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#! /bin/bash
# /usr/bin/pacman2pacman-get
#
# Version 1.5.8
#
# Copyright (C) 2014,2017 Joseph Graham <joseph@xylon.me.uk>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# 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 Affero 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/>.

debugmode=0
[[ ${3} == "-d" ]] && debugmode=1 # if 3rd arg is "-d", enable debug mode

echoerr() { cat <<< "$@" 1>&2; } # print errors to stdout

(( debugmode )) && echoerr "pacman2pacman-get invoked"

shopt -s extglob

torrent_folder='/srv/pacman2pacman/torrents'

pkg_cache_location='/var/cache/pacman/pkg'

# Pacman2pacman should be called like this from /etc/pacman.conf:
# XferCommand = /usr/bin/pacman2pacman-get %u %o

# Check that the args are not empty.
[[ -z ${1} ]] && { echoerr "The first argument should be the download url." ; exit 1 ; }
[[ -z ${2} ]] && { echoerr "The second argument should be the local filename, plus a “.part” extension." ; exit 1 ; }

url="${1}"  # The download url.
filename="${2}"  # This is where the downloaded file needs to be saved
                 # or hardlinked

# Check if transmission daemon is running.
if ! systemctl show --property='ActiveState' transmission | grep -q 'ActiveState=active'
then
    echoerr 'Error: The transmission daemon is not running.'
    exit 1
fi

cd "${torrent_folder}"

# Find the name of the package that will be displayed
pname="${url##*/}"
pname="${pname%%-[[:digit:]]*}"

# Find out if it's a dbfile
if [[ "${url}" == *'.db' ]] || [[ "${url}" == *'.db.sig' ]]
then
    dbfile=1
else
    dbfile=0
fi

fifoname="${TMPDIR-/tmp}/pacman2pacmanpipe"

exittidy() { rm -rf "${fifoname}" "${TMPDIR-/tmp}/pacman2pacman_torrents"* ; }

# Check for a .torrent.

# We will cycle through the mirrors in the mirrorlist, trying to get
# the torrent file for this package. If it fails we keep trying more
# mirrors until we get a 404 or a success, because only a 404
# indicates that the .torrent does not exist.

mkfifo "${fifoname}"

function look_for_torrent()
{
    local torrent_url="${1}"
    local tfile="$(mktemp ${TMPDIR-/tmp}/pacman2pacman_torrents.XXXXXXXXXX)"
    
    (( debugmode )) && echoerr "Looking for torrent at: '${torrent_url}'"

    # Attempt to download the torrent
    curl -o "${tfile}" -f -L -s -A 'Pacman2pacman' -m 10 "${torrent_url}"
    local curlstat="${?}"

    # Did curl download a torrent?
    if [[ "${curlstat}" == 0 ]] && grep "mktorrent" "${tfile}" &>/dev/null
    then
	(( debugmode )) && echoerr "Found torrent"
        echo "found_torrent:${tfile}" > "${fifoname}"
    fi
}

# If it's a .db file then we don't even check for a .torrent
if ! (( dbfile ))
then
    # OK so for three random mirrors we look for a torrent. The first
    # one that responds, we use it. Give up and go to HTTP after 6 seconds.
    while read mirror
    do
        # Remove the `Server = ' part, whether it has spaces or not
        mirror="${mirror##Server?( )=?( )}"

        torrent_url="${mirror%%\$*}torrents/${url##*/}.torrent"

        look_for_torrent "${torrent_url}" &

    done < <(grep '^Server \?= \?' "/etc/pacman.d/mirrorlist" | shuf | head -n 3)

    # Get the name of the torrent downloaded
    read -t 6 response < <(cat "${fifoname}")
fi

(( debugmode )) && echoerr "response var: '${response}'"

gotourbaby=0  # to record if we've got the torrent yet.

