blobstore/blobstore.go
func Send(response http.ResponseWriter, blobKey appengine.BlobKey) {
	hdr := response.Header()
	hdr.Set("X-AppEngine-BlobKey", string(blobKey))

	if hdr.Get("Content-Type") == "" {
		// This value is known to dev_appserver to mean automatic.
		// In production this is remapped to the empty value which
		// means automatic.
		hdr.Set("Content-Type", "application/vnd.google.appengine.auto")
	}
}
func Send(response http.ResponseWriter, blobKey appengine.BlobKey) {
	hdr := response.Header()
	hdr.Set("X-AppEngine-BlobKey", string(blobKey))

	if hdr.Get("Content-Type") == "" {
		// This value is known to dev_appserver to mean automatic.
		// In production this is remapped to the empty value which
		// means automatic.
		hdr.Set("Content-Type", "application/vnd.google.appengine.auto")
	}
}
// Send sets the headers on response to instruct App Engine to send a blob as
// the response body. This is more efficient than reading and writing it out
// manually and isn't subject to normal response size limits.