#!/bin/sh

set -e

die() {
    echo >&2 "novaboot-shell: $*"
    exit 1
}

print_help() {
    cat <<EOF
Target commands:
- console (default command)
- reset
- on
- off
- rsync ...
- get-config

Management commands:
- help
EOF

    if [ "$NB_ADMIN" ]; then
	cat <<EOF
- add-key
- shell (use with ssh -t)
EOF
    fi
    exit 0
}

add_key() {
    local user
    [ "$NB_ADMIN" ] || return 1

    case $# in
	0) die "Usage: ssh ... add-key USERNAME < id_rsa.pub";;
	1) break;;
	*) die "User name must not contain spaces: $*";;
    esac
    user="$1"
    key=$(cat)

    tmp=$(mktemp ~/.ssh/authorized_keys.XXXXXXXX)
    {
	cat ~/.ssh/authorized_keys
	echo "command=\"user $user\" $key"
    } | sort -u > $tmp

    mv $tmp ~/.ssh/authorized_keys
}

exec_shell() {
    [ "$NB_ADMIN" ] || die "Permission denied"
    if ! tty > /dev/null; then
	echo "novaboot-shell: Consider starting the shell with 'ssh -t'"
    fi
    exec /bin/bash || exec /bin/sh
}

lock_queue() {
    lslocks | awk '{ if ($9 == "'"$RUN_DIR"'") { print $2 } }'
}

print_queue() {
    local queue

    queue=$(
	for pid in $(lock_queue); do
	    echo $pid $(sed --null-data -ne '/^NOVABOOT_ID=/ s///p' /proc/$pid/environ)
	done | sort)
    if [ "$queue" ]; then
	echo "Target is occupied by:"
	( echo "PID USER LOGIN_TIME FROM"; echo "$queue" ) | column -t
    fi
}

locked() {
    print_queue
    exec flock --no-fork "$RUN_DIR" "$@"
}

unlocked() {
    exec "$@"
}

read_config() {
    . "${NOVABOOT_SHELL_CONFIG:-$HOME/.novaboot-shell}"
}

# run_subcommand should be called only after permission checks and/or locking
run_subcommand() {
    read_config
    case "$*" in
	"console")
	    trap "rm -f $RUN_DIR/ppid" EXIT
	    echo $NOVABOOT_PPID > $RUN_DIR/ppid
	    echo 'novaboot-shell: Connected'
	    # TODO: $reset_begin_cmd
	    eval exec "${console_cmd:?}";;
	"reset")
	    eval exec "${reset_cmd:?}";;
	"rsync --server "*" . .")
	    if ! [ $# -eq 5 -o \( $# -eq 6 -a "$4" = '--log-format=X' \) ]; then
		die "Unexpected rsync invocation: $*"
	    fi
	    mkdir -p "$HOME/tftproot"
	    cd "$HOME/tftproot"
	    exec "$@";;
	"on")
	    eval exec "${on_cmd:?}";;
	"off")
	    eval exec "${off_cmd:?}";;
    esac
}

main() {
    if [ "$1" = "-c" ]; then
	set -- $2
    elif [ $# -gt 0 ]; then
	die "Permission denied"
    fi

    NB_ADMIN=
    if [ "$1" = "user" ]; then
	# Get user name encoded in ~/.ssh/authorized_keys
	NB_USER="$2";
	[ "$3" = "admin" ] && NB_ADMIN=1
	set -- $SSH_ORIGINAL_COMMAND
    fi

    IP=${SSH_CONNECTION%% *}
    if [ "$IP" ]; then
	HOST=$(getent hosts $IP) || HOST=$IP
    else
	HOST=localhost
    fi
    REMOTE=${HOST##* }
    DATE=$(LANG=C date +'%F_%T')
    export NOVABOOT_ID="${NB_USER:-?} $DATE ${REMOTE}"
    export NOVABOOT_PPID=$PPID

    mkdir -p "$RUN_DIR"

    case "$1" in
	# Commands allowed at any time
	"console"|"") locked $0 console;;
	"get-config") read_config && echo -n "${target_config}"; exit;;
	"add-key") shift; add_key "$@"; exit;;
	"shell") exec_shell; exit;;
	"help") print_help;;

