NAME¶

snappy, unsnappy — Snappy compression and decompression with and without framing

SYNOPSIS¶

DESCRIPTION¶

Without -d, compresses file (standard input stream if "-", the default) with Snappy to the standard output stream, then assesses the compression ratio achieved to the standard error stream.
With -f, the Snappy framing format is produced.

When run as unsnappy, or with -d, decompresses file (likewise) from Snappy, or the Snappy framing format (detected automatically), to the standard output stream.
With -i, decompression and framing errors are ignored and processing continues.

As a format limitation, if file isn't seekable when producing or decompressing unframed Snappy streams, it will be read into memory in its entirety.

EXIT STATUS¶

1

If a decompression error (invalid or truncated Snappy block) or a framing error (Stream identifier (0xFF) frame invalid, unknown reserved unskippable chunk ([0x02, 0x7F]) frame encountered, checksum mismatch).

2

On an I/O error.

3

When compressing without -f and file is larger than 4GiB. (Output unaffected, but see BUGS.)

DIAGNOSTICS¶

After compressing,

SEE ALSO¶

The Snappy homepage

CONFORMING TO¶

The framed format, with MIME type ‘application/x-snappy-framed’, version 2013-10-25: Snappy framing format description.

The unframed format, as described in Snappy compressed format description, as provided by the upstream library “libsnappy”.

BUGS¶

The largest representable unframed stream is of size 4GiB-1B (= 4·1024·1024·1024B-1B = 4294967295B). Above this size the length stored in the header becomes mangled, so the stream may be semantically correct but will produce an incorrect (short) output when decompressing. snappy warns about this and exits 3.

On 32-bit systems it is impossible to produce unframed streams from files larger than 4GiB-1B at all due to an API limitation (EXIT STATUS 2). On 32-bit systems the output size and compression ratio will be misrepresented if compression produces an unframed output larger than 4GiB-1B. It is also impossible to decompress such files there.

Supposedly, compressors which produce checksums with inverted byte order exist in the wild.