Merge pull request #5944 from yossigo/command-filtering

Command Filtering API

src/module.c

@@ -49,6 +49,8 @@ struct RedisModule {
     list *types;    /* Module data types. */
     list *usedby;   /* List of modules using APIs from this one. */
     list *using;    /* List of modules we use some APIs of. */
+    list *filters;  /* List of filters the module has registered. */
+    int in_call;    /* RM_Call() nesting level */
 };
 typedef struct RedisModule RedisModule;
 
@@ -270,6 +272,25 @@ typedef struct RedisModuleDictIter {
     raxIterator ri;
 } RedisModuleDictIter;
 
+typedef struct RedisModuleCommandFilterCtx {
+    RedisModuleString **argv;
+    int argc;
+} RedisModuleCommandFilterCtx;
+
+typedef void (*RedisModuleCommandFilterFunc) (RedisModuleCommandFilterCtx *filter);
+
+typedef struct RedisModuleCommandFilter {
+    /* The module that registered the filter */
+    RedisModule *module;
+    /* Filter callback function */
+    RedisModuleCommandFilterFunc callback;
+    /* REDISMODULE_CMDFILTER_* flags */
+    int flags;
+} RedisModuleCommandFilter;
+
+/* Registered filters */
+static list *moduleCommandFilters;
+
 /* --------------------------------------------------------------------------
  * Prototypes
  * -------------------------------------------------------------------------- */
@@ -731,6 +752,7 @@ void RM_SetModuleAttribs(RedisModuleCtx *ctx, const char *name, int ver, int api
     module->types = listCreate();
     module->usedby = listCreate();
     module->using = listCreate();
+    module->filters = listCreate();
     ctx->module = module;
 }
 
@@ -2724,12 +2746,6 @@ RedisModuleCallReply *RM_Call(RedisModuleCtx *ctx, const char *cmdname, const ch
     RedisModuleCallReply *reply = NULL;
     int replicate = 0; /* Replicate this command? */
 
-    cmd = lookupCommandByCString((char*)cmdname);
-    if (!cmd) {
-        errno = EINVAL;
-        return NULL;
-    }
-
     /* Create the client and dispatch the command. */
     va_start(ap, fmt);
     c = createClient(-1);
@@ -2743,11 +2759,25 @@ RedisModuleCallReply *RM_Call(RedisModuleCtx *ctx, const char *cmdname, const ch
     c->db = ctx->client->db;
     c->argv = argv;
     c->argc = argc;
-    c->cmd = c->lastcmd = cmd;
+    if (ctx->module) ctx->module->in_call++;
+
     /* We handle the above format error only when the client is setup so that
      * we can free it normally. */
     if (argv == NULL) goto cleanup;
 
+    /* Call command filters */
+    moduleCallCommandFilters(c);
+
+    /* Lookup command now, after filters had a chance to make modifications
+     * if necessary.
+     */
+    cmd = lookupCommand(c->argv[0]->ptr);
+    if (!cmd) {
+        errno = EINVAL;
+        goto cleanup;
+    }
+    c->cmd = c->lastcmd = cmd;
+
     /* Basic arity checks. */
     if ((cmd->arity > 0 && cmd->arity != argc) || (argc < -cmd->arity)) {
         errno = EINVAL;
@@ -2797,6 +2827,7 @@ RedisModuleCallReply *RM_Call(RedisModuleCtx *ctx, const char *cmdname, const ch
     autoMemoryAdd(ctx,REDISMODULE_AM_REPLY,reply);
 
 cleanup:
+    if (ctx->module) ctx->module->in_call--;
     freeClient(c);
     return reply;
 }
@@ -4778,6 +4809,214 @@ int moduleUnregisterUsedAPI(RedisModule *module) {
     return count;
 }
 
