add rev scan support

2014-10-20 22:36:16 +08:00 · 2014-10-20 22:36:16 +08:00 · f09e43ad99
parent c527d8ebcb
commit f09e43ad99
19 changed files with 333 additions and 128 deletions
--- a/cmd/ledis-cli/const.go
+++ b/cmd/ledis-cli/const.go
@ -1,4 +1,4 @@
-//This file was generated by .tools/generate_commands.py on Fri Oct 17 2014 11:39:51 +0800 
+//This file was generated by .tools/generate_commands.py on Mon Oct 20 2014 22:35:33 +0800 
 package main

 var helpCommands = [][]string{
@ -16,6 +16,7 @@ var helpCommands = [][]string{
 	{"BRPOP", "key [key ...] timeout", "List"},
 	{"BSETBIT", "key offset value", "Bitmap"},
 	{"BTTL", "key", "Bitmap"},
+	{"BXREVSCAN", "key [MATCH match] [COUNT count]", "Bitmap"},
 	{"BXSCAN", "key [MATCH match] [COUNT count]", "Bitmap"},
 	{"COMMIT", "-", "Transaction"},
 	{"CONFIG REWRITE", "-", "Server"},
@ -50,6 +51,7 @@ var helpCommands = [][]string{
 	{"HSET", "key field value", "Hash"},
 	{"HTTL", "key", "Hash"},
 	{"HVALS", "key", "Hash"},
+	{"HXREVSCAN", "key [MATCH match] [COUNT count]", "Hash"},
 	{"HXSCAN", "key [MATCH match] [COUNT count]", "Hash"},
 	{"INCR", "key", "KV"},
 	{"INCRBY", "key increment", "KV"},
@ -65,6 +67,7 @@ var helpCommands = [][]string{
 	{"LPUSH", "key value [value ...]", "List"},
 	{"LRANGE", "key start stop", "List"},
 	{"LTTL", "key", "List"},
+	{"LXREVSCAN", "key [MATCH match] [COUNT count]", "List"},
 	{"LXSCAN", "key [MATCH match] [COUNT count]", "List"},
 	{"MGET", "key [key ...]", "KV"},
 	{"MSET", "key value [key value ...]", "KV"},
@ -97,10 +100,12 @@ var helpCommands = [][]string{
 	{"STTL", "key", "Set"},
 	{"SUNION", "key [key ...]", "Set"},
 	{"SUNIONSTORE", "destination key [key ...]", "Set"},
+	{"SXREVSCAN", "key [MATCH match] [COUNT count]", "Set"},
 	{"SXSCAN", "key [MATCH match] [COUNT count]", "Set"},
 	{"SYNC", "logid", "Replication"},
 	{"TIME", "-", "Server"},
 	{"TTL", "key", "KV"},
+	{"XREVSCAN", "key [MATCH match] [COUNT count]", "KV"},
 	{"XSCAN", "key [MATCH match] [COUNT count]", "KV"},
 	{"ZADD", "key score member [score member ...]", "ZSet"},
 	{"ZCARD", "key", "ZSet"},
@ -127,5 +132,6 @@ var helpCommands = [][]string{
 	{"ZSCORE", "key member", "ZSet"},
 	{"ZTTL", "key", "ZSet"},
 	{"ZUNIONSTORE", "destkey numkeys key [key ...] [WEIGHTS weight [weight ...]] [AGGREGATE SUM|MIN|MAX]", "ZSet"},
+	{"ZXREVSCAN", "key [MATCH match] [COUNT count]", "ZSet"},
 	{"ZXSCAN", "key [MATCH match] [COUNT count]", "ZSet"},
 }
--- a/doc/DiffRedis.md
+++ b/doc/DiffRedis.md
@ -47,14 +47,14 @@ Transaction API:

 ## Scan

-LedisDB supplies `xscan`, etc, to fetch data iteratively.
+LedisDB supplies `xscan`, `xrevscan`, etc, to fetch data iteratively and reverse iteratively.

