How can I generate zip file without saving to the disk with Ruby?

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I had a similar problem which I solved using the rubyzip gem and the stringio object.
It turns out that rubyzip provides a method that returns a stringio object: ZipOutputStream.write_buffer.

You can create the zip file structure as you like using put_next_entry and write and once you are finished you can rewind the stringio and read the binary data using sysread.

See the following simple example (works for rubyzip 0.9.X)

require 'zip/zip'
stringio = Zip::OutputStream.write_buffer do |zio|
  zio.put_next_entry("test.txt")
  zio.write "Hello world!"
end
stringio.rewind
binary_data = stringio.sysread

Tested on jruby 1.6.5.1 (ruby-1.9.2-p136) (2011-12-27 1bf37c2) (Java HotSpot(TM) 64-Bit Server VM 1.6.0_29) [Windows Server 2008-amd64-java])

The following example works for rubyzip >= 1.0.0

require 'rubygems'    
require 'zip'
stringio = Zip::OutputStream.write_buffer do |zio|
  zio.put_next_entry("test.txt")
  zio.write "Hello world!"
end
binary_data = stringio.string

Tested on jruby 1.7.22 (1.9.3p551) 2015-08-20 c28f492 on OpenJDK 64-Bit Server VM 1.7.0_79-b14 +jit [linux-amd64] and rubyzip gem 1.1.7

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