add todo

** 2018-05-06 optparse-applicative :: Stackage Server

https://www.stackage.org/lts-10.3/package/optparse-applicative-0.14.0.0

* later                                                               :entry:

** 2022-03-12 drop redis-server as rd-api dependency.

- use a built-in key-value db. such as Berkeley db, sqlite3, or leveldb.

  use a well known path for the db name.

  $HOME/.cache/reliable-downloader/rd-api.db

- 

** 2018-05-07 loopUntilAllBlocksReady, how to track progress?

use a thread pool to download blocks, print overall progress when some parts

done or some time elapsed.

* current                                                             :entry:

** 

** 2022-03-12 improve logging on rd-api and rd client.

- For big files, when there is a lot of blocks, rd-api default log is too

  much.

  default INFO level log should be easy to read.

  just enough for the user to understand what's going on.

- on client side, "block xx fetched" is not as useful as "xx/xx block fetched,

  xx%"

- 

** 2021-10-07 When combine blocks to final file, do not use more disk space than original file size.

One way is, open target file in write mode, append block 0, remove block 0.

Append block 1, remove block 1.

...

Until last block.

But this will fail if there is a disk failure.

Maybe only do this when local disk is low on space.

Is there an API that atomically combine two files? Reuse existing disk sectors

of the two files.

- What's the current combine logic?

** 2019-02-28 bug: rd-api -d java/

option -d: cannot parse value `java/'