Add STRLEN

STRLEN returns the length of the string value stored at key.
An error is returned when key holds a non-string value.

strings.go

@@ -2,8 +2,10 @@ package godis
 
 import (
 	"errors"
+	"reflect"
 	"strconv"
 	"time"
+	"unicode/utf8"
 )
 
 func (g *Godis) getSDS(key string) (*SDS, bool) {
@@ -132,3 +134,16 @@ func (g *Godis) MSET(items ...string) bool {
 	}
 	return true
 }
+
+//STRLEN returns the length of the string value stored at key.
+//An error is returned when key holds a non-string value.
+func (g *Godis) STRLEN(key string) (interface{}, bool) {
+	val, err := g.GET(key)
+
+	if !err && reflect.ValueOf(val).Kind() == reflect.String {
+
+		return int64(utf8.RuneCountInString(val)), false
+	}
+	return "", true
+
+}