-+ KV:     `xscan`
-+ Hash:   `hxscan`
-+ List:   `lxscan`
-+ Set:    `sxscan` 
-+ Zset:   `zxscan`
-+ Bitmap: `bxscan`
+ KV:     `xscan`, `xrevscan`
+ Hash:   `hxscan`, `hxrevscan`
+ List:   `lxscan`, `lxrevscan`
+ Set:    `sxscan` , `sxrevscan`
+ Zset:   `zxscan`, `zxrevscan`
+ Bitmap: `bxscan`, `bxrevscan`


 Of course, LedisDB has not implemented all APIs in Redis, you can see full commands in commands.json, commands.doc or [wiki](https://github.com/siddontang/ledisdb/wiki/Commands).
--- a/doc/commands.json
+++ b/doc/commands.json
@ -591,6 +591,42 @@
        "group": "Bitmap",
        "readonly": true
    },
+    
+    "XREVSCAN": {
+        "arguments": "key [MATCH match] [COUNT count]",
+        "group": "KV",
+        "readonly": true
+    },
+
+    "HXREVSCAN": {
+        "arguments": "key [MATCH match] [COUNT count]",
+        "group": "Hash",
+        "readonly": true
+    },
+
+    "LXREVSCAN": {
+        "arguments": "key [MATCH match] [COUNT count]",
+        "group": "List",
+        "readonly": true
+    },
+
+    "SXREVSCAN": {
+        "arguments": "key [MATCH match] [COUNT count]",
+        "group": "Set",
+        "readonly": true
+    },
+
+    "ZXREVSCAN": {
+        "arguments": "key [MATCH match] [COUNT count]",
+        "group": "ZSet",
+        "readonly": true
+    },
+
+    "BXREVSCAN": {
+        "arguments": "key [MATCH match] [COUNT count]",
+        "group": "Bitmap",
+        "readonly": true
+    },

    "FLUSHALL": {
        "arguments": "-",
--- a/doc/commands.md
+++ b/doc/commands.md
@ -27,6 +27,7 @@ Table of Contents
 	- [TTL key](#ttl-key)
 	- [PERSIST key](#persist-key)
 	- [XSCAN key [MATCH match] [COUNT count]](#xscan-key-match-match-count-count)
+	- [XREVSCAN key [MATCH match] [COUNT count]](#xrevscan-key-match-match-count-count)
 - [Hash](#hash)
 	- [HDEL key field [field ...]](#hdel-key-field-field-)
 	- [HEXISTS key field](#hexists-key-field)
@ -46,6 +47,7 @@ Table of Contents
 	- [HTTL key](#httl-key)
 	- [HPERSIST key](#hpersist-key)
 	- [HXSCAN key [MATCH match] [COUNT count]](#hxscan-key-match-match-count-count)
+	- [HXREVSCAN key [MATCH match] [COUNT count]](#hxrevscan-key-match-match-count-count)
 - [List](#list)
 	- [BLPOP key [key ...] timeout](#blpop-key-key--timeout)
 	- [BRPOP key [key ...] timeout](#brpop-key-key--timeout)
@ -63,6 +65,7 @@ Table of Contents
 	- [LTTL key](#lttl-key)
 	- [LPERSIST key](#lpersist-key)
 	- [LXSCAN key [MATCH match] [COUNT count]](#lxscan-key-match-match-count-count)
+	- [LXREVSCAN key [MATCH match] [COUNT count]](#lxrevscan-key-match-match-count-count)
 - [Set](#set)
 	- [SADD key member [member ...]](#sadd-key-member-member-)
 	- [SCARD key](#scard-key)
@ -82,6 +85,7 @@ Table of Contents
 	- [STTL key](#sttl-key)
 	- [SPERSIST key](#spersist-key)
 	- [SXSCAN key [MATCH match] [COUNT count]](#sxscan-key-match-match-count-count)
+	- [SXREVSCAN key [MATCH match] [COUNT count]](#sxrevscan-key-match-match-count-count)
 - [ZSet](#zset)
 	- [ZADD key score member [score member ...]](#zadd-key-score-member-score-member-)
 	- [ZCARD key](#zcard-key)
@ -108,6 +112,7 @@ Table of Contents
    - [ZINTERSTORE destination numkeys key [key ...] [WEIGHTS weight [weight ...]] [AGGREGATE SUM|MIN|MAX]
 ](#zinterstore-destination-numkeys-key-key--weights-weight-weight--aggregate-summinmax)
 	- [ZXSCAN key [MATCH match] [COUNT count]](#zxscan-key-match-match-count-count)
+	- [ZXREVSCAN key [MATCH match] [COUNT count]](#zxrevscan-key-match-match-count-count)
 	- [ZRANGEBYLEX key min max [LIMIT offset count]](#zrangebylex-key-min-max-limit-offset-count)
 	- [ZREMRANGEBYLEX key min max](#zremrangebylex-key-min-max)
 	- [ZLEXCOUNT key min max](#zlexcount-key-min-max)
@ -123,6 +128,7 @@ Table of Contents
 	- [BTTL key](#bttl-key)
 	- [BPERSIST key](#bpersist-key)
 	- [BXSCAN key [MATCH match] [COUNT count]](#bxscan-key-match-match-count-count)
+	- [BXREVSCAN key [MATCH match] [COUNT count]](#bxrevscan-key-match-match-count-count)
 - [Replication](#replication)
 	- [SLAVEOF host port [RESTART] [READONLY]](#slaveof-host-port-restart-readonly)
 	- [FULLSYNC [NEW]](#fullsync-new)
@ -514,6 +520,45 @@ ledis>xscan "c" count 1
 2) []
 ```

+### XREVSCAN key [MATCH match] [COUNT count] 
+
+Reverse iterate KV keys incrementally.
