gzip decompression using zlib library

Question

I have a problem with decompressing some gzip data. I have an array with pointers to dynamically allocated char strings. Each element of this array is one part of the gzip file that I want to uncompress. The first thing which comes to my mind is to concatenate those strings to one, and then decompress data, but I want to avoid this method because of a lot of copying.

So the question is: Is there any way to decompress data divided into few parts, using zlib library ? I was trying to do it, but when I decompress the first part I get Z_DATA_ERROR - and it's normal, because the data is not complete. Is there any way to "wait" for the rest of data to decompress?

Have you seen this? hewgill.com/journal/entries/… You should be able to call inflate() multiple times with the chunks to decompress one by one.... — John Zwinck
yes, I don't have a problem to decompress gzip file when it is in one piece. I am only wondering what to do when I have it in few parts. I wanted to do it one by one, but when I am decompressing the first part I am getting Z_DATA_ERROR because it is not complete, hence it is not decompressed — user3131037
Check the advanced functions in the reference, there you will find the inflateBack function which uses callbacks to read and write data. — Some programmer dude

Mark Adler Mark Adler · Accepted Answer · 2014-09-04T14:27:53

Yes. You can simply call inflate() successively with each of the strings in the appropriate order. for each call of inflate(), you can provide a different pointer and length for the compressed data. Each time, make sure that you first consume all of the uncompressed data generated and that avail_in is zero before moving on to the next chunk of input.

If you are getting a Z_DATA_ERROR that means that either you are not reassembling the original stream correctly, or that the original stream is not a gzip stream.

Note that to decompress a gzip stream, you need to initialize with inflateInit2() and set the parameters appropriately to request gzip decompression.

gzip decompression using zlib library

1 Answers