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Bindings to ZLib for MRuby.


compress & uncompress

compress & uncompress provide a simple API for bulk compression. compress produces a deflate stream wrapped in a zlib header, and uncompress reverses that action.


src = 'test' * 10
# => "testtesttesttesttesttesttesttesttesttest"

# => 40

compressed = ZLib.compress(src)
# => "x\234+I-.)!\002\003\000f\261\021\201"

# => 15

ZLib.uncompress(src.length, compressed)
# => "testtesttesttesttesttesttesttesttesttest"
  • ZLib.compress(src)

    • Compresses src with default settings & returns the compressed result.
    • Returns a deflate stream wrapped in a zlib header/footer
  • ZLib.uncompress(max_size, src)

    • Uncompresses the src string (i.e. reverses ZLib.compress)
    • Raises a ZLib::ZDataError if src is not in the zlib format
    • Raises a ZLib::ZBufferError if max_size is not >= the size of the uncompressed data
    • Raises a ZLib::ZDataError if the input string is incomplete

inflate & deflate

These functions provide a streaming interface for zlib & gzip compression.


src = "example" * 100

stream =
stream.next_in = src
compressed = ZLib.deflate(stream, ZLib::Z_FINISH)
# => "x\234K\255H\314-\310IM\035\245F\251\241F\001\000)h$@"

# => 22

stream =
stream.next_in = compressed
ZLib.inflate(stream, ZLib::Z_FINISH)
# => "exampleexampleexampleexampleexampleexampleexampleexampleexampleexample...
  • ZLib::deflateInit(stream, level = ZLib::Z_DEFAULT_COMPRESSION)

    • Initalizes a stream to deflate at the given level
    • level defaults to 6 (ZLib::Z_DEFAULT_COMPRESSION)
    • Raises a ZLib::ZStreamError if called on a previously initialized stream
  • ZLib.deflate(stream, flush)

    • Deflates all of stream.next_in, possibly returning a chunk of the compressed output
    • Will process the remaining input and return all output if flush is ZLib::Z_FINISH
    • Raises a ZBufferError if Z_FINISH is used twice
    • Raises a ZLib::ZStreamError if used on a stream that has been finished already
  • ZLib::inflateInit(stream)

    • Initalizes a stream to inflate data
    • Raises a ZLib::ZStreamError if called on a previously initialized stream
  • ZLib.inflate(stream, flush)

    • Inflates str, possibly returning a chunk of the uncompressed output
    • Returns the empty string if the stream has already been finished (TODO: should probably raise)
    • Will process the remaining input and return all output if flush is ZLib::Z_FINISH
  • ZLib.inflateEnd(stream) && ZLib.deflateEnd(stream)

    • Are used to cleanup native resources of the stream
    • Called automatically by the MRuby GC when the stream is freed
    • Raise a ZLib::ZStreamError if the stream already ended, or is of the wrong type


These functions provide IO for GZip files similar to C's stdlib fopen, fread, fwrite, etc.

  • ZLib.gzopen(filename, mode)

    • Returns a ZLib::GZFile based on the given filename & mode string
    • Open semantics are like C's fopen ("w" create a file if it doesn't exist, etc.)
    • Returns nil if trying to read a file that doesn't exist
  • ZLib.gzwrite(file, str)

    • Compresses str, then writes it to file (a ZLib::GZFile)
  • ZLib::gzread(file, size)

    • Reads up to size uncompressed bytes from the compressed GZFile file
  • ZLib.gzflush(file, flush)

    • Flushes the given file according to the flush argument
    • flush should be one of ZLib::Z_NO_FLUSH, ZLib::Z_PARTIAL_FLUSH, ZLib::Z_SYNC_FLUSH, ZLib::Z_FULL_FLUSH, or ZLib::Z_FINISH
    • Should be called on GZFiles when finished, to ensure the gz file has the proper footer
  • ZLib.gzclose(file)

    • Closes the given GZFile file
    • Is called automatically when the file is GC'ed, but you may still call it sooner
    • After a file is closed, any attempt to use it will raise a ZLib::ZIOError

The following functions marked [SKIPPED] are implemented already, but lacking automated tests.

  • ZLib.gzsetparams(file, level, strategy)

    • [SKIPPED] Dynamically update the compression level or strategy
  • ZLib.gztell(file)

    • [SKIPPED] Tells the currect seek position
  • ZLib.gzrewind(file)

    • [SKIPPED] Seek to the begining of the file
  • ZLib.gzseek(file, offset, whence)

    • [SKIPPED] Set the location for the next read/write
  • ZLib.gzputs(file, string)

    • [SKIPPED] Writes the string param (which must not contain null characters) to the file
  • ZLib.gzputc(file, char) (char should be an int as in 'a'.ord)

    • [SKIPPED] Writes a character
  • ZLib.gzungetc(char, file) (char should be an int as in 'a'.ord)

    • [SKIPPED] Ungets a character
  • ZLib.gzbuffer(file, size)

    • [SKIPPED] Set the internal buffer size used by this library's functions
  • ZLib.gzclearerr(file)

    • [SKIPPED] Clears the error and end-of-file flags for file
  • ZLib.gzdirect(file)

    • [SKIPPED] Returns true if file is being copied directly while reading, or false if file is a gzip stream being decompressed
  • ZLib.gzdopen(fd, mode)

    • [SKIPPED] gzdopen associates a gzFile * with the file descriptor fd.
  • ZLib.gzeof(file)

    • [SKIPPED] Returns true if the file is at eof, or else false
  • ZLib.gzerror(file)

    • [SKIPPED] Returns the error message for the last error which occurred on the given compressed file
  • ZLib.gzgetc

    • [SKIPPED] Reads one byte from the compressed file.
    • [SKIPPED] Returns the byte (as an int) or -1 in case of end of file or error.
  • ZLib.gzoffset

    • [SKIPPED] Returns the current offset in the file being read or written
    • [SKIPPED] When reading, the offset does not include as yet unused buffered input
    • [SKIPPED] This information can be used for a progress indicator
  • ZLib.gzgets(file)

    • [SKIPPED] Reads until a newline or eof

SUCCESS [0 failed, 19 skipped, 51 total]


ZLib bindings for MRuby



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