database/sql: ensure Stmts are correctly closed.

To make sure that there is no resource leak,
I suggest to fix the 'fakedb' driver such as it fails when any
Stmt is not closed.
First, add a check in fakeConn.Close().
Then, fix all missing Stmt.Close()/Rows.Close().
I am not sure that the strategy choose in fakeConn.Prepare/prepare* is ok.
The weak point in this patch is the change in Tx.Query:
  - Tests pass without this change,
  - I found it by manually analyzing the code,
  - I just try to make Tx.Query look like DB.Query.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5759050

src/pkg/database/sql/fakedb_test.go

@@ -214,6 +214,9 @@ func (c *fakeConn) Close() error {
 	if c.db == nil {
 		return errors.New("can't close fakeConn; already closed")
 	}
+	if c.stmtsMade > c.stmtsClosed {
+		return errors.New("can't close; dangling statement(s)")
+	}
 	c.db = nil
 	return nil
 }
@@ -250,6 +253,7 @@ func errf(msg string, args ...interface{}) error {
 //  just a limitation for fakedb)
 func (c *fakeConn) prepareSelect(stmt *fakeStmt, parts []string) (driver.Stmt, error) {
 	if len(parts) != 3 {
+		stmt.Close()
 		return nil, errf("invalid SELECT syntax with %d parts; want 3", len(parts))
 	}
 	stmt.table = parts[0]
@@ -260,14 +264,17 @@ func (c *fakeConn) prepareSelect(stmt *fakeStmt, parts []string) (driver.Stmt, e
 		}
 		nameVal := strings.Split(colspec, "=")
 		if len(nameVal) != 2 {
+			stmt.Close()
 			return nil, errf("SELECT on table %q has invalid column spec of %q (index %d)", stmt.table, colspec, n)
 		}
 		column, value := nameVal[0], nameVal[1]
 		_, ok := c.db.columnType(stmt.table, column)
 		if !ok {
+			stmt.Close()
 			return nil, errf("SELECT on table %q references non-existent column %q", stmt.table, column)
 		}
 		if value != "?" {
+			stmt.Close()
 			return nil, errf("SELECT on table %q has pre-bound value for where column %q; need a question mark",
 				stmt.table, column)
 		}
@@ -280,12 +287,14 @@ func (c *fakeConn) prepareSelect(stmt *fakeStmt, parts []string) (driver.Stmt, e
 // parts are table|col=type,col2=type2
 func (c *fakeConn) prepareCreate(stmt *fakeStmt, parts []string) (driver.Stmt, error) {
 	if len(parts) != 2 {
+		stmt.Close()
 		return nil, errf("invalid CREATE syntax with %d parts; want 2", len(parts))
 	}
 	stmt.table = parts[0]
 	for n, colspec := range strings.Split(parts[1], ",") {
 		nameType := strings.Split(colspec, "=")
 		if len(nameType) != 2 {
+			stmt.Close()
 			return nil, errf("CREATE table %q has invalid column spec of %q (index %d)", stmt.table, colspec, n)
 		}
 		stmt.colName = append(stmt.colName, nameType[0])
@@ -297,17 +306,20 @@ func (c *fakeConn) prepareCreate(stmt *fakeStmt, parts []string) (driver.Stmt, e
 // parts are table|col=?,col2=val
 func (c *fakeConn) prepareInsert(stmt *fakeStmt, parts []string) (driver.Stmt, error) {
 	if len(parts) != 2 {
+		stmt.Close()
 		return nil, errf("invalid INSERT syntax with %d parts; want 2", len(parts))
 	}
 	stmt.table = parts[0]
 	for n, colspec := range strings.Split(parts[1], ",") {
 		nameVal := strings.Split(colspec, "=")
 		if len(nameVal) != 2 {
+			stmt.Close()
 			return nil, errf("INSERT table %q has invalid column spec of %q (index %d)", stmt.table, colspec, n)
 		}
 		column, value := nameVal[0], nameVal[1]
 		ctype, ok := c.db.columnType(stmt.table, column)
 		if !ok {
+			stmt.Close()
 			return nil, errf("INSERT table %q references non-existent column %q", stmt.table, column)
 		}
 		stmt.colName = append(stmt.colName, column)
@@ -323,10 +335,12 @@ func (c *fakeConn) prepareInsert(stmt *fakeStmt, parts []string) (driver.Stmt, e
 			case "int32":
 				i, err := strconv.Atoi(value)
 				if err != nil {
+					stmt.Close()
 					return nil, errf("invalid conversion to int32 from %q", value)
 				}
 				subsetVal = int64(i) // int64 is a subset type, but not int32
 			default:
+				stmt.Close()
 				return nil, errf("unsupported conversion for pre-bound parameter %q to type %q", value, ctype)
 			}
 			stmt.colValue = append(stmt.colValue, subsetVal)
@@ -362,6 +376,7 @@ func (c *fakeConn) Prepare(query string) (driver.Stmt, error) {
 	case "INSERT":
 		return c.prepareInsert(stmt, parts)
 	default:
+		stmt.Close()
 		return nil, errf("unsupported command type %q", cmd)
 	}
 	return stmt, nil

src/pkg/database/sql/sql.go

@@ -612,9 +612,11 @@ func (tx *Tx) Query(query string, args ...interface{}) (*Rows, error) {
 		return nil, err
 	}
 	rows, err := stmt.Query(args...)
-	if err == nil {
-		rows.closeStmt = stmt
+	if err != nil {
+		stmt.Close()
+		return nil, err
 	}
+	rows.closeStmt = stmt
 	return rows, err
 }
 
@@ -1020,7 +1022,7 @@ func (r *Row) Scan(dest ...interface{}) error {
 	}
 
 	// TODO(bradfitz): for now we need to defensively clone all
-	// []byte that the driver returned (not permitting 
+	// []byte that the driver returned (not permitting
 	// *RawBytes in Rows.Scan), since we're about to close
 	// the Rows in our defer, when we return from this function.
 	// the contract with the driver.Next(...) interface is that it

src/pkg/database/sql/sql_test.go

@@ -251,6 +251,7 @@ func TestStatementQueryRow(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Prepare: %v", err)
 	}
+	defer stmt.Close()
 	var age int
 	for n, tt := range []struct {
 		name string
@@ -291,6 +292,7 @@ func TestExec(t *testing.T) {
 	if err != nil {
 		t.Errorf("Stmt, err = %v, %v", stmt, err)
 	}
+	defer stmt.Close()
 
 	type execTest struct {
 		args    []interface{}
@@ -332,11 +334,14 @@ func TestTxStmt(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Stmt, err = %v, %v", stmt, err)
 	}
+	defer stmt.Close()
 	tx, err := db.Begin()
 	if err != nil {
 		t.Fatalf("Begin = %v", err)
 	}
-	_, err = tx.Stmt(stmt).Exec("Bobby", 7)
+	txs := tx.Stmt(stmt)
+	defer txs.Close()
+	_, err = txs.Exec("Bobby", 7)
 	if err != nil {
 		t.Fatalf("Exec = %v", err)
 	}
@@ -365,6 +370,7 @@ func TestTxQuery(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
+	defer r.Close()
 
 	if !r.Next() {
 		if r.Err() != nil {
@@ -561,6 +567,7 @@ func nullTestRun(t *testing.T, spec nullTestSpec) {
 	if err != nil {
 		t.Fatalf("prepare: %v", err)
 	}
+	defer stmt.Close()
 	if _, err := stmt.Exec(3, "chris", spec.rows[2].nullParam, spec.rows[2].notNullParam); err != nil {
 		t.Errorf("exec insert chris: %v", err)
 	}