sing_command

#!/bin/bash

# By Pierre Rioux, pierre.rioux@mcgill.ca,
# November 2019, December 2019, January 2020
#
# See https://github.com/aces/sing-squashfs-support
#
# The site above gives examples on how to invoke this script as a wrapper for
#
# a) mounting squashfs files using sshfs;
# b) running rsync inside a container with squashfs files;
# c) running any other command too while we're at it.
#
# This program has many capabilities that are triggered
# automatically by how it is NAMED at installation. If it
# is called any of these names, some default behaviors will
# be triggered:
#
#  sing_sftpd   # passthrough container command: sftp-server
#  sing_rsync   # passthrough container command: rsync
#  sing_command_here # default sqfs and image: in install dir
#  sing_sftpd_here   # default sqfs and image: in install dir
#  sing_rsync_here   # default sqfs and image: in install dir

VERSION="3.0"
BASENAME=$(basename $0)
PREFIX="" # -D option

# Important note for developers: the sshd <-> sftp-server
# connection (or the sshd <-> rsync connection) is performed strictly
# with STDIN and STDOUT, so we are not allowed to pollute any
# of these two streams while running this script! If you need to
# debug, echo stuff to files in /tmp instead. E.g. like in
#
#   echo "inspecting prefix=$PREFIX" > /tmp/deb.1
#
# You can also add 'echo' in front of the final
# singularity command to inspect it, as a way
# to inspect its final form.

# Why oh why is this not at the same place?
# When the container is launched, we'll look for both.
RPM_OPEN_SSH_SFTPD="/usr/libexec/openssh/sftp-server" # Centos location
APT_OPEN_SSH_SFTPD="/usr/lib/sftp-server"             # Ubuntu location

# Some build-in commands we support by default:
# For sing_sftpd : (automatically supports the two paths above too)
SFTPD_COMMAND="\$(type -p $RPM_OPEN_SSH_SFTPD || type -p $APT_OPEN_SSH_SFTPD)"
# For sing_rsync :
RSYNC_COMMAND="rsync" # hopefully it's in the search path in the container

# Documentation and usage statement
function usage() {
  cat <<USAGE 1>&2
This is $BASENAME $VERSION by Pierre Rioux

It will run a command in a singularity container that has been started
with a set of overlays. By default, depending on the name of this
program, it will run the OpenSSH 'sftp-server', or the 'rsync' command.

Usage: $BASENAME [-D directory] [-I singularity_image_file] [-O overlay_file_pattern] [command...]

Note: options must be provided in the order shown!

where:

  -D directory

    is an optional base directory for finding both singulariy_image_file
    and overlay_file_pattern. If provided, the program will chdir there
    first before attempting to resolve the other arguments.

    If a directory is given and no other arguments are provided
    (that is, no singularity_image_file and no overlay_file_pattern),
    then the program will pick the first file named "*.simg" (or
    "*.sif") in the directory as its singularity image file, and
    will pick all files ending in .squashfs, .sqs or .ext3 as the
    overlays.

  -I singularity_image_file

    is a path to a singularity container image. The image must contain at
    least the openssh-server package (when running sing_sftpd) or the rsync
    package (when running sing_rsync). It can be a relative or absolute
    path. See also -D above.

  -O overlay_file_pattern

    is a file pattern for a set of overlay image files
    (e.g. /path/to/something*.squashfs).

  command

    an optional command to run in the container. By default the command
    to run depends on the name of this very program:

    When the program is named 'sing_sftpd':
      The command will be $RPM_OPEN_SSH_SFTPD or $APT_OPEN_SSH_SFTPD
      (whichever is first found). This is the OpenSSH sftp-server.
    When the program is named 'sing_rsync':
      The command will be '$RSYNC_COMMAND'.

Installation shortcut:

  If this program is installed in a directory and renamed with
  a '_here' at the end of the name, it will automatically internally
  assume that a '-D' option was provided with the path to the directory
  where the script is installed as argument. E.g.

     /path/to/sing_sftpd_here

  is the same as

     /path/to/sing_sftpd -D /path/to

Examples:

 # Overlays are given with a pattern:
 sing_sftpd -I centos.simg -O '*.squashfs'

 # Using a -D to specify where to look for all the files:
 sing_rsync -D /my/path -I centos.simg -O '*.squashfs' rsync_args_here

 # Using a -D to specify where to look just for the overlays:
 sing_sftpd -D /my/path -I /some/other/place/centos.simg -O '*.squashfs'

 # Using a -D and no other arguments:
 # a) singularity image will be first .simg (or .sif)
 # b) overlays will be all .squashfs, .sqs or .ext3 files
 sing_sftpd -D /my/path/for/everything

