publish: Add support for lzip.

* guix/scripts/publish.scm (show-help, %options): Support '-C METHOD'
and '-C METHOD:LEVEL'.
(default-compression): New procedure.
(bake-narinfo+nar): Add lzip.
(nar-response-port): Likewise.
(string->compression-type): New procedure.
(make-request-handler): Generalize /nar/gzip handler to handle /nar/lzip
as well.
* tests/publish.scm ("/nar/lzip/*"): New test.
("/*.narinfo with lzip compression"): New test.
* doc/guix.texi (Invoking guix publish): Document it.
(Requirements): Mention lzlib.

1 files changed, 19 insertions, 6 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 98c5d1e91d..340b806962 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -758,6 +758,11 @@ Support for build offloading (@pxref{Daemon Offload Setup}) and
 version 0.10.2 or later.
 
 @item
+When @url{https://www.nongnu.org/lzip/lzlib.html, lzlib} is available, lzlib
+substitutes can be used and @command{guix publish} can compress substitutes
+with lzlib.
+
+@item
 When @url{http://www.bzip.org, libbz2} is available,
 @command{guix-daemon} can use it to compress build logs.
 @end itemize
@@ -9656,12 +9661,20 @@ accept connections from any interface.
 Change privileges to @var{user} as soon as possible---i.e., once the
 server socket is open and the signing key has been read.
 
-@item --compression[=@var{level}]
-@itemx -C [@var{level}]
-Compress data using the given @var{level}.  When @var{level} is zero,
-disable compression.  The range 1 to 9 corresponds to different gzip
-compression levels: 1 is the fastest, and 9 is the best (CPU-intensive).
-The default is 3.
+@item --compression[=@var{method}[:@var{level}]]
+@itemx -C [@var{method}[:@var{level}]]
+Compress data using the given @var{method} and @var{level}.  @var{method} is
+one of @code{lzip} and @code{gzip}; when @var{method} is omitted, @code{gzip}
+is used.
+
+When @var{level} is zero, disable compression.  The range 1 to 9 corresponds
+to different compression levels: 1 is the fastest, and 9 is the best
+(CPU-intensive).  The default is 3.
+
+Usually, @code{lzip} compresses noticeably better than @code{gzip} for a small
+increase in CPU usage; see
+@uref{https://nongnu.org/lzip/lzip_benchmark.html,benchmarks on the lzip Web
+page}.
 
 Unless @option{--cache} is used, compression occurs on the fly and
 the compressed streams are not