zstd bindings for Chicken Scheme

Requirements

• zstd version 1.4.0+.

Source Code

Hosted here.

API

[procedure] (zstd-compress src #!key (level 3))

Compress the string or blob src, returning the entire compressed frame as a string. This is faster than using ports but may not be suitable for large inputs.

If level is supplied, it sets the compression level as documented by man zstd, and should be an integer in the range [1-19].

[procedure] (zstd-decompress trg)

Decompress the string or blob trg, which must be a valid zstd frame. Returns the uncompressed data as a string.

Note that zstd-decompress cannot decompress data from the port-based API, because the frame sizes are unknown ahead of time. It is therefore safest to always decompress using the port-based API.

[procedure] (zstd-frame-content-size frame)

Return the size of the uncompressed data stored in frame in number of bytes, or #f if the frame size is unknown. The port-based API will produce frames of unknown sizes. frame can only be decompressed using zstd-decompress if this function returns non-#f.

[procedure] (compressing-output-port output-port #!key (level 3)) => output-port

Returns an output-port to which uncompressed data can be written, and its compressed form will be written to output-port. It is important to close this port in order to flush internal zstd buffers. Closing this output-port does not close output-port.

If level is supplied, it sets the compression level as documented by man zstd, and should be an integer in the range [1-19].

[procedure] (decompressing-input-port input-port) => input-port

Returns an input-port from which uncompressed data can be read. Compressed data read, from input-port, will be read in the process. Closing this input-port does not close input-port.

Examples

Some very basic usage for illustration.

(import zstd chicken.process chicken.io chicken.port)

(with-input-from-pipe ;; => "hello hello hello\n"
 "echo hello hello hello | zstd"
 (lambda () (with-input-from-port (decompressing-input-port) read-string)))

(with-output-to-pipe ;; prints "hello world" to stdout
 "zstd -d"
 (lambda ()
   (current-output-port (compressing-output-port))
   (print "hello world")
   (close-output-port (current-output-port))))

Example code for benchmarking and testing

The code under ./examples may be useful to try things out and compare against the zstd command-line-tool.

> cd examples
> make
csc hello.scm
csc zstd.scm
csc unzstd.scm
> ./hello | pv -cNu | sha1sum
        u: 18.0MiB 0:00:00 [47.2MiB/s]
7c363606a232e640bb0f9dce8b0023a78f7059ba  -
> ./hello | pv -cNu | ./zstd -1 | pv -cNz | ./unzstd | sha1sum
        u: 18.0MiB 0:00:00 [46.2MiB/s]
        z:  343KiB 0:00:00 [ 879KiB/s]
7c363606a232e640bb0f9dce8b0023a78f7059ba  -
> ./hello | pv -cNu | ./zstd -22 | pv -cNz | ./unzstd | sha1sum
        u: 18.0MiB 0:00:22 [ 828KiB/s]
        z:  115KiB 0:00:22 [5.15KiB/s]
7c363606a232e640bb0f9dce8b0023a78f7059ba  -
> ./hello | pv -cNu | zstd -1 | pv -cNz | unzstd | sha1sum
        u: 18.0MiB 0:00:00 [46.5MiB/s]
        z:  486KiB 0:00:00 [1.22MiB/s]
7c363606a232e640bb0f9dce8b0023a78f7059ba  -

Development status

• This egg does not support the dictionary features of the zstd C API.
• This egg does not support re-using z-stream contexts.