Add a api DisableNoDefaultContentType to disable add default conten…

…t type. (#859)

* Add api DisableNoDefaultContentType to disable add default contentype if no Content-Type header.

* Update test case.

* Update api name.

* Update header.go

Co-authored-by: Erik Dubbelboer <erik@dubbelboer.com>

Co-authored-by: Erik Dubbelboer <erik@dubbelboer.com>

header.go

@@ -601,10 +601,15 @@ func (h *ResponseHeader) DisableNormalizing() {
 	h.disableNormalizing = true
 }
 
+// SetNoDefaultContentType allows you to control if a default Content-Type header will be set (false) or not (true).
+func (h *ResponseHeader) SetNoDefaultContentType(noDefaultContentType bool) {
+	h.noDefaultContentType = noDefaultContentType
+}
+
 // Reset clears response header.
 func (h *ResponseHeader) Reset() {
 	h.disableNormalizing = false
-	h.noDefaultContentType = false
+	h.SetNoDefaultContentType(false)
 	h.noDefaultDate = false
 	h.resetSkipNormalize()
 }

header_test.go

@@ -1240,7 +1240,7 @@ func TestResponseContentTypeNoDefaultNotEmpty(t *testing.T) {
 
 	var h ResponseHeader
 
-	h.noDefaultContentType = true
+	h.SetNoDefaultContentType(true)
 	h.SetContentLength(5)
 
 	headers := h.String()
@@ -2193,10 +2193,10 @@ func TestResponseHeaderReadSuccess(t *testing.T) {
 		400, 123, string(defaultContentType), "foiaaa")
 
 	// no content-type and no default
-	h.noDefaultContentType = true
+	h.SetNoDefaultContentType(true)
 	testResponseHeaderReadSuccess(t, h, "HTTP/1.1 400 OK\r\nContent-Length: 123\r\n\r\nfoiaaa",
 		400, 123, "", "foiaaa")
-	h.noDefaultContentType = false
+	h.SetNoDefaultContentType(false)
 
 	// no headers
 	testResponseHeaderReadSuccess(t, h, "HTTP/1.1 200 OK\r\n\r\naaaabbb",