Re: Compress::Zlib inflateInit help
- From: Paul Marquess <paul.marquess@xxxxxxxxxxxxxx>
- Date: Tue, 29 Apr 2008 19:36:45 +0100
hymie! wrote:
In our last episode, the evil Dr. Lacto had captured our hero,
Paul Marquess <paul.marquess@xxxxxxxxxxxxxx>, who said:
Do you have any more info on the structure of the data in the socket. For
example, is there any significance toyou reading $number bytes at a time
from the socket?
Data spec, including java sample code (I don't speak java)
The basic structure of the data is:
<blockTime><blockSequence><blockSize><block>...
blockTime = a 64-bit long representing the time of the block in
milliseconds since the epoc.
blockSequence = a 32-bit int representing a sequence number for the
block of data (see "id" parameter above).
blockSize = a 32-bit int representing the size of the compressed block
in bytes.
block = a compressed chunk of data.
You will need to take the compressed block of data and uncompress it
to produce workable raw data. You should be able to use a standard ZLIB
compression library to do this. This functionality is usually found in
your existing development environment. In Java, ZLIB is built into the
VM itself. You need to hand the data block to a java.util.zip.Inflater.
Example:
Inflater decompresser = new Inflater();
decompresser.setInput(compressedBlock, 0, compressedDataLength);
byte[] result = new byte[2048];
int resultLength = decompresser.inflate(result);
decompresser.end();
String message = new String(result, 0, resultLength, "UTF-8");
If you can get it to work by prefixing every $number bytes with "\x78\x01"
it sounds like you are dealing with one or more RFC1951 data streams.
No. It only works if I re-run inflateInit and *then* prefix the
string with \x78\x01
If you want Compress::Zlib to read an RFC1951 stream, add the WindowsBits
parameter like this when you create the inflation object
($inflate,$status) = inflateInit(WindowBits => -MAX_WBITS);
That works well for my first data chunk, after that I get
1
line ->
status -> stream end
2
line ->
status -> stream end
use IO::Uncompress::RawInflate qw(:all)
my $data ;
rawinflate $socket => \$data
or die "Cannot uncompress: $RawInflateError\n";
Again, this works well for my first data chunk, but doesn't read the
cleartext data preceding the second data chunk:
The key part I didn't know was you are dealing with a sequence of compressed
RFC 1951 data streams that are each prefixed with a bespoke header. So that
means you need to deal with reading both compressed & non-compressed data
from the socket. Is there a link you can post that describes this feed in
more detail?
So assuming nothing else comes down the socket, you could try something like
this - you may need to change the final "N" in the unpack call to a "V" if
the byte order is non-standard.
my $header;
my $header_size = 8 + 4 + 4; # time + sequence + size
while (read($socket, $header, $header_size) == $header_size)
{
my ($time1, $time2, $sequence, $size) = unpack "NNNN", $header;
rawinflate $socket => \$data, InputLength => $size
or die "Cannot uncompress: $RawInflateError\n";
print "$daat\n";
}
cheers
Paul
.
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