Bug #5929

Zlib::Inflate#set_dictionary does not work with short input

Added by drbrain (Eric Hodel) over 8 years ago. Updated over 8 years ago.

Target version:
ruby -v:
ruby 2.0.0dev (2012-01-26 trunk 34377) [x86_64-darwin11.2.0]


If a deflate stream requires a dictionary and the block of data is short it is impossible to decompress the data without modifying the returned bytes. Upon receiving a Zlib::NeedDict exception the documentation for Zlib::Inflate#inflate states:

Set the dictionary by Zlib::Inflate#set_dictionary and then
call this method again with an empty string

Calling inflate with an empty string does not decompress any further bytes due to (({do_inflate()})) ignoring zero-byte strings to avoid a Z_BUF_ERROR.

The attached patch alters the (({do_inflate()})) to inflate more data when either more data was provided by the user or (({z->stream.avail_in})) is nonzero.

Reading (({zstream_run()})) it appears that (({z->stream.avail_in})) will be set to zero upon consuming a chunk of data, so providing an empty string in the middle of a non-dictionary stream will be OK, but please check it.


zlib.c.set_dictionary.patch (2.13 KB) zlib.c.set_dictionary.patch drbrain (Eric Hodel), 01/26/2012 11:59 AM

Related issues

Related to Ruby master - Feature #5937: Zlib::Inflate#add_dictionary to pre-supply dictionaries for inflate streamsClosed01/27/2012Actions

Updated by drbrain (Eric Hodel) over 8 years ago

  • Status changed from Open to Closed
  • % Done changed from 0 to 100

This issue was solved with changeset r34552.
Eric, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

  • ext/zlib/zlib.c (do_inflate): Inflate more data if buffered data exists. Allows Zlib::Inflate#set_dictionary to work. [ruby-trunk - Bug #5929]

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