GZip.jl — A Julia interface for gzip functions in zlib

This module provides a wrapper for the gzip related functions of (zlib), a free, general-purpose, legally unencumbered, lossless data-compression library. These functions allow the reading and writing of gzip files.


  • This interface is only for gzipped files, not the streaming zlib compression interface. Internally, it depends on/uses the streaming interface, but the gzip related functions are higher level functions pertaining to gzip files only.
  • GZipStream is an implementation of IO and can be used virtually anywhere IO is used.
  • This implementation mimics the IOStream implementation, and should be a drop-in replacement for IOStream, with some caveats:
    • seekend() and truncate() are not available
    • readuntil() is available, but is not very efficient. (But readline() works fine.)

In addition to open(), gzopen() and gzdopen(), the following IO/IOStream functions are supported:

  • close()
  • flush()
  • seek()
  • skip()
  • position()
  • eof()
  • read()
  • readuntil()
  • readline()
  • write()
  • peek()

Due to limitations in zlib, seekend() and truncate() are not available.


GZip.open(fname[, gzmode[, buf_size]])

Alias for gzopen(). This is not exported, and must be called using GZip.open().

GZip.gzopen(fname[, gzmode[, buf_size]])

Opens a file with mode (default "r"), setting internal buffer size to buf_size (default Z_DEFAULT_BUFSIZE=8192), and returns a the file as a GZipStream.

gzmode must contain one of

r read
w write, create, truncate
a write, create, append

In addition, gzmode may also contain

x create the file exclusively (fails if file exists)
0-9 compression level

and/or a compression strategy:

f filtered data
h Huffman-only compression
R run-length encoding
F fixed code compression

Note that + is not allowed in gzmode.

If an error occurs, gzopen throws a GZError

GZip.gzdopen(fd[, gzmode[, buf_size]])

Create a GZipStream object from an integer file descriptor. See gzopen() for gzmode and buf_size descriptions.

GZip.gzdopen(s[, gzmode[, buf_size]])

Create a GZipStream object from IOStream s.


type GZip.GZipStream(name, gz_file[, buf_size[, fd[, s]]])

Subtype of IO which wraps a gzip stream. Returned by gzopen() and gzdopen().

type GZip.GZError(err, err_str)

gzip error number and string. Possible error values:

Z_OK No error
Z_ERRNO Filesystem error (consult errno())
Z_STREAM_ERROR Inconsistent stream state
Z_DATA_ERROR Compressed data error
Z_MEM_ERROR Out of memory
Z_BUF_ERROR Input buffer full/output buffer empty
Z_VERSION_ERROR zlib library version is incompatible with caller version