raven-go obscures panic error message

[kevinburke]

If I call panic, usually that error message appears in the stack trace.

package main

func main() {
    panic("error occurred")
}

Generates:

panic: error occurred

goroutine 1 [running]:
panic(0x56000, 0xc42000a130)
    /Users/kevin/go/src/runtime/panic.go:500 +0x1a1
main.main()
    /Users/kevin/foo.go:4 +0x6d
exit status 2

However when I use the RecoveryHandler, I get an empty panic message in the stack trace - I have to check my email or log into Sentry to actually see what the panic was.

Example:

goroutine 44 [running]:
runtime/debug.Stack(0x0, 0x3bb8a5e2010def0, 0x1c5243)
    /Users/kevin/go/src/runtime/debug/stack.go:24 +0x79
runtime/debug.PrintStack()
    /Users/kevin/go/src/runtime/debug/stack.go:16 +0x22
github.com/saintpete/logrole/vendor/github.com/getsentry/raven-go.RecoveryHandler.func1.1(0xc420746c30, 0x791be0, 0xc42023ee70)
    /Users/kevin/code/go/src/github.com/saintpete/logrole/vendor/github.com/getsentry/raven-go/http.go:74 +0x6e
panic(0x46d360, 0xc4204691a0)
    /Users/kevin/go/src/runtime/panic.go:458 +0x243
text/template.errRecover(0xc42010f248)
    /Users/kevin/go/src/text/template/exec.go:146 +0x18e

That panic is generated by this code in template/exec.go:

// errRecover is the handler that turns panics into returns from the top
// level of Parse.
func errRecover(errp *error) {
    e := recover()
    if e != nil {
        switch err := e.(type) {
        case runtime.Error:
            panic(e)
        case writeError:
            *errp = err.Err // Strip the wrapper.
        case ExecError:
            *errp = err // Keep the wrapper.
        default:
            panic(e)
        }
    }
}

In my email I see this:

*errors.errorString: unknown property FriendlyName

But for some reason that string is not in the generated stack trace; I expect it to say something like:

goroutine 44 [running]: unknown property FriendlyName

[kevinburke]

This code in http.go:

            if rval := recover(); rval != nil {
                debug.PrintStack()
                rvalStr := fmt.Sprint(rval)
                packet := NewPacket(rvalStr, NewException(errors.New(rvalStr), NewStacktrace(2, 3, nil)), NewHttp(r))
                Capture(packet, nil)
                w.WriteHeader(http.StatusInternalServerError)
            }

I believe should also call fmt.Println("panic:", rval) before debug.PrintStack()

[kevinburke]

FWIW, here's how the Go standard library prints panics.

// For calling from C.
// Prints an argument passed to panic.
// There's room for arbitrary complexity here, but we keep it
// simple and handle just a few important cases: int, string, and Stringer.
func printany(i interface{}) {
    switch v := i.(type) {
    case nil:
        print("nil")
    case stringer:
        print(v.String())
    case error:
        print(v.Error())
    case int:
        print(v)
    case string:
        print(v)
    default:
        print("(", typestring(i), ") ", i)
    }
}

[mattes]

This is how it looks like in the dashboard:

Was expecting runtime error: invalid memory address or nil pointer dereference