Modules: DEBUG DIGEST interface.

src/debug.c

@@ -239,6 +239,15 @@ void computeDatasetDigest(unsigned char *final) {
                     xorDigest(digest,eledigest,20);
                 }
                 hashTypeReleaseIterator(hi);
+            } else if (o->type == OBJ_MODULE) {
+                RedisModuleDigest md;
+                moduleValue *mv = o->ptr;
+                moduleType *mt = mv->type;
+                moduleInitDigestContext(md);
+                if (mt->digest) {
+                    mt->digest(&md,mv->value);
+                    xorDigest(digest,md.x,sizeof(md.x));
+                }
             } else {
                 serverPanic("Unknown object type");
             }

src/module.c

@@ -3057,6 +3057,66 @@ loaderr:
     return 0; /* Never reached. */
 }
 
+/* --------------------------------------------------------------------------
+ * Key digest API (DEBUG DIGEST interface for modules types)
+ * -------------------------------------------------------------------------- */
+
+/* Add a new element to the digest. This function can be called multiple times
+ * one element after the other, for all the elements that constitute a given
+ * data structure. The function call must be followed by the call to
+ * `RedisModule_DigestEndSequence` eventually, when all the elements that are
+ * always in a given order are added. See the Redis Modules data types
+ * documentation for more info. However this is a quick example that uses Redis
+ * data types as an example.
+ *
+ * To add a sequence of unordered elements (for example in the case of a Redis
+ * Set), the pattern to use is:
+ *
+ * foreach element {
+ *     AddElement(element);
+ *     EndSequence();
+ * }
+ *
+ * Because Sets are not ordered, so every element added has a position that
+ * does not depend from the other. However if instead our elements are
+ * ordered in pairs, like field-value pairs of an Hash, then one should
+ * use:
+ *
+ * foreach key,value {
+ *     AddElement(key);
+ *     AddElement(value);
+ *     EndSquence();
+ * }
+ *
+ * Because the key and value will be always in the above order, while instead
+ * the single key-value pairs, can appear in any position into a Redis hash.
+ *
+ * A list of ordered elements would be implemented with:
+ *
+ * foreach element {
+ *     AddElement(element);
+ * }
+ * EndSequence();
+ *
+ */
+void RM_DigestAddStringBuffer(RedisModuleDigest *md, unsigned char *ele, size_t len) {
+    mixDigest(md->o,ele,len);
+}
+
+/* Like `RedisModule_DigestAddStringBuffer()` but takes a long long as input
+ * that gets converted into a string before adding it to the digest. */
+void RM_DigestAddLongLong(RedisModuleDigest *md, long long ll) {
+    char buf[LONG_STR_SIZE];
+    size_t len = ll2string(buf,sizeof(buf),ll);
+    mixDigest(md->o,buf,len);
+}
+
+/* See the doucmnetation for `RedisModule_DigestAddElement()`. */
+void RM_DigestEndSequence(RedisModuleDigest *md) {
+    xorDigest(md->x,md->o,sizeof(md->o));
+    memset(md->o,0,sizeof(md->o));
+}
+
 /* --------------------------------------------------------------------------
  * AOF API for modules data types
  * -------------------------------------------------------------------------- */
@@ -3818,4 +3878,7 @@ void moduleRegisterCoreAPI(void) {
     REGISTER_API(FreeThreadSafeContext);
     REGISTER_API(ThreadSafeContextLock);
     REGISTER_API(ThreadSafeContextUnlock);
+    REGISTER_API(DigestAddStringBuffer);
+    REGISTER_API(DigestAddLongLong);
+    REGISTER_API(DigestEndSequence);
 }

src/modules/hellotype.c

@@ -238,6 +238,16 @@ void HelloTypeFree(void *value) {
     HelloTypeReleaseObject(value);
 }
 
