Bug #14804: GzipReader cannot read Freebase dump (but gzcat/zless can)

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: Ruby 2.4.1p111 (2017-03-22 revision 58053) [x86_64-darwin17]
• Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
• Tags: ext

[amadan (Goran Topic)]

This is likely related to https://stackoverflow.com/questions/35354951/gzipstream-quietly-fails-on-large-file-stream-ends-at-2gb (and its accepted answer).

The file in question: http://commondatastorage.googleapis.com/freebase-public/rdf/freebase-rdf-latest.gz
(watch out, it's 30Gb compressed!)

Steps to reproduce:

require "zlib"
Zlib::GzipReader.open("freebase-rdf-latest.gz") { |f| f.each_line.count }
# => 14374340

However, the correct answer is different:

$ gzcat freebase-rdf-latest.gz | wc -l
3130753066

Another experiment showed that the last f.tell was 1945715682, while there's considerably more bytes in the uncompressed version. This fits well with the Stack Overflow report from C# linked above, which states the first "substream" contains exactly that many bytes.

If this is a hard constraint from the wrapped library (and thus should be fixed upstream), at least the documentation should mention it.

[amadan (Goran Topic)]

(Note that f.each_line.count would return the wrong result anyway, due to https://bugs.ruby-lang.org/issues/14805 , since 3130753066 is outside int32 range, but it doesn't have the chance to do so, on account of stopping prematurely.)

[jeremyevans0 (Jeremy Evans)]

• Related to Bug #9790: Zlib::GzipReader only decompressed the first of concatenated files added

[jeremyevans0 (Jeremy Evans)]

• Status changed from Open to Closed

This can now be handled using Zlib::GzipReader.zcat, which was recently added to zlib.