Support for archive file names

* doc/misc/tramp.texi (Top, Usage): Add entry "Archive file names".
(History): Mention archive file names.
(GVFS based methods): Mentio "http" and "https" methods.
(Archive file names): New node.
(Frequently Asked Questions): Add Emacs 27 as supported version.

* etc/NEWS: Mention tramp-archive.el.

* lisp/net/tramp.el (tramp-run-real-handler)
(tramp-register-file-name-handlers)
(tramp-register-file-name-handlers, tramp-unload-file-name-handlers):
Add `tramp-archive-file-name-handler'.
(tramp-handle-file-name-completion): Do not insist in Tramp
file names.

* lisp/net/tramp-archive.el: New package.

* lisp/net/tramp-cache.el (tramp-dump-connection-properties): Check for
"archive" method.

* lisp/net/tramp-cmds.el (tramp-cleanup-all-connections): Cleanup also
local copies of archives.

* lisp/net/tramp-compat.el (tramp-compat-use-url-tramp-p): New defconst.

* lisp/net/tramp-gvfs.el (tramp-gvfs-methods): Add "http" and "https".
(tramp-gvfs-gio-mapping): Add "gvfs-mount".
(tramp-gvfs-handler-mounted-unmounted)
(tramp-gvfs-connection-mounted-p, tramp-gvfs-mount-spec):
Handle "uri" and "http".
(tramp-gvfs-unmount): New defun.

* test/lisp/net/tramp-archive-tests.el: New package.

1 files changed, 213 insertions, 3 deletions

diff --git a/doc/misc/tramp.texi b/doc/misc/tramp.texi
index e7d9cb15dee..3869e19fb96 100644
--- a/doc/misc/tramp.texi
+++ b/doc/misc/tramp.texi
@@ -164,6 +164,7 @@ Using @value{tramp}
 * Ad-hoc multi-hops::           Declaring multiple hops in the file name.
 * Remote processes::            Integration with other Emacs packages.
 * Cleanup remote connections::  Cleanup remote connections.
+* Archive file names::          Access to files in file archives.
 
 How file names, directories and localnames are mangled and managed
 
@@ -407,7 +408,8 @@ since April 2007 (and removed in December 2016).  GVFS integration
 started in February 2009.  Remote commands on MS Windows hosts since
 September 2011.  Ad-hoc multi-hop methods (with a changed syntax)
 re-enabled in November 2011.  In November 2012, added Juergen
-Hoetzel's @file{tramp-adb.el}.
+Hoetzel's @file{tramp-adb.el}.  Archive file names are supported since
+December 2017.
 
 XEmacs support was stopped in January 2016.  Since March 2017,
 @value{tramp} syntax mandates a method.
@@ -1134,7 +1136,10 @@ requires the SYNCE-GVFS plugin.
 This user option is a list of external methods for GVFS@.  By default,
 this list includes @option{afp}, @option{dav}, @option{davs},
 @option{gdrive}, @option{obex}, @option{sftp} and @option{synce}.
-Other methods to include are: @option{ftp} and @option{smb}.
+Other methods to include are @option{ftp}, @option{http},
+@option{https} and @option{smb}.  These methods are not intended to be
+used directly as GVFS based method.  Instead, they are added here for
+the benefit of @ref{Archive file names}.
 @end defopt
 
 
@@ -2284,6 +2289,7 @@ is a feature of Emacs that may cause missed prompts when using
 * Ad-hoc multi-hops::           Declaring multiple hops in the file name.
 * Remote processes::            Integration with other Emacs packages.
 * Cleanup remote connections::  Cleanup remote connections.
+* Archive file names::          Access to files in file archives.
 @end menu
 
