support XUSE db THEN command

To solve https://github.com/siddontang/ledisdb/issues/149, but I prefer
XUSE db THEN command like IFFFT, aha.

server/client_resp.go

@@ -134,6 +134,11 @@ func (c *respClient) run() {
 		reqData, err := c.readRequest()
 		if err == nil {
 			err = c.handleRequest(reqData)
+
+			c.cmd = ""
+			c.args = nil
+
+			c.ar.Reset()
 		}
 
 		if err != nil {
@@ -154,6 +159,16 @@ func (c *respClient) handleRequest(reqData [][]byte) error {
 		c.cmd = hack.String(lowerSlice(reqData[0]))
 		c.args = reqData[1:]
 	}
+
+	if c.cmd == "xuse" {
+		err := c.handleUseThenCmd()
+		if err != nil {
+			c.resp.writeError(err)
+			c.resp.flush()
+			return nil
+		}
+	}
+
 	if c.cmd == "quit" {
 		c.activeQuit = true
 		c.resp.writeStatus(OK)
@@ -164,10 +179,35 @@ func (c *respClient) handleRequest(reqData [][]byte) error {
 
 	c.perform()
 
-	c.cmd = ""
-	c.args = nil
+	return nil
+}
 
-	c.ar.Reset()
+// XUSE db THEN command
+func (c *respClient) handleUseThenCmd() error {
+	if len(c.args) <= 2 {
+		// invalid command format
+		return fmt.Errorf("invalid format for XUSE, must XUSE db THEN your command")
+	}
+
+	if hack.String(upperSlice(c.args[1])) != "THEN" {
+		// invalid command format, just resturn here
+		return fmt.Errorf("invalid format for XUSE, must XUSE db THEN your command")
+	}
+
+	index, err := strconv.Atoi(hack.String(c.args[0]))
+	if err != nil {
+		return fmt.Errorf("invalid db for XUSE, err %v", err)
+	}
+
+	db, err := c.app.ldb.Select(index)
+	if err != nil {
+		return fmt.Errorf("invalid db for XUSE, err %v", err)
+	}
+
+	c.db = db
+
+	c.cmd = hack.String(lowerSlice(c.args[2]))
+	c.args = c.args[3:]
 
 	return nil
 }

server/cmd_server_test.go

@@ -0,0 +1,38 @@
+package server
+
+import (
+	"github.com/siddontang/goredis"
+	"testing"
+)
+
+func TestXuse(t *testing.T) {
+	c1 := getTestConn()
+	defer c1.Close()
+
+	c2 := getTestConn()
+	defer c2.Close()
+
+	_, err := c1.Do("XUSE", "1", "THEN", "SET", "tmp_select_key", "1")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = goredis.Int(c2.Do("GET", "tmp_select_key"))
+	if err != goredis.ErrNil {
+		t.Fatal(err)
+	}
+
+	n, _ := goredis.Int(c2.Do("XUSE", "1", "THEN", "GET", "tmp_select_key"))
+	if n != 1 {
+		t.Fatal(n)
+	}
+
+	n, _ = goredis.Int(c2.Do("GET", "tmp_select_key"))
+	if n != 1 {
+		t.Fatal(n)
+	}
+
+	c1.Do("SELECT", 0)
+	c2.Do("SELECT", 0)
+
+}

server/util.go

@@ -134,3 +134,14 @@ func lowerSlice(buf []byte) []byte {
 	}
 	return buf
 }
+
+func upperSlice(buf []byte) []byte {
+	for i, r := range buf {
+		if 'a' <= r && r <= 'z' {
+			r -= 'a' - 'A'
+		}
+
+		buf[i] = r
+	}
+	return buf
+}