sshnfs - ssh with nfs forwarding
Posted by Anonymous on Wed 15th Feb 2023 12:56
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#!/usr/bin/ksh93
#
# sshnfs - remote login client with NFSv4 forwarding
#
# Example usage:
# $ ksh sshnfs.ksh -o NFSURL=nfs://localhost/export/home/rmainz root@10.49.20.207 #
# $ ksh sshnfs.ksh -o NFSURL=nfs://derfwpc5131/export/home/rmainz -o NFSJumphost=rmainz@derfwpc5131,roland.mainz@derfwnb8353 -J rmainz@derfwpc5131,roland.mainz@derfwnb8353 root@10.49.20.207
#
# Written by Roland Mainz <roland.mainz@nrubsig.org>
#

#
# parse url
#
# returns:
# data.protocol
# data.host
# data.port (optional)
# data.path
#
function parse_url
{
        typeset url="$2"
        typeset leftover
        nameref data="$1"

        # ~(E) is POSIX extended regular expression matching (instead of
        # shell pattern)
        leftover="${url//~(Elr)(.+?):\/\/(.+?)(?:|:([[:digit:]]+))(?:\/(.*?))?/X}"

        # All parsed data should be captured via eregex in .sh.match - if
        # there is anything left (except the 'X') then the input string did not
        # properly match the eregex
        [[ "$leftover" == 'X' ]] || { print -u2 -f $"%s: Parser error\n" "$0" ; return 1 ; }

        data.protocol="${.sh.match[1]}"
        data.host="${.sh.match[2]}"
        # bug: should be [[ -v .sh.match[3] }}, but ksh93u has bugs
        [[ "${.sh.match[3]}" != '' ]] && integer data.port="${.sh.match[3]}"
        data.path="${.sh.match[4]}"

        return 0
}

function parse_nfs_url
{
        typeset url="$2"
        nameref data="$1"

        parse_url data "$url" || return 1

        [[ "${data.protocol}" == 'nfs' ]]       || { print -u2 -f $"%s: Not a NFS url\n" "$0" ; return 1 ; }
        [[ "${data.host}" != '' ]]              || { print -u2 -f $"%s: NFS hostname missing\n" "$0" ; return 1 ; }
        [[ "${data.path}" != '' ]]              || { print -u2 -f $"%s: NFS path missing\n" "$0" ; return 1 ; }

        if [[ ! -v data.port ]] ; then
                # use # default NFSv4 TCP port number (see
                # $ getent services nfs #)
                integer data.port=2049
        fi

        return 0
}


function main
{
        integer i
        integer retval
        compound c=(
                # port on THIS machine
                integer local_forward_port=34049

                # TCP port on destination machine where we forward the
                # NFS port from the server
                integer destination_nfs_port=33049

                # fixme: "/tmp" vs. "${XDG_RUNTIME_DIR:-/tmp}" ?
                typeset ssh_control_socket_name="/tmp/sshnfs_ssh-control-socket_${LOGNAME}_${PPID}_$$"
        )

        #set -o xtrace
        typeset mydebug=false # fixme: should be "bool" for ksh93v
        set -o nounset

        typeset c.args=( "$@" )

        for ((i=0 ; i < ${#c.args[@]} ; i++)) ; do
                if [[ "${c.args[i]}" == '-o' ]] ; then
                        case "${c.args[i+1]-}" in
                                'NFSURL='*)
                                        unset c.nfs_server
                                        compound c.nfs_server
                                        typeset c.url="${c.args[i+1]#NFSURL=}"
                                        parse_nfs_url c.nfs_server "${c.url}" || return 1
                                        unset c.args[$i] c.args[$((i+1))]
                                        ((i++))
                                        ;;
                                'NFSJumphost='*)
                                        [[ ! -v c.ssh_jumphost_args ]] && typeset -a c.ssh_jumphost_args
                                        c.ssh_jumphost_args+=( "-J" "${c.args[i+1]#NFSJumphost=}" )
                                        unset c.args[$i] c.args[$((i+1))]
                                        ((i++))
                                        ;;
                        esac
                fi
        done

        if [[ -v c.nfs_server ]] ; then
                # Forward NFS port from server to local machine
                # Notes:
                # - We use $ ssh -M ... # here as a way to terminate the port
                # forwarding process later using "-O exit" without the need
                # for a pid
                print -u2 -f $"# Please enter the login data for NFS server (%s):\n" \
                        "root@${c.nfs_server.host}"
                ssh \
                        -L "${c.local_forward_port}:localhost:${c.nfs_server.port}" \
                        -M -S "${c.ssh_control_socket_name}" \
                        -N \
                        -f -o 'ExitOnForwardFailure=yes' \
                        "${c.ssh_jumphost_args[@]}" \
                        "root@${c.nfs_server.host}"
                if (( $? != 0 )) ; then
                        print -u2 -f $"%s: NFS forwarding ssh failed with error code %d\n" "$0" $?
                        return 1
                fi

                # debug
                ${mydebug} && ssh -S "${c.ssh_control_socket_name}" -O 'check' "root@${c.nfs_server.host}"

                print -u2 -f $"# Use this to mount the directory:\n"
                print -u2 -f $"# $ mkdir /mnt_nfs\n"
                print -u2 -f $"# $ mount -vvv -t nfs -o vers=4,port=%d localhost:/%s /mnt_nfs\n" \
                        c.destination_nfs_port \
                        "${c.nfs_server.path}"

                # add NFS forwarding options to main ssh argument list
                c.args=(
                        '-R' "${c.destination_nfs_port}:localhost:${c.local_forward_port}"
                        '-o' 'ExitOnForwardFailure=yes'
                        "${c.args[@]}"
                )
        fi

        ${mydebug} && print -v c

        print -u2 -f $"# ssh login data for destination machine:\n"
        ssh "${c.args[@]}" ; (( retval=$? ))

        if [[ -v c.nfs_server ]] ; then
                ssh -S "${c.ssh_control_socket_name}" -O 'exit' "root@${c.nfs_server.host}"
        fi

        wait

        return $retval
}

main "$@"
exit $?

# EOF.