[MacPorts] #56237: Use /usr/bin/gzip to decompress .xz files on macOS >= 10.10

[MacPorts]

#56237: Use /usr/bin/gzip to decompress .xz files on macOS >= 10.10
-------------------------+-----------------------------
 Reporter:  raimue       |      Owner:  (none)
     Type:  enhancement  |     Status:  new
 Priority:  Normal       |  Milestone:  MacPorts Future
Component:  base         |    Version:
 Keywords:               |       Port:
-------------------------+-----------------------------
 On macOS >= 10.10, the `/usr/bin/gzip` binary can not only decompress
 gzip, but also accepts data compressed with bzip2 or xz. Note that it can
 only decompress these formats and compression is only supported to the
 gzip format.

 {{{
 $ echo "MacPorts" | xz -c | /usr/bin/gzip -d
 MacPorts
 }}}

 The implementation can be found in
 [https://opensource.apple.com/source/file_cmds/ file_cmds], where
 [https://opensource.apple.com/source/file_cmds/file_cmds-242/gzip/
 file_cmds-242] corresponds to the version shipped with OS X 10.10.

 We should detect this in our configure script. If `xz` was not found, then
 check whether `gzip` also supports the xz format. If it does, fill the
 path to `gzip` into a new `portutil::autoconf::unxz_path` (similar to the
 existing `xz_path`). This variable can then be used as the fallback with
 `findBinary` when the goal is to find a binary for decompression only.
 Extra dependencies on `bin:xz:xz` would only be necessary when `unxz_path`
 is empty.

 {{{
 set xz [findBinary xz ${portutil::autoconf::unxz_path}]
 }}}

 The complicated part will be the check for the configure script. To test
 the decompression, we will need to embed a binary representation of a
 string compressed with xz into the configure script.

 I already came up with the following example which should be POSIX shell
 compatible. Octal seems to be the only standardized format to store such
 data. Note this should not require any special tools for conversion back
 to the binary format before piping to the decompressor.

 Prepare this once for inclusion into the configure script. Compress a
 string and convert the binary data to a string of octal character
 constants.

 {{{
 echo "MacPorts" | xz -c | xxd -p -c 1 | while read c; do printf "\%o"
 0x$c; done; echo
 }}}

 The actual check in the configure script would then look something like
 this:

 {{{
 xzdata="\375\67\172\130\132\0\0\4\346\326\264\106\2\0\41\1\26\0\0\0\164\57\345\243\1\0\10\115\141\143\120\157\162\164\163\12\0\0\0\0\215\276\42\112\33\313\231\317\0\1\41\11\154\30\305\325\37\266\363\175\1\0\0\0\0\4\131\132"
 dec=$(printf $xzdata | gzip -dc 2>/dev/null)
 if [ "$dec" == "MacPorts" ]; then
     ...
 fi
 }}}

-- 
Ticket URL: <https://trac.macports.org/ticket/56237>
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