/*
* Copyright (C) 2014 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 okio;
/**
* A segment of a buffer.
*
* <p>Each segment in a buffer is a circularly-linked list node referencing the following and
* preceding segments in the buffer.
*
* <p>Each segment in the pool is a singly-linked list node referencing the rest of segments in the
* pool.
*
* <p>The underlying byte arrays of segments may be shared between buffers and byte strings. When a
* segment's byte array is shared the segment may not be recycled, nor may its byte data be changed.
* The lone exception is that the owner segment is allowed to append to the segment, writing data at
* {@code limit} and beyond. There is a single owning segment for each byte array. Positions,
* limits, prev, and next references are not shared.
*/
final class Segment {
/** The size of all segments in bytes. */
static final int SIZE = 8192;
final byte[] data;
/** The next byte of application data byte to read in this segment. */
int pos;
/** The first byte of available data ready to be written to. */
int limit;
/** True if other segments or byte strings use the same byte array. */
boolean shared;
/** True if this segment owns the byte array and can append to it, extending {@code limit}. */
boolean owner;
/** Next segment in a linked or circularly-linked list. */
Segment next;
/** Previous segment in a circularly-linked list. */
Segment prev;
Segment() {
this.data = new byte[SIZE];
this.owner = true;
this.shared = false;
}
Segment(Segment shareFrom) {
this(shareFrom.data, shareFrom.pos, shareFrom.limit);
shareFrom.shared = true;
}
Segment(byte[] data, int pos, int limit) {
this.data = data;
this.pos = pos;
this.limit = limit;
this.owner = false;
this.shared = true;
}
/**
* Removes this segment of a circularly-linked list and returns its successor.
* Returns null if the list is now empty.
*/
public Segment pop() {
Segment result = next != this ? next : null;
prev.next = next;
next.prev = prev;
next = null;
prev = null;
return result;
}
/**
* Appends {@code segment} after this segment in the circularly-linked list.
* Returns the pushed segment.
*/
public Segment push(Segment segment) {
segment.prev = this;
segment.next = next;
next.prev = segment;
next = segment;
return segment;
}
/**
* Splits this head of a circularly-linked list into two segments. The first
* segment contains the data in {@code [pos..pos+byteCount)}. The second
* segment contains the data in {@code [pos+byteCount..limit)}. This can be
* useful when moving partial segments from one buffer to another.
*
* <p>Returns the new head of the circularly-linked list.
*/
public Segment split(int byteCount) {
if (byteCount <= 0 || byteCount > limit - pos) throw new IllegalArgumentException();
Segment prefix = new Segment(this);
prefix.limit = prefix.pos + byteCount;
pos += byteCount;
prev.push(prefix);
return prefix;
}
/**
* Call this when the tail and its predecessor may both be less than half
* full. This will copy data so that segments can be recycled.
*/
public void compact() {
if (prev == this) throw new IllegalStateException();
if (!prev.owner) return; // Cannot compact: prev isn't writable.
int byteCount = limit - pos;
int availableByteCount = SIZE - prev.limit + (prev.shared ? 0 : prev.pos);
if (byteCount > availableByteCount) return; // Cannot compact: not enough writable space.
writeTo(prev, byteCount);
pop();
SegmentPool.recycle(this);
}
/** Moves {@code byteCount} bytes from this segment to {@code sink}. */
public void writeTo(Segment sink, int byteCount) {
if (!sink.owner) throw new IllegalArgumentException();
if (sink.limit + byteCount > SIZE) {
// We can't fit byteCount bytes at the sink's current position. Shift sink first.
if (sink.shared) throw new IllegalArgumentException();
if (sink.limit + byteCount - sink.pos > SIZE) throw new IllegalArgumentException();
System.arraycopy(sink.data, sink.pos, sink.data, 0, sink.limit - sink.pos);
sink.limit -= sink.pos;
sink.pos = 0;
}
System.arraycopy(data, pos, sink.data, sink.limit, byteCount);
sink.limit += byteCount;
pos += byteCount;
}
}