# If there's a .torrent we download the package with transmission
# otherwize we just download it by http.
if [[ "${response}" != 'found_torrent:'* ]]
then
    echo "Can't find a torrent file for this package :S"
else
    gotourbaby=1  # assume success unless proven otherwize

    cd "${pkg_cache_location}"

    # Re-write the webseeds in the torrent to make it use the user's
    # own mirror. We can just use the ${url} var.

    # The filename of the torrent
    torntname="${torrent_folder}/${url##*/}.torrent"
    
    # Move the torrent to the correct location
    mv "${response#found_torrent:}" "${torntname}"
    
    # We need to find out the length of the ${url} var.
    len="${#url}"

    sed "s#url-list[[:digit:]]\+.\+.pkg.tar.xz#url-list${len}:${url}#" < "${torntname}" > "${torntname}.modified"

    mv "${torntname}.modified" "${torntname}"

    transmission_output=$(mktemp)

    # If the torrent is already in transmission we remove it because
    # we want it to be fresh (with current webseed list etc)
    if id=$(transmission-remote -l | grep "${url##*/}")
    then
        transmission-remote -t "${id}" -r
    fi

    # Add the torrent to transmission
    (( debugmode )) && transmission-remote -a "${torntname}" -w "${pkg_cache_location}" 2>&1 | tee "${transmission_output}"
    (( debugmode )) || transmission-remote -a "${torntname}" -w "${pkg_cache_location}" 2>&1 > "${transmission_output}"

    if grep "Error: invalid or corrupt torrent file" "${transmission_output}"
    then
	echo "Invalid or corrupt torrent file - falling back to HTTP"
	gotourbaby=0
    else
	# The torrent is now downloading. To get info about the torrent in
	# order to display a progress bar we need to know it's id.

	# Find out the id of the torrent
	id=$(transmission-remote -l | grep "${url##*/}")
	id="${id## }"
	id="${id## }"
	id="${id## }"
	id="${id## }"
	id="${id## }"
	id="${id## }"
	id="${id## }"
	id="${id## }"
	id="${id## }"
	id="${id## }"
	id="${id## }"  # Once should be enough but somehow it's not so I do
                       # it loads of times.
	id="${id%% *}"

	# If there is an error there will be an asterix displayed on the
	# end of the id. We must remove it.
	id="${id%\*}"

	if ! [[ ${id} =~ [[:digit:]] ]]
	then
            echoerr "Error, invalid torrent id: '${id}'"
            exittidy ; exit 1
	fi

	# Display a progress bar until it's finished and then hardlink it to
	# the right place.
	progress='0.0%'

	echo -n "Pacman2pacman p2p download: ${pname}: ${progress}"

	count=0

	declare -a last_webseed_check=(0 'working')

	webseed_check_after='100'

	until [[ "${progress}" == '100%' ]]
	do
            progress=$(transmission-remote -t "${id}" -i | grep 'Percent Done:')
            progress="${progress##* }"  # Remove stuff we don't want

            # If we're still at 0.0% after ${webseed_check_after} attempts
            # then we check if the webseed is actually valid.
            if (( count >= webseed_check_after )) && [[ "${progress}" == '0.0%' ]]
            then
		# Find out if we already checked recently.
		if (( (last_webseed_check[0] + (webseed_check_after / 2)) > count ))
		then
                    if [[ last_webseed_check[1] == 'broken' ]]
                    then
			# Just set the message without checking.
			progress='0.0% Warning: Webseed dead...'
                    else
			# We don't need to do anything
			true
                    fi
		else
                    if ! $(curl -IL "${url}" | grep '200 OK' &>/dev/null)
                    then
			# The webseed seems to be invalid so we print an error
			# message.

			progress='0.0% Warning: Webseed dead...' # This
                                                                 # most
                                                                 # likely
                                                                 # means
                                                                 # the
                                                                 # user
                                                                 # needs
                                                                 # to run
                                                                 # pacman
                                                                 # -Sy, or
                                                                 # that
                                                                 # their
                                                                 # internet
                                                                 # is
                                                                 # down.

