database/sql: use errors.Is when checking ErrBadConn

When drivers return driver.ErrBadConn, no meaningful
information about what the cause of the problem is
returned. Ideally the driver.ErrBadConn would be
always caught with the retry loop, but this is not
always the case. Drivers today must choose between
returning a useful error and use the rety logic.
This allows supporting both.

Fixes #47142

Change-Id: I454573028f041dfdf874eed6c254fb194ccf6d96
Reviewed-on: https://go-review.googlesource.com/c/go/+/333949
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Trust: Ian Lance Taylor <iant@golang.org>
Trust: Daniel Theophanes <kardianos@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 20 insertions, 7 deletions

diff --git a/src/database/sql/fakedb_test.go b/src/database/sql/fakedb_test.go
index 4b68f1cba9..34e97e012b 100644
--- a/src/database/sql/fakedb_test.go
+++ b/src/database/sql/fakedb_test.go
@@ -96,6 +96,19 @@ type fakeDB struct {
 	allowAny bool
 }
 
+type fakeError struct {
+	Message string
+	Wrapped error
+}
+
+func (err fakeError) Error() string {
+	return err.Message
+}
+
+func (err fakeError) Unwrap() error {
+	return err.Wrapped
+}
+
 type table struct {
 	mu      sync.Mutex
 	colname []string
@@ -368,7 +381,7 @@ func (c *fakeConn) isDirtyAndMark() bool {
 
 func (c *fakeConn) Begin() (driver.Tx, error) {
 	if c.isBad() {
-		return nil, driver.ErrBadConn
+		return nil, fakeError{Wrapped: driver.ErrBadConn}
 	}
 	if c.currTx != nil {
 		return nil, errors.New("fakedb: already in a transaction")
@@ -401,7 +414,7 @@ func (c *fakeConn) ResetSession(ctx context.Context) error {
 	c.dirtySession = false
 	c.currTx = nil
 	if c.isBad() {
-		return driver.ErrBadConn
+		return fakeError{Message: "Reset Session: bad conn", Wrapped: driver.ErrBadConn}
 	}
 	return nil
 }
@@ -629,7 +642,7 @@ func (c *fakeConn) PrepareContext(ctx context.Context, query string) (driver.Stm
 	}
 
 	if c.stickyBad || (hookPrepareBadConn != nil && hookPrepareBadConn()) {
-		return nil, driver.ErrBadConn
+		return nil, fakeError{Message: "Preapre: Sticky Bad", Wrapped: driver.ErrBadConn}
 	}
 
 	c.touchMem()
@@ -756,7 +769,7 @@ func (s *fakeStmt) ExecContext(ctx context.Context, args []driver.NamedValue) (d
 	}
 
 	if s.c.stickyBad || (hookExecBadConn != nil && hookExecBadConn()) {
-		return nil, driver.ErrBadConn
+		return nil, fakeError{Message: "Exec: Sticky Bad", Wrapped: driver.ErrBadConn}
 	}
 	if s.c.isDirtyAndMark() {
 		return nil, errFakeConnSessionDirty
@@ -870,7 +883,7 @@ func (s *fakeStmt) QueryContext(ctx context.Context, args []driver.NamedValue) (
 	}
 
 	if s.c.stickyBad || (hookQueryBadConn != nil && hookQueryBadConn()) {
-		return nil, driver.ErrBadConn
+		return nil, fakeError{Message: "Query: Sticky Bad", Wrapped: driver.ErrBadConn}
 	}
 	if s.c.isDirtyAndMark() {
 		return nil, errFakeConnSessionDirty
@@ -1031,7 +1044,7 @@ var hookCommitBadConn func() bool
 func (tx *fakeTx) Commit() error {
 	tx.c.currTx = nil
 	if hookCommitBadConn != nil && hookCommitBadConn() {
-		return driver.ErrBadConn
+		return fakeError{Message: "Commit: Hook Bad Conn", Wrapped: driver.ErrBadConn}
 	}
 	tx.c.touchMem()
 	return nil
@@ -1043,7 +1056,7 @@ var hookRollbackBadConn func() bool
 func (tx *fakeTx) Rollback() error {
 	tx.c.currTx = nil
 	if hookRollbackBadConn != nil && hookRollbackBadConn() {
-		return driver.ErrBadConn
+		return fakeError{Message: "Rollback: Hook Bad Conn", Wrapped: driver.ErrBadConn}
 	}
 	tx.c.touchMem()
 	return nil