cached-json-file: Locally cache a json file obtained by http

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A small library for caching a slow-changing remote json file in a specified directory (under "~/.cache/"). When the json is requested and the cache file is still fresh enough it is read directly from the local cache, otherwise the cached file is refreshed first.

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Versions 0.1.0,, 0.1.1
Change log
Dependencies aeson, base (<5), bytestring, directory, filepath, http-query, time, xdg-basedir [details]
License BSD-3-Clause
Copyright 2021 Jens Petersen <>
Author Jens Petersen <>
Maintainer Jens Petersen <>
Category Network
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Source repo head: git clone
Uploaded by JensPetersen at 2021-12-27T09:52:14Z



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A Haskell library providing a cached json file.

Useful for frequently used programs that use some remote json data which changes rather slowly (like in hours, days, weeks or months), where it is not critical to have always the latest data immediately.


getCachedJSON dir file url minutes caches the json obtained from url in ~/.cache/dir/file for minutes.


import System.Cached.JSON

getSnapshots :: IO Object
getSnapshots =
  getCachedJSON "stackage-snapshots" "snapshots.json" "" 180

main = getSnapshots >>= print

Each time you run this program within 3 hours the data will be read from the local cache file ~/.cache/stackage-snapshots/snapshots.json rather than re-downloading it each time, which helps to speed up the program and avoid unnecessary web queries.

There is also getCachedJSONQuery prog jsonfile webquery minutes which uses webquery :: (FromJSON a, ToJSON a) => IO a to download the json data.

Currently the smallest possible cache time is 1 minute.