+/* Unregister all filters registered by a module.
+ * This is called when a module is being unloaded.
+ * 
+ * Returns the number of filters unregistered. */
+int moduleUnregisterFilters(RedisModule *module) {
+    listIter li;
+    listNode *ln;
+    int count = 0;
+
+    listRewind(module->filters,&li);
+    while((ln = listNext(&li))) {
+        RedisModuleCommandFilter *filter = ln->value;
+        listNode *ln = listSearchKey(moduleCommandFilters,filter);
+        if (ln) {
+            listDelNode(moduleCommandFilters,ln);
+            count++;
+        }
+        zfree(filter);
+    }
+    return count;
+}
+
+/* --------------------------------------------------------------------------
+ * Module Command Filter API
+ * -------------------------------------------------------------------------- */
+
+/* Register a new command filter function.
+ *
+ * Command filtering makes it possible for modules to extend Redis by plugging
+ * into the execution flow of all commands.
+ *
+ * A registered filter gets called before Redis executes *any* command.  This
+ * includes both core Redis commands and commands registered by any module.  The
+ * filter applies in all execution paths including:
+ *
+ * 1. Invocation by a client.
+ * 2. Invocation through `RedisModule_Call()` by any module.
+ * 3. Invocation through Lua 'redis.call()`.
+ * 4. Replication of a command from a master.
+ *
+ * The filter executes in a special filter context, which is different and more
+ * limited than a RedisModuleCtx.  Because the filter affects any command, it
+ * must be implemented in a very efficient way to reduce the performance impact
+ * on Redis.  All Redis Module API calls that require a valid context (such as
+ * `RedisModule_Call()`, `RedisModule_OpenKey()`, etc.) are not supported in a
+ * filter context.
+ *
+ * The `RedisModuleCommandFilterCtx` can be used to inspect or modify the
+ * executed command and its arguments.  As the filter executes before Redis
+ * begins processing the command, any change will affect the way the command is
+ * processed.  For example, a module can override Redis commands this way:
+ *
+ * 1. Register a `MODULE.SET` command which implements an extended version of
+ *    the Redis `SET` command.
+ * 2. Register a command filter which detects invocation of `SET` on a specific
+ *    pattern of keys.  Once detected, the filter will replace the first
+ *    argument from `SET` to `MODULE.SET`.
+ * 3. When filter execution is complete, Redis considers the new command name
+ *    and therefore executes the module's own command.
+ *
+ * Note that in the above use case, if `MODULE.SET` itself uses
+ * `RedisModule_Call()` the filter will be applied on that call as well.  If
+ * that is not desired, the `REDISMODULE_CMDFILTER_NOSELF` flag can be set when
+ * registering the filter.
+ *
+ * The `REDISMODULE_CMDFILTER_NOSELF` flag prevents execution flows that
+ * originate from the module's own `RM_Call()` from reaching the filter.  This
+ * flag is effective for all execution flows, including nested ones, as long as
+ * the execution begins from the module's command context or a thread-safe
+ * context that is associated with a blocking command.
+ *
+ * Detached thread-safe contexts are *not* associated with the module and cannot
+ * be protected by this flag.
+ *
+ * If multiple filters are registered (by the same or different modules), they
+ * are executed in the order of registration.
+ */
+
+RedisModuleCommandFilter *RM_RegisterCommandFilter(RedisModuleCtx *ctx, RedisModuleCommandFilterFunc callback, int flags) {
+    RedisModuleCommandFilter *filter = zmalloc(sizeof(*filter));
+    filter->module = ctx->module;
+    filter->callback = callback;
+    filter->flags = flags;
+
+    listAddNodeTail(moduleCommandFilters, filter);
+    listAddNodeTail(ctx->module->filters, filter);
+    return filter;
+}
+
+/* Unregister a command filter.
+ */
+int RM_UnregisterCommandFilter(RedisModuleCtx *ctx, RedisModuleCommandFilter *filter) {
+    listNode *ln;
+
+    /* A module can only remove its own filters */
+    if (filter->module != ctx->module) return REDISMODULE_ERR;
+
+    ln = listSearchKey(moduleCommandFilters,filter);
+    if (!ln) return REDISMODULE_ERR;
+    listDelNode(moduleCommandFilters,ln);
+    
+    ln = listSearchKey(ctx->module->filters,filter);
+    if (!ln) return REDISMODULE_ERR;    /* Shouldn't happen */
+    listDelNode(ctx->module->filters,ln);
+
+    return REDISMODULE_OK;
+}
+
+void moduleCallCommandFilters(client *c) {
+    if (listLength(moduleCommandFilters) == 0) return;
+
+    listIter li;
+    listNode *ln;
+    listRewind(moduleCommandFilters,&li);
+
+    RedisModuleCommandFilterCtx filter = {
+        .argv = c->argv,
+        .argc = c->argc
+    };
+
+    while((ln = listNext(&li))) {
+        RedisModuleCommandFilter *f = ln->value;
+
+        /* Skip filter if REDISMODULE_CMDFILTER_NOSELF is set and module is
+         * currently processing a command.
+         */
+        if ((f->flags & REDISMODULE_CMDFILTER_NOSELF) && f->module->in_call) continue;
+
+        /* Call filter */
+        f->callback(&filter);
+    }
+
+    c->argv = filter.argv;
+    c->argc = filter.argc;
+}
+
+/* Return the number of arguments a filtered command has.  The number of
+ * arguments include the command itself.
+ */
+int RM_CommandFilterArgsCount(RedisModuleCommandFilterCtx *fctx)
+{
+    return fctx->argc;
+}
+
+/* Return the specified command argument.  The first argument (position 0) is
+ * the command itself, and the rest are user-provided args.
+ */
+const RedisModuleString *RM_CommandFilterArgGet(RedisModuleCommandFilterCtx *fctx, int pos)
+{
+    if (pos < 0 || pos >= fctx->argc) return NULL;
+    return fctx->argv[pos];
+}
+
+/* Modify the filtered command by inserting a new argument at the specified
+ * position.  The specified RedisModuleString argument may be used by Redis
+ * after the filter context is destroyed, so it must not be auto-memory
+ * allocated, freed or used elsewhere.
+ */
+
+int RM_CommandFilterArgInsert(RedisModuleCommandFilterCtx *fctx, int pos, RedisModuleString *arg)
+{
+    int i;
+
+    if (pos < 0 || pos > fctx->argc) return REDISMODULE_ERR;
+
+    fctx->argv = zrealloc(fctx->argv, (fctx->argc+1)*sizeof(RedisModuleString *));
+    for (i = fctx->argc; i > pos; i--) {
+        fctx->argv[i] = fctx->argv[i-1];
+    }
+    fctx->argv[pos] = arg;
+    fctx->argc++;
+
+    return REDISMODULE_OK;
+}
+
+/* Modify the filtered command by replacing an existing argument with a new one.
+ * The specified RedisModuleString argument may be used by Redis after the
+ * filter context is destroyed, so it must not be auto-memory allocated, freed
+ * or used elsewhere.
+ */
+
+int RM_CommandFilterArgReplace(RedisModuleCommandFilterCtx *fctx, int pos, RedisModuleString *arg)
+{
+    if (pos < 0 || pos >= fctx->argc) return REDISMODULE_ERR;
+
+    decrRefCount(fctx->argv[pos]);
+    fctx->argv[pos] = arg;
+
+    return REDISMODULE_OK;
+}
+
+/* Modify the filtered command by deleting an argument at the specified
+ * position.
+ */
+int RM_CommandFilterArgDelete(RedisModuleCommandFilterCtx *fctx, int pos)
+{
+    int i;
+    if (pos < 0 || pos >= fctx->argc) return REDISMODULE_ERR;
+
+    decrRefCount(fctx->argv[pos]);
+    for (i = pos; i < fctx->argc-1; i++) {
+        fctx->argv[i] = fctx->argv[i+1];
+    }
+    fctx->argc--;
+
+    return REDISMODULE_OK;
+}
+
 /* --------------------------------------------------------------------------
  * Modules API internals
  * -------------------------------------------------------------------------- */
@@ -4824,6 +5063,9 @@ void moduleInitModulesSystem(void) {
     moduleFreeContextReusedClient->flags |= CLIENT_MODULE;
     moduleFreeContextReusedClient->user = NULL; /* root user. */
 
+    /* Set up filter list */
+    moduleCommandFilters = listCreate();
+
     moduleRegisterCoreAPI();
     if (pipe(server.module_blocked_pipe) == -1) {
         serverLog(LL_WARNING,
@@ -4873,6 +5115,7 @@ void moduleLoadFromQueue(void) {
 
 void moduleFreeModuleStructure(struct RedisModule *module) {
     listRelease(module->types);
+    listRelease(module->filters);
     sdsfree(module->name);
     zfree(module);
 }
@@ -4964,6 +5207,7 @@ int moduleUnload(sds name) {
     moduleUnregisterCommands(module);
     moduleUnregisterSharedAPI(module);
     moduleUnregisterUsedAPI(module);
+    moduleUnregisterFilters(module);
 
     /* Remove any notification subscribers this module might have */
     moduleUnsubscribeNotifications(module);
@@ -5228,4 +5472,11 @@ void moduleRegisterCoreAPI(void) {
     REGISTER_API(DictCompare);
     REGISTER_API(ExportSharedAPI);
     REGISTER_API(GetSharedAPI);
+    REGISTER_API(RegisterCommandFilter);
+    REGISTER_API(UnregisterCommandFilter);
+    REGISTER_API(CommandFilterArgsCount);
+    REGISTER_API(CommandFilterArgGet);
+    REGISTER_API(CommandFilterArgInsert);
+    REGISTER_API(CommandFilterArgReplace);
+    REGISTER_API(CommandFilterArgDelete);
 }

src/modules/Makefile

@@ -13,7 +13,7 @@ endif
 
 .SUFFIXES: .c .so .xo .o
 
-all: helloworld.so hellotype.so helloblock.so testmodule.so hellocluster.so hellotimer.so hellodict.so
+all: helloworld.so hellotype.so helloblock.so testmodule.so hellocluster.so hellotimer.so hellodict.so hellofilter.so
 
 .c.xo:
 	$(CC) -I. $(CFLAGS) $(SHOBJ_CFLAGS) -fPIC -c $< -o $@
@@ -46,6 +46,10 @@ hellotimer.so: hellotimer.xo
 hellodict.xo: ../redismodule.h
 
 hellodict.so: hellodict.xo
+
+hellofilter.xo: ../redismodule.h
+
+hellofilter.so: hellofilter.xo
 	$(LD) -o $@ $< $(SHOBJ_LDFLAGS) $(LIBS) -lc
 
 testmodule.xo: ../redismodule.h

src/modules/hellofilter.c

@@ -0,0 +1,149 @@
+#define REDISMODULE_EXPERIMENTAL_API
+#include "../redismodule.h"
+
+#include <string.h>
+
+static RedisModuleString *log_key_name;
+
+static const char log_command_name[] = "hellofilter.log";
+static const char ping_command_name[] = "hellofilter.ping";
+static const char unregister_command_name[] = "hellofilter.unregister";
+static int in_log_command = 0;
+
+static RedisModuleCommandFilter *filter = NULL;
+
+int HelloFilter_UnregisterCommand(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
+{
+    (void) argc;
+    (void) argv;
+
+    RedisModule_ReplyWithLongLong(ctx,
+            RedisModule_UnregisterCommandFilter(ctx, filter));
+
+    return REDISMODULE_OK;
+}
+
+int HelloFilter_PingCommand(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
+{
+    (void) argc;
+    (void) argv;
+
+    RedisModuleCallReply *reply = RedisModule_Call(ctx, "ping", "c", "@log");
+    if (reply) {
+        RedisModule_ReplyWithCallReply(ctx, reply);
+        RedisModule_FreeCallReply(reply);
+    } else {
+        RedisModule_ReplyWithSimpleString(ctx, "Unknown command or invalid arguments");
+    }
+
+    return REDISMODULE_OK;
+}
+
+int HelloFilter_LogCommand(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
+{
+    RedisModuleString *s = RedisModule_CreateString(ctx, "", 0);
+
+    int i;
+    for (i = 1; i < argc; i++) {
+        size_t arglen;
+        const char *arg = RedisModule_StringPtrLen(argv[i], &arglen);
+
+        if (i > 1) RedisModule_StringAppendBuffer(ctx, s, " ", 1);
+        RedisModule_StringAppendBuffer(ctx, s, arg, arglen);
+    }
+
+    RedisModuleKey *log = RedisModule_OpenKey(ctx, log_key_name, REDISMODULE_WRITE|REDISMODULE_READ);
+    RedisModule_ListPush(log, REDISMODULE_LIST_HEAD, s);
+    RedisModule_CloseKey(log);
+    RedisModule_FreeString(ctx, s);
+
+    in_log_command = 1;
+
+    size_t cmdlen;
+    const char *cmdname = RedisModule_StringPtrLen(argv[1], &cmdlen);
+    RedisModuleCallReply *reply = RedisModule_Call(ctx, cmdname, "v", &argv[2], argc - 2);
+    if (reply) {
+        RedisModule_ReplyWithCallReply(ctx, reply);
+        RedisModule_FreeCallReply(reply);
+    } else {
+        RedisModule_ReplyWithSimpleString(ctx, "Unknown command or invalid arguments");
+    }
+
+    in_log_command = 0;
+
+    return REDISMODULE_OK;
+}
+
+void HelloFilter_CommandFilter(RedisModuleCommandFilterCtx *filter)
+{
+    if (in_log_command) return;  /* don't process our own RM_Call() from HelloFilter_LogCommand() */
+
+    /* Fun manipulations:
+     * - Remove @delme
+     * - Replace @replaceme
+     * - Append @insertbefore or @insertafter
+     * - Prefix with Log command if @log encounterd
+     */
+    int log = 0;
+    int pos = 0;
+    while (pos < RedisModule_CommandFilterArgsCount(filter)) {
+        const RedisModuleString *arg = RedisModule_CommandFilterArgGet(filter, pos);
+        size_t arg_len;
+        const char *arg_str = RedisModule_StringPtrLen(arg, &arg_len);
+
+        if (arg_len == 6 && !memcmp(arg_str, "@delme", 6)) {
+            RedisModule_CommandFilterArgDelete(filter, pos);
+            continue;
+        } 
+        if (arg_len == 10 && !memcmp(arg_str, "@replaceme", 10)) {
+            RedisModule_CommandFilterArgReplace(filter, pos,
+                    RedisModule_CreateString(NULL, "--replaced--", 12));
+        } else if (arg_len == 13 && !memcmp(arg_str, "@insertbefore", 13)) {
+            RedisModule_CommandFilterArgInsert(filter, pos,
+                    RedisModule_CreateString(NULL, "--inserted-before--", 19));
+            pos++;
+        } else if (arg_len == 12 && !memcmp(arg_str, "@insertafter", 12)) {
+            RedisModule_CommandFilterArgInsert(filter, pos + 1,
+                    RedisModule_CreateString(NULL, "--inserted-after--", 18));
+            pos++;
+        } else if (arg_len == 4 && !memcmp(arg_str, "@log", 4)) {
+            log = 1;
+        }
+        pos++;
+    }
+
+    if (log) RedisModule_CommandFilterArgInsert(filter, 0,
+            RedisModule_CreateString(NULL, log_command_name, sizeof(log_command_name)-1));
+}
+
+int RedisModule_OnLoad(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    if (RedisModule_Init(ctx,"hellofilter",1,REDISMODULE_APIVER_1)
+            == REDISMODULE_ERR) return REDISMODULE_ERR;
+
+    if (argc != 2) {
+        RedisModule_Log(ctx, "warning", "Log key name not specified");
+        return REDISMODULE_ERR;
+    }
+
+    long long noself = 0;
+    log_key_name = RedisModule_CreateStringFromString(ctx, argv[0]);
+    RedisModule_StringToLongLong(argv[1], &noself);
+
+    if (RedisModule_CreateCommand(ctx,log_command_name,
+                HelloFilter_LogCommand,"write deny-oom",1,1,1) == REDISMODULE_ERR)
+            return REDISMODULE_ERR;
+
+    if (RedisModule_CreateCommand(ctx,ping_command_name,
+                HelloFilter_PingCommand,"deny-oom",1,1,1) == REDISMODULE_ERR)
+            return REDISMODULE_ERR;
+
+    if (RedisModule_CreateCommand(ctx,unregister_command_name,
+                HelloFilter_UnregisterCommand,"write deny-oom",1,1,1) == REDISMODULE_ERR)
+            return REDISMODULE_ERR;
+
+    if ((filter = RedisModule_RegisterCommandFilter(ctx, HelloFilter_CommandFilter, 
+                    noself ? REDISMODULE_CMDFILTER_NOSELF : 0))
+            == NULL) return REDISMODULE_ERR;
+
+    return REDISMODULE_OK;
+}

src/redismodule.h

@@ -133,6 +133,11 @@
  * of timers that are going to expire, sorted by expire time. */
 typedef uint64_t RedisModuleTimerID;
 
+/* CommandFilter Flags */
+
+/* Do filter RedisModule_Call() commands initiated by module itself. */
+#define REDISMODULE_CMDFILTER_NOSELF    (1<<0)
+
 /* ------------------------- End of common defines ------------------------ */
 
 #ifndef REDISMODULE_CORE
@@ -151,6 +156,8 @@ typedef struct RedisModuleBlockedClient RedisModuleBlockedClient;
 typedef struct RedisModuleClusterInfo RedisModuleClusterInfo;
 typedef struct RedisModuleDict RedisModuleDict;
 typedef struct RedisModuleDictIter RedisModuleDictIter;
+typedef struct RedisModuleCommandFilterCtx RedisModuleCommandFilterCtx;
+typedef struct RedisModuleCommandFilter RedisModuleCommandFilter;
 
 typedef int (*RedisModuleCmdFunc)(RedisModuleCtx *ctx, RedisModuleString **argv, int argc);
 typedef void (*RedisModuleDisconnectFunc)(RedisModuleCtx *ctx, RedisModuleBlockedClient *bc);
@@ -163,6 +170,7 @@ typedef void (*RedisModuleTypeDigestFunc)(RedisModuleDigest *digest, void *value
 typedef void (*RedisModuleTypeFreeFunc)(void *value);
 typedef void (*RedisModuleClusterMessageReceiver)(RedisModuleCtx *ctx, const char *sender_id, uint8_t type, const unsigned char *payload, uint32_t len);
 typedef void (*RedisModuleTimerProc)(RedisModuleCtx *ctx, void *data);
+typedef void (*RedisModuleCommandFilterFunc) (RedisModuleCommandFilterCtx *filter);
 
 #define REDISMODULE_TYPE_METHOD_VERSION 1
 typedef struct RedisModuleTypeMethods {
@@ -339,6 +347,13 @@ void REDISMODULE_API_FUNC(RedisModule_SetDisconnectCallback)(RedisModuleBlockedC
 void REDISMODULE_API_FUNC(RedisModule_SetClusterFlags)(RedisModuleCtx *ctx, uint64_t flags);
 int REDISMODULE_API_FUNC(RedisModule_ExportSharedAPI)(RedisModuleCtx *ctx, const char *apiname, void *func);
 void *REDISMODULE_API_FUNC(RedisModule_GetSharedAPI)(RedisModuleCtx *ctx, const char *apiname);
+RedisModuleCommandFilter *REDISMODULE_API_FUNC(RedisModule_RegisterCommandFilter)(RedisModuleCtx *ctx, RedisModuleCommandFilterFunc cb, int flags);
+int REDISMODULE_API_FUNC(RedisModule_UnregisterCommandFilter)(RedisModuleCtx *ctx, RedisModuleCommandFilter *filter);
+int REDISMODULE_API_FUNC(RedisModule_CommandFilterArgsCount)(RedisModuleCommandFilterCtx *fctx);
+const RedisModuleString *REDISMODULE_API_FUNC(RedisModule_CommandFilterArgGet)(RedisModuleCommandFilterCtx *fctx, int pos);
+int REDISMODULE_API_FUNC(RedisModule_CommandFilterArgInsert)(RedisModuleCommandFilterCtx *fctx, int pos, RedisModuleString *arg);
+int REDISMODULE_API_FUNC(RedisModule_CommandFilterArgReplace)(RedisModuleCommandFilterCtx *fctx, int pos, RedisModuleString *arg);
+int REDISMODULE_API_FUNC(RedisModule_CommandFilterArgDelete)(RedisModuleCommandFilterCtx *fctx, int pos);
 #endif
 
 /* This is included inline inside each Redis module. */
@@ -502,6 +517,13 @@ static int RedisModule_Init(RedisModuleCtx *ctx, const char *name, int ver, int
     REDISMODULE_GET_API(SetClusterFlags);
     REDISMODULE_GET_API(ExportSharedAPI);
     REDISMODULE_GET_API(GetSharedAPI);
+    REDISMODULE_GET_API(RegisterCommandFilter);
+    REDISMODULE_GET_API(UnregisterCommandFilter);
+    REDISMODULE_GET_API(CommandFilterArgsCount);
+    REDISMODULE_GET_API(CommandFilterArgGet);
+    REDISMODULE_GET_API(CommandFilterArgInsert);
+    REDISMODULE_GET_API(CommandFilterArgReplace);
+    REDISMODULE_GET_API(CommandFilterArgDelete);
 #endif
 
     if (RedisModule_IsModuleNameBusy && RedisModule_IsModuleNameBusy(name)) return REDISMODULE_ERR;

src/scripting.c

@@ -462,6 +462,11 @@ int luaRedisGenericCommand(lua_State *lua, int raise_error) {
     c->argc = argc;
     c->user = server.lua_caller->user;
 
+    /* Process module hooks */
+    moduleCallCommandFilters(c);
+    argv = c->argv;
+    argc = c->argc;
+
     /* Log the command if debugging is active. */
     if (ldb.active && ldb.step) {
         sds cmdlog = sdsnew("<redis>");

src/server.c

@@ -3268,6 +3268,8 @@ void call(client *c, int flags) {
  * other operations can be performed by the caller. Otherwise
  * if C_ERR is returned the client was destroyed (i.e. after QUIT). */
 int processCommand(client *c) {
+    moduleCallCommandFilters(c);
+
     /* The QUIT command is handled separately. Normal command procs will
      * go through checking for replication and QUIT will cause trouble
      * when FORCE_REPLICATION is enabled and would be implemented in

src/server.h

@@ -1492,7 +1492,7 @@ size_t moduleCount(void);
 void moduleAcquireGIL(void);
 void moduleReleaseGIL(void);
 void moduleNotifyKeyspaceEvent(int type, const char *event, robj *key, int dbid);
-
+void moduleCallCommandFilters(client *c);
 
 /* Utils */
 long long ustime(void);

tests/modules/commandfilter.tcl

@@ -0,0 +1,84 @@
+set testmodule [file normalize src/modules/hellofilter.so]
+
+start_server {tags {"modules"}} {
+    r module load $testmodule log-key 0
+
+    test {Command Filter handles redirected commands} {
+        r set mykey @log
+        r lrange log-key 0 -1
+    } "{set mykey @log}"
+
+    test {Command Filter can call RedisModule_CommandFilterArgDelete} {
+        r rpush mylist elem1 @delme elem2
+        r lrange mylist 0 -1
+    } {elem1 elem2}
+
+    test {Command Filter can call RedisModule_CommandFilterArgInsert} {
+        r del mylist
+        r rpush mylist elem1 @insertbefore elem2 @insertafter elem3
+        r lrange mylist 0 -1
+    } {elem1 --inserted-before-- @insertbefore elem2 @insertafter --inserted-after-- elem3}
+
+    test {Command Filter can call RedisModule_CommandFilterArgReplace} {
+        r del mylist
+        r rpush mylist elem1 @replaceme elem2
+        r lrange mylist 0 -1
+    } {elem1 --replaced-- elem2}
+
+    test {Command Filter applies on RM_Call() commands} {
+        r del log-key
+        r hellofilter.ping
+        r lrange log-key 0 -1
+    } "{ping @log}"
+
+    test {Command Filter applies on Lua redis.call()} {
+        r del log-key
+        r eval "redis.call('ping', '@log')" 0
+        r lrange log-key 0 -1
+    } "{ping @log}"
+
+    test {Command Filter applies on Lua redis.call() that calls a module} {
+        r del log-key
+        r eval "redis.call('hellofilter.ping')" 0
+        r lrange log-key 0 -1
+    } "{ping @log}"
+
+    test {Command Filter is unregistered implicitly on module unload} {
+        r del log-key
+        r module unload hellofilter
+        r set mykey @log
+        r lrange log-key 0 -1
+    } {}
+
+    r module load $testmodule log-key 0
+
+    test {Command Filter unregister works as expected} {
+        # Validate reloading succeeded
+        r del log-key
+        r set mykey @log
+        assert_equal "{set mykey @log}" [r lrange log-key 0 -1]
+
+        # Unregister
+        r hellofilter.unregister
+        r del log-key
+
+        r set mykey @log
+        r lrange log-key 0 -1
+    } {}
+
+    r module unload hellofilter
+    r module load $testmodule log-key 1
+
+    test {Command Filter REDISMODULE_CMDFILTER_NOSELF works as expected} {
+        r set mykey @log
+        assert_equal "{set mykey @log}" [r lrange log-key 0 -1]
+
+        r del log-key
+        r hellofilter.ping
+        assert_equal {} [r lrange log-key 0 -1]
+
+        r eval "redis.call('hellofilter.ping')" 0
+        assert_equal {} [r lrange log-key 0 -1]
+    }
+
+} 

tests/test_helper.tcl

@@ -63,6 +63,7 @@ set ::all_tests {
     unit/lazyfree
     unit/wait
     unit/pendingquerybuf
+    modules/commandfilter
 }
 # Index to the next test to run in the ::all_tests list.
 set ::next_test 0