Fix intercepting headers in middlewares

context.go

@@ -711,7 +711,7 @@ func bodyAllowedForStatus(status int) bool {
 
 // Status sets the HTTP response code.
 func (c *Context) Status(code int) {
-	c.writermem.WriteHeader(code)
+	c.Writer.WriteHeader(code)
 }
 
 // Header is a intelligent shortcut for c.Writer.Header().Set(key, value).

context_go17_test.go

@@ -0,0 +1,50 @@
+// +build go1.7
+
+package gin
+
+import (
+	"bytes"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+type interceptedWriter struct {
+	ResponseWriter
+	b *bytes.Buffer
+}
+
+func (i interceptedWriter) WriteHeader(code int) {
+	i.Header().Del("X-Test")
+	i.ResponseWriter.WriteHeader(code)
+}
+func TestInterceptedHeader(t *testing.T) {
+	w := httptest.NewRecorder()
+	c, r := CreateTestContext(w)
+
+	r.Use(func(c *Context) {
+		i := interceptedWriter{
+			ResponseWriter: c.Writer,
+			b:              bytes.NewBuffer(nil),
+		}
+		c.Writer = i
+		c.Next()
+		c.Header("X-Test", "overridden")
+		c.Writer = i.ResponseWriter
+	})
+	r.GET("/", func(c *Context) {
+		c.Header("X-Test", "original")
+		c.Header("X-Test-2", "present")
+		c.String(http.StatusOK, "hello world")
+	})
+	c.Request = httptest.NewRequest("GET", "/", nil)
+	r.HandleContext(c)
+	// Result() has headers frozen when WriteHeaderNow() has been called
+	// Compared to this time, this is when the response headers will be flushed
+	// As response is flushed on c.String, the Header cannot be set by the first
+	// middleware. Assert this
+	assert.Equal(t, "", w.Result().Header.Get("X-Test"))
+	assert.Equal(t, "present", w.Result().Header.Get("X-Test-2"))
+}