+
+Key is the start for the current iteration.
+Match is the regexp for checking matched key.
+Count is the maximum retrieved elememts number, default is 10.
+
+**Return value**
+
+an array of two values, first value is the key for next iteration, second value is an array of elements.
+
+**Examples**
+
+```
+ledis>set a 1
+OK
+ledis>set b 2
+OK
+ledis>set c 3
+OK
+127.0.0.1:6380>xrevscan "" 
+1) ""
+2) ["c" "b" "a"]
+ledis>xrevscan "" count 1
+1) "c"
+2) ["c"]
+ledis>xrevscan "c" count 1
+1) "b"
+2) ["b"]
+ledis>xrevscan "b" count 1
+1) "a"
+2) ["a"]
+ledis>xrevscan "a" count 1
+1) ""
+2) []
+```
+
+
 ## Hash

 ### HDEL key field [field ...]
@ -883,6 +928,12 @@ Iterate Hash keys incrementally.

 See [XSCAN](#xscan-key-match-match-count-count) for more information.

+### HXREVSCAN key [MATCH match] [COUNT count] 
+
+Reverse iterate Hash keys incrementally.
+
+See [XREVSCAN](#xrevscan-key-match-match-count-count) for more information.
+
 ## List

 ### BLPOP key [key ...] timeout
@ -1211,6 +1262,12 @@ Iterate list keys incrementally.

 See [XSCAN](#xscan-key-match-match-count-count) for more information.

+### LXREVSCAN key [MATCH match] [COUNT count] 
+
+Reverse iterate list keys incrementally.
+
+See [XREVSCAN](#xrevscan-key-match-match-count-count) for more information.
+

 ## Set

@ -1640,6 +1697,12 @@ Iterate Set keys incrementally.
 See [XSCAN](#xscan-key-match-match-count-count) for more information.


+### SXREVSCAN key [MATCH match] [COUNT count] 
+
+Reverse iterate Set keys incrementally.
+
+See [XREVSCAN](#xrevscan-key-match-match-count-count) for more information.
+
 ## ZSet

 ### ZADD key score member [score member ...]
@ -2265,6 +2328,12 @@ Iterate ZSet keys incrementally.

 See [XSCAN](#xscan-key-match-match-count-count) for more information.

+### ZXREVSCAN key [MATCH match] [COUNT count] 
+
+Reverse iterate ZSet keys incrementally.
+
+See [XREVSCAN](#xrevscan-key-match-match-count-count) for more information.
+
 ### ZRANGEBYLEX key min max [LIMIT offset count]

 When all the elements in a sorted set are inserted with the same score, in order to force lexicographical ordering, this command returns all the elements in the sorted set at key with a value between min and max.
@ -2496,6 +2565,12 @@ Iterate Bitmap keys incrementally.

 See [XSCAN](#xscan-key-match-match-count-count) for more information.

+### BXREVSCAN key [MATCH match] [COUNT count] 
+
+Reverse iterate Bitmap keys incrementally.
+
+See [XREVSCAN](#xrevscan-key-match-match-count-count) for more information.
