Support MIRAGE_CACHE_DIR env variable

README.md

@@ -73,11 +73,15 @@ or *~/.config/mirage/settings.json*.
 For Flatpak users, this will be
 *~/.var/app/io.github.mirukana.mirage/config/mirage* instead.
 
-The config folder where *settings.json* is located can be overriden by
+The config folder where *accounts.json* and  *settings.json* is located can be
-setting the `MIRAGE_CONFIG_DIR` environment variable.  
+overriden by setting the `MIRAGE_CONFIG_DIR` environment variable.  
-The user data folder where *themes*, saved encryption data and other files
+
+The user data folder where *themes*, encryption data and interface states
 are saved can be overriden with `MIRAGE_DATA_DIR`.
 
+The cache folder where downloaded files and thumbnails are saved can be
+overriden with `MIRAGE_CACHE_DIR`.
+
 The `theme` setting can be:
 
 - The filename of a built-in theme (`Midnight.qpl` or `Glass.qpl`)

src/backend/backend.py

@@ -2,6 +2,7 @@
 
 import asyncio
 import logging as log
+import os
 import sys
 import traceback
 from pathlib import Path
@@ -102,7 +103,10 @@ class Backend:
         self.send_locks: DefaultDict[str, asyncio.Lock] = \
                 DefaultDict(asyncio.Lock)  # {room_id: lock}
 
-        cache_dir                    = Path(self.appdirs.user_cache_dir)
+        cache_dir = Path(
+            os.environ.get("MIRAGE_CACHE_DIR") or self.appdirs.user_cache_dir,
+        )
+
         self.media_cache: MediaCache = MediaCache(self, cache_dir)