#!/bin/bash

THIS=$0

ARGS=$@

name=$(basename $THIS)

usage () {

    cat <<EOF

Usage: $name: redirect input/output/error of a running process

Two ways to run this program:

    $name [-q][-o <outfile>] [-e <errorfile>] [-i <inputfile>] [-n <fd>:<filename> ] <pid>

or simply:

    $name [-q] <pid>

The first form files specified in -o, -e, and -i options will become

standard output, standard error, and standard input.  At least one

option must be specified, or second form will be assumed.

For example, using Bash syntax:

    bash -c 'sleep 1m && echo "rise and shine"' &

    $name -o /tmp/test \$!

The same with explicit stdout descriptor number (1) using -n option:

    bash -c 'sleep 1m && echo "rise and shine"' &

    $name -n 0:/tmp/test \$!

In the second form, current in/out/err are remapped into the process.

For example, using Bash syntax:

    bash -c 'sleep 1m && echo "rise and shine"' &

    $name \$! >>/tmp/test

These examples should be equivalent (i.e. -o foo will append to file foo,

if it already exists) with respect to stdout, but in the second stdin and

stderr are remapped as well.

Option (-n) allows explicit specification of file descriptors.

It can be given multiple times, e.g.:

    $name -n 0:/tmp/stdin -n 1:/tmp/stdout -n 2:/tmp/stderr PID

is equivalent to, using Bash syntax:

    $name PID </tmp/stdin >/tmp/stdout 2>/tmp/stderr

All files specified in (-n) option are opened in read/write & append mode.

Summary of options:

    -i <stdin>  specify filename of the new standard input

    -o <stdout> specify filename of the new standard output

    -e <stderr> specify filename of the new standard error

    -n <fd>:<filename> specify descriptor number and filename to remap to

    -q          be quiet

    -h          this help

EOF

}

warn () {

    echo "$name: $@" >&2

}

# XXX add multiple -n option

quiet="no"

nopt=""

while getopts "ho:e:i:qn:" opt; do

    case $opt in

        ( o ) stdout=$OPTARG; ;;

        ( e ) stderr=$OPTARG; ;;

        ( i ) stdin=$OPTARG; ;;

  ( n ) nopt="$nopt $OPTARG"; ;;

        ( q ) quiet="yes"; ;;

        ( * ) usage; exit 0; ;;

    esac

done

shift $((OPTIND-1))

if [ $# != 1 ]; then

    usage

    exit 1

fi

if [ -n "$stdout" ] && ! 2>/dev/null : >> $stdout ; then

    warn "Cannot write to (-o) $stdout"

    exit 1

fi

if [ -n "$stderr" ] && ! 2>/dev/null : >> $stderr ; then

    warn "Cannot write to (-e) $stderr"

    exit 1

fi

if [ -n "$stdin" ] && ! 2>/dev/null : >> $stdin ; then

    warn "Cannot write to (-i) $stdin"

    exit 1

fi

fds=""

if [ -n "$nopt" ]; then

    for n_f in $nopt; do

  n=${n_f%%:*}

  f=${n_f##*:}

  if [ -n "${n//[0-9]/}" ] || [ -z "$f" ]; then 

      warn "Error parsing descriptor (-n $n_f)"

      exit 1

  fi

  if ! 2>/dev/null : >> $f; then

      warn "Cannot write to (-n $n_f) $f"

      exit 1

  fi

  fds="$fds $n"

  fns[$n]=$f

    done

fi

if [ -z "$stdout" ] && [ -z "$stderr" ] && [ -z "$stdin" ] && [ -z "$nopt" ]; then

    #second invocation form: dup to my own in/err/out

    [ -e /proc/$$/fd/0 ] &&  stdin=$(readlink /proc/$$/fd/0)

    [ -e /proc/$$/fd/1 ] && stdout=$(readlink /proc/$$/fd/1)

    [ -e /proc/$$/fd/2 ] && stderr=$(readlink /proc/$$/fd/2)

    if [ -z "$stdout" ] && [ -z "$stderr" ] && [ -z "$stdin" ]; then

  warn "Could not determine current standard in/out/err"

  exit 1

    fi

fi

PID=$1

if ! 2>/dev/null kill -0 $PID; then

    warn "Error accessing PID $PID"

    exit 1

fi

if [ "$quiet" != "yes" ]; then

    msg_stdout="Remaining standard output of $PID is redirected to $stdout\n"

    msg_stderr="Remaining standard error of $PID is redircted to $stderr\n"

fi

gdb_cmds () {

    local _name=$1

    local _mode=$2

    local _desc=$3

    local _msgs=$4

    local _len

    [ -w "/proc/$PID/fd/$_desc" ] || _msgs=""

    if [ -d "/proc/$PID/fd" ] && ! [ -e "/proc/$PID/fd/$_desc" ]; then

  warn "Attempting to remap non-existent fd $n of PID ($PID)"

    fi

    [ -z "$_name" ] && return

    echo "set \$fd=open(\"$_name\", $_mode)"

    echo "set \$xd=dup($_desc)"

    echo "call dup2(\$fd, $_desc)"

    echo "call close(\$fd)"

    if  [ $((_mode & 3)) ] && [ -n "$_msgs" ]; then

        _len=$(echo -en "$_msgs" | wc -c)

        echo "call write(\$xd, \"$_msgs\", $_len)"

    fi

    echo "call close(\$xd)"

}

trap '/bin/rm -f $GDBCMD' EXIT

GDBCMD=$(mktemp /tmp/gdbcmd.XXXX)

{

    #Linux file flags (from /usr/include/bits/fcntl.sh)

    O_RDONLY=00

    O_WRONLY=01

    O_RDWR=02 

    O_CREAT=0100

    O_APPEND=02000

    echo "#gdb script generated by running '$0 $ARGS'"

    echo "attach $PID"

    gdb_cmds "$stdin"  $((O_RDONLY)) 0 "$msg_stdin"

    gdb_cmds "$stdout" $((O_WRONLY|O_CREAT|O_APPEND)) 1 "$msg_stdout"

    gdb_cmds "$stderr" $((O_WRONLY|O_CREAT|O_APPEND)) 2 "$msg_stderr"

    for n in $fds; do

  msg="Descriptor $n of $PID is remapped to ${fns[$n]}\n"

  gdb_cmds ${fns[$n]} $((O_RDWR|O_CREAT|O_APPEND)) $n "$msg"

    done

    #echo "quit"

} > $GDBCMD

cat $GDBCMD

echo

if gdb -batch -n -x $GDBCMD >/dev/null </dev/null; then

    [ "$quiet" != "yes" ] && echo "Success" >&2

else

    warn "Remapping failed"

fi

#cp $GDBCMD /tmp/gdbcmd

rm -f $GDBCMD