Add prepend command

src/redis.c

@@ -124,6 +124,8 @@ struct redisCommand redisCommandTable[] = {
     {"setex",setexCommand,4,"wm",0,NULL,1,1,1,0,0},
     {"psetex",psetexCommand,4,"wm",0,NULL,1,1,1,0,0},
     {"append",appendCommand,3,"wm",0,NULL,1,1,1,0,0},
+    {"prepend",prependCommand,3,"wm",0,NULL,1,1,1,0,0},
+    {"prependfe",prependfeCommand,3,"wm",0,NULL,1,1,1,0,0},
     {"strlen",strlenCommand,2,"rF",0,NULL,1,1,1,0,0},
     {"del",delCommand,-2,"w",0,NULL,1,-1,1,0,0},
     {"exists",existsCommand,2,"rF",0,NULL,1,1,1,0,0},

src/redis.h

@@ -1394,6 +1394,8 @@ void blpopCommand(redisClient *c);
 void brpopCommand(redisClient *c);
 void brpoplpushCommand(redisClient *c);
 void appendCommand(redisClient *c);
+void prependCommand(redisClient *c);
+void prependfeCommand(redisClient *c);
 void strlenCommand(redisClient *c);
 void zrankCommand(redisClient *c);
 void zrevrankCommand(redisClient *c);

src/sds.c

@@ -250,6 +250,26 @@ sds sdscatlen(sds s, const void *t, size_t len) {
     return s;
 }
 
+/* Prepend the specified binary-safe string pointed by 't' of 'len' bytes to the
+ * beginning of the specified sds string 's'.
+ *
+ * After the call, the passed sds string is no longer valid and all the
+ * references must be substituted with the new pointer returned by the call. */
+sds sdsprecatlen(sds s, const void *t, size_t len) {
+    struct sdshdr *sh;
+    size_t curlen = sdslen(s);
+
+    s = sdsMakeRoomFor(s,len);
+    if (s == NULL) return NULL;
+    sh = (void*) (s-(sizeof(struct sdshdr)));
+    memmove(s+len, s, curlen);
+    memcpy(s, t, len);
+    sh->len = curlen+len;
+    sh->free = sh->free-len;
+    s[curlen+len] = '\0';
+    return s;
+}
+
 /* Append the specified null termianted C string to the sds string 's'.
  *
  * After the call, the passed sds string is no longer valid and all the

src/sds.h

@@ -63,6 +63,7 @@ void sdsfree(sds s);
 size_t sdsavail(const sds s);
 sds sdsgrowzero(sds s, size_t len);
 sds sdscatlen(sds s, const void *t, size_t len);
+sds sdsprecatlen(sds s, const void *t, size_t len);
 sds sdscat(sds s, const char *t);
 sds sdscatsds(sds s, const sds t);
 sds sdscpylen(sds s, const char *t, size_t len);

src/t_string.c

@@ -439,6 +439,81 @@ void appendCommand(redisClient *c) {
     addReplyLongLong(c,totlen);
 }
 
+void prependCommand(redisClient *c) {
+    size_t totlen;
+    robj *o, *prepend;
+
+    o = lookupKeyWrite(c->db,c->argv[1]);
+    if (o == NULL) {
+        /* Create the key */
+        c->argv[2] = tryObjectEncoding(c->argv[2]);
+        dbAdd(c->db,c->argv[1],c->argv[2]);
+        incrRefCount(c->argv[2]);
+        totlen = stringObjectLen(c->argv[2]);
+    } else {
+        /* Key exists, check type */
+        if (checkType(c,o,REDIS_STRING))
+            return;
+
+        /* "prepend" is an argument, so always an sds */
+        prepend = c->argv[2];
+        totlen = stringObjectLen(o)+sdslen(prepend->ptr);
+        if (checkStringLength(c,totlen) != REDIS_OK)
+            return;
+
+        /* Prepend the value */
+        o = dbUnshareStringValue(c->db,c->argv[1],o);
+        o->ptr = sdsprecatlen(o->ptr,prepend->ptr,sdslen(prepend->ptr));
+        totlen = sdslen(o->ptr);
+    }
+    signalModifiedKey(c->db,c->argv[1]);
+    notifyKeyspaceEvent(REDIS_NOTIFY_STRING,"prepend",c->argv[1],c->db->id);
+    server.dirty++;
+    addReplyLongLong(c,totlen);
+}
+
+void prependfeCommand(redisClient *c) {
+    size_t totlen;
+    robj *o, *prepend;
+
+    o = lookupKeyWrite(c->db,c->argv[1]);
+    if (o == NULL) {
+        /* Create the key */
+        c->argv[2] = tryObjectEncoding(c->argv[2]);
+        dbAdd(c->db,c->argv[1],c->argv[2]);
+        incrRefCount(c->argv[2]);
+        totlen = stringObjectLen(c->argv[2]);
+    } else {
+        /* Key exists, check type */
+        if (checkType(c,o,REDIS_STRING))
+            return;
+
+        /* "prepend" is an argument, so always an sds */
+        prepend = c->argv[2];
+        totlen = stringObjectLen(o)+sdslen(prepend->ptr);
+        if (checkStringLength(c,totlen) != REDIS_OK)
+            return;
+
+        /* Check to see if the first bytes match */
+        /* if they do, no change is needed */
+        if(((char*)o->ptr)[0] == ((char*)prepend->ptr)[0]){
+          addReplyLongLong(c,stringObjectLen(o));
+          return;
+        }
+
+        /* Prepend the value */
+        else {
+          o = dbUnshareStringValue(c->db,c->argv[1],o);
+          o->ptr = sdsprecatlen(o->ptr,prepend->ptr,sdslen(prepend->ptr));
+          totlen = sdslen(o->ptr);
+        }
+    }
+    signalModifiedKey(c->db,c->argv[1]);
+    notifyKeyspaceEvent(REDIS_NOTIFY_STRING,"prepend",c->argv[1],c->db->id);
+    server.dirty++;
+    addReplyLongLong(c,totlen);
+}
+
 void strlenCommand(redisClient *c) {
     robj *o;
     if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.czero)) == NULL ||