ssh: handle case where hg serve_forever doesn't serve forever

serve_forever will no longer exit in Mercurial 5.7 .
This changed with https://mercurial-scm.org/repo/hg/rev/b7b8a1538161 .

vcs: move ssh handlers out of "backends"

The ssh handlers are much more high-level than the low-level backends ... and
not used as a part of the "backends" concept at all.

lib: drop own asbool implementation and consistently use tg.support.converters as utils2.asbool

str2bool never reported error on odd input such as '' or '-1', but the tg
asbool behaviour of raising ValueError("String is not true/false: %r" % obj) in
that case seems fine.

ssh: handle IPv6 ssh connections

Performing ssh actions towards Kallithea via an IPv6 connection gave the
following error:

$ hg incoming ssh://kallithea@example.com/repo
remote: Traceback (most recent call last):
remote: File ".../bin/kallithea-cli", line 11, in <module>
remote: load_entry_point('Kallithea', 'console_scripts', 'kallithea-cli')()
remote: File ".../python2.7/site-packages/click/core.py", line 764, in __call__
remote: return self.main(*args, **kwargs)
remote: File ".../python2.7/site-packages/click/core.py", line 717, in main
remote: rv = self.invoke(ctx)
remote: File ".../python2.7/site-packages/click/core.py", line 1137, in invoke
remote: return _process_result(sub_ctx.command.invoke(sub_ctx))
remote: File ".../python2.7/site-packages/click/core.py", line 956, in invoke
remote: return ctx.invoke(self.callback, **ctx.params)
remote: File ".../python2.7/site-packages/click/core.py", line 555, in invoke
remote: return callback(*args, **kwargs)
remote: File ".../kallithea/bin/kallithea_cli_base.py", line 79, in runtime_wrapper
remote: return annotated(*args, **kwargs)
remote: File ".../kallithea/bin/kallithea_cli_ssh.py", line 74, in ssh_serve
remote: vcs_handler.serve(user_id, key_id, client_ip)
remote: File ".../kallithea/lib/vcs/backends/ssh.py", line 65, in serve
remote: self.authuser = AuthUser.make(dbuser=dbuser, ip_addr=client_ip)
remote: File ".../kallithea/lib/auth.py", line 407, in make
remote: if not check_ip_access(source_ip=ip_addr, allowed_ips=allowed_ips):
remote: File ".../kallithea/lib/auth.py", line 860, in check_ip_access
remote: if ipaddr.IPAddress(source_ip) in ipaddr.IPNetwork(ip):
remote: File ".../kallithea/lib/ipaddr.py", line 76, in IPAddress
remote:
remote: ValueError: '2' does not appear to be an IPv4 or IPv6 address
abort: no suitable response from remote hg!


This was caused by IPv4-exclusive parsing of the SSH_CONNECTION variable.
With an IPv6 address starting with '2a02:1810:', only the first '2' would
survive.

According to 'man 1 ssh':

SSH_CONNECTION Identifies the client and server ends of the con‐
nection. The variable contains four space-sepa‐
rated values: client IP address, client port num‐
ber, server IP address, and server port number.


So, the client IP address will be the first space-separated word, regardless
of IPv4 or IPv6. Use that knowledge without further parsing.

(commit message by Thomas De Schampheleire)

ssh: set a valid locale in the ssh-serve process

In the SSH client configuration, the setting 'SendEnv' could contain variables
like 'LANG', 'LC_ALL', and others. This causes these environment variables
(with their values at the client-side) to be set in the server. However, not
every locale setting valid in the client, is also valid on the server.

This could lead to the error:
'locale.Error: unsupported locale setting'
when 'from mercurial import archival, merge as hg_merge, patch, ui' is
called.

Fix this problem by providing an ini setting 'ssh_locale' that the user can
set correctly, and which will be used to set LC_ALL and LANGUAGE in the
'kallithea-cli ssh-serve' process.

If an environment variable LC_ALL is set, it takes precedence over all other
'LC_xxx' variables, as well as over LANG. So, setting LC_ALL ensures that no
user setting of 'LC_xxx' or 'LANG' could influence ssh-serve badly.

There is one environment variable that might overrule LC_ALL, specifically
for showing messages: 'LANGUAGE'. GNU gettext lets it take precedence over
LC_ALL [1]:
"GNU gettext gives preference to LANGUAGE over LC_ALL and LANG for the
purpose of message handling"

So, also set LANGUAGE to the same value as we set LC_ALL to.


The principle of setting a specific locale in the server process to fix this
error, was first proposed by Dominik Ruf.

[1] https://www.gnu.org/software/gettext/manual/html_node/The-LANGUAGE-variable.html#The-LANGUAGE-variable

ssh: introduce 'kallithea-cli ssh-update-authorized-keys' command for updating authorized_keys file

Based on work by Ilya Beda <ir4y.ix@gmail.com> on
https://bitbucket.org/ir4y/rhodecode/commits/branch/ssh_server_support ,
incorporating gearbox support by Anton Schur <tonich.sh@gmail.com> and also
heavily modified by Mads Kiilerich.

This commit also incorporates a fix for Windows by Dominik Ruf,
and better handling of the case where the parent dir of 'authorized_keys'
does not exist or is not writable, by Bradley M. Kuhn <bkuhn@ebb.org>.

ssh: introduce 'kallithea-cli ssh-serve' command for providing actual protocol access over ssh

To be invoked from ~/.ssh/authorized_keys as
command=".../kallithea-cli ssh-serve -c .../my.ini 1007 7",... ssh-rsa AAA...=

The command is not supposed to be used directly by users, and is thus hidden.

Based on work by Ilya Beda <ir4y.ix@gmail.com> on
https://bitbucket.org/ir4y/rhodecode/commits/branch/ssh_server_support ,
also incorporating updates for gearbox by Anton Schur <tonich.sh@gmail.com>,
and further heavily refactored and rewritten by Mads Kiilerich.