			# If there are no peers we remove the torrent from
			# transmission, print an error message and exit.
			if (( $(transmission-remote -t "${id}" -pi | wc -l) < 2 ))
			then
                            echo "Webseed dead and no peers, removing torrent from transmission and try by HTTP."
                            transmission-remote -t "${id}" -r > /dev/null
			    gotourbaby=0
			    break
			fi

			last_webseed_check[0]="${count}"
			last_webseed_check[1]="broken"
                    else
			# The webseed is valid so we just record that we checked
			last_webseed_check[0]="${count}"
			last_webseed_check[1]="working"
                    fi
		fi
            fi

            printf "\rPacman2pacman p2p download: %s: %s   " "${pname}" "${progress}"

            sleep 0.7

            (( count ++ ))
	done

	echo

	if (( gotourbaby ))
	then
	    err_count=0
	    until mv -f "${pkg_cache_location}/${url##*/}" "${filename}" 2>/dev/null
	    do
		if (( err_count > 50 ))
		then
		    echo "error moving \"${pkg_cache_location}/${url##*/}\". removing torrent from transmission"
		    transmission-remote -t "${id}" -r > /dev/null
		    exittidy ; exit 1
		fi

		sleep 0.1

		(( ++ err_count ))
	    done
	fi
    fi

    rm -f "${transmission_output}"
fi

if ! (( gotourbaby ))
then
    cd "${pkg_cache_location}"

    # There's no .torrent so we download it by just HTTP.

    # We must do some complicated stuff to customise the progress
    # meter how we want it, to make it consistent with the progress
    # bar when we download stuff with transmission.

    mod_time=$(stat -c %Y "/srv/pacman2pacman/dbcache/${filename##*/}" 2>/dev/null)

    progress='0.0%'

    echo -n "Pacman2pacman http download: ${pname}: ${progress}"

    # The first loop gets rid of all the backspace and '#'es and
    # stuff. The second loop isolates the percent done number.
    {
        # For dbs we check if they are modified
        if (( dbfile ))
        then
            if [[ -f "/srv/pacman2pacman/dbcache/${filename##*/}" ]]
            then
                curl -# -f -L -z "/srv/pacman2pacman/dbcache/${filename##*/}" -o "/srv/pacman2pacman/dbcache/${filename##*/}" -A 'Pacman2pacman' "${url}" 2>&1
            else
                curl -# -f -L -o "/srv/pacman2pacman/dbcache/${filename##*/}" -A 'Pacman2pacman' "${url}" 2>&1
            fi
        else
            curl -# -f -L -o "${filename}" -A 'Pacman2pacman' "${url}" 2>&1
        fi
    } |
    while read -N 1 char
    do
        [[ "${char}" =~ [[:digit:].%\ ] ]] && echo -n "${char}"
    done |
    {
        while read -d '%' word
        do
            progress="${word}%"

            # There's a crazy bug that causes it to display 100% at the
            # start of the download. This should fix it.
            [[ "${progress}" == '100.0%' ]] && continue

            printf "\rPacman2pacman http download: %s: %s   " "${pname}" "${progress}"
        done

        # It's the end of the download so we can now display 100%
        if [[ "${progress}" == '100.0%' ]]
        then
            progress='100%'
            printf "\rPacman2pacman http download: %s: %s   " "${pname}" "${progress}"
        fi
    }

    # What was the result of the download?
    if (( dbfile ))
    then
        # If we fail to stat it that means it doesn't exist so the
        # download failed.
        if ! new_mod_time=$(stat -c %Y "/srv/pacman2pacman/dbcache/${filename##*/}" 2>/dev/null)
        then
            progress='failed'
            printf "\rPacman2pacman http download: %s: %s   " "${pname}" "${progress}"

        # If the file was not modified we display such
        elif [[ "${new_mod_time}" == "${mod_time}" ]]
        then
            progress='file not modified'
            printf "\rPacman2pacman http download: %s: %s   " "${pname}" "${progress}"
        fi
    else
        # It's not a dbfile. Just check the output file exists.
        if ! [[ -f "${filename}" ]]
        then
            progress='failed'
            printf "\rPacman2pacman http download: %s: %s   " "${pname}" "${progress}"
        fi
    fi
 
    echo

    if (( dbfile )) && [[ -f "/srv/pacman2pacman/dbcache/${filename##*/}" ]]
    then
        cp "/srv/pacman2pacman/dbcache/${filename##*/}" "${filename}" 2>/dev/null
    fi

    [[ -f "${filename}" ]] || { exittidy ; exit 1 ; }

fi

exittidy

exit