improve:GetCharsetDesc (pingcap#256)

charset/charset.go

@@ -119,17 +119,20 @@ func GetCharsetInfo(cs string) (string, string, error) {
 
 // GetCharsetDesc gets charset descriptions in the local charsets.
 func GetCharsetDesc(cs string) (*Desc, error) {
-	c, ok := charsets[strings.ToLower(cs)]
-	if !ok {
+	switch strings.ToLower(cs) {
+	case CharsetUTF8:
+		return descs[0], nil
+	case CharsetUTF8MB4:
+		return descs[1], nil
+	case CharsetASCII:
+		return descs[2], nil
+	case CharsetLatin1:
+		return descs[3], nil
+	case CharsetBin:
+		return descs[4], nil
+	default:
 		return nil, errors.Errorf("Unknown charset %s", cs)
 	}
-	desc := &Desc{
-		Name:             c.Name,
-		DefaultCollation: c.DefaultCollation,
-		Desc:             c.Desc,
-		Maxlen:           c.Maxlen,
-	}
-	return desc, nil
 }
 
 // GetCharsetInfoByID returns charset and collation for id as cs_number.

charset/charset_test.go

@@ -14,6 +14,7 @@
 package charset
 
 import (
+	"math/rand"
 	"testing"
 
 	. "github.com/pingcap/check"
@@ -98,3 +99,40 @@ func (s *testCharsetSuite) TestGetDefaultCollation(c *C) {
 		testGetDefaultCollation(c, tt.cs, tt.co, tt.succ)
 	}
 }
+
+func (s *testCharsetSuite) TestGetCharsetDesc(c *C) {
+	defer testleak.AfterTest(c)()
+	tests := []struct {
+		cs     string
+		result string
+		succ   bool
+	}{
+		{"utf8", "utf8", true},
+		{"UTF8", "utf8", true},
+		{"utf8mb4", "utf8mb4", true},
+		{"ascii", "ascii", true},
+		{"binary", "binary", true},
+		{"latin1", "latin1", true},
+		{"invalid_cs", "", false},
+		{"", "utf8_bin", false},
+	}
+	for _, tt := range tests {
+		desc, err := GetCharsetDesc(tt.cs)
+		if !tt.succ {
+			c.Assert(err, NotNil)
+		} else {
+			c.Assert(desc.Name, Equals, tt.result)
+		}
+	}
+}
+
+func BenchmarkGetCharsetDesc(b *testing.B) {
+	b.ResetTimer()
+	charsets := []string{CharsetUTF8, CharsetUTF8MB4, CharsetASCII, CharsetLatin1, CharsetBin}
+	index := rand.Intn(len(charsets))
+	cs := charsets[index]
+
+	for i := 0; i < b.N; i++ {
+		GetCharsetDesc(cs)
+	}
+}