gap-4.11.1: Is gzip compression for Input/OutputTextfile active?

[kiryph]

As noted in CHANGES.md for gap-4.11.1:

Other fixed bugs

• Implement compression/decompression of filenames ending .gz #3963 Provide automatic compression/decompression of filenames ending .gz (as is claimed for example in the documentation of InputTextFile)

Therefore, I assume that I can write gzipped files.

Documentation

• InputTextFile(filename).
  [...] If filename ends in .gz and the file is a valid gzipped file, then the file will be transparently uncompressed.
• OutputTextFile(filename, append)
  If filename ends in .gz, then the file will be written with gzip compression.

https://www.gap-system.org/Manuals/doc/ref/chap10.html#X80B5F2E4856D8980

Observed behaviour

$ gap
gap> dir := Directory(".");;
gap> fname := Filename(dir, "test.txt.gz");;
gap> stream := OutputTextFile( fname, false );;
gap> PrintTo( stream, "a very long line that GAP is going to wrap at 80 chars by default if we don't do anything about it\n");
gap> CloseStream(stream);
gap> quit;
$ file test.txt.gz
test.txt.gz: ASCII text
$ gzip --force test.txt.gz
$ file test.txt.gz.gz # gzip adds another .gz extension
test.txt.gz.gz: gzip compressed data, was "test.txt.gz", last modified: Fri May  7 13:02:38 2021, from Unix, original size modulo 2^32 99

Expected behaviour

$ gap
gap> dir := Directory(".");;
gap> fname := Filename(dir, "test.txt.gz");;
gap> stream := OutputTextFile( fname, false );;
gap> PrintTo( stream, "a very long line that GAP is going to wrap at 80 chars by default if we don't do anything about it\n");
gap> CloseStream(stream);
gap> quit;
$ file test.txt.gz
test.txt.gz: gzip compressed data

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gap installed with /~https://github.com/gap-system/homebrew-gap

The comment in the test file
/~https://github.com/gap-system/gap/blob/stable-4.11/tst/testinstall/compressed.tst#L20

Check file really is compressed (FIXME: disabled in stable-4.11)

indicates that in contrast to CHANGES.md compressing is currently disabled.

Can someone confirm this and clarify whether compression can be used?

[fingolfin]

IIRC automatic compression was disabled because it lead to issues with code that did not expect it, and which eg tried to write already compressed data.

In the upcoming 4.12 there will be a OutputGzipFile

[fingolfin]

@ChrisJefferson it seems we forgot to update the documentation for OutputTextFile, at least in stable-4.11 ?

[kiryph]

Thanks for the clarification.
Update the commit 069a649 on branch disabled compression for OutputTextFile

Updating the documentation for OutputTextFile would be great. But also CHANGES.md 4.11.1 could be clearer:

#3963 Provide automatic compression/ decompression of filenames ending .gz (as is claimed for example in the documentation of InputTextFile).

[fingolfin]

In PR #4989 the CHANGES entry is fixed as suggested by @kiryph . The documentation for OutputTextFile is adjusted at least in master / GAP 4.12 (to be released this week). It now says:

OutputTextFile( filename, append ) returns an output stream in the category IsOutputTextFile that writes received characters to the file filename. If append is false, then the file is emptied first, otherwise received characters are added at the end of the file. OutputGzipFile acts identically to OutputTextFile, except it compresses the output with gzip.

So I think once PR #4989 is merged we can close this