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Add clarifying error message when user tries to use non-existing image archive and update README #23

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8707e7d
Add message to clarify when non-existent docker image archive is given
charles-l Oct 21, 2020
53c0623
Update README with latest parameters and fixed examples.
charles-l Oct 21, 2020
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26 changes: 15 additions & 11 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -2,29 +2,34 @@ Unpacks a Docker image.

## Usage

usage: undocker.py [-h] [--ignore-errors] [--output OUTPUT] [--verbose]
[--debug] [--list] [--layer LAYER]
image
usage: undocker [-h] [--ignore-errors] [--output OUTPUT] [--layers] [--list]
[--layer LAYER] [--no-whiteouts] [--verbose] [--debug]
[image]

positional arguments:
image
image The docker image tar archive from `docker save`. Read
from stdin if left empty.

optional arguments:
-h, --help show this help message and exit
--ignore-errors, -i Ignore OS errors when extracting files
--output OUTPUT, -o OUTPUT
Output directory (defaults to ".")
--verbose, -v
--debug, -d
--list, --ls List layers in an image
--layers List layers in an image
--list, --ls List images/tags contained in archive
--layer LAYER, -l LAYER
Extract only the specified layer
--no-whiteouts, -W Do not process whiteout (.wh.*) files

Logging options:
--verbose, -v
--debug, -d

## Examples

Extract an entire image:

$ docker save busybox | undocker -i -o busybox busybox
$ docker save busybox | undocker -i -o busybox

The `-i` option is necessary here because I am not running as root,
and the extract operation will fail when it attempts to create device
Expand All @@ -42,14 +47,13 @@ Extract only specific layers:

$ docker save busybox |
undocker -o busybox -v \
-l 4986bf8c15363d1c5d15512d5266f8777bfba4974ac56e3270e7760f6f0a8125 \
busybox
-l 4986bf8c15363d1c5d15512d5266f8777bfba4974ac56e3270e7760f6f0a8125
INFO:undocker:extracting image busybox (4986bf8c15363d1c5d15512d5266f8777bfba4974ac56e3270e7760f6f0a8125)
INFO:undocker:extracting layer 4986bf8c15363d1c5d15512d5266f8777bfba4974ac56e3270e7760f6f0a8125

## License

undocker -- a tool for decomposing Docker images
undocker -- a tool for decomposing Docker images
Copyright (C) 2015 Lars Kellogg-Stedman <lars@oddbit.com>

This program is free software: you can redistribute it and/or modify
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5 changes: 4 additions & 1 deletion undocker.py
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Expand Up @@ -51,7 +51,7 @@ def parse_args():
const=logging.DEBUG,
dest='loglevel')

p.add_argument('image', nargs='?')
p.add_argument('image', nargs='?', help='The docker image tar archive from `docker save`. Read from stdin if left empty.')

p.set_defaults(level=logging.WARN)
return p.parse_args()
Expand Down Expand Up @@ -95,6 +95,9 @@ def main():
args = parse_args()
logging.basicConfig(level=args.loglevel)

if args.image and not os.path.exists(args.image):
raise Exception(f'Expected "{args.image}" to be a docker image tar file.')

with tempfile.NamedTemporaryFile() as fd, (
open(args.image, 'rb') if args.image
else io.open(sys.stdin.fileno(), 'rb')) as image:
Expand Down