Add novalues option to command HSCAN. (#12765)

Add a way to HSCAN a hash key, and get only the filed names.
Command syntax is now:
```
HSCAN key cursor [MATCH pattern] [COUNT count] [NOVALUES]
```
when `NOVALUES` is on, the command will only return keys in the hash.

---------

Co-authored-by: Viktor Söderqvist <viktor.soderqvist@est.tech>

src/commands.def

@@ -3567,6 +3567,7 @@ struct COMMAND_ARG HSCAN_Args[] = {
 {MAKE_ARG("cursor",ARG_TYPE_INTEGER,-1,NULL,NULL,NULL,CMD_ARG_NONE,0,NULL)},
 {MAKE_ARG("pattern",ARG_TYPE_PATTERN,-1,"MATCH",NULL,NULL,CMD_ARG_OPTIONAL,0,NULL)},
 {MAKE_ARG("count",ARG_TYPE_INTEGER,-1,"COUNT",NULL,NULL,CMD_ARG_OPTIONAL,0,NULL)},
+{MAKE_ARG("novalues",ARG_TYPE_PURE_TOKEN,-1,"NOVALUES",NULL,NULL,CMD_ARG_OPTIONAL,0,NULL)},
 };
 
 /********** HSET ********************/
@@ -10713,7 +10714,7 @@ struct COMMAND_STRUCT redisCommandTable[] = {
 {MAKE_CMD("hmget","Returns the values of all fields in a hash.","O(N) where N is the number of fields being requested.","2.0.0",CMD_DOC_NONE,NULL,NULL,"hash",COMMAND_GROUP_HASH,HMGET_History,0,HMGET_Tips,0,hmgetCommand,-3,CMD_READONLY|CMD_FAST,ACL_CATEGORY_HASH,HMGET_Keyspecs,1,NULL,2),.args=HMGET_Args},
 {MAKE_CMD("hmset","Sets the values of multiple fields.","O(N) where N is the number of fields being set.","2.0.0",CMD_DOC_DEPRECATED,"`HSET` with multiple field-value pairs","4.0.0","hash",COMMAND_GROUP_HASH,HMSET_History,0,HMSET_Tips,0,hsetCommand,-4,CMD_WRITE|CMD_DENYOOM|CMD_FAST,ACL_CATEGORY_HASH,HMSET_Keyspecs,1,NULL,2),.args=HMSET_Args},
 {MAKE_CMD("hrandfield","Returns one or more random fields from a hash.","O(N) where N is the number of fields returned","6.2.0",CMD_DOC_NONE,NULL,NULL,"hash",COMMAND_GROUP_HASH,HRANDFIELD_History,0,HRANDFIELD_Tips,1,hrandfieldCommand,-2,CMD_READONLY,ACL_CATEGORY_HASH,HRANDFIELD_Keyspecs,1,NULL,2),.args=HRANDFIELD_Args},
-{MAKE_CMD("hscan","Iterates over fields and values of a hash.","O(1) for every call. O(N) for a complete iteration, including enough command calls for the cursor to return back to 0. N is the number of elements inside the collection.","2.8.0",CMD_DOC_NONE,NULL,NULL,"hash",COMMAND_GROUP_HASH,HSCAN_History,0,HSCAN_Tips,1,hscanCommand,-3,CMD_READONLY,ACL_CATEGORY_HASH,HSCAN_Keyspecs,1,NULL,4),.args=HSCAN_Args},
+{MAKE_CMD("hscan","Iterates over fields and values of a hash.","O(1) for every call. O(N) for a complete iteration, including enough command calls for the cursor to return back to 0. N is the number of elements inside the collection.","2.8.0",CMD_DOC_NONE,NULL,NULL,"hash",COMMAND_GROUP_HASH,HSCAN_History,0,HSCAN_Tips,1,hscanCommand,-3,CMD_READONLY,ACL_CATEGORY_HASH,HSCAN_Keyspecs,1,NULL,5),.args=HSCAN_Args},
 {MAKE_CMD("hset","Creates or modifies the value of a field in a hash.","O(1) for each field/value pair added, so O(N) to add N field/value pairs when the command is called with multiple field/value pairs.","2.0.0",CMD_DOC_NONE,NULL,NULL,"hash",COMMAND_GROUP_HASH,HSET_History,1,HSET_Tips,0,hsetCommand,-4,CMD_WRITE|CMD_DENYOOM|CMD_FAST,ACL_CATEGORY_HASH,HSET_Keyspecs,1,NULL,2),.args=HSET_Args},
 {MAKE_CMD("hsetnx","Sets the value of a field in a hash only when the field doesn't exist.","O(1)","2.0.0",CMD_DOC_NONE,NULL,NULL,"hash",COMMAND_GROUP_HASH,HSETNX_History,0,HSETNX_Tips,0,hsetnxCommand,4,CMD_WRITE|CMD_DENYOOM|CMD_FAST,ACL_CATEGORY_HASH,HSETNX_Keyspecs,1,NULL,3),.args=HSETNX_Args},
 {MAKE_CMD("hstrlen","Returns the length of the value of a field.","O(1)","3.2.0",CMD_DOC_NONE,NULL,NULL,"hash",COMMAND_GROUP_HASH,HSTRLEN_History,0,HSTRLEN_Tips,0,hstrlenCommand,3,CMD_READONLY|CMD_FAST,ACL_CATEGORY_HASH,HSTRLEN_Keyspecs,1,NULL,2),.args=HSTRLEN_Args},

