concatenate Cookie HPACK headers for the HTTP request

fixes #338

h2quic/request.go

@@ -5,6 +5,7 @@ import (
 	"net/http"
 	"net/url"
 	"strconv"
+	"strings"
 
 	"golang.org/x/net/http2/hpack"
 )
@@ -30,6 +31,11 @@ func requestFromHeaders(headers []hpack.HeaderField) (*http.Request, error) {
 		}
 	}
 
+	// concatenate cookie headers, see https://tools.ietf.org/html/rfc6265#section-5.4
+	if len(httpHeaders["Cookie"]) > 0 {
+		httpHeaders.Set("Cookie", strings.Join(httpHeaders["Cookie"], "; "))
+	}
+
 	if len(path) == 0 || len(authority) == 0 || len(method) == 0 {
 		return nil, errors.New(":path, :authority and :method must not be empty")
 	}