EC
http.ErrNoCookie
GoERRORCommonHTTP

http: named cookie not present

Quick Answer

Check the error from r.Cookie("name") before using the result; return a 400 if the cookie is required.

What this means

Returned by Request.Cookie when no cookie with the specified name is found in the request. Always check for this before using the cookie value.

Why it happens
  1. 1Client did not send the expected cookie
  2. 2Cookie name mismatch between client and server code

Fix

Check and respond with 400

Check and respond with 400
c, err := r.Cookie("session")
if errors.Is(err, http.ErrNoCookie) {
    http.Error(w, "missing cookie", 400)
    return
}

Why this works

Early return prevents nil pointer dereference when the cookie is absent.

Code examples
Detectgo
c, err := r.Cookie("token")
if errors.Is(err, http.ErrNoCookie) {
    fmt.Println("no cookie")
}
Use cookie value safelygo
c, err := r.Cookie("session")
if err == nil {
    fmt.Println(c.Value)
}
Set cookiego
http.SetCookie(w, &http.Cookie{
    Name: "session", Value: "abc123",
})
Sources
Official documentation ↗

Go standard library

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