Inform database/sql when connections die

conn.go

@@ -116,6 +116,7 @@ func (e ProtocolError) Error() string {
 }
 
 var NotificationTimeoutError = errors.New("Notification Timeout")
+var DeadConnError = errors.New("Connection is dead")
 
 // Connect establishes a connection with a PostgreSQL server using config. One
 // of config.Socket or config.Host must be specified. config.User
@@ -966,8 +967,7 @@ func (c *Conn) rxMsg() (t byte, r *MessageReader, err error) {
 
 func (c *Conn) rxMsgHeader() (t byte, bodySize int32, err error) {
 	if !c.alive {
-		err = errors.New("Connection is dead")
-		return
+		return 0, 0, DeadConnError
 	}
 
 	defer func() {
@@ -987,7 +987,7 @@ func (c *Conn) rxMsgHeader() (t byte, bodySize int32, err error) {
 
 func (c *Conn) rxMsgBody(bodySize int32) (*bytes.Buffer, error) {
 	if !c.alive {
-		return nil, errors.New("Connection is dead")
+		return nil, DeadConnError
 	}
 
 	buf := c.getBuf()
@@ -1135,7 +1135,7 @@ func (c *Conn) txStartupMessage(msg *startupMessage) (err error) {
 
 func (c *Conn) txMsg(identifier byte, buf *bytes.Buffer, flush bool) (err error) {
 	if !c.alive {
-		return errors.New("Connection is dead")
+		return DeadConnError
 	}
 
 	defer func() {

stdlib/sql.go

@@ -36,6 +36,10 @@ type Conn struct {
 }
 
 func (c *Conn) Prepare(query string) (driver.Stmt, error) {
+	if !c.conn.IsAlive() {
+		return nil, driver.ErrBadConn
+	}
+
 	name := fmt.Sprintf("pgx_%d", c.psCount)
 	c.psCount++
 
@@ -52,6 +56,10 @@ func (c *Conn) Close() error {
 }
 
 func (c *Conn) Begin() (driver.Tx, error) {
+	if !c.conn.IsAlive() {
+		return nil, driver.ErrBadConn
+	}
+
 	_, err := c.conn.Execute("begin")
 	if err != nil {
 		return nil, err
@@ -74,12 +82,20 @@ func (s *Stmt) NumInput() int {
 }
 
 func (s *Stmt) Exec(argsV []driver.Value) (driver.Result, error) {
+	if !s.conn.IsAlive() {
+		return nil, driver.ErrBadConn
+	}
+
 	args := valueToInterface(argsV)
 	commandTag, err := s.conn.Execute(s.ps.Name, args...)
 	return driver.RowsAffected(commandTag.RowsAffected()), err
 }
 
 func (s *Stmt) Query(argsV []driver.Value) (driver.Rows, error) {
+	if !s.conn.IsAlive() {
+		return nil, driver.ErrBadConn
+	}
+
 	args := valueToInterface(argsV)
 
 	rowCount := 0