net.Conn = nil panicing with logentries and gin-gonic

[mnbb...@gmail.com]

I'm trying to use logentries (via https://github.com/bsphere/le_go) with my 

application that is using the gin web framework (https://github.com/gin-gonic/gin) and it keeps panicing when checking if the logger.conn (net.Conn) is nil.

2014/11/18 22:31:34 PANIC: runtime error: invalid memory address or nil pointer dereference

/usr/local/Cellar/go/1.3.3/libexec/src/pkg/runtime/panic.c:552 (0x147cd)

panicstring: runtime·panic(err);

/usr/local/Cellar/go/1.3.3/libexec/src/pkg/runtime/os_darwin.c:454 (0x1346e)

sigpanic: runtime·panicstring("invalid memory address or nil pointer dereference");

/Users/mnbbrown/Code/go/src/github.com/bsphere/le_go/le.go:68 (0xd2999)

(*Logger).isOpenConnection: if logger.conn == nil {

/Users/mnbbrown/Code/go/src/github.com/bsphere/le_go/le.go:93 (0xd2c39)

(*Logger).ensureOpenConnection: if !logger.isOpenConnection() {

/Users/mnbbrown/Code/go/src/github.com/bsphere/le_go/le.go:173 (0xd339f)

(*Logger).Write: if err := logger.ensureOpenConnection(); err != nil {

/Users/mnbbrown/Code/go/src/github.com/bsphere/le_go/le.go:122 (0xd2ec7)

(*Logger).Output: _, err := logger.Write([]byte(s))

/Users/mnbbrown/Code/go/src/github.com/bsphere/le_go/le.go:158 (0xd32e0)

(*Logger).Println: logger.Output(2, fmt.Sprintln(v...))

/Users/mnbbrown/Code/go/src/bitbucket.org/mnbbrown/sewca/sewca.go:65 (0x3644)

SendEmail: logger.Println(l)

/Users/mnbbrown/Code/go/src/github.com/gin-gonic/gin/context.go:106 (0x35796)

(*Context).Next: c.handlers[c.index](c)

/Users/mnbbrown/Code/go/src/github.com/gin-gonic/gin/logger.go:19 (0x3b3a0)

func.007: c.Next()

/Users/mnbbrown/Code/go/src/github.com/gin-gonic/gin/context.go:106 (0x35796)

(*Context).Next: c.handlers[c.index](c)

/Users/mnbbrown/Code/go/src/github.com/gin-gonic/gin/recovery.go:96 (0x3bc8e)

func.010: c.Next()

/Users/mnbbrown/Code/go/src/github.com/gin-gonic/gin/context.go:106 (0x35796)

(*Context).Next: c.handlers[c.index](c)

/Users/mnbbrown/Code/go/src/github.com/gin-gonic/gin/logger.go:46 (0x3b4c9)

func.008: c.Next()

/Users/mnbbrown/Code/go/src/github.com/gin-gonic/gin/context.go:106 (0x35796)

(*Context).Next: c.handlers[c.index](c)

/Users/mnbbrown/Code/go/src/github.com/gin-gonic/gin/gin.go:197 (0x3b1aa)

func.004: c.Next()

/Users/mnbbrown/Code/go/src/github.com/julienschmidt/httprouter/router.go:276 (0x11f156)

(*Router).ServeHTTP: handle(w, req, ps)

/Users/mnbbrown/Code/go/src/github.com/gin-gonic/gin/gin.go:125 (0x37d59)

(*Engine).ServeHTTP: engine.router.ServeHTTP(w, req)

/usr/local/Cellar/go/1.3.3/libexec/src/pkg/net/http/server.go:1673 (0x5954f)

serverHandler.ServeHTTP: handler.ServeHTTP(rw, req)

/usr/local/Cellar/go/1.3.3/libexec/src/pkg/net/http/server.go:1174 (0x5702e)

(*conn).serve: serverHandler{c.server}.ServeHTTP(w, w.req)

/usr/local/Cellar/go/1.3.3/libexec/src/pkg/runtime/proc.c:1445 (0x18540)

goexit: runtime·goexit(void)

Has this got something to do with access net.Conn from multiple goroutines?
Is there a more efficient way to stream text to a tcp connection?
Should the le_go library be written differently? 

[cm...@golang.org]

You are permitted to access a net.Conn from multiple goroutines: https://code.google.com/p/go/source/browse/src/pkg/net/net.go?name=release#59.

Either way, `logger.conn == nil` could only panic if logger were nil.  I can't see the code in the SendEmail function that calls logger.Println, but I'd guess that logger used there is probably nil. It only panics on the line you see because that's the first time in the chain of method calls that you access a specific field.

[cm...@golang.org]

Actually, looking slightly closer at

/Users/mnbbrown/Code/go/src/bitbucket.org/mnbbrown/sewca/sewca.go:65 (0x3644)

SendEmail: logger.Println(l)

I doubt `0x3644` is a valid address. Could you share that details of how that method creates a logger?

[Dave Cheney]

It is likely that when the logger was created the error was not checked.

[mnbb...@gmail.com]

That address does look strange.

I am checking for an error on creation and I write to the logger outside the request context. It seems like it only panics inside the context of a gin or http request.

conf_logentries_token := os.Getenv("LOGENTRIES_TOKEN")

logger, err := le_go.Connect(conf_logentries_token)
if err != nil {
 log.Fatalln(err)
}

logger.Println("Starting Application!")

The le_go.Connect function looks like this:

func Connect(token string) (*Logger, error) {
 logger := Logger{
 token: token,
 }


 if err := logger.openConnection(); err != nil {
 return nil, err
 }


 return &logger, nil
}

and logger.openConnection() looks like this:

func (logger *Logger) openConnection() error {

conn, err := net.Dial("tcp", "data.logentries.com:80")

if err != nil {

return err

}

logger.conn = conn

return nil

}

All this comes from logentries' 'suggested' library: https://github.com/bsphere/le_go 

[Dave Cheney]

I would avoid that package, it is not safe for use by multiple goroutines.

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[mnbb...@gmail.com]

Do you have an another package that I could model off to create a package that can handle the multiple goroutines?
Something that is streaming data over a TCP/UDP?

Cheers.