net/http: check if strings.Cut was successful before trimming the cookie name

src/net/http/cookie.go

@@ -70,10 +70,10 @@ func readSetCookies(h Header) []*Cookie {
 		}
 		parts[0] = textproto.TrimString(parts[0])
 		name, value, ok := strings.Cut(parts[0], "=")
-		name = textproto.TrimString(name)
 		if !ok {
 			continue
 		}
+		name = textproto.TrimString(name)
 		if !isCookieNameValid(name) {
 			continue
 		}

src/net/http/cookie_test.go

@@ -352,6 +352,8 @@ var readSetCookiesTests = []struct {
 		Header{"Set-Cookie": {`special-8=","`}},
 		[]*Cookie{{Name: "special-8", Value: ",", Raw: `special-8=","`}},
 	},
+	// Make sure we can properly read back the Set-Cookie headers
+	// for names containing spaces:
 	{
 		Header{"Set-Cookie": {`special-9 =","`}},
 		[]*Cookie{{Name: "special-9", Value: ",", Raw: `special-9 =","`}},