## Remoteusage without password-free login requirement

This is alternative to [[remoteusage|remoteusage]] where password-free
login is not a requirement. See [[remoteusage|remoteusage]] page for
other requirements and general information.

This solution uses one pre-made ssh connection where the client is put
into "master" mode (-M) for connection sharing. The wrapper script then
uses the control socket created by this pre-made ssh connection for
its own connection. As long as master ssh connection is live, slave
can use it. Disconnecting master all future attempts to connect
from the script will fail.

## The script

Write the following code to a file, for example `remote-notmuch.sh`.

	#!/bin/bash

	# http://notmuchmail.org/remoteusage/aboriginal/

	set -eu
	# To trace execution, outcomment next line. Note that emacs input may ...
	#exec 2>>remote-errors; echo -- >&2; set -x # ... change (no stderr).

	readonly SSH_CONTROL_SOCK='~'/.ssh/master-user@host:22

	readonly notmuch=notmuch

	printf -v ARGS '%q ' "$@" # bash feature

	readonly SSH_CONTROL_ARGS='-oControlMaster=no -S '$SSH_CONTROL_SOCK

	if ssh -q $SSH_CONTROL_ARGS 0.1 $notmuch $ARGS
	then exit 0
	else ev=$?
	fi

	# continuing here in case ssh exited with nonzero value.

	case $* in
	 'config get user.primary_email') echo 'nobody@nowhere.invalid'; exit 0 ;;
	 'config get user.name') echo 'nobody'; exit 0 ;;
	 'count'*'--batch'*) while read line; do echo 1; done; exit 0 ;;
	 'count'*) echo 1; exit 0 ;;
	 'search-tags'*) echo 'errors'; exit 0 ;;
	 'search'*'--output=tags'*) echo 'errors'; exit 0 ;;
	esac

	if ssh $SSH_CONTROL_ARGS -O check 0.1
	then
	 echo ' Control socket is alive but something failed during data transmission.'
	 exit $ev
	fi

	echo " See`sed '1d;2d;s/.//;q' "$0"` for help."

Note the `0.1` in ssh command line. It is used to avoid any opportunistic
behaviour ssh might do; for example if control socket is not alive ssh
would attempt to do it's own ssh connection to remote ssh server. As
address `0.1` is invalid this attempt will fail early.

## Test

Easiest way to test this script is to run the pre-made ssh connection
using the following command line:

        ssh -M -S '~'/.ssh/master-user@host:22 [user@]remotehost

(replace `[user@]remotehost` with your login info). Doing this the
above script can be run unmodified. After the above command has been
run on one terminal, enter `chmod +x remote-notmuch.sh` in another
terminal and then test the script with `./remote-notmuch.sh help`

Note that the '~' is inside single quotes for a reason. In this
case shell never expand it to `$HOME` -- ssh does it by not reading
`$HOME` but checking the real user home directory from `/etc/passwd`.
For security purposes this is just how it should be.

## Tune

The path `'~'/.ssh/master-user@host:22` might look too generic to be
used as is as the control socket after initial testing (but it can
be used). It is presented as a template for what could be configured
to `$HOME/.ssh/config`. For example:

        Host *
            ControlPath ~/.ssh/master-%h@%p:%r

is a good entry to be written in `$HOME/.ssh/config`;
[[remoteusage|remoteusage]] uses the same. Now, let's say you'd
make your pre-made ssh connection with command

        ssh -M alice@example.org

After configuring
`readonly SSH_CONTROL_SOCK='~'/.ssh/master-alice@example.org:22`
to the `./remote-notmuch.sh` wrapper script testing with
`./remote-notmuch.sh help` should work fine.

## Configure Emacs on the client computer ##

See the section *Configure Emacs on the client computer* in
[[remoteusage|remoteusage]] how to do this. The instructions are the same.