USAGE
  exit 2
}

##########################################
# When this program is renamed to end with
# the string "_here", then it behaves as
# if the option "-D $PWD" was given.
##########################################
if test "X${BASENAME/*_here/Y}" = "XY" ; then
  # Note that 'readlink -e' only exists on Linux
  PREFIX=$(dirname $(readlink -e "$0")) || exit
fi

####################################
# Validation of arguments
####################################

if test -z "$PREFIX" -a $# -lt 2 ; then
  usage
fi

# Optional PREFIX in -D
if test "X$1" = "X-D" ; then
  PREFIX="$2"
  shift ; shift
  if ! test -d "$PREFIX" ; then
    echo "Error: '$PREFIX' for option -D is not a directory." 1>&2
    exit 2
  fi
fi

# Option -I: the path of the singularity image
if test "X$1" = "X-I" ; then
  test $# -lt 2 && usage
  SING_IMAGE="$2" # can be empty string if -D provided
  shift ; shift
fi

# Option -O: the path (or pattern) for one or several overlay images
if test "X$1" = "X-O" ; then
  test $# -lt 2 && usage
  OVERLAYS="$2";  # can also be empty if -D provided
  shift ; shift
fi

# Find image and overlays if necessary
if test -n "$PREFIX" ; then

  # This is important, and it makes all the path
  # resolution code below relative to it now.
  cd "$PREFIX" || exit 2

  # Auto find image
  if test -z "$SING_IMAGE" ; then # if no image given, find one
    SING_IMAGE=$(ls -1 | egrep '\.simg$|\.sif$' | head -1)
    if test -z "$SING_IMAGE" ; then
      echo "Error: can't find a .simg or .sif image in directory '$PREFIX'." 1>&2
      exit 2
    fi
  fi

  # Auto find overlays
  if test -z "$OVERLAYS" ; then
    OVERLAYS=$(ls -1 | egrep '\.squashfs$|\.sqs$|\.ext3$')
  fi

fi

# Validate image file
if ! test -f "$SING_IMAGE" ; then
  test -n "$PREFIX" && echo "Error: while switched to directory '$PREFIX':" 1>&2
  echo "Error: '$SING_IMAGE' doesn't seem to be present and an image file." 1>&2
  echo "Maybe you need to provide the path with -I ?"                       1>&2
  exit 2
fi

# Validate overlays patterns
if test -z "$OVERLAYS" ; then
  echo "Error: no patterns for the overlays files provided." 1>&2
  echo "Maybe you need to provide the path with -O ?"        1>&2
  exit 2
fi

# Generate singularity overlays options, expanding patterns at the same time.
# Note that this is a place where errors can occur silently:
# if the user provide bad patterns that do not match any files, the
# pattern will be ignored.
SING_OVERLAYS=$(ls -1 $OVERLAYS | sed -e 's/^/--overlay=/' -e 's/\.sqs$/.sqs:ro/' -e 's/\.squashfs/.squashfs:ro/')

# Figure out what program to run now;
# if this script is provided with a command, we run that;
# if this script is named "sing_sftpd", we run the OpenSSH sftp-server;
# if this script is named "sing_rsync", we run the rsync command.
# if this script is named "sing_shell", we start an interactive shell with no command.
COMMAND=""
MODE="exec"
if echo $BASENAME | grep sing_sftpd >/dev/null ; then
  COMMAND="$SFTPD_COMMAND"
elif echo $BASENAME | grep sing_rsync >/dev/null ; then
  COMMAND="$RSYNC_COMMAND"
elif echo $BASENAME | grep sing_shell >/dev/null ; then
  MODE="shell"
fi

# Help messages
if test "X$*" = "X-h" -o "X$*" = "X-help" -o "X$*" = "X--help" ; then
  usage
  exit 2
fi

# EXEC requires a command
if test "$MODE" = "exec" ; then
  if test -z "$COMMAND" && test -z "$*" ; then
    echo "Error: we do not know what command to run in the container." 1>&2
    echo "Try \"$0 -h\" for help" 1>&2
    exit 2
  fi
fi

# SHELL requires no commands
if test "$MODE" = "shell" ; then
  if test -n "$COMMAND" || test -n "$*" ; then
    echo "Error: when starting an interactive shell, no commands are allowed." 1>&2
    echo "Try \"$0 -h\" for help" 1>&2
    exit 2
  fi
fi

if test $MODE = "exec" ; then
  # OK do the main work now.
  #
  # I use two 'exec's to simplify the process hierarchy!
  #
  # How glorious!
  exec singularity -s exec \
    $SING_OVERLAYS         \
    $SING_IMAGE            \
    bash -c "exec $COMMAND $*"
else # interactive shell
  exec singularity -s shell \
    $SING_OVERLAYS          \
    $SING_IMAGE
fi

# If bash reaches this point, something is clearly wrong.