+

 ## Replication

--- a/ledis/scan.go
+++ b/ledis/scan.go
@ -1,8 +1,8 @@
 package ledis

 import (
-	"bytes"
 	"errors"
+	"github.com/siddontang/ledisdb/store"
 	"regexp"
 )

@ -10,6 +10,15 @@ var errDataType = errors.New("error data type")
 var errMetaKey = errors.New("error meta key")

 func (db *DB) scan(dataType byte, key []byte, count int, inclusive bool, match string) ([][]byte, error) {
+	return db.scanGeneric(dataType, key, count, inclusive, match, false)
+}
+
+func (db *DB) revscan(dataType byte, key []byte, count int, inclusive bool, match string) ([][]byte, error) {
+	return db.scanGeneric(dataType, key, count, inclusive, match, true)
+}
+
+func (db *DB) scanGeneric(dataType byte, key []byte, count int,
+	inclusive bool, match string, reverse bool) ([][]byte, error) {
 	var minKey, maxKey []byte
 	var err error
 	var r *regexp.Regexp
@ -20,40 +29,46 @@ func (db *DB) scan(dataType byte, key []byte, count int, inclusive bool, match s
 		}
 	}

-	if len(key) > 0 {
-		if err = checkKeySize(key); err != nil {
+	tp := store.RangeOpen
+
+	if !reverse {
+		if minKey, err = db.encodeScanMinKey(dataType, key); err != nil {
 			return nil, err
 		}
-		if minKey, err = db.encodeScanKey(dataType, key); err != nil {
+		if maxKey, err = db.encodeScanMaxKey(dataType, nil); err != nil {
 			return nil, err
 		}

+		if inclusive {
+			tp = store.RangeROpen
+		}
 	} else {
-		if minKey, err = db.encodeScanMinKey(dataType); err != nil {
+		if minKey, err = db.encodeScanMinKey(dataType, nil); err != nil {
+			return nil, err
+		}
+		if maxKey, err = db.encodeScanMaxKey(dataType, key); err != nil {
 			return nil, err
 		}
-	}

-	if maxKey, err = db.encodeScanMaxKey(dataType); err != nil {
-		return nil, err
+		if inclusive {
+			tp = store.RangeLOpen
+		}
 	}

 	if count <= 0 {
 		count = defaultScanCount
 	}

-	v := make([][]byte, 0, count)
-
-	it := db.bucket.NewIterator()
-	it.Seek(minKey)
-
-	if !inclusive {
-		if it.Valid() && bytes.Equal(it.RawKey(), minKey) {
-			it.Next()
-		}
+	var it *store.RangeLimitIterator
+	if !reverse {
+		it = db.bucket.RangeIterator(minKey, maxKey, tp)
+	} else {
+		it = db.bucket.RevRangeIterator(minKey, maxKey, tp)
 	}

-	for i := 0; it.Valid() && i < count && bytes.Compare(it.RawKey(), maxKey) < 0; it.Next() {
+	v := make([][]byte, 0, count)
+
+	for i := 0; it.Valid() && i < count; it.Next() {
 		if k, err := db.decodeScanKey(dataType, it.Key()); err != nil {
 			continue
 		} else if r != nil && !r.Match(k) {
@ -67,11 +82,26 @@ func (db *DB) scan(dataType byte, key []byte, count int, inclusive bool, match s
 	return v, nil
 }

-func (db *DB) encodeScanMinKey(dataType byte) ([]byte, error) {
-	return db.encodeScanKey(dataType, nil)
+func (db *DB) encodeScanMinKey(dataType byte, key []byte) ([]byte, error) {
+	if len(key) == 0 {
+		return db.encodeScanKey(dataType, nil)
+	} else {
+		if err := checkKeySize(key); err != nil {
+			return nil, err
+		}
+		return db.encodeScanKey(dataType, key)
+	}
 }

-func (db *DB) encodeScanMaxKey(dataType byte) ([]byte, error) {
+func (db *DB) encodeScanMaxKey(dataType byte, key []byte) ([]byte, error) {
+	if len(key) > 0 {
+		if err := checkKeySize(key); err != nil {
+			return nil, err
+		}
+
