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From Andreas Lehmkühler (Commented) (JIRA) <j...@apache.org>
Subject [jira] [Commented] (PDFBOX-1232) FlateDecoder in stream mode
Date Fri, 09 Mar 2012 07:11:57 GMT

    [ https://issues.apache.org/jira/browse/PDFBOX-1232?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13225903#comment-13225903
] 

Andreas Lehmkühler commented on PDFBOX-1232:
--------------------------------------------

Just to be sure, what is the expected result of the decompression of the given 5 value stream?
                
> FlateDecoder in stream mode
> ---------------------------
>
>                 Key: PDFBOX-1232
>                 URL: https://issues.apache.org/jira/browse/PDFBOX-1232
>             Project: PDFBox
>          Issue Type: Bug
>            Reporter: Dave Smith
>
> The zlib (the unlying spec for Flate compression) does not require an Z_STREAM_END to
terminate the compression. The Java InflateInputStream is really assuming that you are reading
a zip or gzip file which will always have a Z_STREAM_END (Z_STREAM_END is a constant in the
zlib library which Java calls natively) . So the following chunk decodes fine using  the jcraft
zlib decoder, but fails using the InflateInputStream.
> 3 0 obj
> <<
> /Type /XObject
> /Subtype /Form
> /FormType 1
> /Resources << /Font 4 0 R
> /ProcSet [/PDF /ImageC /Text]>>
> /BBox [0 0 595 842]
> /Matrix [1 0 0 1 0 0]
> /Filter /FlateDecode
> /Length 5 >>
> stream
> H<89>^C^@
> endstream
> endobj
> The blob is 72, -119, 3, 0, 13 decimal. It decodes to an empty string.
> The fix is to use Inflater and check to see if it has consumed all of the input buffer
and make sure it has nothing to write into the output buffer.
> protected ByteArrayOutputStream decompress(InputStream in)
>       throws IOException, DataFormatException
>   {
>       ByteArrayOutputStream out = new ByteArrayOutputStream();
>       byte buf[] = new byte[1000];
>       Inflater inflater = new Inflater();
>       int read = in.read(buf);
>       if(read == 0)
>       {
>               return out;
>       }
>       inflater.setInput(buf,0,read);
>       byte res[] = new byte[1000];
>       while(true)
>       {
>               int resRead = inflater.inflate(res);
>               if(resRead !=0)
>               {
>                       out.write(res,0,resRead);
>                       continue;
>               }
>               if(inflater.finished() || inflater.needsDictionary() ||  in.available()==0)
>               {
>                       out.close();
>                       return out;
>               }
>              read = in.read(buf);
>              inflater.setInput(buf,0,read);
>     
>       }
>   }
> We then need to change FlateFilter.decode(InputStream compressedData, OutputStream result,
> COSDictionary options, int filterIndex )
> to look like ...
>  if (compressedData.available() > 0)
>           {
>               try
>               {
>                       baos =  decompress(compressedData);
>               }
> if (predictor==-1 || predictor == 1 )
>               {
>                  result.write(baos.toByteArray());
>               }
> else
> {
>  use the bytearrayoutput stream as before ...
> }

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