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package de.danoeh.antennapod.util.id3reader;
import java.io.IOException;
import java.io.InputStream;
import java.io.PushbackInputStream;
import de.danoeh.antennapod.util.id3reader.model.FrameHeader;
import de.danoeh.antennapod.util.id3reader.model.TagHeader;
/**
* Reads the ID3 Tag of a given file. In order to use this class, you should
* create a subclass of it and overwrite the onStart* - or onEnd* - methods.
*/
public class ID3Reader {
private static final int HEADER_LENGTH = 10;
private static final int ID3_LENGTH = 3;
private static final int FRAME_ID_LENGTH = 4;
protected static final int ACTION_SKIP = 1;
protected static final int ACTION_DONT_SKIP = 2;
protected int readerPosition;
private static final char[] LITTLE_ENDIAN_BOM = { 0xff, 0xfe };
private static final char[] BIG_ENDIAN_BOM = { 0xfe, 0xff };
public ID3Reader() {
}
public final void readInputStream(InputStream input) throws IOException,
ID3ReaderException {
int rc;
readerPosition = 0;
char[] tagHeaderSource = readBytes(input, HEADER_LENGTH);
TagHeader tagHeader = createTagHeader(tagHeaderSource);
if (tagHeader == null) {
onNoTagHeaderFound();
} else {
rc = onStartTagHeader(tagHeader);
if (rc == ACTION_SKIP) {
onEndTag();
} else {
while (readerPosition < tagHeader.getSize()) {
FrameHeader frameHeader = createFrameHeader(readBytes(
input, HEADER_LENGTH));
if (checkForNullString(frameHeader.getId())) {
break;
} else {
rc = onStartFrameHeader(frameHeader, input);
if (rc == ACTION_SKIP) {
skipBytes(input, frameHeader.getSize());
}
}
}
onEndTag();
}
}
}
/** Returns true if string only contains null-bytes. */
private boolean checkForNullString(String s) {
if (!s.isEmpty()) {
int i = 0;
if (s.charAt(i) == 0) {
for (i = 1; i < s.length(); i++) {
if (s.charAt(i) != 0) {
return false;
}
}
return true;
}
return false;
} else {
return true;
}
}
/**
* Read a certain number of bytes from the given input stream. This method
* changes the readerPosition-attribute.
*/
protected char[] readBytes(InputStream input, int number)
throws IOException, ID3ReaderException {
char[] header = new char[number];
for (int i = 0; i < number; i++) {
int b = input.read();
readerPosition++;
if (b != -1) {
header[i] = (char) b;
} else {
throw new ID3ReaderException("Unexpected end of stream");
}
}
return header;
}
/**
* Skip a certain number of bytes on the given input stream. This method
* changes the readerPosition-attribute.
*/
protected void skipBytes(InputStream input, int number) throws IOException {
int skipped = 0;
while (skipped < number) {
skipped += input.skip(number - skipped);
}
readerPosition += number;
}
private TagHeader createTagHeader(char[] source) throws ID3ReaderException {
boolean hasTag = (source[0] == 0x49) && (source[1] == 0x44)
&& (source[2] == 0x33);
if (source.length != HEADER_LENGTH) {
throw new ID3ReaderException("Length of header must be "
+ HEADER_LENGTH);
}
if (hasTag) {
String id = null;
id = new String(source, 0, ID3_LENGTH);
char version = (char) ((source[3] << 8) | source[4]);
byte flags = (byte) source[5];
int size = (source[6] << 24) | (source[7] << 16) | (source[8] << 8)
| source[9];
return new TagHeader(id, size, version, flags);
} else {
return null;
}
}
private FrameHeader createFrameHeader(char[] source)
throws ID3ReaderException {
if (source.length != HEADER_LENGTH) {
throw new ID3ReaderException("Length of header must be "
+ HEADER_LENGTH);
}
String id = null;
id = new String(source, 0, FRAME_ID_LENGTH);
int size = (((int) source[4]) << 24) | (((int) source[5]) << 16)
| (((int) source[6]) << 8) | source[7];
char flags = (char) ((source[8] << 8) | source[9]);
return new FrameHeader(id, size, flags);
}
protected String readString(InputStream input, int max) throws IOException,
ID3ReaderException {
char[] bom = readBytes(input, 2);
if (bom == LITTLE_ENDIAN_BOM || bom == BIG_ENDIAN_BOM) {
return readUnicodeString(input, bom, max);
} else {
PushbackInputStream pi = new PushbackInputStream(input, 2);
pi.unread(bom[1]);
pi.unread(bom[0]);
return readISOString(pi, max);
}
}
private String readISOString(InputStream input, int max)
throws IOException, ID3ReaderException {
int bytesRead = 0;
StringBuilder builder = new StringBuilder();
char c;
while (++bytesRead <= max && (c = (char) input.read()) > 0) {
builder.append(c);
}
return builder.toString();
}
private String readUnicodeString(InputStream input, char[] bom, int max)
throws IOException, ID3ReaderException {
StringBuffer builder = new StringBuffer();
char c1 = (char) input.read();
char c2 = (char) input.read();
int bytesRead = 2;
while ((c1 > 0 && c2 > 0) && ++bytesRead <= max) {
builder.append(c1);
c1 = c2;
c2 = (char) input.read();
}
if (bom == LITTLE_ENDIAN_BOM) {
builder.reverse();
}
return builder.toString();
}
public int onStartTagHeader(TagHeader header) {
return ACTION_SKIP;
}
public int onStartFrameHeader(FrameHeader header, InputStream input)
throws IOException, ID3ReaderException {
return ACTION_SKIP;
}
public void onEndTag() {
}
public void onNoTagHeaderFound() {
}
}
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