+/* Compute the sha1 of string at 's' with 'len' bytes long.
+ * The SHA1 is then xored againt the string pointed by digest.
+ * Since xor is commutative, this operation is used in order to
+ * "add" digests relative to unordered elements.
+ *
+ * So digest(a,b,c,d) will be the same of digest(b,a,c,d) */
+static void xorDigest(unsigned char *digest, void *ptr, size_t len) {
+ SHA1_CTX ctx;
+ unsigned char hash[20], *s = ptr;
+ int j;
+
+ SHA1Init(&ctx);
+ SHA1Update(&ctx,s,len);
+ SHA1Final(hash,&ctx);
+
+ for (j = 0; j < 20; j++)
+ digest[j] ^= hash[j];
+}
+
+static void xorObjectDigest(unsigned char *digest, robj *o) {
+ o = getDecodedObject(o);
+ xorDigest(digest,o->ptr,sdslen(o->ptr));
+ decrRefCount(o);
+}
+
+/* This function instead of just computing the SHA1 and xoring it
+ * against diget, also perform the digest of "digest" itself and
+ * replace the old value with the new one.
+ *
+ * So the final digest will be:
+ *
+ * digest = SHA1(digest xor SHA1(data))
+ *
+ * This function is used every time we want to preserve the order so
+ * that digest(a,b,c,d) will be different than digest(b,c,d,a)
+ *
+ * Also note that mixdigest("foo") followed by mixdigest("bar")
+ * will lead to a different digest compared to "fo", "obar".
+ */
+static void mixDigest(unsigned char *digest, void *ptr, size_t len) {
+ SHA1_CTX ctx;
+ char *s = ptr;
+
+ xorDigest(digest,s,len);
+ SHA1Init(&ctx);
+ SHA1Update(&ctx,digest,20);
+ SHA1Final(digest,&ctx);
+}
+
+static void mixObjectDigest(unsigned char *digest, robj *o) {
+ o = getDecodedObject(o);
+ mixDigest(digest,o->ptr,sdslen(o->ptr));
+ decrRefCount(o);
+}
+
+/* Compute the dataset digest. Since keys, sets elements, hashes elements
+ * are not ordered, we use a trick: every aggregate digest is the xor
+ * of the digests of their elements. This way the order will not change
+ * the result. For list instead we use a feedback entering the output digest
+ * as input in order to ensure that a different ordered list will result in
+ * a different digest. */
+static void computeDatasetDigest(unsigned char *final) {
+ unsigned char digest[20];
+ char buf[128];
+ dictIterator *di = NULL;
+ dictEntry *de;
+ int j;
+ uint32_t aux;
+
+ memset(final,0,20); /* Start with a clean result */
+
+ for (j = 0; j < server.dbnum; j++) {
+ redisDb *db = server.db+j;
+
+ if (dictSize(db->dict) == 0) continue;
+ di = dictGetIterator(db->dict);
+
+ /* hash the DB id, so the same dataset moved in a different
+ * DB will lead to a different digest */
+ aux = htonl(j);
+ mixDigest(final,&aux,sizeof(aux));
+
+ /* Iterate this DB writing every entry */
+ while((de = dictNext(di)) != NULL) {
+ robj *key, *o, *kcopy;
+ time_t expiretime;
+
+ memset(digest,0,20); /* This key-val digest */
+ key = dictGetEntryKey(de);
+
+ if (!server.vm_enabled) {
+ mixObjectDigest(digest,key);
+ o = dictGetEntryVal(de);
+ } else {
+ /* Don't work with the key directly as when VM is active
+ * this is unsafe: TODO: fix decrRefCount to check if the
+ * count really reached 0 to avoid this mess */
+ kcopy = dupStringObject(key);
+ mixObjectDigest(digest,kcopy);
+ o = lookupKeyRead(db,kcopy);
+ decrRefCount(kcopy);
+ }
+ aux = htonl(o->type);
+ mixDigest(digest,&aux,sizeof(aux));
+ expiretime = getExpire(db,key);
+
+ /* Save the key and associated value */
+ if (o->type == REDIS_STRING) {
+ mixObjectDigest(digest,o);
+ } else if (o->type == REDIS_LIST) {
+ list *list = o->ptr;
+ listNode *ln;
+ listIter li;
+
+ listRewind(list,&li);
+ while((ln = listNext(&li))) {
+ robj *eleobj = listNodeValue(ln);
+
+ mixObjectDigest(digest,eleobj);
+ }
+ } else if (o->type == REDIS_SET) {
+ dict *set = o->ptr;
+ dictIterator *di = dictGetIterator(set);
+ dictEntry *de;
+
+ while((de = dictNext(di)) != NULL) {
+ robj *eleobj = dictGetEntryKey(de);
+
+ xorObjectDigest(digest,eleobj);
+ }
+ dictReleaseIterator(di);
+ } else if (o->type == REDIS_ZSET) {
+ zset *zs = o->ptr;
+ dictIterator *di = dictGetIterator(zs->dict);
+ dictEntry *de;
+
+ while((de = dictNext(di)) != NULL) {
+ robj *eleobj = dictGetEntryKey(de);
+ double *score = dictGetEntryVal(de);
+ unsigned char eledigest[20];
+
+ snprintf(buf,sizeof(buf),"%.17g",*score);
+ memset(eledigest,0,20);
+ mixObjectDigest(eledigest,eleobj);
+ mixDigest(eledigest,buf,strlen(buf));
+ xorDigest(digest,eledigest,20);
+ }
+ dictReleaseIterator(di);
+ } else if (o->type == REDIS_HASH) {
+ hashIterator *hi;
+ robj *obj;
+
+ hi = hashInitIterator(o);
+ while (hashNext(hi) != REDIS_ERR) {
+ unsigned char eledigest[20];
+
+ memset(eledigest,0,20);
+ obj = hashCurrent(hi,REDIS_HASH_KEY);
+ mixObjectDigest(eledigest,obj);
+ decrRefCount(obj);
+ obj = hashCurrent(hi,REDIS_HASH_VALUE);
+ mixObjectDigest(eledigest,obj);
+ decrRefCount(obj);
+ xorDigest(digest,eledigest,20);
+ }
+ hashReleaseIterator(hi);
+ } else {
+ redisPanic("Unknown object type");
+ }
+ /* If the key has an expire, add it to the mix */
+ if (expiretime != -1) xorDigest(digest,"!!expire!!",10);
+ /* We can finally xor the key-val digest to the final digest */
+ xorDigest(final,digest,20);
+ }
+ dictReleaseIterator(di);
+ }
+}
+
projects / redis.git / blobdiff