stdlib_libraries/compressed_streams.rb

tests/_examples/stdlib_libraries/compressed_streams.rb in the metorex repository.

# Compressed streams: the two checksums zlib keeps, the encoding underneath,
# and the gzip wrapper that carries it.

require 'zlib'
require 'stringio'

p Zlib.crc32 ""
p Zlib.crc32 "123456789"
p Zlib.adler32 "123456789"
p Zlib.crc_table.length

held = "the quick brown fox " * 20
p Zlib.inflate(Zlib.deflate(held)) == held
p Zlib.gunzip(Zlib.gzip(held)) == held

# A stream written by any other zlib reads back here.
written = [120, 156, 99, 96, 128, 1, 0, 0, 10, 0, 1].pack "C*"
p Zlib.inflate(written) == "\000" * 10

# A gzip member carries the name and time it was written with.
member = [31, 139, 8, 0, 44, 220, 209, 71, 0, 3, 51, 52, 50, 54, 49, 77,
          76, 74, 78, 73, 5, 0, 157, 5, 0, 36, 10, 0, 0, 0].pack "C*"
reader = Zlib::GzipReader.new StringIO.new(member)
p reader.read
p reader.eof?
reader.close

# The reader walks what it holds a line or a character at a time.
lines = Zlib::GzipReader.new StringIO.new(Zlib.gzip("one\ntwo\n"))
p lines.readlines
p Zlib::GzipReader.new(StringIO.new(Zlib.gzip("ab"))).each_char.to_a

# A member that has been closed has nothing left to say about itself.
closed = Zlib::GzipReader.new StringIO.new(member)
closed.close
begin
  closed.orig_name
rescue Zlib::GzipFile::Error => problem
  p problem.message
end

Output:

0
3421780262
152961502
256
true
true
true
"12345abcde"
true
["one\n", "two\n"]
["a", "b"]
"closed gzip stream"