src/commands/hscan.json

@@ -56,6 +56,12 @@
                 "name": "count",
                 "type": "integer",
                 "optional": true
+            },
+            {
+                "token": "NOVALUES",
+                "name": "novalues",
+                "type": "pure-token",
+                "optional": true
             }
         ],
         "reply_schema": {
@@ -69,7 +75,7 @@
                     "type": "string"
                 },
                 {
-                    "description": "list of key/value pairs from the hash where each even element is the key, and each odd element is the value",
+                    "description": "list of key/value pairs from the hash where each even element is the key, and each odd element is the value, or when novalues option is on, a list of keys from the hash",
                     "type": "array",
                     "items": {
                         "type": "string"

src/db.c

@@ -1052,6 +1052,7 @@ typedef struct {
     long long type; /* the particular type when scan the db */
     sds pattern;  /* pattern string, NULL means no pattern */
     long sampled; /* cumulative number of keys sampled */
+    int no_values; /* set to 1 means to return keys only */
 } scanData;
 
 /* Helper function to compare key type in scan commands */
@@ -1114,7 +1115,7 @@ void scanCallback(void *privdata, const dictEntry *de) {
     }
 
     listAddNodeTail(keys, key);
-    if (val) listAddNodeTail(keys, val);
+    if (val && !data->no_values) listAddNodeTail(keys, val);
 }
 
 /* Try to parse a SCAN cursor stored at object 'o':
@@ -1187,7 +1188,7 @@ void scanGenericCommand(client *c, robj *o, unsigned long long cursor) {
     sds pat = NULL;
     sds typename = NULL;
     long long type = LLONG_MAX;
-    int patlen = 0, use_pattern = 0;
+    int patlen = 0, use_pattern = 0, no_values = 0;
     dict *ht;
 
     /* Object must be NULL (to iterate keys names), or the type of the object
@@ -1233,6 +1234,13 @@ void scanGenericCommand(client *c, robj *o, unsigned long long cursor) {
                 return; */
             }
             i+= 2;
+        } else if (!strcasecmp(c->argv[i]->ptr, "novalues")) {
+            if (!o || o->type != OBJ_HASH) {
+                addReplyError(c, "NOVALUES option can only be used in HSCAN");
+                return;
+            }
+            no_values = 1;
+            i++;
         } else {
             addReplyErrorObject(c,shared.syntaxerr);
             return;
@@ -1287,17 +1295,20 @@ void scanGenericCommand(client *c, robj *o, unsigned long long cursor) {
          * it is possible to fetch more data in a type-dependent way;
          * 3. data.type: the specified type scan in the db, LLONG_MAX means
          * type matching is no needed;
-         * 4. data.pattern: the pattern string
+         * 4. data.pattern: the pattern string;
          * 5. data.sampled: the maxiteration limit is there in case we're
          * working on an empty dict, one with a lot of empty buckets, and
          * for the buckets are not empty, we need to limit the spampled number
-         * to prevent a long hang time caused by filtering too many keys*/
+         * to prevent a long hang time caused by filtering too many keys;
+         * 6. data.no_values: to control whether values will be returned or 
+         * only keys are returned. */
         scanData data = {
             .keys = keys,
             .o = o,
             .type = type,
             .pattern = use_pattern ? pat : NULL,
             .sampled = 0,
+            .no_values = no_values,
         };
 
         /* A pattern may restrict all matching keys to one cluster slot. */
@@ -1352,8 +1363,10 @@ void scanGenericCommand(client *c, robj *o, unsigned long long cursor) {
             /* add key object */
             listAddNodeTail(keys, sdsnewlen(str, len));
             /* add value object */
-            str = lpGet(p, &len, intbuf);
+            if (!no_values) {
-            listAddNodeTail(keys, sdsnewlen(str, len));
+                str = lpGet(p, &len, intbuf);
+                listAddNodeTail(keys, sdsnewlen(str, len));
+            }
             p = lpNext(o->ptr, p);
         }
         cursor = 0;

tests/unit/scan.tcl

@@ -272,6 +272,10 @@ proc test_scan {type} {
 
             set keys2 [lsort -unique $keys2]
             assert_equal $count [llength $keys2]
+
+            # Test NOVALUES 
+            set res [r hscan hash 0 count 1000 novalues]
+            assert_equal [lsort $keys2] [lsort [lindex $res 1]]
         }
     }
 
@@ -368,6 +372,13 @@ proc test_scan {type} {
         lsort -unique [lindex $res 1]
     } {1 10 foo foobar}
 
+    test "{$type} HSCAN with NOVALUES" {
+        r del mykey
+        r hmset mykey foo 1 fab 2 fiz 3 foobar 10 1 a 2 b 3 c 4 d
+        set res [r hscan mykey 0 NOVALUES]
+        lsort -unique [lindex $res 1]
+    } {1 2 3 4 fab fiz foo foobar}
+
     test "{$type} ZSCAN with PATTERN" {
         r del mykey
         r zadd mykey 1 foo 2 fab 3 fiz 10 foobar