From 5e20bc66270a8b176bfe14930e9f3c8c8d45a4af Mon Sep 17 00:00:00 2001
From: Thibault Jamet <tjamet@users.noreply.github.com>
Date: Wed, 7 Mar 2018 01:11:14 +0100
Subject: [PATCH] Fix intercepting headers in middlewares

As explained in the TestInterceptedHeader test, in case a middleware
filters out the headers, this middleware can be done inefficient in case
one following handler is using c.String or other methods writing to the
response body directly.

This commit fixes the issue by using c.Writer when writing the Status as
done in other c.Header, c.SetCookie and other response writers.

The bug has been originally discovered using
https://github.com/gin-contrib/gzip where a failing test has been added
here: https://github.com/tjamet/gzip/blob/header/gzip_test.go#L71

Signed-off-by: Thibault Jamet <tjamet@users.noreply.github.com>
---
 context.go      |  2 +-
 context_test.go | 39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/context.go b/context.go
index 90d4c6e59e..57232ea6ed 100644
--- a/context.go
+++ b/context.go
@@ -578,7 +578,7 @@ 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).
diff --git a/context_test.go b/context_test.go
index 9024cfc127..85a0c46734 100644
--- a/context_test.go
+++ b/context_test.go
@@ -1377,3 +1377,42 @@ func TestContextGetRawData(t *testing.T) {
 	assert.Nil(t, err)
 	assert.Equal(t, "Fetch binary post data", string(data))
 }
+
+type interceptedWriter struct {
+	ResponseWriter
+	b *bytes.Buffer
+}
+
+func (i interceptedWriter) WriteHeader(code int) {
+	i.Header().Del("X-Test")
+	i.ResponseWriter.WriteHeader(code)
+}
+
+func TestInterceptedWrite(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"))
+}