implement Copy command

README.md

@@ -34,6 +34,7 @@ Implemented commands:
    - SWAPDB
    - QUIT
  - Key
+   - COPY
    - DEL
    - EXISTS
    - EXPIRE

cmd_generic.go

@@ -35,6 +35,8 @@ func commandsGeneric(m *Miniredis) {
 	m.srv.Register("TTL", m.cmdTTL)
 	m.srv.Register("TYPE", m.cmdType)
 	m.srv.Register("SCAN", m.cmdScan)
+	// COPY
+	m.srv.Register("COPY", m.cmdCopy)
 }
 
 // generic expire command for EXPIRE, PEXPIRE, EXPIREAT, PEXPIREAT
@@ -541,3 +543,35 @@ func (m *Miniredis) cmdScan(c *server.Peer, cmd string, args []string) {
 		}
 	})
 }
+
+// COPY
+func (m *Miniredis) cmdCopy(c *server.Peer, cmd string, args []string) {
+	if len(args) != 2 {
+		setDirty(c)
+		c.WriteError(errWrongNumber(cmd))
+		return
+	}
+	if !m.handleAuth(c) {
+		return
+	}
+	if m.checkPubsub(c, cmd) {
+		return
+	}
+
+	from, to := args[0], args[1]
+
+	withTx(m, c, func(c *server.Peer, ctx *connCtx) {
+		db := m.db(ctx.selectedDB)
+
+		if !db.exists(from) {
+			c.WriteInt(0)
+			return
+		}
+
+		if !db.copy(from, to) {
+			c.WriteInt(0)
+			return
+		}
+		c.WriteInt(1)
+	})
+}

cmd_generic_test.go

@@ -762,3 +762,33 @@ func TestRenamenx(t *testing.T) {
 		)
 	})
 }
+
+func TestCopy(t *testing.T) {
+	s, err := Run()
+	ok(t, err)
+	defer s.Close()
+	c, err := proto.Dial(s.Addr())
+	ok(t, err)
+	defer c.Close()
+
+	s.Set("key1", "value")
+	s.CheckGet(t, "key1", "value")
+	s.Copy("key1", "key2")
+	// should return 1 after a successful copy operation:
+	must1(t, c, "COPY", "key1", "key2")
+	s.CheckGet(t, "key2", "value")
+
+	// should return 0 when trying to copy a nonexistent key:
+	t.Run("nonexistent key", func(t *testing.T) {
+		must0(t, c, "COPY", "nosuch", "to")
+	})
+
+	// should return 0 when trying to overwrite an existing key:
+	t.Run("existing key", func(t *testing.T) {
+		s.Set("existingkey", "value")
+		s.Set("newkey", "newvalue")
+		must0(t, c, "COPY", "newkey", "existingkey")
+		// existing key value should remain unchanged:
+		s.CheckGet(t, "existingkey", "value")
+	})
+}

db.go

@@ -112,6 +112,37 @@ func (db *RedisDB) rename(from, to string) {
 	db.del(from, true)
 }
 
+func (db *RedisDB) copy(from, to string) bool {
+	if _, ok := db.keys[to]; ok {
+		return false
+	}
+	db.keys[to] = from
+	switch db.t(from) {
+	case "string":
+		db.stringKeys[to] = db.stringKeys[from]
+	case "hash":
+		db.hashKeys[to] = db.hashKeys[from]
+	case "list":
+		db.listKeys[to] = db.listKeys[from]
+	case "set":
+		db.setKeys[to] = db.setKeys[from]
+	case "zset":
+		db.sortedsetKeys[to] = db.sortedsetKeys[from]
+	case "stream":
+		db.streamKeys[to] = db.streamKeys[from]
+	case "hll":
+		db.hllKeys[to] = db.hllKeys[from]
+	default:
+		panic("missing case")
+	}
+	db.keys[to] = db.keys[from]
+	db.keyVersion[to]++
+	if v, ok := db.ttl[from]; ok {
+		db.ttl[to] = v
+	}
+	return true
+}
+
 func (db *RedisDB) del(k string, delTTL bool) {
 	if !db.exists(k) {
 		return

direct.go

@@ -793,3 +793,19 @@ func (db *RedisDB) HllMerge(destKey string, sourceKeys ...string) error {
 
 	return db.hllMerge(append([]string{destKey}, sourceKeys...))
 }
+
+func (m *Miniredis) Copy(src, dest string) (bool, error) {
+	return m.DB(m.selectedDB).Copy(src, dest)
+}
+
+func (db *RedisDB) Copy(src, dest string) (bool, error) {
+	db.master.Lock()
+	defer db.master.Unlock()
+	defer db.master.signal.Broadcast()
+
+	if !db.exists(src) {
+		return false, ErrKeyNotFound
+	}
+	// return db.copy(src, dest), nil
+	return true, nil
+}

integration/generic_test.go

@@ -299,3 +299,16 @@ func TestPersist(t *testing.T) {
 		c.Do("TTL", "foo")
 	})
 }
+
+func TestCopy(t *testing.T) {
+	testRaw(t, func(c *client) {
+		c.Error("wrong number", "COPY")
+		c.Error("wrong number", "COPY", "a")
+
+		c.Do("SET", "a", "1")
+		c.Do("COPY", "a", "b") // returns 1 - successfully copied
+		c.Do("EXISTS", "b")
+		c.Do("COPY", "nonexistent", "c") // returns 1 - not successfully copied
+		c.Do("RENAME", "b", "c")         // rename the copied key
+	})
+}