templates: Another context fix when host header is missing port

middleware/context.go

@@ -110,6 +110,10 @@ func (c Context) Host() (string, error) {
 func (c Context) Port() (string, error) {
 	_, port, err := net.SplitHostPort(c.Req.Host)
 	if err != nil {
+		if !strings.Contains(c.Req.Host, ":") {
+			// common with sites served on the default port 80
+			return "80", nil
+		}
 		return "", err
 	}
 	return port, nil

middleware/context_test.go

@@ -260,14 +260,19 @@ func TestPort(t *testing.T) {
 		},
 		{
 			input:        "localhost",
-			expectedPort: "",
-			shouldErr:    true, // missing port in address
+			expectedPort: "80", // assuming 80 is the default port
+			shouldErr:    false,
 		},
 		{
 			input:        ":8080",
 			expectedPort: "8080",
 			shouldErr:    false,
 		},
+		{
+			input:        "[::]",
+			expectedPort: "",
+			shouldErr:    true,
+		},
 	}
 
 	for _, test := range tests {