%, 80%], the result is [100%, 70%, 80%].
//
//
// Splitting segments
//
// Occasionally we write only part of a source buffer to a sink buffer. For
// example, given a sink [51%, 91%], we may want to write the first 30% of
// a source [92%, 82%] to it. To simplify, we first transform the source to
// an equivalent buffer [30%, 62%, 82%] and then move the head segment,
// yielding sink [51%, 91%, 30%] and source [62%, 82%].
require(source !== this) { "source == this" }
checkOffsetAndCount(source.sizeMut, 0, byteCount)
var remainingByteCount = byteCount
while (remainingByteCount > 0L) {
// Is a prefix of the source's head segment all that we need to move?
if (remainingByteCount < source.head!!.size) {
val tail = tail
if (tail != null && tail.owner &&
remainingByteCount + tail.limit - (if (tail.shared) 0 else tail.pos) <= Segment.SIZE
) {
// Our existing segments are sufficient. Move bytes from source's head to our tail.
source.head!!.writeTo(tail, remainingByteCount.toInt())
source.sizeMut -= remainingByteCount
sizeMut += remainingByteCount
return
} else {
// We're going to need another segment. Split the source's head
// segment in two, then move the first of those two to this buffer.
source.head = source.head!!.split(remainingByteCount.toInt())
}
}
// Remove the source's head segment and append it to our tail.
val segmentToMove = source.head!!
val movedByteCount = segmentToMove.size.toLong()
source.head = segmentToMove.pop()
if (source.head == null) {
source.tail = null
}
pushSegment(segmentToMove, true)
source.sizeMut -= movedByteCount
sizeMut += movedByteCount
remainingByteCount -= movedByteCount
}
}
override fun transferFrom(source: RawSource): Long {
var totalBytesRead = 0L
while (true) {
val readCount = source.readAtMostTo(this, Segment.SIZE.toLong())
if (readCount == -1L) break
totalBytesRead += readCount
}
return totalBytesRead
}
override fun writeByte(byte: Byte) {
writableSegment(1).writeByte(byte)
sizeMut += 1L
}
override fun writeShort(short: Short) {
writableSegment(2).writeShort(short)
sizeMut += 2L
}
override fun writeInt(int: Int) {
writableSegment(4).writeInt(int)
sizeMut += 4L
}
override fun writeLong(long: Long) {
writableSegment(8).writeLong(long)
sizeMut += 8L
}
/**
* Returns a deep copy of this buffer.
*/
public fun copy(): Buffer {
val result = Buffer()
if (size == 0L) return result
val head = this.head!!
val headCopy = head.sharedCopy()
result.head = headCopy
result.tail = headCopy
var s = head.next
while (s != null) {
result.tail = result.tail!!.push(s.sharedCopy())
s = s.next
}
result.sizeMut = size
return result
}
/**
* This method does not affect the buffer.
*/
override fun close(): Unit = Unit
/**
* Returns a human-readable string that describes the contents of this buffer. For buffers containing
* few bytes, this is a string like `Buffer(size=4 hex=0000ffff)`. However, if the buffer is too large,
* a string will contain its size and only a prefix of data, like `Buffer(size=1024 hex=01234…)`.
* Thus, the string could not be used to compare buffers or verify buffer's content.
*
* @sample kotlinx.io.samples.KotlinxIoCoreCommonSamples.bufferToString
*/
@OptIn(UnsafeIoApi::class)
override fun toString(): String {
if (size == 0L) return "Buffer(size=0)"
val maxPrintableBytes = 64
val len = minOf(maxPrintableBytes, size).toInt()
val builder = StringBuilder(len * 2 + if (size > maxPrintableBytes) 1 else 0)
var bytesWritten = 0
UnsafeBufferOperations.forEachSegment(this) { ctx, segment ->
var idx = 0
while (bytesWritten < len && idx < segment.size) {
val b = ctx.getUnchecked(segment, idx++)
bytesWritten++
builder
.append(HEX_DIGIT_CHARS[(b shr 4) and 0xf])
.append(HEX_DIGIT_CHARS[b and 0xf])
}
}
if (size > maxPrintableBytes) {
builder.append('…')
}
return "Buffer(size=$size hex=$builder)"
}
/**
* Unlinks and recycles this buffer's head.
*
* If head had a successor, it'll become a new head.
* Otherwise, both [head] and [tail] will be set to null.
*
* It's up to a caller to ensure that the head exists.
*/
internal fun recycleHead() {
val oldHead = head!!
val nextHead = oldHead.next
head = nextHead
if (nextHead == null) {
tail = null
} else {
nextHead.prev = null
}
oldHead.next = null
SegmentPool.recycle(oldHead)
}
/**
* Unlinks and recycles this buffer's tail segment.
*
* If tail had a predecessor, it'll become a new tail.
* Otherwise, both [head] and [tail] will be set to null.
*
* It's up to a caller to ensure that the tail exists.
*/
@PublishedApi
@JvmSynthetic
internal fun recycleTail() {
val oldTail = tail!!
val newTail = oldTail.prev
tail = newTail
if (newTail == null) {
head = null
} else {
newTail.next = null
}
oldTail.prev = null
SegmentPool.recycle(oldTail)
}
@Suppress("NOTHING_TO_INLINE")
private inline fun pushSegment(newTail: Segment, tryCompact: Boolean = false) {
if (head == null) {
head = newTail
tail = newTail
} else if (tryCompact) {
tail = tail!!.push(newTail).compact()
if (tail!!.prev == null) {
head = tail
}
} else {
tail = tail!!.push(newTail)
}
}
}
/**
* Invoke `lambda` with the segment and offset at `fromIndex`. Searches from the front or the back
* depending on what's closer to `fromIndex`.
*/
@PublishedApi
@JvmSynthetic
@OptIn(ExperimentalContracts::class)
internal inline fun Buffer.seek(
fromIndex: Long,
lambda: (Segment?, Long) -> T
): T {
contract {
callsInPlace(lambda, EXACTLY_ONCE)
}
if (this.head == null) {
return lambda(null, -1L)
}
if (size - fromIndex < fromIndex) {
var s = tail
// We're scanning in the back half of this buffer. Find the segment starting at the back.
var offset = size
while (s != null && offset > fromIndex) {
offset -= (s.limit - s.pos).toLong()
if (offset <= fromIndex) break
s = s.prev
}
return lambda(s, offset)
} else {
var s = this.head
// We're scanning in the front half of this buffer. Find the segment starting at the front.
var offset = 0L
while (s != null) {
val nextOffset = offset + (s.limit - s.pos)
if (nextOffset > fromIndex) break
s = s.next
offset = nextOffset
}
return lambda(s, offset)
}
}
