org.mozilla.universalchardet.UnicodeBOMInputStream Maven / Gradle / Ivy
// (‑●‑●)> released under the WTFPL v2 license, by Gregory Pakosz (@gpakosz)
package org.mozilla.universalchardet;
import java.io.IOException;
import java.io.InputStream;
import java.io.PushbackInputStream;
/**
* The UnicodeBOMInputStream class wraps any
* InputStream and detects the presence of any Unicode BOM
* (Byte Order Mark) at its beginning, as defined by
* RFC 3629 - UTF-8, a
* transformation format of ISO 10646
*
* The
* Unicode FAQ
* defines 5 types of BOMs:
* 00 00 FE FF = UTF-32, big-endian
FF FE 00 00 = UTF-32, little-endian
FE FF = UTF-16, big-endian
FF FE = UTF-16, little-endian
EF BB BF = UTF-8
*
* Use the {@link #getBOM()} method to know whether a BOM has been detected
* or not.
*
* Use the {@link #skipBOM()} method to remove the detected BOM from the
* wrapped InputStream object.
*
* @author Gregory Pakosz
* @version 1.0
*/
public class UnicodeBOMInputStream extends InputStream {
/**
* Type safe enumeration class that describes the different types of Unicode
* BOMs.
*/
public static final class BOM {
final byte bytes[];
private final String description;
/**
* NONE.
*/
public static final BOM NONE = new BOM(new byte[] {}, "NONE");
/**
* UTF-8 BOM (EF BB BF).
*/
public static final BOM UTF_8 = new BOM(new byte[] { (byte) 0xEF, (byte) 0xBB, (byte) 0xBF }, "UTF-8");
/**
* UTF-16, little-endian (FF FE).
*/
public static final BOM UTF_16_LE = new BOM(new byte[] { (byte) 0xFF, (byte) 0xFE }, "UTF-16 little-endian");
/**
* UTF-16, big-endian (FE FF).
*/
public static final BOM UTF_16_BE = new BOM(new byte[] { (byte) 0xFE, (byte) 0xFF }, "UTF-16 big-endian");
/**
* UTF-32, little-endian (FF FE 00 00).
*/
public static final BOM UTF_32_LE = new BOM(new byte[] { (byte) 0xFF, (byte) 0xFE, (byte) 0x00, (byte) 0x00 },
"UTF-32 little-endian");
/**
* UTF-32, big-endian (00 00 FE FF).
*/
public static final BOM UTF_32_BE = new BOM(new byte[] { (byte) 0x00, (byte) 0x00, (byte) 0xFE, (byte) 0xFF },
"UTF-32 big-endian");
/**
* Returns a String representation of this BOM
* value.
*/
public final String toString() {
return description;
}
/**
* Returns the bytes corresponding to this BOM value.
* @return the bytes corresponding to this BOM value.
*/
public final byte[] getBytes() {
final int length = bytes.length;
final byte[] result = new byte[length];
// make a defensive copy
System.arraycopy(bytes, 0, result, 0, length);
return result;
}
private BOM(final byte bom[], final String description) {
assert (bom != null) : "invalid BOM: null is not allowed";
assert (description != null) : "invalid description: null is not allowed";
assert (description.length() != 0) : "invalid description: empty string is not allowed";
this.bytes = bom;
this.description = description;
}
} // BOM
private final PushbackInputStream in;
private final BOM bom;
private boolean skipped = false;
/**
* Constructs a new UnicodeBOMInputStream that wraps the
* specified InputStream. By default skip BOM bytes
*
* @param inputStream an InputStream.
*
* @throws NullPointerException when inputStream is
* null.
* @throws IOException on reading from the specified InputStream
* when trying to detect the Unicode BOM.
*/
public UnicodeBOMInputStream(final InputStream inputStream) throws IOException {
this(inputStream, true);
}
/**
* Constructs a new UnicodeBOMInputStream that wraps the
* specified InputStream.
*
* @param inputStream an InputStream.
* @param skipIfFound to automatically skip BOM bytes if found
*
* @throws NullPointerException when inputStream is
* null.
* @throws IOException on reading from the specified InputStream
* when trying to detect the Unicode BOM.
*/
public UnicodeBOMInputStream(final InputStream inputStream,
boolean skipIfFound) throws IOException {
if (inputStream == null) {
throw new NullPointerException(
"invalid input stream: null is not allowed");
}
in = new PushbackInputStream(inputStream, 4);
final byte bom[] = new byte[4];
final int read = in.read(bom);
switch (read) {
case 4:
if ((bom[0] == (byte) 0xFF) && (bom[1] == (byte) 0xFE)
&& (bom[2] == (byte) 0x00) && (bom[3] == (byte) 0x00)) {
this.bom = BOM.UTF_32_LE;
break;
} else if ((bom[0] == (byte) 0x00) && (bom[1] == (byte) 0x00)
&& (bom[2] == (byte) 0xFE) && (bom[3] == (byte) 0xFF)) {
this.bom = BOM.UTF_32_BE;
break;
}
case 3:
if ((bom[0] == (byte) 0xEF) && (bom[1] == (byte) 0xBB)
&& (bom[2] == (byte) 0xBF)) {
this.bom = BOM.UTF_8;
break;
}
case 2:
if ((bom[0] == (byte) 0xFF) && (bom[1] == (byte) 0xFE)) {
this.bom = BOM.UTF_16_LE;
break;
} else if ((bom[0] == (byte) 0xFE) && (bom[1] == (byte) 0xFF)) {
this.bom = BOM.UTF_16_BE;
break;
}
default:
this.bom = BOM.NONE;
break;
}
if (read > 0) {
in.unread(bom, 0, read);
}
if (skipIfFound) {
this.skipBOM();
}
}
/**
* Returns the BOM that was detected in the wrapped
* InputStream object.
*
* @return a BOM value.
*/
public final BOM getBOM() {
// BOM type is immutable.
return bom;
}
/**
* Skips the BOM that was found in the wrapped
* InputStream object.
*
* @return this UnicodeBOMInputStream.
*
* @throws IOException when trying to skip the BOM from the wrapped
* InputStream object.
*/
public final synchronized UnicodeBOMInputStream skipBOM()
throws IOException {
if (!skipped) {
long bytesToSkip = bom.bytes.length;
long bytesSkipped = in.skip(bytesToSkip);
for (long i = bytesSkipped; i < bytesToSkip; i++) {
in.read();
}
skipped = true;
}
return this;
}
/**
* {@inheritDoc}
*/
public int read() throws IOException {
this.skipped = true;
return in.read();
}
/**
* {@inheritDoc}
*/
public int read(final byte b[]) throws IOException {
this.skipped = true;
return in.read(b, 0, b.length);
}
/**
* {@inheritDoc}
*/
public int read(final byte b[], final int off, final int len) throws IOException {
this.skipped = true;
return in.read(b, off, len);
}
/**
* {@inheritDoc}
*/
public long skip(final long n) throws IOException {
this.skipped = true;
return in.skip(n);
}
/**
* {@inheritDoc}
*/
public int available() throws IOException {
return in.available();
}
/**
* {@inheritDoc}
*/
public void close() throws IOException {
in.close();
}
/**
* {@inheritDoc}
*/
public synchronized void mark(final int readlimit) {
in.mark(readlimit);
}
/**
* {@inheritDoc}
*/
public synchronized void reset() throws IOException {
in.reset();
}
/**
* {@inheritDoc}
*/
public boolean markSupported() {
return in.markSupported();
}
}
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