RewindStream fails for compressed files

[fingolfin]

GAP supports reading from gzip compressed files transparently. I.e. GAP code need not be aware of this, it just happens "automatically".

However, RewindStream does not work in that case -- not surprising, given that we implement this by piping the data through a separate gunzip process.

One way to fix this would be to implement native gzip decompression (see issue #916). But of course it is probably much easier to fix just this special case. To do that, we probably would have to modify SEEK_POSITION_FILE or SyFseek in the kernel somehow.

By the way, this issue results in GAP not support gzip compressed manual.six files, which is why Debian includes a workaround fix which replaces a RewindStream call in the help system by code which closes the file and reopens it. See also this issue on our old private tracker: http://tracker.gap-system.org/issues/466

[ChrisJefferson]

At the moment we don't store the filename a stream is based on, but we could certainly store that, and then try to reopen the file later.

[fingolfin]

@ChrisJefferson I wonder if this is now fixed with the use of zlib?

[ChrisJefferson]

It is, works fine in master!

[fingolfin]

Great, so this was resolved by PR #2509 -- and that even adds a check for seeking, in commit 40d3c87. So we can close this.