+		return db.encodeScanKey(dataType, key)
+	}
+
 	k, err := db.encodeScanKey(dataType, nil)
 	if err != nil {
 		return nil, err
--- a/ledis/scan_test.go
+++ b/ledis/scan_test.go
@ -4,6 +4,18 @@ import (
 	"testing"
 )

+func checkTestScan(t *testing.T, v [][]byte, args ...string) {
+	if len(v) != len(args) {
+		t.Fatal(len(v), len(args))
+	}
+
+	for i := range v {
+		if string(v[i]) != args[i] {
+			t.Fatalf("%q %q", v, args)
+		}
+	}
+}
+
 func TestDBScan(t *testing.T) {
 	db := getTestDB()

@ -15,44 +27,86 @@ func TestDBScan(t *testing.T) {
 		t.Fatal(len(v))
 	}

+	if v, err := db.RevScan(nil, 10, true, ""); err != nil {
+		t.Fatal(err)
+	} else if len(v) != 0 {
+		t.Fatal(len(v))
+	}
+
 	db.Set([]byte("a"), []byte{})
 	db.Set([]byte("b"), []byte{})
 	db.Set([]byte("c"), []byte{})

 	if v, err := db.Scan(nil, 1, true, ""); err != nil {
 		t.Fatal(err)
-	} else if len(v) != 1 {
-		t.Fatal(len(v))
+	} else {
+		checkTestScan(t, v, "a")
 	}

 	if v, err := db.Scan([]byte("a"), 2, false, ""); err != nil {
 		t.Fatal(err)
-	} else if len(v) != 2 {
-		t.Fatal(len(v))
+	} else {
+		checkTestScan(t, v, "b", "c")
 	}

 	if v, err := db.Scan(nil, 3, true, ""); err != nil {
 		t.Fatal(err)
-	} else if len(v) != 3 {
-		t.Fatal(len(v))
+	} else {
+		checkTestScan(t, v, "a", "b", "c")
 	}

 	if v, err := db.Scan(nil, 3, true, "b"); err != nil {
 		t.Fatal(err)
-	} else if len(v) != 1 {
-		t.Fatal(len(v))
+	} else {
+		checkTestScan(t, v, "b")
 	}

 	if v, err := db.Scan(nil, 3, true, "."); err != nil {
 		t.Fatal(err)
-	} else if len(v) != 3 {
-		t.Fatal(len(v))
+	} else {
+		checkTestScan(t, v, "a", "b", "c")
 	}

 	if v, err := db.Scan(nil, 3, true, "a+"); err != nil {
 		t.Fatal(err)
-	} else if len(v) != 1 {
-		t.Fatal(len(v))
+	} else {
+		checkTestScan(t, v, "a")
+	}
+
+	if v, err := db.RevScan(nil, 1, true, ""); err != nil {
+		t.Fatal(err)
+	} else {
+		checkTestScan(t, v, "c")
+	}
+
+	if v, err := db.RevScan([]byte("c"), 2, false, ""); err != nil {
+		t.Fatal(err)
+	} else {
+		checkTestScan(t, v, "b", "a")
+	}
+
+	if v, err := db.RevScan(nil, 3, true, ""); err != nil {
+		t.Fatal(err)
+	} else {
+		checkTestScan(t, v, "c", "b", "a")
+	}
+
+	if v, err := db.RevScan(nil, 3, true, "b"); err != nil {
+		t.Fatal(err)
+	} else {
+		checkTestScan(t, v, "b")
+	}
+
+	if v, err := db.RevScan(nil, 3, true, "."); err != nil {
+		t.Fatal(err)
+	} else {
+		checkTestScan(t, v, "c", "b", "a")
+	}
+
+	if v, err := db.RevScan(nil, 3, true, "c+"); err != nil {
+		t.Fatal(err)
+	} else {
+		checkTestScan(t, v, "c")
 	}

 }
--- a/ledis/t_bit.go
+++ b/ledis/t_bit.go
@ -913,6 +913,10 @@ func (db *DB) BScan(key []byte, count int, inclusive bool, match string) ([][]by
 	return db.scan(BitMetaType, key, count, inclusive, match)
 }

+func (db *DB) BRevScan(key []byte, count int, inclusive bool, match string) ([][]byte, error) {
+	return db.revscan(BitMetaType, key, count, inclusive, match)
+}
+
 func (db *DB) bFlush() (drop int64, err error) {
 	t := db.binBatch
 	t.Lock()
--- a/ledis/t_hash.go
+++ b/ledis/t_hash.go
@ -464,6 +464,10 @@ func (db *DB) HScan(key []byte, count int, inclusive bool, match string) ([][]by
 	return db.scan(HSizeType, key, count, inclusive, match)
 }

