Panic when a closed connnection is used

[ghost]

i use git clone get new code, if I kill the mysql connection:
under linux(centos i686), it fatal.
under windows(xp, x32), it not autoreconnect

mysql version 5.1.69(contos x64)

[wanghl@localhost iVega]$ go run testdb.go
2013/10/29 15:13:29 insert 0
2013/10/29 15:13:32 insert 1
2013/10/29 15:13:35 insert 2
2013/10/29 15:13:38 insert 3
2013/10/29 15:13:41 insert 4
[MySQL] 2013/10/29 15:13:41 packets.go:30: EOF
2013/10/29 15:13:41 wanghl! driver: bad connection
2013/10/29 15:13:44 insert 5
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x1 pc=0x8078693]

goroutine 1 [running]:
github.com/go-sql-driver/mysql.(_mysqlStmt).writeExecutePacket(0x1835b900, 0x1835f330, 0x5, 0x5, 0x1, ...)
/home/wanghl/mygo/src/github.com/go-sql-driver/mysql/packets.go:818 +0x1a03
github.com/go-sql-driver/mysql.(_mysqlStmt).Exec(0x1835b900, 0x1835f330, 0x5, 0x5, 0x1835f330, ...)
/home/wanghl/mygo/src/github.com/go-sql-driver/mysql/statement.go:38 +0x41
database/sql.resultFromStatement(0x1835b960, 0x1835f180, 0x1835f1b0, 0x1835b900, 0xb73f8f00, ...)
/usr/local/go/src/pkg/database/sql/sql.go:1077 +0x1df
database/sql.(*Stmt).Exec(0x18363140, 0xb73f8f00, 0x5, 0x5, 0x0, ...)
/usr/local/go/src/pkg/database/sql/sql.go:1056 +0x13d
main.Insert(0x7, 0x5, 0x81a0108, 0x3, 0x18300488, ...)
/home/wanghl/mygo/src/iVega/testdb.go:66 +0x14c
main.main()
/home/wanghl/mygo/src/iVega/testdb.go:31 +0x269

goroutine 2 [syscall]:
exit status 2

E:\mygo>go run testdb.go
2013/10/29 15:12:57 insert 0
2013/10/29 15:13:00 insert 1
2013/10/29 15:13:03 insert 2
2013/10/29 15:13:06 insert 3
2013/10/29 15:13:09 insert 4
[MySQL] 2013/10/29 15:13:09 packets.go:31: EOF
2013/10/29 15:13:09 wanghl! driver: bad connection
2013/10/29 15:13:12 insert 5
[MySQL] 2013/10/29 15:13:12 packets.go:88: WSASend tcp 172.7.3.42:60823: An esta
blished connection was aborted by the software in your host machine.
2013/10/29 15:13:12 wanghl! driver: bad connection
2013/10/29 15:13:15 insert 6
[MySQL] 2013/10/29 15:13:15 packets.go:88: WSASend tcp 172.7.3.42:60823: An esta
blished connection was aborted by the software in your host machine.
2013/10/29 15:13:15 wanghl! driver: bad connection
2013/10/29 15:13:18 insert 7
[MySQL] 2013/10/29 15:13:18 packets.go:88: WSASend tcp 172.7.3.42:60823: An esta
blished connection was aborted by the software in your host machine.

My test code is here:
http://play.golang.org/p/XuCQ7Ug-O2

I also test Query(), it work fine

[ghost]

Stmt.Exec() have problem, db.Exec() is OK

[arnehormann]

It looks like #98 - we can't do much about that, it's a problem in go's database/sql. They don't accept a fix until go version 1.2 is released.

[julienschmidt]

At least the panic in the driver code shouldn't happen.

[arnehormann]

We found the cause.
When Close is called in connection.go, a buffer used by the connection is set to nil.
When the connection is used, writeExecutePacket dereferences a nil pointer (mc.buf).
You (or in this case database/sql) should not reuse closed connections, but the driver should not panic.
We will create a PR to return a meaningful error instead.

[ghost]

go 1.2rc2 test fail, it does not seem to fix.

[arnehormann]

@better0332 yes, we only identified the bug, the pull request with a partial fix (don't panic, just return an error) is not done yet. And we can't really fix this until this bugfix by @julienschmidt is integrated in Go: https://codereview.appspot.com/14920046 - and it looks like that will only take place after Go 1.2

[arnehormann]

fixed in #143