lib/readers: add NoCloser to stop upgrades from io.Reader to io.ReadCloser

lib/readers/noclose.go

@@ -0,0 +1,29 @@
+package readers
+
+import "io"
+
+// noClose is used to wrap an io.Reader to stop it being upgraded
+type noClose struct {
+	in io.Reader
+}
+
+// Read implements io.Closer by passing it straight on
+func (nc noClose) Read(p []byte) (n int, err error) {
+	return nc.in.Read(p)
+}
+
+// NoCloser makes sure that the io.Reader passed in can't upgraded to
+// an io.Closer.
+//
+// This is for use with http.NewRequest to make sure the body doesn't
+// get upgraded to an io.Closer and the body closed unexpectedly.
+func NoCloser(in io.Reader) io.Reader {
+	if in == nil {
+		return in
+	}
+	// if in doesn't implement io.Closer, just return it
+	if _, canClose := in.(io.Closer); !canClose {
+		return in
+	}
+	return noClose{in: in}
+}