Use write interceptor from faas-provider

We now have two write interceptors, with one moved into
faas-provider. This commit makes the gateway use the new
external package and deletes its own.

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alex@openfaas.com>

gateway/vendor/github.com/openfaas/faas-provider/httputil/write_interceptor.go

@@ -0,0 +1,57 @@
+package httputil
+
+import (
+	"bufio"
+	"net"
+	"net/http"
+)
+
+func NewHttpWriteInterceptor(w http.ResponseWriter) *HttpWriteInterceptor {
+	return &HttpWriteInterceptor{w, 0}
+}
+
+type HttpWriteInterceptor struct {
+	http.ResponseWriter
+	statusCode int
+}
+
+func (c *HttpWriteInterceptor) Status() int {
+	if c.statusCode == 0 {
+		return http.StatusOK
+	}
+	return c.statusCode
+}
+
+func (c *HttpWriteInterceptor) Header() http.Header {
+	return c.ResponseWriter.Header()
+}
+
+func (c *HttpWriteInterceptor) Write(data []byte) (int, error) {
+	if c.statusCode == 0 {
+		c.WriteHeader(http.StatusOK)
+	}
+	return c.ResponseWriter.Write(data)
+}
+
+func (c *HttpWriteInterceptor) WriteHeader(code int) {
+	c.statusCode = code
+	c.ResponseWriter.WriteHeader(code)
+}
+
+func (c *HttpWriteInterceptor) Flush() {
+	fl := c.ResponseWriter.(http.Flusher)
+	fl.Flush()
+}
+
+func (c *HttpWriteInterceptor) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+	hj := c.ResponseWriter.(http.Hijacker)
+	return hj.Hijack()
+}
+
+func (c *HttpWriteInterceptor) CloseNotify() <-chan bool {
+	notifier, ok := c.ResponseWriter.(http.CloseNotifier)
+	if ok == false {
+		return nil
+	}
+	return notifier.CloseNotify()
+}

gateway/vendor/github.com/openfaas/faas-provider/httputil/writers.go

@@ -0,0 +1,12 @@
+package httputil
+
+import (
+	"fmt"
+	"net/http"
+)
+
+// Errorf sets the response status code and write formats the provided message as the
+// response body
+func Errorf(w http.ResponseWriter, statusCode int, msg string, args ...interface{}) {
+	http.Error(w, fmt.Sprintf(msg, args...), statusCode)
+}