/*
* Copyright (C) 2015 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;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Arrays;
import static okio.Util.arrayRangeEquals;
import static okio.Util.checkOffsetAndCount;
/**
* An immutable byte string composed of segments of byte arrays. This class exists to implement
* efficient snapshots of buffers. It is implemented as an array of segments, plus a directory in
* two halves that describes how the segments compose this byte string.
*
* <p>The first half of the directory is the cumulative byte count covered by each segment. The
* element at {@code directory[0]} contains the number of bytes held in {@code segments[0]}; the
* element at {@code directory[1]} contains the number of bytes held in {@code segments[0] +
* segments[1]}, and so on. The element at {@code directory[segments.length - 1]} contains the total
* size of this byte string. The first half of the directory is always monotonically increasing.
*
* <p>The second half of the directory is the offset in {@code segments} of the first content byte.
* Bytes preceding this offset are unused, as are bytes beyond the segment's effective size.
*
* <p>Suppose we have a byte string, {@code [A, B, C, D, E, F, G, H, I, J, K, L, M]} that is stored
* across three byte arrays: {@code [x, x, x, x, A, B, C, D, E, x, x, x]}, {@code [x, F, G]}, and
* {@code [H, I, J, K, L, M, x, x, x, x, x, x]}. The three byte arrays would be stored in {@code
* segments} in order. Since the arrays contribute 5, 2, and 6 elements respectively, the directory
* starts with {@code [5, 7, 13} to hold the cumulative total at each position. Since the offsets
* into the arrays are 4, 1, and 0 respectively, the directory ends with {@code 4, 1, 0]}.
* Concatenating these two halves, the complete directory is {@code [5, 7, 13, 4, 1, 0]}.
*
* <p>This structure is chosen so that the segment holding a particular offset can be found by
* binary search. We use one array rather than two for the directory as a micro-optimization.
*/
final class SegmentedByteString extends ByteString {
transient final byte[][] segments;
transient final int[] directory;
SegmentedByteString(Buffer buffer, int byteCount) {
super(null);
checkOffsetAndCount(buffer.size, 0, byteCount);
// Walk through the buffer to count how many segments we'll need.
int offset = 0;
int segmentCount = 0;
for (Segment s = buffer.head; offset < byteCount; s = s.next) {
if (s.limit == s.pos) {
throw new AssertionError("s.limit == s.pos"); // Empty segment. This should not happen!
}
offset += s.limit - s.pos;
segmentCount++;
}
// Walk through the buffer again to assign segments and build the directory.
this.segments = new byte[segmentCount][];
this.directory = new int[segmentCount * 2];
offset = 0;
segmentCount = 0;
for (Segment s = buffer.head; offset < byteCount; s = s.next) {
segments[segmentCount] = s.data;
offset += s.limit - s.pos;
directory[segmentCount] = offset;
directory[segmentCount + segments.length] = s.pos;
s.shared = true;
segmentCount++;
}
}
@Override public String utf8() {
return toByteString().utf8();
}
@Override public String base64() {
return toByteString().base64();
}
@Override public String hex() {
return toByteString().hex();
}
@Override public ByteString toAsciiLowercase() {
return toByteString().toAsciiLowercase();
}
@Override public ByteString toAsciiUppercase() {
return toByteString().toAsciiUppercase();
}
@Override public ByteString md5() {
return toByteString().md5();
}
@Override public ByteString sha256() {
return toByteString().sha256();
}
@Override public String base64Url() {
return toByteString().base64Url();
}
@Override public ByteString substring(int beginIndex) {
return toByteString().substring(beginIndex);
}
@Override public ByteString substring(int beginIndex, int endIndex) {
return toByteString().substring(beginIndex, endIndex);
}
@Override public byte getByte(int pos) {
checkOffsetAndCount(directory[segments.length - 1], pos, 1);
int segment = segment(pos);
int segmentOffset = segment == 0 ? 0 : directory[segment - 1];
int segmentPos = directory[segment + segments.length];
return segments[segment][pos - segmentOffset + segmentPos];
}
/** Returns the index of the segment that contains the byte at {@code pos}. */
private int segment(int pos) {
// Search for (pos + 1) instead of (pos) because the directory holds sizes, not indexes.
int i = Arrays.binarySearch(directory, 0, segments.length, pos + 1);
return i >= 0 ? i : ~i; // If i is negative, bitflip to get the insert position.
