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https://issues.apache.org/jira/browse/IO-331?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Gary D. Gregory resolved IO-331.
--------------------------------
Resolution: Fixed
Fix Version/s: 2.4
Committed revision 1346400.
> BOMInputStream wrongly detects UTF-32LE_BOM files as UTF-16LE_BOM files in
> method getBOM()
> ------------------------------------------------------------------------------------------
>
> Key: IO-331
> URL: https://issues.apache.org/jira/browse/IO-331
> Project: Commons IO
> Issue Type: Bug
> Components: Streams/Writers
> Affects Versions: 2.3
> Environment: OS: Win 7 x64
> JDK: 1.7.03
> Reporter: David Gao
> Labels: BOMInputStream, UTF-32LE
> Fix For: 2.4
>
> Attachments: UTF-32LE_Y.txt
>
>
> Hi,
> The BOMInputStream works great for most UTF encoded files when detecting Byte
> Order Marks. However, if a file is UTF-32LE encoded with BOM the class takes
> it as UTF-16LE instead. This is not expected behavior.
> The problem comes from method getBOM(). And the first two bytes for UTF-16LE
> and UTF-32LE are the same, which might be the root cause of the problem.
> The following lists the bytes for UTF encodings for reference. The content is
> a BOM followed by letter 't'.
> ||Encoding||Byte 1||Byte 2||Byte 3||Byte 4|| || || || ||
> |UTF8|EF|BB|BF|74| | | | |
> |UTF16-LE|FF|FE|74|00| | | | |
> |UTF16-BE|FE|FF|00|74| | | | |
> |UTF32-LE|FF|FE|00|00|74|00|00|00
> |UTF32-BE|00|00|FE|FF|00|00|00|74
> I personally used the following code to work around this problem at the
> moment. Hope it helps.
> {code}
> private void detectBOM(InputStream in) throws IOException{
> List<ByteOrderMark> all=availableBOMs();
> int max=0;
> for (ByteOrderMark bom : all) {
> max = Math.max(max, bom.length());
> }
> byte[] firstBytes=new byte[max];
> for (int i = 0; i < max; i++) {
> firstBytes[i]=(byte) in.read();
> System.out.print(Integer.toHexString(firstBytes[i] &
> 0xff).toUpperCase()+" ");
> }
>
> boolean found=false;
> for (int j = max; j >1; j--) {
> byte[] _copy=Arrays.copyOf(firstBytes, j);
> for (ByteOrderMark mark : all) {
> found=Arrays.equals(_copy, mark.getBytes());
> if (found) {
> System.out.println("\nBOM is:
> "+mark.getCharsetName());
> break;
> }
> }
> if (found) break;
> }
> }
>
> private static List<ByteOrderMark> availableBOMs(){
> List<ByteOrderMark> all=new ArrayList<ByteOrderMark>();
> all.add(ByteOrderMark.UTF_8);
> all.add(ByteOrderMark.UTF_16BE);
> all.add(ByteOrderMark.UTF_16LE);
> all.add(ByteOrderMark.UTF_32BE);
> all.add(ByteOrderMark.UTF_32LE);
> return all;
> }
> {code}
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