fix get host from req.header

Author: liaojianqi.rd

config.go

@@ -36,7 +36,10 @@ func (cors *cors) applyCors(c *gin.Context) {
 		// request is not a CORS request
 		return
 	}
-	host := c.Request.Header.Get("Host")
+	// go/net/http//request.go
+	// For incoming requests, the Host header is promoted to the
+	// Request.Host field and removed from the Header map.
+	host := c.Request.Host
 	if origin == "http://"+host || origin == "https://"+host {
 		// request is not a CORS request but have origin header.
 		// for example, use fetch api

cors_test.go

@@ -42,7 +42,14 @@ func performRequest(r http.Handler, method, origin string) *httptest.ResponseRec
 
 func performRequestWithHeaders(r http.Handler, method, origin string, headers map[string]string) *httptest.ResponseRecorder {
 	req, _ := http.NewRequest(method, "/", nil)
+	// go/net/http//request.go
+	// For incoming requests, the Host header is promoted to the
+	// Request.Host field and removed from the Header map.
 	for k, v := range headers {
+		if k == "Host" {
+			req.Host = v
+			continue
+		}
 		req.Header.Set(k, v)
 	}
 	if len(origin) > 0 {