On Thu, May 2, 2019 at 11:31 AM XXX ZZZ <emartinez1...@gmail.com> wrote:
>
> Hello,
>
> We are having a random panic on our go application that is happening once
> every million requests or so, and so far we haven't been able to reproduce it
> nor to even grasp what's going on.
>
> Basically our code goes like:
>
> type Subid_info struct{
> Affiliate_subid string
> Second_subid string
> Second_subid_8 string
> S2 string
> Internal_subid string
> Internal_subid_9 string
> Internal_subid_12 string
> Result string
> }
>
> func (r *Subid_info) Prepare_subid_logic(){
> r.Second_subid_8=fmt.Sprintf("1%07v", r.Second_subid) ----> panic happens
> here.
> }
>
> And the trace we get is:
>
> panic: runtime error: invalid memory address or nil pointer dereference
> [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x466b6e]
>
> goroutine 17091 [running]:
> unicode/utf8.RuneCountInString(0x0, 0x5, 0xc048c275a8)
> /usr/local/go/src/unicode/utf8/utf8.go:411 +0x2e
> fmt.(*fmt).padString(0xc023c17780, 0x0, 0x5)
> /usr/local/go/src/fmt/format.go:113 +0x134
> fmt.(*fmt).fmtS(0xc023c17780, 0x0, 0x5)
> /usr/local/go/src/fmt/format.go:347 +0x61
> fmt.(*pp).fmtString(0xc023c17740, 0x0, 0x5, 0xc000000076)
Right here in fmtString, the function gets a 0x0, 0x5 arg, which is I
believe a string of length 5 with a nil slice. So it looks like
somehow r.Second_subid has nil buffer here. When a string is used as
an interface{}, afaik, the interface keeps the value, not the pointer
to the string. So I can't see how this is possible. But I wonder if
copying the value before sprintf could fix it:
x:=r.Second_subid
r.Second_subid_8=fmt.Sprintf("1%07v", x)
> /usr/local/go/src/fmt/print.go:448 +0x132
> fmt.(*pp).printArg(0xc023c17740, 0x9978e0, 0xc016a68a30, 0x76)
> /usr/local/go/src/fmt/print.go:684 +0x880
> fmt.(*pp).doPrintf(0xc023c17740, 0xa6e22f, 0x5, 0xc048c27818, 0x1, 0x1)
> /usr/local/go/src/fmt/print.go:1112 +0x3ff
> fmt.Sprintf(0xa6e22f, 0x5, 0xc048c27818, 0x1, 0x1, 0x80, 0xa36200)
> /usr/local/go/src/fmt/print.go:214 +0x66
> code/sharedobjects/sources.(*Subid_info).Prepare_subid_logic(0xc019292f80,
> 0x2)
>
> Given that we can't reproduce it, what's the logical way to debug this and
> find out what's happening?
>
> Thanks!
>
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