net/http: return ErrNoCookie from Request.Cookie when name is ""

Request.Cookie(name string) will return the first cookie
when cookie name is "". Since readCookies in
file net/http/cookie.go at line 247 return all cookies
when second parameter is a empty string.

To fix it, Return ErrNoCookie from Request.Cookie(""),
instead of the first cookie in the request.

Fixes #53181

Change-Id: Ie623ca4c53da64ef7623a7863292a2d771f76832
GitHub-Last-Rev: 01098cd5dbcc8d65e9c0893e0586601584e5f8b9
GitHub-Pull-Request: golang/go#53183
Reviewed-on: https://go-review.googlesource.com/c/go/+/409754
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Damien Neil <dneil@google.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/net/http/request.go b/src/net/http/request.go
index 5439cb3646..a03a54b943 100644
--- a/src/net/http/request.go
+++ b/src/net/http/request.go
@@ -416,6 +416,9 @@ var ErrNoCookie = errors.New("http: named cookie not present")
 // If multiple cookies match the given name, only one cookie will
 // be returned.
 func (r *Request) Cookie(name string) (*Cookie, error) {
+	if name == "" {
+		return nil, ErrNoCookie
+	}
 	for _, c := range readCookies(r.Header, name) {
 		return c, nil
 	}