fix(tools/mysql): fix encoded text for mysql (#1161)

Update the type conversion to according to the types that mysql driver
returns: https://github.com/go-sql-driver/mysql/blob/v1.9.3/fields.go

All `scanTypeBytes` or `scanTypeString` or `scanTypeNullString` will now
be converted into string. Remaining types (numeric types or
`scanTypeUnknown`) are all returned as is.

Separately handle "JSON" to prevent double marshaling.

Fixes #840

internal/tools/mysql/mysqlcommon/mysqlcommon.go

@@ -0,0 +1,43 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package mysqlcommon
+
+import (
+	"database/sql"
+	"encoding/json"
+	"reflect"
+)
+
+// ConvertToType handles casting mysql returns to the right type
+// types for mysql driver: https://github.com/go-sql-driver/mysql/blob/v1.9.3/fields.go
+// all numeric type or unknown type will be return as is.
+func ConvertToType(t *sql.ColumnType, v any) (any, error) {
+	switch t.ScanType() {
+	case reflect.TypeOf(""), reflect.TypeOf([]byte{}), reflect.TypeOf(sql.NullString{}):
+		// unmarshal JSON data before returning to prevent double marshaling
+		if t.DatabaseTypeName() == "JSON" {
+			// unmarshal JSON data before storing to prevent double marshaling
+			var unmarshaledData any
+			err := json.Unmarshal(v.([]byte), &unmarshaledData)
+			if err != nil {
+				return nil, err
+			}
+			return unmarshaledData, nil
+		}
+		return string(v.([]byte)), nil
+	default:
+		return v, nil
+	}
+}

internal/tools/mysql/mysqlexecutesql/mysqlexecutesql.go

@@ -24,6 +24,7 @@ import (
 	"github.com/googleapis/genai-toolbox/internal/sources/cloudsqlmysql"
 	"github.com/googleapis/genai-toolbox/internal/sources/mysql"
 	"github.com/googleapis/genai-toolbox/internal/tools"
+	"github.com/googleapis/genai-toolbox/internal/tools/mysql/mysqlcommon"
 	"github.com/googleapis/genai-toolbox/internal/util"
 )
 
@@ -168,13 +169,9 @@ func (t Tool) Invoke(ctx context.Context, params tools.ParamValues, accessToken
 				continue
 			}
 
-			// mysql driver return []uint8 type for "TEXT", "VARCHAR", and "NVARCHAR"
-			// we'll need to cast it back to string
-			switch colTypes[i].DatabaseTypeName() {
-			case "TEXT", "VARCHAR", "NVARCHAR":
-				vMap[name] = string(val.([]byte))
-			default:
-				vMap[name] = val
+			vMap[name], err = mysqlcommon.ConvertToType(colTypes[i], val)
+			if err != nil {
+				return nil, fmt.Errorf("errors encountered when converting values: %w", err)
 			}
 		}
 		out = append(out, vMap)

internal/tools/mysql/mysqlsql/mysqlsql.go

@@ -17,7 +17,6 @@ package mysqlsql
 import (
 	"context"
 	"database/sql"
-	"encoding/json"
 	"fmt"
 
 	yaml "github.com/goccy/go-yaml"
@@ -25,6 +24,7 @@ import (
 	"github.com/googleapis/genai-toolbox/internal/sources/cloudsqlmysql"
 	"github.com/googleapis/genai-toolbox/internal/sources/mysql"
 	"github.com/googleapis/genai-toolbox/internal/tools"
+	"github.com/googleapis/genai-toolbox/internal/tools/mysql/mysqlcommon"
 )
 
 const kind string = "mysql-sql"
@@ -178,21 +178,9 @@ func (t Tool) Invoke(ctx context.Context, params tools.ParamValues, accessToken
 				continue
 			}
 
-			// mysql driver return []uint8 type for "TEXT", "VARCHAR", and "NVARCHAR"
-			// we'll need to cast it back to string
-			switch colTypes[i].DatabaseTypeName() {
-			case "JSON":
-				// unmarshal JSON data before storing to prevent double marshaling
-				var unmarshaledData any
-				err := json.Unmarshal(val.([]byte), &unmarshaledData)
-				if err != nil {
-					return nil, fmt.Errorf("unable to unmarshal json data %s", val)
-				}
-				vMap[name] = unmarshaledData
-			case "TEXT", "VARCHAR", "NVARCHAR":
-				vMap[name] = string(val.([]byte))
-			default:
-				vMap[name] = val
+			vMap[name], err = mysqlcommon.ConvertToType(colTypes[i], val)
+			if err != nil {
+				return nil, fmt.Errorf("errors encountered when converting values: %w", err)
 			}
 		}
 		out = append(out, vMap)