+func (db *DB) HRevScan(key []byte, count int, inclusive bool, match string) ([][]byte, error) {
+	return db.revscan(HSizeType, key, count, inclusive, match)
+}
+
 func (db *DB) HExpire(key []byte, duration int64) (int64, error) {
 	if duration <= 0 {
 		return 0, errExpireValue
--- a/ledis/t_kv.go
+++ b/ledis/t_kv.go
@ -312,6 +312,11 @@ func (db *DB) Scan(key []byte, count int, inclusive bool, match string) ([][]byt
 	return db.scan(KVType, key, count, inclusive, match)
 }

+//if inclusive is true, revscan range (-inf, key] else (inf, key)
+func (db *DB) RevScan(key []byte, count int, inclusive bool, match string) ([][]byte, error) {
+	return db.revscan(KVType, key, count, inclusive, match)
+}
+
 func (db *DB) Expire(key []byte, duration int64) (int64, error) {
 	if duration <= 0 {
 		return 0, errExpireValue
--- a/ledis/t_list.go
+++ b/ledis/t_list.go
@ -484,6 +484,10 @@ func (db *DB) LScan(key []byte, count int, inclusive bool, match string) ([][]by
 	return db.scan(LMetaType, key, count, inclusive, match)
 }

+func (db *DB) LRevScan(key []byte, count int, inclusive bool, match string) ([][]byte, error) {
+	return db.revscan(LMetaType, key, count, inclusive, match)
+}
+
 func (db *DB) lEncodeMinKey() []byte {
 	return db.lEncodeMetaKey(nil)
 }
--- a/ledis/t_set.go
+++ b/ledis/t_set.go
@ -599,3 +599,7 @@ func (db *DB) SPersist(key []byte) (int64, error) {
 func (db *DB) SScan(key []byte, count int, inclusive bool, match string) ([][]byte, error) {
 	return db.scan(SSizeType, key, count, inclusive, match)
 }
+
+func (db *DB) SRevScan(key []byte, count int, inclusive bool, match string) ([][]byte, error) {
+	return db.revscan(SSizeType, key, count, inclusive, match)
+}
--- a/ledis/t_zset.go
+++ b/ledis/t_zset.go
@ -940,6 +940,10 @@ func (db *DB) ZScan(key []byte, count int, inclusive bool, match string) ([][]by
 	return db.scan(ZSizeType, key, count, inclusive, match)
 }

+func (db *DB) ZRevScan(key []byte, count int, inclusive bool, match string) ([][]byte, error) {
+	return db.revscan(ZSizeType, key, count, inclusive, match)
+}
+
 func (db *DB) ZRangeByLex(key []byte, min []byte, max []byte, rangeType uint8, offset int, count int) ([][]byte, error) {
 	if min == nil {
 		min = db.zEncodeStartSetKey(key)
--- a/server/cmd_bit.go
+++ b/server/cmd_bit.go
@ -275,24 +275,11 @@ func bpersistCommand(c *client) error {
 }

 func bxscanCommand(c *client) error {
-	key, match, count, err := parseScanArgs(c)
-	if err != nil {
-		return err
-	}
+	return xscanGeneric(c, c.db.BScan)
+}

-	if ay, err := c.db.BScan(key, count, false, match); err != nil {
-		return err
-	} else {
-		data := make([]interface{}, 2)
-		if len(ay) < count {
-			data[0] = []byte("")
-		} else {
-			data[0] = ay[len(ay)-1]
-		}
-		data[1] = ay
-		c.resp.writeArray(data)
-	}
-	return nil
+func bxrevscanCommand(c *client) error {
+	return xscanGeneric(c, c.db.BRevScan)
 }

 func init() {
@ -308,4 +295,5 @@ func init() {
 	register("bttl", bttlCommand)
 	register("bpersist", bpersistCommand)
 	register("bxscan", bxscanCommand)
+	register("bxrevscan", bxrevscanCommand)
 }
--- a/server/cmd_hash.go
+++ b/server/cmd_hash.go
@ -293,24 +293,11 @@ func hpersistCommand(c *client) error {
 }

 func hxscanCommand(c *client) error {