}
@Override public int size() {
return directory[segments.length - 1];
}
@Override public byte[] toByteArray() {
byte[] result = new byte[directory[segments.length - 1]];
int segmentOffset = 0;
for (int s = 0, segmentCount = segments.length; s < segmentCount; s++) {
int segmentPos = directory[segmentCount + s];
int nextSegmentOffset = directory[s];
System.arraycopy(segments[s], segmentPos, result, segmentOffset,
nextSegmentOffset - segmentOffset);
segmentOffset = nextSegmentOffset;
}
return result;
}
@Override public void write(OutputStream out) throws IOException {
if (out == null) throw new IllegalArgumentException("out == null");
int segmentOffset = 0;
for (int s = 0, segmentCount = segments.length; s < segmentCount; s++) {
int segmentPos = directory[segmentCount + s];
int nextSegmentOffset = directory[s];
out.write(segments[s], segmentPos, nextSegmentOffset - segmentOffset);
segmentOffset = nextSegmentOffset;
}
}
@Override void write(Buffer buffer) {
int segmentOffset = 0;
for (int s = 0, segmentCount = segments.length; s < segmentCount; s++) {
int segmentPos = directory[segmentCount + s];
int nextSegmentOffset = directory[s];
Segment segment = new Segment(segments[s], segmentPos,
segmentPos + nextSegmentOffset - segmentOffset);
if (buffer.head == null) {
buffer.head = segment.next = segment.prev = segment;
} else {
buffer.head.prev.push(segment);
}
segmentOffset = nextSegmentOffset;
}
buffer.size += segmentOffset;
}
@Override public boolean rangeEquals(
int offset, ByteString other, int otherOffset, int byteCount) {
if (offset > size() - byteCount) return false;
// Go segment-by-segment through this, passing arrays to other's rangeEquals().
for (int s = segment(offset); byteCount > 0; s++) {
int segmentOffset = s == 0 ? 0 : directory[s - 1];
int segmentSize = directory[s] - segmentOffset;
int stepSize = Math.min(byteCount, segmentOffset + segmentSize - offset);
int segmentPos = directory[segments.length + s];
int arrayOffset = offset - segmentOffset + segmentPos;
if (!other.rangeEquals(otherOffset, segments[s], arrayOffset, stepSize)) return false;
offset += stepSize;
otherOffset += stepSize;
byteCount -= stepSize;
}
return true;
}
@Override public boolean rangeEquals(int offset, byte[] other, int otherOffset, int byteCount) {
if (offset > size() - byteCount || otherOffset > other.length - byteCount) return false;
// Go segment-by-segment through this, comparing ranges of arrays.
for (int s = segment(offset); byteCount > 0; s++) {
int segmentOffset = s == 0 ? 0 : directory[s - 1];
int segmentSize = directory[s] - segmentOffset;
int stepSize = Math.min(byteCount, segmentOffset + segmentSize - offset);
int segmentPos = directory[segments.length + s];
int arrayOffset = offset - segmentOffset + segmentPos;
if (!arrayRangeEquals(segments[s], arrayOffset, other, otherOffset, stepSize)) return false;
offset += stepSize;
otherOffset += stepSize;
byteCount -= stepSize;
}
return true;
}
/** Returns a copy as a non-segmented byte string. */
private ByteString toByteString() {
return new ByteString(toByteArray());
}
@Override public boolean equals(Object o) {
if (o == this) return true;
return o instanceof ByteString
&& ((ByteString) o).size() == size()
&& rangeEquals(0, ((ByteString) o), 0, size());
}
@Override public int hashCode() {
int result = hashCode;
if (result != 0) return result;
// Equivalent to Arrays.hashCode(toByteArray()).
result = 1;
int segmentOffset = 0;
for (int s = 0, segmentCount = segments.length; s < segmentCount; s++) {
byte[] segment = segments[s];
int segmentPos = directory[segmentCount + s];
int nextSegmentOffset = directory[s];
int segmentSize = nextSegmentOffset - segmentOffset;
for (int i = segmentPos, limit = segmentPos + segmentSize; i < limit; i++) {
result = (31 * result) + segment[i];
}
segmentOffset = nextSegmentOffset;
}
return (hashCode = result);
}
@Override public String toString() {
return toByteString().toString();
}
private Object writeReplace() {
return toByteString();
}
}