Add in-memory support.

fastapi_cache/backends/inmemory.py

@@ -0,0 +1,46 @@
+import time
+from dataclasses import dataclass
+from threading import Lock
+from typing import Dict, Optional, Tuple
+
+from fastapi_cache.backends import Backend
+
+
+@dataclass
+class Value:
+    data: str
+    ttl_ts: int
+
+
+class InMemoryBackend(Backend):
+    _store: Dict[str, Value] = {}
+    _lock = Lock()
+
+    @property
+    def _now(self) -> int:
+        return int(time.time())
+
+    def _get(self, key: str):
+        v = self._store.get(key)
+        if v:
+            if v.ttl_ts < self._now:
+                del self._store[key]
+            else:
+                return v
+
+    async def get_with_ttl(self, key: str) -> Tuple[int, Optional[str]]:
+        with self._lock:
+            v = self._get(key)
+            if v:
+                return v.ttl_ts - self._now, v.data
+            return 0, None
+
+    async def get(self, key: str) -> str:
+        with self._lock:
+            v = self._get(key)
+            if v:
+                return v.data
+
+    async def set(self, key: str, value: str, expire: int = None):
+        with self._lock:
+            self._store[key] = Value(value, self._now + expire)