file-replicator 0.1.11
Replicate files to another computer for remote development
License: MIT
Requires Python: >=3.6,<4.0
Keywords: development,copying,replication,synchronisation,sync,files

# File Replicator

Replicate files one-way to another computer e.g. for remote development.

A key use-case is to keep in sync a directory of development files from a computer on which
the files are edited with a copy of those files in a docker container running on a remote docker host.

Tested and known to work between two Linux machines. Support for developing on macOS coming...

# Installation

Dependencies are:
* Python 3 and some Python packages on the development machine.
* Ability to run a shell (bash or bash-like) on the remote machine with connected `stdin`.
* The tar utility (the full version, not the busybox version) on both machines.

Note that nothing is installed remotely, there are no ports to open, and the remote user only needs
the ability to create the files and directories at the specified location.

So to install `file-replicator` on the machine with the source files to replicate:

    pip install file-replicator

Nothing needs to be installed on the destination machine so long as it has `bash`
(busybox bash is fine) and `tar` (gnu). Note that on alpine linux, the busybox tar
is insufficient, so install gnu tar with:

    apk install tar

# How it works

The approach involves running a small bash program on the remote (destination) end which is able to
add/update new files in (potentially) new directories. It receives these files over `stdin`
using the `tar` format (binary).

The controlling (source) end then simply sends files over to the `stdin` of the receiving bash
program, which pipes them through `tar` to unpack them again. Note that gnu `tar` is able to extract from
non-blocking file descriptor (as well as blocking), which means it keeps trying until it has all the data.
NB the busybox tar does not have this behaviour.

Establishing the connection to the remote end is outside the remit of the tool, but `file-replicator`
requires as an argument the command to make such a connection. See examples below.

Once a connection has been made, two phases of operation occur:

1. first, recursively walk a source tree of files and send them "over the wire" to the destination
2. then, watch for changes or new files and directories before sending them "over the wire" to the destination

So there is no "difference algorithm" like rsync, no attempt to compress (although of course the connection
could already be compressing e.g. if over ssh), the connection is made entirely using standard means like
ssh and docker, there are no ports to open, and even the bash program on the remote end is sent over every time
so nothing is installed remotely.

This is sufficient for editing code on a local computer and automatically replicating them to a
remote server or docker container whenever a file is created or modified.

# Usage and examples

See help with `file-replicate --help`:

    Usage: file-replicator [OPTIONS] SRC_DIR DEST_PARENT_DIR \
                           [CONNECTION_COMMAND]...

    Replicate files to another computer e.g. for remote development.

    SRC_DIR is the source directory on this machine.

    DEST_PARENT_DIR is the (absolute) destination parent directory on the
    remote machine accessed using the CONNECTION_COMMAND.

    The CONNECTION_COMMAND must result in a running instance of bash ready to
    receive commands on stdin.

    Example CONNECTION_COMMANDs include:

        ssh some.host.com bash

        docker exec -i my_container bash

        docker-compose exec -T my_container bash

    So a full use of the tool might look like:

        file-replicator my_code_dir /home/code -- docker exec -i a_container bash

    (the use of "--" prevents any further processing of command line arguments
    by file-replicator, leaving them all for docker)

    Initially, all files and required directories are recursively copied. Then
    it waits for changes before copying each modified or new file. This can be
    modified with the switches.

    Note that empty directories are not replicated until they contain a file.

    Options:
    --clean-out-first               Optionally start by cleaning out the
                                    destination directory.
    --with-initial-replication / --no-initial-replication
                                    Perform (or not) an initial replication of
                                    all files.
    --replicate-on-change / --no-replicate-on-change
                                    Perform (or not) a wait-for-change-and-
                                    replicate cycle.
    --gitignore / --no-gitignore    Use .gitignore (or not) to filter files.
    --debugging                     Print debugging information.
    --version                       Show the version and exit.
    --help                          Show this message and exit.

For example, to replicate files from local directory `my_project_dir` to directory
`/home/code/my_project_dir` on remote machine called `my.server.com`:

    file-replicator my_project_dir /home/code ssh my.server.com bash

As another example, to replicate files from local directory `my_project_dir` to directory
`/home/code/my_project_dir` in a running docker container called `my_container` on a potentially
remote host (depending upon the `DOCKER*` environment variables e.g. as set by `docker-machine eval`):

    file-replicator my_project_dir /home/code -- docker exec -i my_container bash

Or to do the same but using `docker-compose` instead:

    file-replicator my_project_dir /home/code -- docker-compose exec -T my_container bash

Lastly, as a degenerate example which doesn't actually connect to a remote machine at all
but replicates into the local `/tmp/my_project_dir`:

    file-replicator my_project_dir /tmp bash

The unit tests use this degenerate approach to test the tool.

# Limitations

Due to limitations with inotify (race conditions around watching for changes in newly created directories), it
is possible that the watching-for-changes phase becomes out of step. In which case, just restart the whole program.
The tool includes some self-restarting behaviour, but ultimately a full restart may sometimes be needed.

Information printed to stdout indicates when this happens.

# Tests

    ============================= test session starts ==============================
    platform linux -- Python 3.6.7, pytest-3.10.1, py-1.8.0, pluggy-0.12.0 -- /home/tcorbettclark/.cache/pypoetry/virtualenvs/file-replicator-py3.6/bin/python
    cachedir: .pytest_cache
    rootdir: /home/tcorbettclark/code/file-replicator, inifile:
    collecting ... collected 8 items

    tests/test_lib.py::test_empty_directories_are_copied PASSED                [ 12%]
    tests/test_lib.py::test_copy_one_file PASSED                               [ 25%]
    tests/test_lib.py::test_copy_file_with_unusual_characters_in_name PASSED   [ 37%]
    tests/test_lib.py::test_make_missing_parent_directories PASSED             [ 50%]
    tests/test_lib.py::test_replicate_all_files PASSED                         [ 62%]
    tests/test_lib.py::test_detect_and_copy_new_file PASSED                    [ 75%]
    tests/test_lib.py::test_detect_and_copy_modified_file PASSED               [ 87%]
    tests/test_lib.py::test_detect_and_copy_new_file_in_new_directories PASSED [100%]

    =========================== 8 passed in 4.00 seconds ===========================

# Contributions

Pull-requests are welcome! Please consider including tests and updating docs at the same time.

The package is maintained using poetry (https://poetry.eustace.io) and pyenv (https://github.com/pyenv/pyenv).

The code is formatted using black (https://black.readthedocs.io/en/stable) and isort (https://github.com/timothycrosley/isort).

It is tested using pytest (https://pytest.org).

# Commit checklist

1. `isort -rc .`
1. `black .`
1. `pytest -v`
1. clock version in `pyproject.toml`
1. clock version in `file_replicator/__init__.py`
1. `git tag`
1. update this README.md with the latest output from the tests
1. update this README.md with the latest output from the --help option