Create differential tarballs

Note: The conda-incubator/conda-mirror#9 adds this tool to conda-mirror.

This tools allows you to create differential tarballs of a (usually mirrored) conda repository. The resulting tarball can be used to update a copy of the mirror on a remote (air-gapped) system, without having to copy the entire conda repository. The workflow is a follows:

1. we assume that the remote and local repository are in sync
2. create a reference.json file of the local repository
3. update the local repository using conda-mirror or some other tools
4. create the "differential" tarball
5. move the differential tarball to the remote machine, and unpack it
6. now that the remote repository is up-to-date, we should create a new reference.json on the local machine. That is, step 2

Notes:

The file reference.json is a collection of all repodata.json files (linux-64, win-32, noarch, etc.) of the local repository. It is created in order to compare a future state of the repository to the state of the repository when reference.json it was created.

The differential tarball contains files which either have been updated (such as repodata.json) or new files (new conda packages). It is meant to be unpacked on top of the existing mirror on the remote machine by:

cd <repository>
tar xf update.tar
# or y using tar's -C option from any directory
tar xf update.tar -C <repository>

Example:

In this example we assume that a conda mirror is located in ./repo. Create reference.json:

python mk_diff_tar.py --reference ./repo

Show the files in respect to the latest reference point file (which would be included in the differential tarball). Since we just created the reference file, we don't expect any output:

python mk_diff_tar.py --show ./repo

Now, we can update the mirror:

conda-mirror --upstream-channel conda-forge --target-directory ./repo ...

Create the actual differential tarball:

$ python mk_diff_tar.py --create ./repo
Wrote: update.tar
$ tar tf update.tar
noarch/repodata.json
noarch/repodata.json.bz2
noarch/ablog-0.9.2-py_0.tar.bz2
noarch/aws-amicleaner-0.2.2-py_0.tar.bz2
...