powerboost.sh

#!/bin/sh
# Wed Aug 26 19:25:48 PDT 2009 by epixoip
# a "download manager" tailored for comcast subscribers, ensuring "powerboost"
# speeds for the entire duration of a download. if you are unfamiliar with
# comcast powerboost: http://www.dslreports.com/faq/14520
# (this is really just an excuse to write a "multi-threaded" shell script)

usage() {
cat >&2 <<EOF
powerboost - ensures comcast powerboost speeds for duration of download
Syntax:    $0 [options] URL

Options:
    -t    Number of concurrent "threads"
    -o    Output file name
    -h    Display this message

EOF

exit 1
}

error()
{
    echo "error: $1" >&2
    usage
}

warn()
{
    echo "warning: $1" >&2
}

spawn_thread()
{
    r_start=$((r_end + 1))

    if test "$r_start" -gt "$filesize"; then
        return
    fi

    r_end=$((r_start + 20000000))

    if test "$r_end" -gt "$filesize"; then
        r_end="$filesize"
    fi

    chunk=$((chunk + 1))

    echo "Retrieving chunk $chunk ($r_start - $r_end)"

    curl -so $outfile.$chunk -r $r_start-$r_end $url &

    pids="$pids $!"
}

waitall()
{
    while true; do
        for pid in "$@"; do
            shift
            if kill -0 "$pid" 2>/dev/null; then
                set -- "$@" "$pid"
            else
                wait "$pid"
            fi
        done

        if test "$#" -lt 1; then
            break
        fi

        sleep 0.3
   done
}

while getopts "ht:o:" opts; do
    case $opts in
        t) threads="$OPTARG";;
        o) outfile="$OPTARG";;
        h) usage;;
        ?) usage;; 
    esac
    x="$OPTIND"
done

if test -n "$x" && test "$x" -gt 0; then
    shift $((x - 1))
fi

if test -z "$1"; then
    usage
fi


url="$1"
threads="${threads:-4}"
outfile="${outfile:-$(basename $url)}"
pids=""

filesize="$(curl -sI $url | sed -rn 's/Content-Length:\W+([0-9]+).*$/\1/ip')"

if test -z "$filesize"; then
    error "$(basename $url) does not exist on server $(dirname $url)"
fi

maxthreads=$((filesize / 20000000))

if test "$threads" -gt "$maxthreads"; then
    warn "more threads were requested than needed; reducing threads to $maxthreads"
    threads=$maxthreads
fi

r_start=0
r_end=-1
chunk=0
start_time=$(date +%s)

set -o monitor

for t in $(seq 1 $threads); do
    spawn_thread
    sleep 0.3
done

while test "$r_end" -lt "$filesize"; do
    trap spawn_thread CHLD
    wait
done

waitall $pids

end_time=$(date +%s)
elapsed=$((end_time - start_time))
speed=$(echo "scale=2; $filesize / $elapsed" | bc)

echo "Retrieved $filesize bytes in $elapsed seconds [avg $speed bytes/sec]"

echo "Reassembling file..."

> $outfile

for i in $(seq 1 $chunk); do
    cat $outfile.$i >>$outfile
    rm -f $outfile.$i
done

echo 'Done!'