net/http: invalid byte in Cookie.Value; dropping invalid bytes

[Tong Sun]

Hi Gophers, 

I'm facing a very weird error:

func getUserName(w http.ResponseWriter, r *http.Request) string {
c, err := r.Cookie("session")
if err != nil {
http.Redirect(w, r, rootUrl, http.StatusSeeOther)
return ""
}
log.Println("session raw", c.Value)

var s session
fmt.Printf("%+v\n", s)
reader := strings.NewReader(c.Value)
if err := gob.NewDecoder(reader).Decode(&s); err != nil {
log.Println(err)
http.Error(w, "server error: gob decoding", http.StatusInternalServerError)
return ""
}

return s.Name // userName
}

With the above code, I'm getting the following:

2023/07/21 18:11:00 net/http: invalid byte '\x7f' in Cookie.Value; dropping invalid bytes
2023/07/21 18:11:00 session raw &sessionNameTextA
{Name: Text:}
2023/07/21 18:11:00 unexpected EOF

The Cookie session is encoded with gob Encode. It should only contain plain text strings right? So where does the problem come from?

The whole program is at:

https://github.com/suntong/lang/blob/master/lang/Go/src/net/HttpD/demo-redirect.go

The recent change that got me into the problem is:

https://github.com/suntong/lang/commit/ee5adac80edaf3b8d04e483b2257786268d5250f

Please help. Thx.

[Kurtis Rader]

> The Cookie session is encoded with gob Encode. It should only contain plain text strings right?

No. Where did you get that idea? See https://pkg.go.dev/encoding/gob#hdr-Encoding_Details

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Kurtis Rader

Caretaker of the exceptional canines Junior and Hank