+void HelloTypeDigest(RedisModuleDigest *md, void *value) {
+    struct HelloTypeObject *hto = value;
+    struct HelloTypeNode *node = hto->head;
+    while(node) {
+        RedisModule_DigestAddLongLong(md,node->value);
+        node = node->next;
+    }
+    RedisModule_DigestEndSequence(md);
+}
+
 /* This function must be present on each Redis module. It is used in order to
  * register the commands into the Redis server. */
 int RedisModule_OnLoad(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
@@ -253,7 +263,8 @@ int RedisModule_OnLoad(RedisModuleCtx *ctx, RedisModuleString **argv, int argc)
         .rdb_save = HelloTypeRdbSave,
         .aof_rewrite = HelloTypeAofRewrite,
         .mem_usage = HelloTypeMemUsage,
-        .free = HelloTypeFree
+        .free = HelloTypeFree,
+        .digest = HelloTypeDigest
     };
 
     HelloType = RedisModule_CreateDataType(ctx,"hellotype",0,&tm);

src/redismodule.h

@@ -218,6 +218,9 @@ RedisModuleCtx *REDISMODULE_API_FUNC(RedisModule_GetThreadSafeContext)(RedisModu
 void REDISMODULE_API_FUNC(RedisModule_FreeThreadSafeContext)(RedisModuleCtx *ctx);
 void REDISMODULE_API_FUNC(RedisModule_ThreadSafeContextLock)(RedisModuleCtx *ctx);
 void REDISMODULE_API_FUNC(RedisModule_ThreadSafeContextUnlock)(RedisModuleCtx *ctx);
+void REDISMODULE_API_FUNC(RedisModule_DigestAddStringBuffer)(RedisModuleDigest *md, unsigned char *ele, size_t len);
+void REDISMODULE_API_FUNC(RedisModule_DigestAddLongLong)(RedisModuleDigest *md, long long ele);
+void REDISMODULE_API_FUNC(RedisModule_DigestEndSequence)(RedisModuleDigest *md);
 
 /* This is included inline inside each Redis module. */
 static int RedisModule_Init(RedisModuleCtx *ctx, const char *name, int ver, int apiver) __attribute__((unused));
@@ -330,6 +333,9 @@ static int RedisModule_Init(RedisModuleCtx *ctx, const char *name, int ver, int
     REDISMODULE_GET_API(FreeThreadSafeContext);
     REDISMODULE_GET_API(ThreadSafeContextLock);
     REDISMODULE_GET_API(ThreadSafeContextUnlock);
+    REDISMODULE_GET_API(DigestAddStringBuffer);
+    REDISMODULE_GET_API(DigestAddLongLong);
+    REDISMODULE_GET_API(DigestEndSequence);
 
     RedisModule_SetModuleAttribs(ctx,name,ver,apiver);
     return REDISMODULE_OK;

src/server.h

@@ -546,6 +546,22 @@ typedef struct RedisModuleIO {
     iovar.ctx = NULL; \
 } while(0);
 
+/* This is a structure used to export DEBUG DIGEST capabilities to Redis
+ * modules. We want to capture both the ordered and unordered elements of
+ * a data structure, so that a digest can be created in a way that correctly
+ * reflects the values. See the DEBUG DIGEST command implementation for more
+ * background. */
+typedef struct RedisModuleDigest {
+    unsigned char o[20];    /* Ordered elements. */
+    unsigned char x[20];    /* Xored elements. */
+} RedisModuleDigest;
+
+/* Just start with a digest composed of all zero bytes. */
+#define moduleInitDigestContext(mdvar) do { \
+    memset(mdvar.o,0,sizeof(mdvar.o)); \
+    memset(mdvar.x,0,sizeof(mdvar.x)); \
+} while(0);
+
 /* Objects encoding. Some kind of objects like Strings and Hashes can be
  * internally represented in multiple ways. The 'encoding' field of the object
  * is set to one of this fields for this object. */
@@ -1993,6 +2009,8 @@ void disableWatchdog(void);
 void watchdogScheduleSignal(int period);
 void serverLogHexDump(int level, char *descr, void *value, size_t len);
 int memtest_preserving_test(unsigned long *m, size_t bytes, int passes);
+void mixDigest(unsigned char *digest, void *ptr, size_t len);
+void xorDigest(unsigned char *digest, void *ptr, size_t len);
 
 #define redisDebug(fmt, ...) \
     printf("DEBUG %s:%d > " fmt "\n", __FILE__, __LINE__, __VA_ARGS__)