 
@@ -2913,6 +2919,209 @@ that remote connection.
 @end deffn
 
 
+@node Archive file names
+@section Archive file names
+@cindex file archives
+@cindex archive file names
+@cindex method archive
+@cindex archive method
+
+@value{tramp} offers also transparent access to files inside file
+archives.  This is possible only on machines which have installed the
+virtual file system for the Gnome Desktop (GVFS), @ref{GVFS based
+methods}.  Internally, file archives are mounted via the GVFS
+@option{archive} method.
+
+A file archive is a regular file of kind @file{/path/to/dir/file.EXT}.
+The extension @samp{.EXT} identifies the type of the file archive.  A
+file inside a file archive, called archive file name, has the name
+@file{/path/to/dir/file.EXT/dir/file}.
+
+Most of the @ref{Magic File Names, , magic file name operations,
+elisp}, are implemented for archive file names, exceptions are all
+operations which write into a file archive, and process related
+operations.  Therefore, functions like
+
+@lisp
+(copy-file "/path/to/dir/file.tar/dir/file" "/somewhere/else")
+@end lisp
+
+@noindent
+work out of the box.  This is also true for file name completion, and
+for libraries like @code{dired} or @code{ediff}, which accept archive
+file names as well.
+
+@vindex tramp-archive-suffixes
+File archives are identified by the file name extension @samp{.EXT}.
+Since GVFS uses internally the library @code{libarchive(3)}, all
+suffixes, which are accepted by this library, work also for archive
+file names.  Accepted suffixes are listed in the constant
+@code{tramp-archive-suffixes}.  They are
+
+@itemize
+@item @samp{.7z} ---
+7-Zip archives
+@cindex 7z, file archive suffix
+@cindex file archive suffix 7z
+
+@item @samp{.apk} ---
+Android package kits
+@cindex apk, file archive suffix
+@cindex file archive suffix apk
+
+@item @samp{.ar} ---
+UNIX archiver formats
+@cindex ar, file archive suffix
+@cindex file archive suffix ar
+
+@item @samp{.cab}, @samp{.CAB} ---
+Microsoft Windows cabinets
+@cindex cab, file archive suffix
+@cindex CAB, file archive suffix
+@cindex file archive suffix cab
+@cindex file archive suffix CAB
+
+@item @samp{.cpio} ---
+CPIO archives
+@cindex cpio, file archive suffix
+@cindex file archive suffix cpio
+
+@item @samp{.deb} ---
+Debian packages
+@cindex deb, file archive suffix
+@cindex file archive suffix deb
+
+@item @samp{.depot} ---
+HP-UX SD depots
+@cindex depot, file archive suffix
+@cindex file archive suffix depot
+
+@item @samp{.exe} ---
+Self extracting Microsoft Windows EXE files
+@cindex exe, file archive suffix
+@cindex file archive suffix exe
+
+@item @samp{.iso} ---
+ISO 9660 images
+@cindex iso, file archive suffix
+@cindex file archive suffix iso
+
+@item @samp{.jar} ---
+Java archives
+@cindex jar, file archive suffix
+@cindex file archive suffix jar
+
+@item @samp{.lzh}, @samp{LZH} ---
+Microsoft Windows compressed LHA archives
+@cindex lzh, file archive suffix
+@cindex LZH, file archive suffix
+@cindex file archive suffix lzh
+@cindex file archive suffix LZH
+
+@item @samp{.mtree} ---
+BSD mtree format
+@cindex mtree, file archive suffix
+@cindex file archive suffix mtree
+
+@item @samp{.pax} ---
+Posix archives
+@cindex pax, file archive suffix
+@cindex file archive suffix pax
+
+@item @samp{.rar} ---
+RAR archives
+@cindex rar, file archive suffix
+@cindex file archive suffix rar
+
+@item @samp{.rpm} ---
+Red Hat packages
