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https://github.com/karlicoss/arctee

Atomic tee
https://github.com/karlicoss/arctee

backup data-liberation export

Last synced: 6 days ago
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Atomic tee

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README 

        
#+EXPORT_EXCLUDE_TAGS: noexport



#+begin_src python :exports output :results replace raw

import arctee 

return arctee.__doc__

#+end_src



#+RESULTS:



Helper script to run your data exports.

It works kind of like [[https://en.wikipedia.org/wiki/Tee_(command)][*tee* command]], but:



- *a*: writes output atomically

- *r*: supports retrying command

- *c*: supports compressing output



You can read more on how it's used [[https://beepb00p.xyz/exports.html#arctee][here]].



* Motivation

Many things are very common to all data exports, regardless of the source.

In the vast majority of cases, you want to fetch some data, save it in a file (e.g. JSON) along with a timestamp and potentially compress.



This script aims to minimize the common boilerplate:



- =path= argument allows easy ISO8601 timestamping and guarantees atomic writing, so you'd never end up with corrupted exports.

- =--compression= allows to compress simply by passing the extension. No more =tar -zcvf=!

- =--retries= allows easy exponential backoff in case service you're querying is flaky.



Example:



: arctee '/exports/rtm/{utcnow}.ical.zstd' --compression zstd --retries 3 -- /soft/export/rememberthemilk.py



1. runs =/soft/export/rememberthemilk.py=, retrying it up to three times if it fails



   The script is expected to dump its result in stdout; stderr is simply passed through.

2. once the data is fetched it's compressed as =zstd=

3. timestamp is computed and compressed data is written to =/exports/rtm/20200102T170015Z.ical.zstd=



* Do you really need a special script for that?



- why not use =date= command for timestamps?



  passing =$(date -Iseconds --utc).json= as =path= works, however I need it for *most* of my exports; so it ends up polluting my crontabs.



Next, I want to do several things one after another here.

That sounds like a perfect candidate for *pipes*, right?

Sadly, there are serious caveats:



- *pipe errors don't propagate*. If one parts of your pipe fail, it doesn't fail everything



  That's a major problem that often leads to unexpected behaviours.



  In bash you can fix this by setting =set -o pipefail=. However:



  - default cron shell is =/bin/sh=. Ok, you can change it to ~SHELL=/bin/bash~, but

  - you can't set it to =/bin/bash -o pipefail=



    You'd have to prepend all of your pipes with =set -o pipefail=, which is quite boilerplaty



- you can't use pipes for *retrying*; you need some wrapper script anyway



  E.g. similar to how you need a wrapper script when you want to stop your program on timeout.



- it's possible to use pipes for atomically writing output to a file, however I haven't found any existing tools to do that



  E.g. I want something like =curl https://some.api/get-data | tee --atomic /path/to/data.sjon=.



  If you know any existing tool please let me know!



- it's possible to pipe compression



  However due to the above concerns (timestamping/retrying/atomic writing), it has to be part of the script as well.



It feels that cron isn't a suitable tool for my needs due to pipe handling and the need for retries, however I haven't found a better alternative.

If you think any of these things can be simplified, I'd be happy to know and remove them in favor of more standard solutions!



* Installation



This can be installed with pip by running: =pip3 install --user git+https://github.com/karlicoss/arctee=



You can also manually install this by installing =atomicwrites= (=pip3 install atomicwrites=) and downloading and running =arctee.py= directly



** Optional Dependencies

- =pip3 install --user backoff=



  [[https://github.com/litl/backoff][backoff]] is a library to simplify backoff and retrying. Only necessary if you want to use --retries--.

- =apt install atool=



  [[https://www.nongnu.org/atool][atool]] is a tool to create archives in any format. Only necessary if you want to use compression.



# end of autogenerated stuff



* Usage



#+begin_src sh :results output :exports output

arctee --help

#+end_src



# TODO ugh. seems that github chokes over #+RESULT: here

#+begin_example

usage: arctee [-h] [-r RETRIES] [-c COMPRESSION] path



Wrapper for automating boilerplate for reliable and regular data exports.



Example: arctee '/exports/rtm/{utcnow}.ical.zstd' --compression zstd --retries 3 -- /soft/export/rememberthemilk.py --user "[email protected]"



Arguments past '--' are the actuall command to run.



positional arguments:

  path                  Path with borg-style placeholders. Supported: {utcnow}, {hostname}, {platform}.



                        Example: '/exports/pocket/pocket_{utcnow}.json'



                        (see https://manpages.debian.org/testing/borgbackup/borg-placeholders.1.en.html)



optional arguments:

  -h, --help            show this help message and exit

  -r RETRIES, --retries RETRIES

                        Total number of tries, 1 (default) means only try once. Uses exponential backoff.

  -c COMPRESSION, --compression COMPRESSION

                        Set compression format.



                        See 'man apack' for list of supported formats. In addition, 'zstd' is also supported.

#+end_example



* TODOs                                                            :noexport: