Implement module api for aux data in rdb

Other changes:
* fix memory leak in error handling of rdb loading of type OBJ_MODULE

runtest-moduleapi

@@ -13,4 +13,4 @@ then
 fi
 
 make -C tests/modules && \
-$TCLSH tests/test_helper.tcl --single unit/moduleapi/commandfilter "${@}"
+$TCLSH tests/test_helper.tcl --single unit/moduleapi/commandfilter --single unit/moduleapi/testrdb "${@}"

src/module.c

@@ -29,6 +29,7 @@
 
 #include "server.h"
 #include "cluster.h"
+#include "rdb.h"
 #include <dlfcn.h>
 
 #define REDISMODULE_CORE 1
@@ -3078,6 +3079,11 @@ moduleType *RM_CreateDataType(RedisModuleCtx *ctx, const char *name, int encver,
         moduleTypeMemUsageFunc mem_usage;
         moduleTypeDigestFunc digest;
         moduleTypeFreeFunc free;
+        struct {
+            moduleTypeAuxLoadFunc aux_load;
+            moduleTypeAuxSaveFunc aux_save;
+            int aux_save_triggers;
+        } v2;
     } *tms = (struct typemethods*) typemethods_ptr;
 
     moduleType *mt = zcalloc(sizeof(*mt));
@@ -3089,6 +3095,11 @@ moduleType *RM_CreateDataType(RedisModuleCtx *ctx, const char *name, int encver,
     mt->mem_usage = tms->mem_usage;
     mt->digest = tms->digest;
     mt->free = tms->free;
+    if (tms->version >= 2) {
+        mt->aux_load = tms->v2.aux_load;
+        mt->aux_save = tms->v2.aux_save;
+        mt->aux_save_triggers = tms->v2.aux_save_triggers;
+    }
     memcpy(mt->name,name,sizeof(mt->name));
     listAddNodeTail(ctx->module->types,mt);
     return mt;
@@ -3355,6 +3366,36 @@ loaderr:
     return 0; /* Never reached. */
 }
 
+/* Iterate over modules, and trigger rdb aux saving for the ones modules types
+ * who asked for it. */
+ssize_t rdbSaveModulesAux(rio *rdb, int when) {
+    size_t total_written = 0;
+    dictIterator *di = dictGetIterator(modules);
+    dictEntry *de;
+
+    while ((de = dictNext(di)) != NULL) {
+        struct RedisModule *module = dictGetVal(de);
+        listIter li;
+        listNode *ln;
+
+        listRewind(module->types,&li);
+        while((ln = listNext(&li))) {
+            moduleType *mt = ln->value;
+            if (!mt->aux_save || !(mt->aux_save_triggers & when))
+                continue;
+            ssize_t ret = rdbSaveSingleModuleAux(rdb, when, mt);
+            if (ret==-1) {
+                dictReleaseIterator(di);
+                return -1;
+            }
+            total_written += ret;
+        }
+    }
+
+    dictReleaseIterator(di);
+    return total_written;
+}
+
 /* --------------------------------------------------------------------------
  * Key digest API (DEBUG DIGEST interface for modules types)
  * -------------------------------------------------------------------------- */

src/rdb.c

@@ -971,7 +971,6 @@ ssize_t rdbSaveObject(rio *rdb, robj *o, robj *key) {
         RedisModuleIO io;
         moduleValue *mv = o->ptr;
         moduleType *mt = mv->type;
-        moduleInitIOContext(io,mt,rdb,key);
 
         /* Write the "module" identifier as prefix, so that we'll be able
          * to call the right module during loading. */
@@ -980,9 +979,12 @@ ssize_t rdbSaveObject(rio *rdb, robj *o, robj *key) {
         io.bytes += retval;
 
         /* Then write the module-specific representation + EOF marker. */
+        moduleInitIOContext(io,mt,rdb,key);
         mt->rdb_save(&io,mv->value);
         retval = rdbSaveLen(rdb,RDB_MODULE_OPCODE_EOF);
-        if (retval == -1) return -1;
+        if (retval == -1)
+            io.error = 1;
+        else
             io.bytes += retval;
 
         if (io.ctx) {
@@ -1101,6 +1103,40 @@ int rdbSaveInfoAuxFields(rio *rdb, int flags, rdbSaveInfo *rsi) {
     return 1;
 }
 
+ssize_t rdbSaveSingleModuleAux(rio *rdb, int when, moduleType *mt) {
+    /* Save a module-specific aux value. */
+    RedisModuleIO io;
+    int retval = rdbSaveType(rdb, RDB_OPCODE_MODULE_AUX);
+
+    /* Write the "module" identifier as prefix, so that we'll be able
+     * to call the right module during loading. */
+    retval = rdbSaveLen(rdb,mt->id);
+    if (retval == -1) return -1;
+    io.bytes += retval;
+
+    /* write the 'when' so that we can provide it on loading */
+    retval = rdbSaveLen(rdb,when);
+    if (retval == -1) return -1;
+    io.bytes += retval;
+
+    /* Then write the module-specific representation + EOF marker. */
+    moduleInitIOContext(io,mt,rdb,NULL);
+    mt->aux_save(&io,when);
+    retval = rdbSaveLen(rdb,RDB_MODULE_OPCODE_EOF);
+    if (retval == -1)
+        io.error = 1;
+    else
+        io.bytes += retval;
+
+    if (io.ctx) {
+        moduleFreeContext(io.ctx);
+        zfree(io.ctx);
+    }
+    if (io.error)
+        return -1;
+    return io.bytes;
+}
+
 /* Produces a dump of the database in RDB format sending it to the specified
  * Redis I/O channel. On success C_OK is returned, otherwise C_ERR
  * is returned and part of the output, or all the output, can be
@@ -1122,6 +1158,7 @@ int rdbSaveRio(rio *rdb, int *error, int flags, rdbSaveInfo *rsi) {
     snprintf(magic,sizeof(magic),"REDIS%04d",RDB_VERSION);
     if (rdbWriteRaw(rdb,magic,9) == -1) goto werr;
     if (rdbSaveInfoAuxFields(rdb,flags,rsi) == -1) goto werr;
+    if (rdbSaveModulesAux(rdb, REDISMODULE_AUX_BEFORE_RDB) == -1) goto werr;
 
     for (j = 0; j < server.dbnum; j++) {
         redisDb *db = server.db+j;
@@ -1183,6 +1220,8 @@ int rdbSaveRio(rio *rdb, int *error, int flags, rdbSaveInfo *rsi) {
         di = NULL; /* So that we don't release it again on error. */
     }
 
+    if (rdbSaveModulesAux(rdb, REDISMODULE_AUX_AFTER_RDB) == -1) goto werr;
+
     /* EOF opcode */
     if (rdbSaveType(rdb,RDB_OPCODE_EOF) == -1) goto werr;
 
@@ -2089,15 +2128,11 @@ int rdbLoadRio(rio *rdb, rdbSaveInfo *rsi, int loading_aof) {
             decrRefCount(auxval);
             continue; /* Read type again. */
         } else if (type == RDB_OPCODE_MODULE_AUX) {
-            /* This is just for compatibility with the future: we have plans
+            /* Load module data that is not related to the Redis key space.
-             * to add the ability for modules to store anything in the RDB
+             * Such data can be potentially be stored both before and after the
-             * file, like data that is not related to the Redis key space.
+             * RDB keys-values section. */
-             * Such data will potentially be stored both before and after the
-             * RDB keys-values section. For this reason since RDB version 9,
-             * we have the ability to read a MODULE_AUX opcode followed by an
-             * identifier of the module, and a serialized value in "MODULE V2"
-             * format. */
             uint64_t moduleid = rdbLoadLen(rdb,NULL);
+            int when = rdbLoadLen(rdb,NULL);
             if (rioGetReadError(rdb)) goto eoferr;
             moduleType *mt = moduleTypeLookupModuleByID(moduleid);
             char name[10];
@@ -2108,10 +2143,32 @@ int rdbLoadRio(rio *rdb, rdbSaveInfo *rsi, int loading_aof) {
                 serverLog(LL_WARNING,"The RDB file contains AUX module data I can't load: no matching module '%s'", name);
                 exit(1);
             } else if (!rdbCheckMode && mt != NULL) {
-                /* This version of Redis actually does not know what to do
+                if (!mt->aux_load) {
-                 * with modules AUX data... */
+                    /* Module doesn't support AUX. */
-                serverLog(LL_WARNING,"The RDB file contains AUX module data I can't load for the module '%s'. Probably you want to use a newer version of Redis which implements aux data callbacks", name);
+                    serverLog(LL_WARNING,"The RDB file contains module AUX data, but the module '%s' doesn't seem to support it.", name);
                     exit(1);
+                }
+
+                RedisModuleIO io;
+                moduleInitIOContext(io,mt,rdb,NULL);
+                io.ver = 2;
+                /* Call the rdb_load method of the module providing the 10 bit
+                 * encoding version in the lower 10 bits of the module ID. */
+                if (mt->aux_load(&io,moduleid&1023, when) || io.error) {
+                    moduleTypeNameByID(name,moduleid);
+                    serverLog(LL_WARNING,"The RDB file contains module AUX data for the module type '%s', that the responsible module is not able to load. Check for modules log above for additional clues.", name);
+                    exit(1);
+                }
+                if (io.ctx) {
+                    moduleFreeContext(io.ctx);
+                    zfree(io.ctx);
+                }
+                uint64_t eof = rdbLoadLen(rdb,NULL);
+                if (eof != RDB_MODULE_OPCODE_EOF) {
+                    serverLog(LL_WARNING,"The RDB file contains module AUX data for the module '%s' that is not terminated by the proper module value EOF marker", name);
+                    exit(1);
+                }
+                continue;
             } else {
                 /* RDB check mode. */
                 robj *aux = rdbLoadCheckModuleValue(rdb,name);

src/rdb.h

@@ -145,6 +145,7 @@ size_t rdbSavedObjectLen(robj *o);
 robj *rdbLoadObject(int type, rio *rdb, robj *key);
 void backgroundSaveDoneHandler(int exitcode, int bysignal);
 int rdbSaveKeyValuePair(rio *rdb, robj *key, robj *val, long long expiretime);
+ssize_t rdbSaveSingleModuleAux(rio *rdb, int when, moduleType *mt);
 robj *rdbLoadStringObject(rio *rdb);
 ssize_t rdbSaveStringObject(rio *rdb, robj *obj);
 ssize_t rdbSaveRawString(rio *rdb, unsigned char *s, size_t len);

src/redismodule.h

@@ -129,6 +129,10 @@
 
 #define REDISMODULE_NOT_USED(V) ((void) V)
 
+/* Bit flags for aux_save_triggers and the aux_load and aux_save callbacks */
+#define REDISMODULE_AUX_BEFORE_RDB (1<<0)
+#define REDISMODULE_AUX_AFTER_RDB (1<<1)
+
 /* This type represents a timer handle, and is returned when a timer is
  * registered and used in order to invalidate a timer. It's just a 64 bit
  * number, because this is how each timer is represented inside the radix tree
@@ -166,6 +170,8 @@ typedef void (*RedisModuleDisconnectFunc)(RedisModuleCtx *ctx, RedisModuleBlocke
 typedef int (*RedisModuleNotificationFunc)(RedisModuleCtx *ctx, int type, const char *event, RedisModuleString *key);
 typedef void *(*RedisModuleTypeLoadFunc)(RedisModuleIO *rdb, int encver);
 typedef void (*RedisModuleTypeSaveFunc)(RedisModuleIO *rdb, void *value);
+typedef int (*RedisModuleTypeAuxLoadFunc)(RedisModuleIO *rdb, int encver, int when);
+typedef void (*RedisModuleTypeAuxSaveFunc)(RedisModuleIO *rdb, int when);
 typedef void (*RedisModuleTypeRewriteFunc)(RedisModuleIO *aof, RedisModuleString *key, void *value);
 typedef size_t (*RedisModuleTypeMemUsageFunc)(const void *value);
 typedef void (*RedisModuleTypeDigestFunc)(RedisModuleDigest *digest, void *value);
@@ -174,7 +180,7 @@ typedef void (*RedisModuleClusterMessageReceiver)(RedisModuleCtx *ctx, const cha
 typedef void (*RedisModuleTimerProc)(RedisModuleCtx *ctx, void *data);
 typedef void (*RedisModuleCommandFilterFunc) (RedisModuleCommandFilterCtx *filter);
 
-#define REDISMODULE_TYPE_METHOD_VERSION 1
+#define REDISMODULE_TYPE_METHOD_VERSION 2
 typedef struct RedisModuleTypeMethods {
     uint64_t version;
     RedisModuleTypeLoadFunc rdb_load;
@@ -183,6 +189,9 @@ typedef struct RedisModuleTypeMethods {
     RedisModuleTypeMemUsageFunc mem_usage;
     RedisModuleTypeDigestFunc digest;
     RedisModuleTypeFreeFunc free;
+    RedisModuleTypeAuxLoadFunc aux_load;
+    RedisModuleTypeAuxSaveFunc aux_save;
+    int aux_save_triggers;
 } RedisModuleTypeMethods;
 
 #define REDISMODULE_GET_API(name) \

src/server.h

@@ -536,6 +536,10 @@ typedef long long mstime_t; /* millisecond time type. */
 #define REDISMODULE_TYPE_ENCVER(id) (id & REDISMODULE_TYPE_ENCVER_MASK)
 #define REDISMODULE_TYPE_SIGN(id) ((id & ~((uint64_t)REDISMODULE_TYPE_ENCVER_MASK)) >>REDISMODULE_TYPE_ENCVER_BITS)
 
+/* Bit flags for moduleTypeAuxSaveFunc */
+#define REDISMODULE_AUX_BEFORE_RDB (1<<0)
+#define REDISMODULE_AUX_AFTER_RDB (1<<1)
+
 struct RedisModule;
 struct RedisModuleIO;
 struct RedisModuleDigest;
@@ -548,6 +552,8 @@ struct redisObject;
  * is deleted. */
 typedef void *(*moduleTypeLoadFunc)(struct RedisModuleIO *io, int encver);
 typedef void (*moduleTypeSaveFunc)(struct RedisModuleIO *io, void *value);
+typedef int (*moduleTypeAuxLoadFunc)(struct RedisModuleIO *rdb, int encver, int when);
+typedef void (*moduleTypeAuxSaveFunc)(struct RedisModuleIO *rdb, int when);
 typedef void (*moduleTypeRewriteFunc)(struct RedisModuleIO *io, struct redisObject *key, void *value);
 typedef void (*moduleTypeDigestFunc)(struct RedisModuleDigest *digest, void *value);
 typedef size_t (*moduleTypeMemUsageFunc)(const void *value);
@@ -564,6 +570,9 @@ typedef struct RedisModuleType {
     moduleTypeMemUsageFunc mem_usage;
     moduleTypeDigestFunc digest;
     moduleTypeFreeFunc free;
+    moduleTypeAuxLoadFunc aux_load;
+    moduleTypeAuxSaveFunc aux_save;
+    int aux_save_triggers;
     char name[10]; /* 9 bytes name + null term. Charset: A-Z a-z 0-9 _- */
 } moduleType;
 
@@ -1528,6 +1537,7 @@ void moduleAcquireGIL(void);
 void moduleReleaseGIL(void);
 void moduleNotifyKeyspaceEvent(int type, const char *event, robj *key, int dbid);
 void moduleCallCommandFilters(client *c);
+ssize_t rdbSaveModulesAux(rio *rdb, int when);
 
 /* Utils */
 long long ustime(void);

tests/modules/Makefile

@@ -13,12 +13,16 @@ endif
 
 .SUFFIXES: .c .so .xo .o
 
-all: commandfilter.so
+all: commandfilter.so testrdb.so
 
 .c.xo:
 	$(CC) -I../../src $(CFLAGS) $(SHOBJ_CFLAGS) -fPIC -c $< -o $@
 
 commandfilter.xo: ../../src/redismodule.h
+testrdb.xo: ../../src/redismodule.h
 
 commandfilter.so: commandfilter.xo
 	$(LD) -o $@ $< $(SHOBJ_LDFLAGS) $(LIBS) -lc
+
+testrdb.so: testrdb.xo
+	$(LD) -o $@ $< $(SHOBJ_LDFLAGS) $(LIBS) -lc

tests/modules/testrdb.c

@@ -0,0 +1,229 @@
+#include "redismodule.h"
+
+#include <string.h>
+#include <assert.h>
+
+/* Module configuration, save aux or not? */
+long long conf_aux_count = 0;
+
+/* Registered type */
+RedisModuleType *testrdb_type = NULL;
+
+/* Global values to store and persist to aux */
+RedisModuleString *before_str = NULL;
+RedisModuleString *after_str = NULL;
+
+void *testrdb_type_load(RedisModuleIO *rdb, int encver) {
+    int count = RedisModule_LoadSigned(rdb);
+    assert(count==1);
+    assert(encver==1);
+    RedisModuleString *str = RedisModule_LoadString(rdb);
+    return str;
+}
+
+void testrdb_type_save(RedisModuleIO *rdb, void *value) {
+    RedisModuleString *str = (RedisModuleString*)value;
+    RedisModule_SaveSigned(rdb, 1);
+    RedisModule_SaveString(rdb, str);
+}
+
+void testrdb_aux_save(RedisModuleIO *rdb, int when) {
+    if (conf_aux_count==1) assert(when == REDISMODULE_AUX_AFTER_RDB);
+    if (conf_aux_count==0) assert(0);
+    if (when == REDISMODULE_AUX_BEFORE_RDB) {
+        if (before_str) {
+            RedisModule_SaveSigned(rdb, 1);
+            RedisModule_SaveString(rdb, before_str);
+        } else {
+            RedisModule_SaveSigned(rdb, 0);
+        }
+    } else {
+        if (after_str) {
+            RedisModule_SaveSigned(rdb, 1);
+            RedisModule_SaveString(rdb, after_str);
+        } else {
+            RedisModule_SaveSigned(rdb, 0);
+        }
+    }
+}
+
+int testrdb_aux_load(RedisModuleIO *rdb, int encver, int when) {
+    assert(encver == 1);
+    if (conf_aux_count==1) assert(when == REDISMODULE_AUX_AFTER_RDB);
+    if (conf_aux_count==0) assert(0);
+    RedisModuleCtx *ctx = RedisModule_GetContextFromIO(rdb);
+    if (when == REDISMODULE_AUX_BEFORE_RDB) {
+        if (before_str)
+            RedisModule_FreeString(ctx, before_str);
+        before_str = NULL;
+        int count = RedisModule_LoadSigned(rdb);
+        if (count)
+            before_str = RedisModule_LoadString(rdb);
+    } else {
+        if (after_str)
+            RedisModule_FreeString(ctx, after_str);
+        after_str = NULL;
+        int count = RedisModule_LoadSigned(rdb);
+        if (count)
+            after_str = RedisModule_LoadString(rdb);
+    }
+    return REDISMODULE_OK;
+}
+
+void testrdb_type_free(void *value) {
+    RedisModule_FreeString(NULL, (RedisModuleString*)value);
+}
+
+int testrdb_set_before(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
+{
+    if (argc != 2) {
+        RedisModule_WrongArity(ctx);
+        return REDISMODULE_OK;
+    }
+
+    if (before_str)
+        RedisModule_FreeString(ctx, before_str);
+    before_str = argv[1];
+    RedisModule_RetainString(ctx, argv[1]);
+    RedisModule_ReplyWithLongLong(ctx, 1);
+    return REDISMODULE_OK;
+}
+
+int testrdb_get_before(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
+{
+    REDISMODULE_NOT_USED(argv);
+    if (argc != 1){
+        RedisModule_WrongArity(ctx);
+        return REDISMODULE_OK;
+    }
+    if (before_str)
+        RedisModule_ReplyWithString(ctx, before_str);
+    else
+        RedisModule_ReplyWithStringBuffer(ctx, "", 0);
+    return REDISMODULE_OK;
+}
+
+int testrdb_set_after(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
+{
+    if (argc != 2){
+        RedisModule_WrongArity(ctx);
+        return REDISMODULE_OK;
+    }
+
+    if (after_str)
+        RedisModule_FreeString(ctx, after_str);
+    after_str = argv[1];
+    RedisModule_RetainString(ctx, argv[1]);
+    RedisModule_ReplyWithLongLong(ctx, 1);
+    return REDISMODULE_OK;
+}
+
+int testrdb_get_after(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
+{
+    REDISMODULE_NOT_USED(argv);
+    if (argc != 1){
+        RedisModule_WrongArity(ctx);
+        return REDISMODULE_OK;
+    }
+    if (after_str)
+        RedisModule_ReplyWithString(ctx, after_str);
+    else
+        RedisModule_ReplyWithStringBuffer(ctx, "", 0);
+    return REDISMODULE_OK;
+}
+
+int testrdb_set_key(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
+{
+    if (argc != 3){
+        RedisModule_WrongArity(ctx);
+        return REDISMODULE_OK;
+    }
+
+    RedisModuleKey *key = RedisModule_OpenKey(ctx, argv[1], REDISMODULE_WRITE);
+    RedisModuleString *str = RedisModule_ModuleTypeGetValue(key);
+    if (str)
+        RedisModule_FreeString(ctx, str);
+    RedisModule_ModuleTypeSetValue(key, testrdb_type, argv[2]);
+    RedisModule_RetainString(ctx, argv[2]);
+    RedisModule_CloseKey(key);
+    RedisModule_ReplyWithLongLong(ctx, 1);
+    return REDISMODULE_OK;
+}
+
+int testrdb_get_key(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
+{
+    if (argc != 2){
+        RedisModule_WrongArity(ctx);
+        return REDISMODULE_OK;
+    }
+
+    RedisModuleKey *key = RedisModule_OpenKey(ctx, argv[1], REDISMODULE_WRITE);
+    RedisModuleString *str = RedisModule_ModuleTypeGetValue(key);
+    RedisModule_CloseKey(key);
+    RedisModule_ReplyWithString(ctx, str);
+    return REDISMODULE_OK;
+}
+
+int RedisModule_OnLoad(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
+    REDISMODULE_NOT_USED(argv);
+    REDISMODULE_NOT_USED(argc);
+
+    if (RedisModule_Init(ctx,"testrdb",1,REDISMODULE_APIVER_1) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
+    if (argc > 0)
+        RedisModule_StringToLongLong(argv[0], &conf_aux_count);
+
+    if (conf_aux_count==0) {
+        RedisModuleTypeMethods datatype_methods = {
+            .version = 1,
+            .rdb_load = testrdb_type_load,
+            .rdb_save = testrdb_type_save,
+            .aof_rewrite = NULL,
+            .digest = NULL,
+            .free = testrdb_type_free,
+        };
+
+        testrdb_type = RedisModule_CreateDataType(ctx, "test__rdb", 1, &datatype_methods);
+        if (testrdb_type == NULL)
+            return REDISMODULE_ERR;
+    } else {
+        RedisModuleTypeMethods datatype_methods = {
+            .version = REDISMODULE_TYPE_METHOD_VERSION,
+            .rdb_load = testrdb_type_load,
+            .rdb_save = testrdb_type_save,
+            .aof_rewrite = NULL,
+            .digest = NULL,
+            .free = testrdb_type_free,
+            .aux_load = testrdb_aux_load,
+            .aux_save = testrdb_aux_save,
+            .aux_save_triggers = (conf_aux_count == 1 ?
+                                  REDISMODULE_AUX_AFTER_RDB :
+                                  REDISMODULE_AUX_BEFORE_RDB | REDISMODULE_AUX_AFTER_RDB)
+        };
+
+        testrdb_type = RedisModule_CreateDataType(ctx, "test__rdb", 1, &datatype_methods);
+        if (testrdb_type == NULL)
+            return REDISMODULE_ERR;
+    }
+
+    if (RedisModule_CreateCommand(ctx,"testrdb.set.before", testrdb_set_before,"deny-oom",0,0,0) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
+    if (RedisModule_CreateCommand(ctx,"testrdb.get.before", testrdb_get_before,"",0,0,0) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
+    if (RedisModule_CreateCommand(ctx,"testrdb.set.after", testrdb_set_after,"deny-oom",0,0,0) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
+    if (RedisModule_CreateCommand(ctx,"testrdb.get.after", testrdb_get_after,"",0,0,0) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
+    if (RedisModule_CreateCommand(ctx,"testrdb.set.key", testrdb_set_key,"deny-oom",1,1,1) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
+    if (RedisModule_CreateCommand(ctx,"testrdb.get.key", testrdb_get_key,"",1,1,1) == REDISMODULE_ERR)
+        return REDISMODULE_ERR;
+
+    return REDISMODULE_OK;
+}

tests/unit/moduleapi/testrdb.tcl

@@ -0,0 +1,62 @@
+set testmodule [file normalize tests/modules/testrdb.so]
+
+proc restart_and_wait {} {
+    catch {
+        r debug restart
+    }
+
+    # wait for the server to come back up
+    set retry 50
+    while {$retry} {
+        if {[catch { r ping }]} {
+            after 100
+        } else {
+            break
+        }
+        incr retry -1
+    }
+}
+
+tags "modules" {
+    start_server [list overrides [list loadmodule "$testmodule"]] {
+        test {modules are able to persist types} {
+            r testrdb.set.key key1 value1
+            assert_equal "value1" [r testrdb.get.key key1]
+            r debug reload
+            assert_equal "value1" [r testrdb.get.key key1]
+        }
+
+        test {modules global are lost without aux} {
+            r testrdb.set.before global1
+            assert_equal "global1" [r testrdb.get.before]
+            restart_and_wait
+            assert_equal "" [r testrdb.get.before]
+        }
+    }
+
+    start_server [list overrides [list loadmodule "$testmodule 2"]] {
+        test {modules are able to persist globals before and after} {
+            r testrdb.set.before global1
+            r testrdb.set.after global2
+            assert_equal "global1" [r testrdb.get.before]
+            assert_equal "global2" [r testrdb.get.after]
+            restart_and_wait
+            assert_equal "global1" [r testrdb.get.before]
+            assert_equal "global2" [r testrdb.get.after]
+        }
+
+    }
+
+    start_server [list overrides [list loadmodule "$testmodule 1"]] {
+        test {modules are able to persist globals just after} {
+            r testrdb.set.after global2
+            assert_equal "global2" [r testrdb.get.after]
+            restart_and_wait
+            assert_equal "global2" [r testrdb.get.after]
+        }
+    }
+
+
+    # TODO: test short read handling
+
+}