Squashed 'external/toxcore/c-toxcore/' content from commit 67badf69

git-subtree-dir: external/toxcore/c-toxcore
git-subtree-split: 67badf69416a74e74f6d7eb51dd96f37282b8455

toxcore/shared_key_cache.h

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+/* SPDX-License-Identifier: GPL-3.0-or-later
+ * Copyright © 2022 The TokTok team.
+ */
+
+#ifndef C_TOXCORE_TOXCORE_SHARED_KEY_CACHE_H
+#define C_TOXCORE_TOXCORE_SHARED_KEY_CACHE_H
+
+#include <stdint.h>     // uint*_t
+
+#include "crypto_core.h"
+#include "mono_time.h"
+
+/**
+ * This implements a cache for shared keys, since key generation is expensive.
+ */
+
+typedef struct Shared_Key_Cache Shared_Key_Cache;
+
+/**
+ * @brief Initializes a new shared key cache.
+ * @param time Time object for retrieving current time.
+ * @param self_secret_key Our own secret key of length CRYPTO_SECRET_KEY_SIZE,
+ * it must not change during the lifetime of the cache.
+ * @param timeout Number of milliseconds, after which a key should be evicted.
+ * @param keys_per_slot There are 256 slots, this controls how many keys are stored per slot and the size of the cache.
+ * @return nullptr on error.
+ */
+non_null()
+Shared_Key_Cache *shared_key_cache_new(const Mono_Time *time,
+                                       const uint8_t *self_secret_key,
+                                       uint64_t timeout, uint8_t keys_per_slot);
+
+/**
+ * @brief Deletes the cache and frees all resources.
+ * @param cache Cache to delete or nullptr.
+ */
+nullable(1)
+void shared_key_cache_free(Shared_Key_Cache *cache);
+
+/**
+ * @brief Looks up a key from the cache or computes it if it didn't exist yet.
+ * @param cache Cache to perform the lookup on.
+ * @param public_key Public key, used for the lookup and computation.
+ *
+ * @return The shared key of length CRYPTO_SHARED_KEY_SIZE, matching the public key and our secret key.
+ * @return nullptr on error.
+ */
+non_null()
+const uint8_t* shared_key_cache_lookup(Shared_Key_Cache *cache, const uint8_t public_key[CRYPTO_PUBLIC_KEY_SIZE]);
+
+#endif // C_TOXCORE_TOXCORE_SHARED_KEY_CACHE_H