+@cindex rpm, file archive suffix
+@cindex file archive suffix rpm
+
+@item @samp{.shar} ---
+Shell archives
+@cindex shar, file archive suffix
+@cindex file archive suffix shar
+
+@item @samp{.tar}, @samp{tbz}, @samp{tgz}, @samp{tlz}, @samp{txz} ---
+(Compressed) tape archives
+@cindex tar, file archive suffix
+@cindex tbz, file archive suffix
+@cindex tgz, file archive suffix
+@cindex tlz, file archive suffix
+@cindex txz, file archive suffix
+@cindex file archive suffix tar
+@cindex file archive suffix tbz
+@cindex file archive suffix tgz
+@cindex file archive suffix tlz
+@cindex file archive suffix txz
+
+@item @samp{.warc} ---
+Web archives
+@cindex warc, file archive suffix
+@cindex file archive suffix warc
+
+@item @samp{.xar} ---
+macOS XAR archives
+@cindex xar, file archive suffix
+@cindex file archive suffix xar
+
+@item @samp{.xps} ---
+Open XML Paper Specification (OpenXPS) documents
+@cindex xps, file archive suffix
+@cindex file archive suffix xps
+
+@item @samp{.zip}, @samp{.ZIP} ---
+ZIP archives
+@cindex zip, file archive suffix
+@cindex ZIP, file archive suffix
+@cindex file archive suffix zip
+@cindex file archive suffix ZIP
+@end itemize
+
+@vindex tramp-archive-compression-suffixes
+File archives could also be compressed, identified by an additional
+compression suffix.  Valid compression suffixes are listed in the
+constant @code{tramp-archive-compression-suffixes}.  They are
+@samp{.bz2}, @samp{.gz}, @samp{.lrz}, @samp{.lz}, @samp{.lz4},
+@samp{.lzma}, @samp{.lzo}, @samp{.uu}, @samp{.xz} and @samp{.Z}.  A
+valid archive file name would be
+@file{/path/to/dir/file.tar.gz/dir/file}.  Even several suffixes in a
+row are possible, like @file{/path/to/dir/file.tar.gz.uu/dir/file}.
+
+@vindex tramp-archive-all-gvfs-methods
+An archive file name could be a remote file name, as in
+@file{/ftp:anonymous@@ftp.gnu.org:/gnu/tramp/tramp-2.3.2.tar.gz/INSTALL}.
+Since all file operations are mapped internally to GVFS operations,
+remote file names supported by @code{tramp-gvfs} perform better,
+because no local copy of the file archive must be downloaded first.
+For example, @samp{/sftp:user@@host:...} performs better than the
+similar @samp{/scp:user@@host:...}.  See the constant
+@code{tramp-archive-all-gvfs-methods} for a complete list of
+@code{tramp-gvfs} supported method names.
+
+If @code{url-handler-mode} is enabled, archives could be visited via
+URLs, like @file{https://ftp.gnu.org/gnu/tramp/tramp-2.3.2.tar.gz/INSTALL}.
+This allows complex file operations like
+
+@lisp
+@group
+(ediff-directories
+ "https://ftp.gnu.org/gnu/tramp/tramp-2.3.1.tar.gz/tramp-2.3.1"
+ "https://ftp.gnu.org/gnu/tramp/tramp-2.3.2.tar.gz/tramp-2.3.2" "")
+@end group
+@end lisp
+
+It is even possible to access file archives in file archives, as
+
+@lisp
+@group
+(find-file
+ "http://ftp.debian.org/debian/pool/main/c/coreutils/coreutils_8.28-1_amd64.deb/control.tar.gz/control")
+@end group
+@end lisp
+
+
 @node Bug Reports
 @chapter Reporting Bugs and Problems
 @cindex bug reports
@@ -2997,7 +3206,8 @@ Where is the latest @value{tramp}?
 @item
 Which systems does it work on?
 
-The package works successfully on Emacs 24, Emacs 25, and Emacs 26.
+The package works successfully on Emacs 24, Emacs 25, Emacs 26, and
+Emacs 27.
 
 While Unix and Unix-like systems are the primary remote targets,
 @value{tramp} has equal success connecting to other platforms, such as