sshnfs - ssh with nfs forwarding
Posted by Anonymous on Fri 10th Feb 2023 11:58
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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://localhost/export/home/rmainz -o NFSJumphost=derfwpc5131 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 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
                integer data.port=2049
        fi

        return 0
}


function main
{
        integer i
        compound c
        compound c.nfs_data
        integer c.forward_port=34049
        integer retval

        #set -o xtrace
        set -o nounset

        typeset c.args=( "$@" )

        for ((i=0 ; i < ${#c.args[@]} ; i++)) ; do
                if [[ "${c.args[i]}" == '-o' ]] ; then
                        case "${c.args[i+1]-}" in
                                'NFSURL='*)
                                        unset c.nfs_data
                                        typeset c.url="${c.args[i+1]#NFSURL=}"
                                        parse_nfs_url c.nfs_data "${c.url}" || return 1
                                        unset c.args[$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

        # bug: should be [[ -v c.nfs_data ]], but ksh93u has bugs
        if [[ -v c.nfs_data.host ]] ; 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
                printf $"# Please enter the password for NFS server (%s)\n" \
                        "root@${c.nfs_data.host}"
                ssh \
                        -L "${c.forward_port}:localhost:${c.nfs_data.port}" \
                        -M -S "$PWD/ssh-control-socket" \
                        -N \
                        -f -o ExitOnForwardFailure=yes \
                        "${c.ssh_jumphost_args[@]}" \
                        "root@${c.nfs_data.host}"
                if (( $? != 0 )) ; then
                        printf $"%s: NFS forwarding ssh failed with error code %d\n" "$0" $?
                        return 1
                fi
                #ssh -S "$PWD/ssh-control-socket" -O 'check' "root@${c.nfs_data.host}"

                printf $"# Use this to mount the directory:\n"
                printf $"# $ mkdir /mnt_nfs\n"
                printf $"# $ mount -vvv -t nfs -o vers=4,port=%d localhost:/%s /mnt_nfs\n" \
                        33049 \
                        "${c.nfs_data.path}"

                # add NFS forwarding options to main ssh argument list
                c.args=( "-R" "33049:localhost:${c.forward_port}" "${c.args[@]}" )
        fi

        ssh "${c.args[@]}" ; (( retval=$? ))

        if [[ -v c.nfs_data.host ]] ; then
                ssh -S "$PWD/ssh-control-socket" -O 'exit' "root@${c.nfs_data.host}"
        fi

        wait

        return $retval
}

main "$@"

# EOF.