Transactions: Implementation of the IF command

src/db.c

@@ -62,7 +62,7 @@ robj *lookupKeyRead(redisDb *db, robj *key) {
 
     if (expireIfNeeded(db,key) == 1) {
         /* Key expired. If we are in the context of a master, expireIfNeeded()
-         * returns 0 only when the key does not exist at all, so it's save
+         * returns 0 only when the key does not exist at all, so it's safe
          * to return NULL ASAP. */
         if (server.masterhost == NULL) return NULL;
 

src/multi.c

@@ -304,6 +304,9 @@ void touchWatchedKeysOnFlush(int dbid) {
     }
 }
 
+/* WATCH key key key ...
+ * Add keys to the set of watched keys. If those keys are modified
+ * before the next transaction is executed, the transaction aborts. */
 void watchCommand(redisClient *c) {
     int j;
 
@@ -316,8 +319,47 @@ void watchCommand(redisClient *c) {
     addReply(c,shared.ok);
 }
 
+/* UNWATCH
+ * Flush the set of watched keys. */
 void unwatchCommand(redisClient *c) {
     unwatchAllKeys(c);
     c->flags &= (~REDIS_DIRTY_CAS);
     addReply(c,shared.ok);
 }
+
+/* IF XX key key key ...
+ * IF NX key key key ...
+ * Abort transaction if condition is not met. */
+void ifCommand(redisClient *c) {
+    int j;
+    int xx = 0, nx = 0;
+
+    if (!(c->flags & REDIS_MULTI)) {
+        addReplyError(c,"IF outside MULTI is not allowed");
+        return;
+    }
+
+    /* Check if it's xx or nx option, trying to do it reasonably fast. */
+    char *a = c->argv[1]->ptr;
+    if ((a[0] == 'n' || a[0] == 'N') &&
+        (a[1] == 'x' || a[1] == 'X') && a[2] == '\0')
+    {
+        nx = 1;
+    } else if ((a[0] == 'x' || a[0] == 'X') &&
+               (a[1] == 'x' || a[1] == 'X') && a[2] == '\0')
+    {
+        xx = 1;
+    } else {
+        addReply(c,shared.syntaxerr);
+        return;
+    }
+
+    /* Check if keys exist / don't exist, and flag the transaction if
+     * at least one key fails the test according to NX / XX option. */
+    for (j = 2; j < c->argc; j++) {
+        robj *o = lookupKeyRead(c->db,c->argv[j]);
+        if ((o != NULL && nx) || (o == NULL && xx))
+            c->flags |= REDIS_DIRTY_CAS;
+    }
+    addReply(c,shared.ok);
+}

src/redis.c

@@ -261,6 +261,7 @@ struct redisCommand redisCommandTable[] = {
     {"pubsub",pubsubCommand,-2,"pltrR",0,NULL,0,0,0,0,0},
     {"watch",watchCommand,-2,"rsF",0,NULL,1,-1,1,0,0},
     {"unwatch",unwatchCommand,1,"rsF",0,NULL,0,0,0,0,0},
+    {"if",ifCommand,-2,"rsF",0,NULL,2,-1,1,0,0},
     {"cluster",clusterCommand,-2,"ar",0,NULL,0,0,0,0,0},
     {"restore",restoreCommand,-4,"wm",0,NULL,1,1,1,0,0},
     {"restore-asking",restoreCommand,-4,"wmk",0,NULL,1,1,1,0,0},
@@ -2336,7 +2337,7 @@ int processCommand(redisClient *c) {
 
     /* Exec the command */
     if (c->flags & REDIS_MULTI &&
-        c->cmd->proc != execCommand && c->cmd->proc != discardCommand &&
+        c->cmd->proc != execCommand && c->cmd->proc != ifCommand &&
         c->cmd->proc != multiCommand && c->cmd->proc != watchCommand)
     {
         queueMultiCommand(c);

src/redis.h

@@ -1561,6 +1561,7 @@ void pfcountCommand(redisClient *c);
 void pfmergeCommand(redisClient *c);
 void pfdebugCommand(redisClient *c);
 void latencyCommand(redisClient *c);
+void ifCommand(redisClient *c);
 
 #if defined(__GNUC__)
 void *calloc(size_t count, size_t size) __attribute__ ((deprecated));