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+/*
+ * Copyright (c) 2021, Redis Ltd.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   * Redistributions of source code must retain the above copyright notice,
+ *     this list of conditions and the following disclaimer.
+ *   * Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *   * Neither the name of Redis nor the names of its contributors may be used
+ *     to endorse or promote products derived from this software without
+ *     specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef __FUNCTIONS_H_
+#define __FUNCTIONS_H_
+
+/*
+ * functions.c unit provides the Redis Functions API:
+ * * FUNCTION CREATE
+ * * FUNCTION CALL
+ * * FUNCTION DELETE
+ * * FUNCTION KILL
+ * * FUNCTION INFO
+ *
+ * Also contains implementation for:
+ * * Save/Load function from rdb
+ * * Register engines
+ */
+
+#include "server.h"
+#include "script.h"
+#include "redismodule.h"
+
+typedef struct functionLibInfo functionLibInfo;
+
+typedef struct engine {
+    /* engine specific context */
+    void *engine_ctx;
+
+    /* Create function callback, get the engine_ctx, and function code
+     * engine_ctx - opaque struct that was created on engine initialization
+     * li - library information that need to be provided and when add functions
+     * code - the library code
+     * timeout - timeout for the library creation (0 for no timeout)
+     * err - description of error (if occurred)
+     * returns NULL on error and set sds to be the error message */
+    int (*create)(void *engine_ctx, functionLibInfo *li, sds code, size_t timeout, sds *err);
+
+    /* Invoking a function, r_ctx is an opaque object (from engine POV).
+     * The r_ctx should be used by the engine to interaction with Redis,
+     * such interaction could be running commands, set resp, or set
+     * replication mode
+     */
+    void (*call)(scriptRunCtx *r_ctx, void *engine_ctx, void *compiled_function,
+            robj **keys, size_t nkeys, robj **args, size_t nargs);
+
+    /* get current used memory by the engine */
+    size_t (*get_used_memory)(void *engine_ctx);
+
+    /* Return memory overhead for a given function,
+     * such memory is not counted as engine memory but as general
+     * structs memory that hold different information */
+    size_t (*get_function_memory_overhead)(void *compiled_function);
+
+    /* Return memory overhead for engine (struct size holding the engine)*/
+    size_t (*get_engine_memory_overhead)(void *engine_ctx);
+
+    /* free the given function */
+    void (*free_function)(void *engine_ctx, void *compiled_function);
+} engine;
+
+/* Hold information about an engine.
+ * Used on rdb.c so it must be declared here. */
+typedef struct engineInfo {
+    sds name;       /* Name of the engine */
+    engine *engine; /* engine callbacks that allows to interact with the engine */
+    client *c;      /* Client that is used to run commands */
+} engineInfo;
+
+/* Hold information about the specific function.
+ * Used on rdb.c so it must be declared here. */
+typedef struct functionInfo {
+    sds name;            /* Function name */
+    void *function;      /* Opaque object that set by the function's engine and allow it
+                            to run the function, usually it's the function compiled code. */
+    functionLibInfo* li; /* Pointer to the library created the function */
+    sds desc;            /* Function description */
+    uint64_t f_flags;    /* Function flags */
+} functionInfo;
+
+/* Hold information about the specific library.
+ * Used on rdb.c so it must be declared here. */
+struct functionLibInfo {
+    sds name;        /* Library name */
+    dict *functions; /* Functions dictionary */
+    engineInfo *ei;  /* Pointer to the function engine */
+    sds code;        /* Library code */
+};
+
+int functionsRegisterEngine(const char *engine_name, engine *engine_ctx);
+sds functionsCreateWithLibraryCtx(sds code, int replace, sds* err, functionsLibCtx *lib_ctx, size_t timeout);
+unsigned long functionsMemory(void);
+unsigned long functionsMemoryOverhead(void);
+unsigned long functionsNum(void);
+unsigned long functionsLibNum(void);
+dict* functionsLibGet(void);
+size_t functionsLibCtxfunctionsLen(functionsLibCtx *functions_ctx);
+functionsLibCtx* functionsLibCtxGetCurrent(void);
+functionsLibCtx* functionsLibCtxCreate(void);
+void functionsLibCtxClearCurrent(int async);
+void functionsLibCtxFree(functionsLibCtx *lib_ctx);
+void functionsLibCtxClear(functionsLibCtx *lib_ctx);
+void functionsLibCtxSwapWithCurrent(functionsLibCtx *lib_ctx);
+
+int functionLibCreateFunction(sds name, void *function, functionLibInfo *li, sds desc, uint64_t f_flags, sds *err);
+
+int luaEngineInitEngine(void);
+int functionsInit(void);
+
+#endif /* __FUNCTIONS_H_ */