	# Commands allowed only when nobody or the same user is connected
	# to the console. "The same user" means that we were executed by
	# the same sshd process that has the lock. This is ensured by
	# using SSH connection sharing on client side.
	reset | rsync | on | off)
	    ALLOWED_PPID=$(cat $RUN_DIR/ppid 2>/dev/null || :)
	    if [ "$PPID" -eq "${ALLOWED_PPID:-0}" ]; then run=unlocked; else run=locked; fi
	    $run $0 "$@";;
	*)
	    echo >&2 "novaboot-shell: Command not allowed: $*"
	    logger -p error "novaboot-shell: Command not allowed: $*"
	    exit 1;;
    esac
}

RUN_DIR="$HOME"

if [ -z "$NOVABOOT_ID" ]; then
    main "$@"
else
    run_subcommand "$@"
fi
exit

: <<EOF
=encoding utf8

=head1 NAME

novaboot-shell - provides novaboot with unified SSH-based interface for controlling target hardware

=head1 SYNOPSIS

B<novaboot-shell> -c "[command [arguments...]]"

B<novaboot-shell> [command [arguments...]]

B<ssh target@server> [command [arguments...]]

=head1 DESCRIPTION

B<novaboot-shell> provides L<novaboot(1)> with a unified SSH-based
interface for controlling the target hardware. This simplifies
client-side configuration, because clients typically need only the
I<--ssh=...> option. B<novaboot-shell> is typically configured as a
login shell of special user accounts associated with the target
hardware (as set by L<adduser-novaboot(8)>). It ensures that users can
perform only a limited set of actions (see L</COMMANDS> below) with
the target and have no shell access on the server.

=head1 COMMANDS

=over 8

=item console

Connect to target console (usually serial line). When somebody is
connected to the console, other users are blocked from controlling the
target. Blocked users see a message indicating who blocks them.

The user connected to the console is able to invoke other commands
such as L</reset>, but only when the command is invoked via the same
SSH connection. This can be accomplished by using SSH connection
sharing, which is what L<novaboot(1)> uses (see I<-M> and I<-S> in
L<ssh(1)>).

This is the default command when no command is specified on command
line.

=item reset

Reset the target hardware.

=item on

Power on the target hardware.

=item off

Power off the target hardware.

=item rsync [...]

This command is not meant to be invoked directly by the user. It
allows using L<rsync(1)> to copy files to the target, perhaps for TFTP
server. The rsync command must be invoked as: C<rsync ...
target@server:>, i.e. without specifying destination path. The files
will be stored into I<$HOME/tftproot>.

=item user <uernamename> [admin]

User command is meant to be used with C<command=> option in SSH's
L<authorized_keys(5)> file. It allows the shell to display
human-readable names when printing information about who blocks the
target. Then, the real command is taken from SSH_ORIGINAL_COMMAND
environment variable.

When "admin" is specified after the user name, this user is considered
an administrator and is allowed to run L</add-key> and L</shell>
commands.

=item get-config

Prints novaboot configuration options needed for the target. One
option per line.

=back

=head2 Administration commands

Only administrators (see L</user>) are allowed to execute these
commands.

=over 8

=item add-key <username>

Reads the SSH public key from standard input and adds it into in
F<~/.ssh/authorized_keys>.

Example: C<ssh target@server add-key johndoe < john_rsa.pub>

=item shell

Runs shell on the server. Useful for editing configuration file. It is
better used with allocated pseudo-terminal.

Example: C<ssh -t target@server shell>

=back

=head1 CONFIGURATION FILE

B<novaboot-shell> reads configuration file from
F<$HOME/.novaboot-shell>. It should define values for the following
variables in the SH syntax.

=over 8

=item console_cmd

Command to C<exec> that connects to target's console.

=item reset_cmd

Command to C<exec> that resets the Target.

=item on_cmd

Command to C<exec> that powers the target on.

=item off_cmd

Command to C<exec> that powers the target off.

=item target_config

Novaboot command line options that specify which boot loader is used
by the target (L<novaboot(1)> rejects other, possibly dangerous, options).
Each option is on its own line and no quoting, escaping or stripping
is performed on the values.

Example:

  target_config="\
  --uboot=(uboot)
  --uboot-init=setenv serverip 192.168.1.1; setenv ipaddr 192.168.1.10
  --uboot-addr=kernel=0x8100000
  --uboot-addr=fdt=0x83000000
  --uboot-addr=ramdisk=0x83100000
  "


=back

=head1 AUTHORS

Michal Sojka <sojkam1@fel.cvut.cz>

Latest version can be found at
L<https://github.com/wentasah/novaboot>.

=cut
EOF