1 gzip Compression and File Creation

(require file/gzip)

The file/gzip library provides utilities to create archive files in gzip format, or simply to compress data using the pkzip “deflate” method.

(gzip in-file [out-file]) → void?

in-file : path-string?

out-file : path-string? = (string-append in-file ".gz")

Compresses data to the same format as the gzip utility, writing the compressed data directly to a file. The in-file argument is the name of the file to compress. If the file named by out-file exists, it will be overwritten.

(gzip-through-ports   in             out             orig-filename             timestamp)   →   void?

in : input-port?

out : output-port?

orig-filename : (or/c string? false/c)

timestamp : exact-integer?

Reads the port in for data and compresses it to out, outputting the same format as the gzip utility. The orig-filename string is embedded in this output; orig-filename can be #f to omit the filename from the compressed stream. The timestamp number is also embedded in the output stream, as the modification date of the original file (in Unix seconds, as file-or-directory-modify-seconds would report under Unix).

(deflate in out)   →   exact-nonnegative-integer? exact-nonnegative-integer? exact-nonnegative-integer?

in : input-port?

out : output-port?

Writes pkzip-format “deflated” data to the port out, compressing data from the port in. The data in a file created by gzip uses this format (preceded with header information).

The result is three values: the number of bytes read from in, the number of bytes written to out, and a cyclic redundancy check (CRC) value for the input.