surface original network errors and create error stacks (#425)

Author: gleonid

packet/conn.go

@@ -94,7 +94,7 @@ func (c *Conn) ReadPacketTo(w io.Writer) error {
 	header := []byte{0, 0, 0, 0}
 
 	if _, err := io.ReadFull(c.reader, header); err != nil {
-		return ErrBadConn
+		return errors.Wrapf(ErrBadConn, "io.ReadFull(header) failed. err %v", err)
 	}
 
 	length := int(uint32(header[0]) | uint32(header[1])<<8 | uint32(header[2])<<16)
@@ -112,16 +112,16 @@ func (c *Conn) ReadPacketTo(w io.Writer) error {
 	}
 
 	if n, err := io.CopyN(w, c.reader, int64(length)); err != nil {
-		return ErrBadConn
+		return errors.Wrapf(ErrBadConn, "io.CopyN failed. err %v, copied %v, expected %v", err, n, length)
 	} else if n != int64(length) {
-		return ErrBadConn
+		return errors.Wrapf(ErrBadConn, "io.CopyN failed(n != int64(length)). %v bytes copied, while %v expected", n, length)
 	} else {
 		if length < MaxPayloadLen {
 			return nil
 		}
 
 		if err := c.ReadPacketTo(w); err != nil {
-			return err
+			return errors.Wrap(err, "ReadPacketTo failed")
 		}
 	}
 
@@ -141,9 +141,9 @@ func (c *Conn) WritePacket(data []byte) error {
 		data[3] = c.Sequence
 
 		if n, err := c.Write(data[:4+MaxPayloadLen]); err != nil {
-			return ErrBadConn
+			return errors.Wrapf(ErrBadConn, "Write(payload portion) failed. err %v", err)
 		} else if n != (4 + MaxPayloadLen) {
-			return ErrBadConn
+			return errors.Wrapf(ErrBadConn, "Write(payload portion) failed. only %v bytes written, while %v expected", n, 4+MaxPayloadLen)
 		} else {
 			c.Sequence++
 			length -= MaxPayloadLen
@@ -157,9 +157,9 @@ func (c *Conn) WritePacket(data []byte) error {
 	data[3] = c.Sequence
 
 	if n, err := c.Write(data); err != nil {
-		return ErrBadConn
+		return errors.Wrapf(ErrBadConn, "Write failed. err %v", err)
 	} else if n != len(data) {
-		return ErrBadConn
+		return errors.Wrapf(ErrBadConn, "Write failed. only %v bytes written, while %v expected", n, len(data))
 	} else {
 		c.Sequence++
 		return nil
@@ -177,7 +177,7 @@ func (c *Conn) WriteClearAuthPacket(password string) error {
 	copy(data[4:], password)
 	data[4+pktLen-1] = 0x00
 
-	return c.WritePacket(data)
+	return errors.Wrap(c.WritePacket(data), "WritePacket failed")
 }
 
 // WritePublicKeyAuthPacket: Caching sha2 authentication. Public key request and send encrypted password
@@ -186,17 +186,19 @@ func (c *Conn) WritePublicKeyAuthPacket(password string, cipher []byte) error {
 	// request public key
 	data := make([]byte, 4+1)
 	data[4] = 2 // cachingSha2PasswordRequestPublicKey
-	c.WritePacket(data)
+	if err := c.WritePacket(data); err != nil {
+		return errors.Wrap(err, "WritePacket(single byte) failed")
+	}
 
 	data, err := c.ReadPacket()
 	if err != nil {
-		return err
+		return errors.Wrap(err, "ReadPacket failed")
 	}
 
 	block, _ := pem.Decode(data[1:])
 	pub, err := x509.ParsePKIXPublicKey(block.Bytes)
 	if err != nil {
-		return err
+		return errors.Wrap(err, "x509.ParsePKIXPublicKey failed")
 	}
 
 	plain := make([]byte, len(password)+1)
@@ -209,15 +211,15 @@ func (c *Conn) WritePublicKeyAuthPacket(password string, cipher []byte) error {
 	enc, _ := rsa.EncryptOAEP(sha1v, rand.Reader, pub.(*rsa.PublicKey), plain, nil)
 	data = make([]byte, 4+len(enc))
 	copy(data[4:], enc)
-	return c.WritePacket(data)
+	return errors.Wrap(c.WritePacket(data), "WritePacket failed")
 }
 
 func (c *Conn) WriteEncryptedPassword(password string, seed []byte, pub *rsa.PublicKey) error {
 	enc, err := EncryptPassword(password, seed, pub)
 	if err != nil {
-		return err
+		return errors.Wrap(err, "EncryptPassword failed")
 	}
-	return c.WriteAuthSwitchPacket(enc, false)
+	return errors.Wrap(c.WriteAuthSwitchPacket(enc, false), "WriteAuthSwitchPacket failed")
 }
 
 // http://dev.mysql.com/doc/internals/en/connection-phase-packets.html#packet-Protocol::AuthSwitchResponse
@@ -234,7 +236,7 @@ func (c *Conn) WriteAuthSwitchPacket(authData []byte, addNUL bool) error {
 		data[pktLen-1] = 0x00
 	}
 
-	return c.WritePacket(data)
+	return errors.Wrap(c.WritePacket(data), "WritePacket failed")
 }
 
 func (c *Conn) ResetSequence() {
@@ -244,7 +246,7 @@ func (c *Conn) ResetSequence() {
 func (c *Conn) Close() error {
 	c.Sequence = 0
 	if c.Conn != nil {
-		return c.Conn.Close()
+		return errors.Wrap(c.Conn.Close(), "Conn.Close failed")
 	}
 	return nil
 }