-	key, match, count, err := parseScanArgs(c)
-	if err != nil {
-		return err
-	}
+	return xscanGeneric(c, c.db.HScan)
+}

-	if ay, err := c.db.HScan(key, count, false, match); err != nil {
-		return err
-	} else {
-		data := make([]interface{}, 2)
-		if len(ay) < count {
-			data[0] = []byte("")
-		} else {
-			data[0] = ay[len(ay)-1]
-		}
-		data[1] = ay
-		c.resp.writeArray(data)
-	}
-	return nil
+func hxrevscanCommand(c *client) error {
+	return xscanGeneric(c, c.db.HRevScan)
 }

 func init() {
@ -335,4 +322,5 @@ func init() {
 	register("httl", httlCommand)
 	register("hpersist", hpersistCommand)
 	register("hxscan", hxscanCommand)
+	register("hxrevscan", hxrevscanCommand)
 }
--- a/server/cmd_kv.go
+++ b/server/cmd_kv.go
@ -322,13 +322,14 @@ func parseScanArgs(c *client) (key []byte, match string, count int, err error) {
 	return
 }

-func xscanCommand(c *client) error {
+func xscanGeneric(c *client,
+	f func(key []byte, count int, inclusive bool, match string) ([][]byte, error)) error {
 	key, match, count, err := parseScanArgs(c)
 	if err != nil {
 		return err
 	}

-	if ay, err := c.db.Scan(key, count, false, match); err != nil {
+	if ay, err := f(key, count, false, match); err != nil {
 		return err
 	} else {
 		data := make([]interface{}, 2)
@ -343,6 +344,14 @@ func xscanCommand(c *client) error {
 	return nil
 }

+func xscanCommand(c *client) error {
+	return xscanGeneric(c, c.db.Scan)
+}
+
+func xrevscanCommand(c *client) error {
+	return xscanGeneric(c, c.db.RevScan)
+}
+
 func init() {
 	register("decr", decrCommand)
 	register("decrby", decrbyCommand)
@ -361,4 +370,5 @@ func init() {
 	register("ttl", ttlCommand)
 	register("persist", persistCommand)
 	register("xscan", xscanCommand)
+	register("xrevscan", xrevscanCommand)
 }
--- a/server/cmd_list.go
+++ b/server/cmd_list.go
@ -232,24 +232,11 @@ func lpersistCommand(c *client) error {
 }

 func lxscanCommand(c *client) error {
-	key, match, count, err := parseScanArgs(c)
-	if err != nil {
-		return err
-	}
+	return xscanGeneric(c, c.db.LScan)
+}

-	if ay, err := c.db.LScan(key, count, false, match); err != nil {
-		return err
-	} else {
-		data := make([]interface{}, 2)
-		if len(ay) < count {
-			data[0] = []byte("")
-		} else {
-			data[0] = ay[len(ay)-1]
-		}
-		data[1] = ay
-		c.resp.writeArray(data)
-	}
-	return nil
+func lxrevscanCommand(c *client) error {
+	return xscanGeneric(c, c.db.LRevScan)
 }

 func blpopCommand(c *client) error {
@ -319,4 +306,5 @@ func init() {
 	register("lttl", lttlCommand)
 	register("lpersist", lpersistCommand)
 	register("lxscan", lxscanCommand)
+	register("lxrevscan", lxrevscanCommand)
 }
--- a/server/cmd_set.go
+++ b/server/cmd_set.go
@ -263,24 +263,11 @@ func spersistCommand(c *client) error {
 }

 func sxscanCommand(c *client) error {
-	key, match, count, err := parseScanArgs(c)
-	if err != nil {
-		return err
-	}
+	return xscanGeneric(c, c.db.SScan)
+}

-	if ay, err := c.db.SScan(key, count, false, match); err != nil {
-		return err
-	} else {
-		data := make([]interface{}, 2)
-		if len(ay) < count {
-			data[0] = []byte("")
-		} else {
-			data[0] = ay[len(ay)-1]
-		}
-		data[1] = ay
-		c.resp.writeArray(data)
-	}
-	return nil
