Add stream context metadata options for compress.zlib:// protocol wrapper so that original mtime and name can be given

[cmanley]

Description

Currently, when writing to a gz file using the compress.zlib:// protocol wrapper it is not possible to pass the mtime or name of the original file. It would be nice if we could do so without having to reopen the gzip file in write mode for write the metadata directly into it as in this bug report https://bugs.php.net/bug.php?id=46577
I believe that this can be done by adding new stream context options for zlib (similar to those for phar). See https://www.php.net/manual/en/context.php

The gzip file format supports the following meta data:

• compression method
• itype (text or binary)
• mtime (nice to have)
• size (thankfully set by compress.zlib:// )
• os
• original file name (nice to have)
• comment

[cmb69]

I agree that this would make sense, but zlib streams are currently implemented using the gzip file access functions, and these do not allow any header manipulation to my knowledge (besides setting the compression level, what is already supported by the undocumented ["zlib"]["level"] option, and the strategy). So we would need to rewrite that stream implementation to use the advanced functions, so that we can manipulate the gz_header. So I think this requires an RFC. Do you want to pursue this process?

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PS: ["zlib"]["level"] is now documented

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[bukka]

I don't see why this necessary requires RFC as it's quite specific and could be potentially merged without RFC if there are no objections.