Properly filter out custom query params in MySQL DB driver

Addresses: https://github.com/golang-migrate/migrate/issues/272

database/mysql/mysql.go

@@ -97,6 +97,23 @@ func WithInstance(instance *sql.DB, config *Config) (database.Driver, error) {
 	return mx, nil
 }
 
+// extractCustomQueryParams extracts the custom query params (ones that start with "x-") from
+// mysql.Config.Params (connection parameters) as to not interfere with connecting to MySQL
+func extractCustomQueryParams(c *mysql.Config) (map[string]string, error) {
+	if c == nil {
+		return nil, ErrNilConfig
+	}
+	customQueryParams := map[string]string{}
+
+	for k, v := range c.Params {
+		if strings.HasPrefix(k, "x-") {
+			customQueryParams[k] = v
+			delete(c.Params, k)
+		}
+	}
+	return customQueryParams, nil
+}
+
 func urlToMySQLConfig(url string) (*mysql.Config, error) {
 	config, err := mysql.ParseDSN(strings.TrimPrefix(url, "mysql://"))
 	if err != nil {
@@ -174,6 +191,13 @@ func (m *Mysql) Open(url string) (database.Driver, error) {
 	if err != nil {
 		return nil, err
 	}
+	fmt.Printf("config: %+v\n", config)
+
+	customParams, err := extractCustomQueryParams(config)
+	if err != nil {
+		return nil, err
+	}
+	fmt.Printf("config: %+v\n", config)
 
 	db, err := sql.Open("mysql", config.FormatDSN())
 	if err != nil {
@@ -182,7 +206,7 @@ func (m *Mysql) Open(url string) (database.Driver, error) {
 
 	mx, err := WithInstance(db, &Config{
 		DatabaseName:    config.DBName,
-		MigrationsTable: config.Params["x-migrations-table"],
+		MigrationsTable: customParams["x-migrations-table"],
 	})
 	if err != nil {
 		return nil, err

database/mysql/mysql_test.go

@@ -6,17 +6,17 @@ import (
 	sqldriver "database/sql/driver"
 	"fmt"
 	"log"
-
-	"github.com/golang-migrate/migrate/v4"
 	"testing"
 )
 
 import (
 	"github.com/dhui/dktest"
 	"github.com/go-sql-driver/mysql"
+	"github.com/stretchr/testify/assert"
 )
 
 import (
+	"github.com/golang-migrate/migrate/v4"
 	dt "github.com/golang-migrate/migrate/v4/database/testing"
 	"github.com/golang-migrate/migrate/v4/dktesting"
 	_ "github.com/golang-migrate/migrate/v4/source/file"
@@ -175,6 +175,62 @@ func TestLockWorks(t *testing.T) {
 	})
 }
 
+func TestExtractCustomQueryParams(t *testing.T) {
+	testcases := []struct {
+		name                 string
+		config               *mysql.Config
+		expectedParams       map[string]string
+		expectedCustomParams map[string]string
+		expectedErr          error
+	}{
+		{name: "nil config", expectedErr: ErrNilConfig},
+		{
+			name:                 "no params",
+			config:               mysql.NewConfig(),
+			expectedCustomParams: map[string]string{},
+		},
+		{
+			name:                 "no custom params",
+			config:               &mysql.Config{Params: map[string]string{"hello": "world"}},
+			expectedParams:       map[string]string{"hello": "world"},
+			expectedCustomParams: map[string]string{},
+		},
+		{
+			name: "one param, one custom param",
+			config: &mysql.Config{
+				Params: map[string]string{"hello": "world", "x-foo": "bar"},
+			},
+			expectedParams:       map[string]string{"hello": "world"},
+			expectedCustomParams: map[string]string{"x-foo": "bar"},
+		},
+		{
+			name: "multiple params, multiple custom params",
+			config: &mysql.Config{
+				Params: map[string]string{
+					"hello": "world",
+					"x-foo": "bar",
+					"dead":  "beef",
+					"x-cat": "hat",
+				},
+			},
+			expectedParams:       map[string]string{"hello": "world", "dead": "beef"},
+			expectedCustomParams: map[string]string{"x-foo": "bar", "x-cat": "hat"},
+		},
+	}
+	for _, tc := range testcases {
+		t.Run(tc.name, func(t *testing.T) {
+			customParams, err := extractCustomQueryParams(tc.config)
+			if tc.config != nil {
+				assert.Equal(t, tc.expectedParams, tc.config.Params,
+					"Expected config params have custom params properly removed")
+			}
+			assert.Equal(t, tc.expectedErr, err, "Expected errors to match")
+			assert.Equal(t, tc.expectedCustomParams, customParams,
+				"Expected custom params to be properly extracted")
+		})
+	}
+}
+
 func TestURLToMySQLConfig(t *testing.T) {
 	testcases := []struct {
 		name        string