+func sxrevscanCommand(c *client) error {
+	return xscanGeneric(c, c.db.SRevScan)
 }

 func init() {
@ -302,4 +289,5 @@ func init() {
 	register("sttl", sttlCommand)
 	register("spersist", spersistCommand)
 	register("sxscan", sxscanCommand)
+	register("sxrevscan", sxrevscanCommand)
 }
--- a/server/cmd_zset.go
+++ b/server/cmd_zset.go
@ -642,24 +642,11 @@ func zinterstoreCommand(c *client) error {
 }

 func zxscanCommand(c *client) error {
-	key, match, count, err := parseScanArgs(c)
-	if err != nil {
-		return err
-	}
+	return xscanGeneric(c, c.db.ZScan)
+}

-	if ay, err := c.db.ZScan(key, count, false, match); err != nil {
-		return err
-	} else {
-		data := make([]interface{}, 2)
-		if len(ay) < count {
-			data[0] = []byte("")
-		} else {
-			data[0] = ay[len(ay)-1]
-		}
-		data[1] = ay
-		c.resp.writeArray(data)
-	}
-	return nil
+func zxrevscanCommand(c *client) error {
+	return xscanGeneric(c, c.db.ZRevScan)
 }

 func zparseMemberRange(minBuf []byte, maxBuf []byte) (min []byte, max []byte, rangeType uint8, err error) {
@ -816,4 +803,5 @@ func init() {
 	register("zttl", zttlCommand)
 	register("zpersist", zpersistCommand)
 	register("zxscan", zxscanCommand)
+	register("zxrevscan", zxrevscanCommand)
 }
--- a/server/scan_test.go
+++ b/server/scan_test.go
@ -77,6 +77,29 @@ func checkScan(t *testing.T, c *ledis.Client, cmd string) {

 }

+func checkRevScan(t *testing.T, c *ledis.Client, cmd string) {
+	if ay, err := ledis.Values(c.Do(cmd, "", "count", 5)); err != nil {
+		t.Fatal(err)
+	} else if len(ay) != 2 {
+		t.Fatal(len(ay))
+	} else if n := ay[0].([]byte); string(n) != "5" {
+		t.Fatal(string(n))
+	} else {
+		checkScanValues(t, ay[1], 9, 8, 7, 6, 5)
+	}
+
+	if ay, err := ledis.Values(c.Do(cmd, "5", "count", 6)); err != nil {
+		t.Fatal(err)
+	} else if len(ay) != 2 {
+		t.Fatal(len(ay))
+	} else if n := ay[0].([]byte); string(n) != "" {
+		t.Fatal(string(n))
+	} else {
+		checkScanValues(t, ay[1], 4, 3, 2, 1, 0)
+	}
+
+}
+
 func testKVScan(t *testing.T, c *ledis.Client) {
 	for i := 0; i < 10; i++ {
 		if _, err := c.Do("set", fmt.Sprintf("%d", i), []byte("value")); err != nil {
@ -85,6 +108,7 @@ func testKVScan(t *testing.T, c *ledis.Client) {
 	}

 	checkScan(t, c, "xscan")
+	checkRevScan(t, c, "xrevscan")
 }

 func testHashScan(t *testing.T, c *ledis.Client) {
@ -95,6 +119,7 @@ func testHashScan(t *testing.T, c *ledis.Client) {
 	}

 	checkScan(t, c, "hxscan")
+	checkRevScan(t, c, "hxrevscan")
 }

 func testListScan(t *testing.T, c *ledis.Client) {
@ -105,6 +130,7 @@ func testListScan(t *testing.T, c *ledis.Client) {
 	}

 	checkScan(t, c, "lxscan")
+	checkRevScan(t, c, "lxrevscan")
 }

 func testZSetScan(t *testing.T, c *ledis.Client) {
@ -115,6 +141,7 @@ func testZSetScan(t *testing.T, c *ledis.Client) {
 	}

 	checkScan(t, c, "zxscan")
+	checkRevScan(t, c, "zxrevscan")
 }

 func testSetScan(t *testing.T, c *ledis.Client) {
@ -125,6 +152,7 @@ func testSetScan(t *testing.T, c *ledis.Client) {
 	}

 	checkScan(t, c, "sxscan")
+	checkRevScan(t, c, "sxrevscan")
 }

 func testBitScan(t *testing.T, c *ledis.Client) {
@ -135,4 +163,5 @@ func testBitScan(t *testing.T, c *ledis.Client) {
 	}

 	checkScan(t, c, "bxscan")
+	checkRevScan(t, c, "bxrevscan")
 }