fix driver.ErrBadConn behavior

The spec says that ErrBadConn should only be returned when a connection is
in a bad state. We overused it, which lead to re-executed queries in some
cases.
With this fix, all instances of driver.ErrBadConn are replaced with
ErrInvalidConn unless they are in an exported function and appear
before the network is hit.
I also removed it as a return value from Close, where retrying makes
no sense whatsoever.

Author: arnehormann

packets.go

@@ -31,7 +31,7 @@ func (mc *mysqlConn) readPacket() ([]byte, error) {
 		if err != nil {
 			errLog.Print(err)
 			mc.Close()
-			return nil, driver.ErrBadConn
+			return nil, ErrInvalidConn
 		}
 
 		// Packet Length [24 bit]
@@ -40,7 +40,7 @@ func (mc *mysqlConn) readPacket() ([]byte, error) {
 		if pktLen < 1 {
 			errLog.Print(ErrMalformPkt)
 			mc.Close()
-			return nil, driver.ErrBadConn
+			return nil, ErrInvalidConn
 		}
 
 		// Check Packet Sync [8 bit]
@@ -58,7 +58,7 @@ func (mc *mysqlConn) readPacket() ([]byte, error) {
 		if err != nil {
 			errLog.Print(err)
 			mc.Close()
-			return nil, driver.ErrBadConn
+			return nil, ErrInvalidConn
 		}
 
 		isLastPacket := (pktLen < maxPacketSize)
@@ -117,7 +117,7 @@ func (mc *mysqlConn) writePacket(data []byte) error {
 		} else {
 			errLog.Print(err)
 		}
-		return driver.ErrBadConn
+		return ErrInvalidConn
 	}
 }
 
@@ -241,7 +241,7 @@ func (mc *mysqlConn) writeAuthPacket(cipher []byte) error {
 	if data == nil {
 		// can not take the buffer. Something must be wrong with the connection
 		errLog.Print(ErrBusyBuffer)
-		return driver.ErrBadConn
+		return ErrInvalidConn
 	}
 
 	// ClientFlags [32 bit]
@@ -312,7 +312,7 @@ func (mc *mysqlConn) writeOldAuthPacket(cipher []byte) error {
 	if data == nil {
 		// can not take the buffer. Something must be wrong with the connection
 		errLog.Print(ErrBusyBuffer)
-		return driver.ErrBadConn
+		return ErrInvalidConn
 	}
 
 	// Add the scrambled password [null terminated string]
@@ -334,7 +334,7 @@ func (mc *mysqlConn) writeCommandPacket(command byte) error {
 	if data == nil {
 		// can not take the buffer. Something must be wrong with the connection
 		errLog.Print(ErrBusyBuffer)
-		return driver.ErrBadConn
+		return ErrInvalidConn
 	}
 
 	// Add command byte
@@ -353,7 +353,7 @@ func (mc *mysqlConn) writeCommandPacketStr(command byte, arg string) error {
 	if data == nil {
 		// can not take the buffer. Something must be wrong with the connection
 		errLog.Print(ErrBusyBuffer)
-		return driver.ErrBadConn
+		return ErrInvalidConn
 	}
 
 	// Add command byte
@@ -374,7 +374,7 @@ func (mc *mysqlConn) writeCommandPacketUint32(command byte, arg uint32) error {
 	if data == nil {
 		// can not take the buffer. Something must be wrong with the connection
 		errLog.Print(ErrBusyBuffer)
-		return driver.ErrBadConn
+		return ErrInvalidConn
 	}
 
 	// Add command byte
@@ -767,7 +767,7 @@ func (stmt *mysqlStmt) writeExecutePacket(args []driver.Value) error {
 	if data == nil {
 		// can not take the buffer. Something must be wrong with the connection
 		errLog.Print(ErrBusyBuffer)
-		return driver.ErrBadConn
+		return ErrInvalidConn
 	}
 
 	// command [1 byte]

statement.go

@@ -22,7 +22,7 @@ type mysqlStmt struct {
 func (stmt *mysqlStmt) Close() error {
 	if stmt.mc == nil || stmt.mc.netConn == nil {
 		errLog.Print(ErrInvalidConn)
-		return driver.ErrBadConn
+		return ErrInvalidConn
 	}
 
 	err := stmt.mc.writeCommandPacketUint32(comStmtClose, stmt.id)