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JDBC Type 4 driver for MySQL
/*
* Copyright (c) 2002, 2020, Oracle and/or its affiliates.
*
* This program is free software; you can redistribute it and/or modify it under
* the terms of the GNU General Public License, version 2.0, as published by the
* Free Software Foundation.
*
* This program is also distributed with certain software (including but not
* limited to OpenSSL) that is licensed under separate terms, as designated in a
* particular file or component or in included license documentation. The
* authors of MySQL hereby grant you an additional permission to link the
* program and your derivative works with the separately licensed software that
* they have included with MySQL.
*
* Without limiting anything contained in the foregoing, this file, which is
* part of MySQL Connector/J, is also subject to the Universal FOSS Exception,
* version 1.0, a copy of which can be found at
* http://oss.oracle.com/licenses/universal-foss-exception.
*
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
* FOR A PARTICULAR PURPOSE. See the GNU General Public License, version 2.0,
* for more details.
*
* You should have received a copy of the GNU General Public License along with
* this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
package com.mysql.cj.protocol;
import java.io.IOException;
import java.io.InputStream;
import java.util.Arrays;
import com.mysql.cj.log.Log;
/**
* A non-blocking buffered input stream. Reads more if it can, won't block to fill the buffer, only blocks to satisfy a request of read(byte[])
*/
public class ReadAheadInputStream extends InputStream {
private final static int DEFAULT_BUFFER_SIZE = 4096;
private InputStream underlyingStream;
private byte buf[];
protected int endOfCurrentData;
protected int currentPosition;
protected boolean doDebug = false;
protected Log log;
private void fill(int readAtLeastTheseManyBytes) throws IOException {
checkClosed();
this.currentPosition = 0; /* no mark: throw away the buffer */
this.endOfCurrentData = this.currentPosition;
// Read at least as many bytes as the caller wants, but don't block to fill the whole buffer (like java.io.BufferdInputStream does)
int bytesToRead = Math.min(this.buf.length - this.currentPosition, readAtLeastTheseManyBytes);
int bytesAvailable = this.underlyingStream.available();
if (bytesAvailable > bytesToRead) {
// Great, there's more available, let's grab those bytes too! (read-ahead)
bytesToRead = Math.min(this.buf.length - this.currentPosition, bytesAvailable);
}
if (this.doDebug) {
StringBuilder debugBuf = new StringBuilder();
debugBuf.append(" ReadAheadInputStream.fill(");
debugBuf.append(readAtLeastTheseManyBytes);
debugBuf.append("), buffer_size=");
debugBuf.append(this.buf.length);
debugBuf.append(", current_position=");
debugBuf.append(this.currentPosition);
debugBuf.append(", need to read ");
debugBuf.append(Math.min(this.buf.length - this.currentPosition, readAtLeastTheseManyBytes));
debugBuf.append(" bytes to fill request,");
if (bytesAvailable > 0) {
debugBuf.append(" underlying InputStream reports ");
debugBuf.append(bytesAvailable);
debugBuf.append(" total bytes available,");
}
debugBuf.append(" attempting to read ");
debugBuf.append(bytesToRead);
debugBuf.append(" bytes.");
if (this.log != null) {
this.log.logTrace(debugBuf.toString());
} else {
System.err.println(debugBuf.toString());
}
}
int n = this.underlyingStream.read(this.buf, this.currentPosition, bytesToRead);
if (n > 0) {
this.endOfCurrentData = n + this.currentPosition;
}
}
private int readFromUnderlyingStreamIfNecessary(byte[] b, int off, int len) throws IOException {
checkClosed();
int avail = this.endOfCurrentData - this.currentPosition;
if (this.doDebug) {
StringBuilder debugBuf = new StringBuilder();
debugBuf.append("ReadAheadInputStream.readIfNecessary(");
debugBuf.append(Arrays.toString(b));
debugBuf.append(",");
debugBuf.append(off);
debugBuf.append(",");
debugBuf.append(len);
debugBuf.append(")");
if (avail <= 0) {
debugBuf.append(" not all data available in buffer, must read from stream");
if (len >= this.buf.length) {
debugBuf.append(", amount requested > buffer, returning direct read() from stream");
}
}
if (this.log != null) {
this.log.logTrace(debugBuf.toString());
} else {
System.err.println(debugBuf.toString());
}
}
if (avail <= 0) {
if (len >= this.buf.length) {
return this.underlyingStream.read(b, off, len);
}
fill(len);
avail = this.endOfCurrentData - this.currentPosition;
if (avail <= 0) {
return -1;
}
}
int bytesActuallyRead = (avail < len) ? avail : len;
System.arraycopy(this.buf, this.currentPosition, b, off, bytesActuallyRead);
this.currentPosition += bytesActuallyRead;
return bytesActuallyRead;
}
@Override
public synchronized int read(byte b[], int off, int len) throws IOException {
checkClosed(); // Check for closed stream
if ((off | len | (off + len) | (b.length - (off + len))) < 0) {
throw new IndexOutOfBoundsException();
} else if (len == 0) {
return 0;
}
int totalBytesRead = 0;
while (true) {
int bytesReadThisRound = readFromUnderlyingStreamIfNecessary(b, off + totalBytesRead, len - totalBytesRead);
// end-of-stream?
if (bytesReadThisRound <= 0) {
if (totalBytesRead == 0) {
totalBytesRead = bytesReadThisRound;
}
break;
}
totalBytesRead += bytesReadThisRound;
// Read _at_least_ enough bytes
if (totalBytesRead >= len) {
break;
}
// Nothing to read?
if (this.underlyingStream.available() <= 0) {
break;
}
}
return totalBytesRead;
}
@Override
public int read() throws IOException {
checkClosed();
if (this.currentPosition >= this.endOfCurrentData) {
fill(1);
if (this.currentPosition >= this.endOfCurrentData) {
return -1;
}
}
return this.buf[this.currentPosition++] & 0xff;
}
@Override
public int available() throws IOException {
checkClosed();
return this.underlyingStream.available() + (this.endOfCurrentData - this.currentPosition);
}
private void checkClosed() throws IOException {
if (this.buf == null) {
throw new IOException("Stream closed");
}
}
public ReadAheadInputStream(InputStream toBuffer, boolean debug, Log logTo) {
this(toBuffer, DEFAULT_BUFFER_SIZE, debug, logTo);
}
public ReadAheadInputStream(InputStream toBuffer, int bufferSize, boolean debug, Log logTo) {
this.underlyingStream = toBuffer;
this.buf = new byte[bufferSize];
this.doDebug = debug;
this.log = logTo;
}
@Override
public void close() throws IOException {
if (this.underlyingStream != null) {
try {
this.underlyingStream.close();
} finally {
this.underlyingStream = null;
this.buf = null;
this.log = null;
}
}
}
@Override
public boolean markSupported() {
return false;
}
@Override
public long skip(long n) throws IOException {
checkClosed();
if (n <= 0) {
return 0;
}
long bytesAvailInBuffer = this.endOfCurrentData - this.currentPosition;
if (bytesAvailInBuffer <= 0) {
fill((int) n);
bytesAvailInBuffer = this.endOfCurrentData - this.currentPosition;
if (bytesAvailInBuffer <= 0) {
return 0;
}
}
long bytesSkipped = (bytesAvailInBuffer < n) ? bytesAvailInBuffer : n;
this.currentPosition += bytesSkipped;
return bytesSkipped;
}
}