src/apps/common: rewrite cache to use getters/setters

src/apps/common/cache.py

@@ -1,18 +1,25 @@
-seed = None
+_seed, _state = None, None
 
 
 def get_state():
-    global seed
-    if seed is None:
-        return None
-    else:
-        from trezor.crypto import bip32
-        from trezor.crypto.hashlib import blake2s
-        node = bip32.from_seed(seed, 'secp256k1')
-        state = blake2s(node.public_key()).digest()
-        return state
+    global _state
+    return _state
+
+
+def get_seed():
+    global _seed
+    return _seed
+
+
+def set_seed(seed):
+    from trezor.crypto import bip32
+    from trezor.crypto.hashlib import blake2s
+    node = bip32.from_seed(seed, 'secp256k1')
+    state = blake2s(node.public_key()).digest()
+    global _seed, _state
+    _seed, _state = seed, state
 
 
 def clear():
-    global seed
-    seed = None
+    global _seed, _state
+    _seed, _state = None

src/apps/common/seed.py

@@ -15,9 +15,10 @@ async def derive_node(ctx: wire.Context, path=[], curve_name=_DEFAULT_CURVE):
 
 async def _get_seed(ctx: wire.Context) -> bytes:
     from . import cache
-    if cache.seed is None:
-        cache.seed = await _compute_seed(ctx)
-    return cache.seed
+    if cache.get_seed() is None:
+        seed = await _compute_seed(ctx)
+        cache.set_seed(seed)
+    return cache.get_seed()
 
 
 async def _compute_seed(ctx: wire.Context) -> bytes:

src/apps/homescreen/__init__.py

@@ -10,7 +10,7 @@ async def respond_Features(ctx, msg):
     from trezor.messages.Features import Features
 
     if msg.__qualname__ == 'Initialize':
-        if not hasattr(msg, 'state') or msg.state != cache.get_state():
+        if msg.state is None or msg.state != cache.get_state():
             cache.clear()
 
     f = Features()