change default cache directory for unix systems

Use either $XDG_CACHE_HOME or ~/.cache (if the former isn't set)
and store potentially sensitive cookies and tokens in a user's
home directory and not in the world-readable /tmp.

docs/configuration.rst

@@ -1492,7 +1492,8 @@ cache.file
 ----------
 =========== =====
 Type        |Path|_
-Default     |tempfile.gettempdir()|_ + ``".gallery-dl.cache"``
+Default     * |tempfile.gettempdir()|_ + ``".gallery-dl.cache"`` on Windows
+            * (``$XDG_CACHE_HOME`` or ``"~/.cache"``) + ``".gallery-dl.cache"`` on all other platforms
 Description Path of the SQLite3 database used to cache login sessions,
             cookies and API tokens across `gallery-dl` invocations.
 

gallery_dl/cache.py

@@ -189,13 +189,17 @@ def clear():
 
 def _path():
     path = config.get(("cache", "file"), -1)
+    if path != -1:
+        return util.expand_path(path)
 
-    if path == -1:
+    if os.name == "nt":
         import tempfile
-        import os.path
-        return os.path.join(tempfile.gettempdir(), ".gallery-dl.cache")
+        cachedir = tempfile.gettempdir()
+    else:
+        cachedir = util.expand_path(
+            os.environ.get("XDG_CACHE_HOME", "~/.cache"))
 
-    return util.expand_path(path)
+    return os.path.join(cachedir, ".gallery-dl.cache")
 
 
 try:

gallery_dl/version.py

@@ -6,4 +6,4 @@
 # it under the terms of the GNU General Public License version 2 as
 # published by the Free Software Foundation.
 
-__version__ = "1.9.1-dev"
+__version__ = "1.10.0-dev"