fix unicode support related bugs in s3select (#7877)

pkg/s3select/csv/reader.go

@@ -141,9 +141,8 @@ func NewReader(readCloser io.ReadCloser, args *ReaderArgs) (*Reader, error) {
 	// If LazyQuotes is true, a quote may appear in an unquoted field and a
 	// non-doubled quote may appear in a quoted field.
 	csvReader.LazyQuotes = true
-	// If TrimLeadingSpace is true, leading white space in a field is ignored.
-	// This is done even if the field delimiter, Comma, is white space.
-	csvReader.TrimLeadingSpace = true
+	// We do not trim leading space to keep consistent with s3.
+	csvReader.TrimLeadingSpace = false
 
 	r := &Reader{
 		args:       args,

pkg/s3select/sql/funceval.go

@@ -196,7 +196,7 @@ func charlen(v *Value) (*Value, error) {
 		err := fmt.Errorf("%s/%s expects a string argument", sqlFnCharLength, sqlFnCharacterLength)
 		return nil, errIncorrectSQLFunctionArgumentType(err)
 	}
-	return FromInt(int64(len(s))), nil
+	return FromInt(int64(len([]rune(s)))), nil
 }
 
 func lowerCase(v *Value) (*Value, error) {

pkg/s3select/sql/stringfuncs.go

@@ -142,18 +142,29 @@ func dropRune(text string) (res string, ok bool) {
 }
 
 func evalSQLSubstring(s string, startIdx, length int) (res string, err error) {
-	if startIdx <= 0 || startIdx > len(s) {
-		return "", errInvalidSubstringIndexLen
+	rs := []rune(s)
+
+	// According to s3 document, if startIdx < 1, it is set to 1.
+	if startIdx < 1 {
+		startIdx = 1
 	}
+
+	if startIdx > len(rs) {
+		startIdx = len(rs) + 1
+	}
+
 	// StartIdx is 1-based in the input
 	startIdx--
-
-	rs := []rune(s)
 	endIdx := len(rs)
 	if length != -1 {
-		if length < 0 || startIdx+length > len(s) {
+		if length < 0 {
 			return "", errInvalidSubstringIndexLen
 		}
+
+		if length > (endIdx - startIdx) {
+			length = endIdx - startIdx
+		}
+
 		endIdx = startIdx + length
 	}
 

pkg/s3select/sql/stringfuncs_test.go

@@ -105,3 +105,27 @@ func TestEvalSQLLike(t *testing.T) {
 		}
 	}
 }
+
+func TestEvalSQLSubstring(t *testing.T) {
+	evalCases := []struct {
+		s           string
+		startIdx    int
+		length      int
+		resExpected string
+		errExpected error
+	}{
+		{"abcd", 1, 1, "a", nil},
+		{"abcd", -1, 1, "a", nil},
+		{"abcd", 999, 999, "", nil},
+		{"", 999, 999, "", nil},
+		{"测试abc", 1, 1, "测", nil},
+		{"测试abc", 5, 5, "c", nil},
+	}
+
+	for i, tc := range evalCases {
+		res, err := evalSQLSubstring(tc.s, tc.startIdx, tc.length)
+		if res != tc.resExpected || err != tc.errExpected {
+			t.Errorf("Eval Case %d failed: %v %v", i, res, err)
+		}
+	}
+}