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Filename : complete.sh
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# shellcheck shell=bash
#
#  Copyright (C) 2017 Canonical Ltd
#
#  This program is free software: you can redistribute it and/or modify
#  it under the terms of the GNU General Public License version 3 as
#  published by the Free Software Foundation.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program.  If not, see <http://www.gnu.org/licenses/>.

# _complete_from_snap performs the tab completion request by calling the
# appropriate 'snap run --command=complete' with serialized args, and
# deserializes the response into the usual tab completion result.
#
# How snap command completion works is:
# 1. snapd's complete.sh is sourced into the user's shell environment
# 2. user performs '<command> <tab>'. If '<command>' is a snap command,
#    proceed to step '3', otherwise perform normal bash completion
# 3. run 'snap run --command=complete ...', converting bash completion
#    environment into serialized command line arguments
# 4. 'snap run --command=complete ...' exec()s 'etelpmoc.sh' within the snap's
#    runtime environment and confinement
# 5. 'etelpmoc.sh' takes the serialized command line arguments from step '3'
#    and puts them back into the bash completion environment variables
# 6. 'etelpmoc.sh' sources the snap's 'completer' script, performs the bash
#    completion and serializes the resulting completion environment variables
#    by printing to stdout the results in a format that snapd's complete.sh
#    will understand, then exits
# 7. control returns to snapd's 'complete.sh' and it deserializes the output
#    from 'etelpmoc.sh', validates the results and puts the validated results
#    into the bash completion environment variables
# 8. bash displays the results to the user
type -t _complete_from_snap > /dev/null ||
_complete_from_snap() {
    {
        # De-serialize the output of 'snap run --command=complete ...' into the format
        # bash expects:
        read -r -a opts
        # opts is expected to be a series of compopt options
        if [[ ${#opts[@]} -gt 0 ]]; then
            if [[ "${opts[0]}" == "cannot" ]]; then
                # older snap-execs sent errors over stdout :-(
                return 1
            fi

            for i in "${opts[@]}"; do
                if ! [[ "$i" =~ ^[a-z]+$ ]]; then
                    # only lowercase alpha characters allowed
                    return 2
                fi
            done
        fi

        read -r bounced
        case "$bounced" in
            ""|"alias"|"export"|"job"|"variable")
                # OK
                ;;
            *)
                # unrecognised bounce
                return 2
                ;;
        esac

        read -r sep
        if [ -n "$sep" ]; then
            # non-blank separator? madness!
            return 2
        fi
        local oldIFS="$IFS"

        if [ ! "$bounced" ]; then
            local IFS=$'\n'
            # Ignore any suspicious results that are uncommon in filenames and that
            # might be used to trick the user. A whitelist approach would be better
            # but is impractical with UTF-8 and common characters like quotes.
            COMPREPLY=( $( command grep -v '[[:cntrl:];&?*{}]' ) )
            IFS="$oldIFS"
        fi

        if [[ ${#opts[@]} -gt 0 ]]; then
            # shellcheck disable=SC2046
            # (we *want* word splitting to happen here)
            compopt $(printf " -o %s" "${opts[@]}")
        fi
        if [ "$bounced" ]; then
            # We validated '$bounced' above and '${COMP_WORDS[$COMP_CWORD]}' is
            # coming from the user's session, not the snap so skip input
            # validation: we aren't trying to protect the user from themselves.
            COMPREPLY+=(compgen -A "$bounced" -- "${COMP_WORDS[$COMP_CWORD]}")
        fi
    } < <(
        snap run --command=complete "$1" "$COMP_TYPE" "$COMP_KEY" "$COMP_POINT" "$COMP_CWORD" "$COMP_WORDBREAKS" "$COMP_LINE" "${COMP_WORDS[@]}" 2>/dev/null || return 1
    )

}

# this file can be sourced directly as e.g. /usr/lib/snapd/complete.sh, or via
# a symlink from /var/lib/snapd/desktop/bash-completion/completions/. In the first case we
# want to load the default loader; in the second, the specific one.
#
if [[ "${BASH_SOURCE[0]}" =~ ^(/var/lib/snapd/desktop|/usr/share)/bash-completion/completions/ ]]; then
    complete -F _complete_from_snap "$1"
else

    # _complete_from_snap_maybe calls _complete_from_snap if the command is in
    # bin/snap, and otherwise does bash-completion's _completion_loader (which is
    # what -D would've done before).
    type -t _complete_from_snap_maybe > /dev/null ||
    _complete_from_snap_maybe() {
        local etel=snap/core/current/usr/lib/snapd/etelpmoc.sh
        # catch /snap/bin and /var/lib/snapd/snap/bin
        if [[ "$(command -v "$1")" =~ ^(/var/lib/snapd)?/snap/bin/ && ( -e "/var/lib/snapd/$etel" || -e "/$etel" )  ]]; then
            complete -F _complete_from_snap "$1"
            return 124
        fi
        # fallback to the old -D
        _completion_loader "$1"
    }

    complete -D -F _complete_from_snap_maybe
fi