CORS errors when calling this from application

[stucchio]

Currently I'm trying to get Jupyter to call emacs edit server via an extension. Unfortunately this fails due to a CORS error.

This can be resolved by adding "Access-Control-Allow-Origin: *\n" to the response header as follows:

(defun edit-server-send-response (proc &optional body progress)
  "Send an HTTP 200 OK response back to process PROC.
Optional second argument BODY specifies the response content:
    - If nil, the HTTP response will have null content.
    - If a string, the string is sent as response content.
    - Any other value will cause the contents of the current
      buffer to be sent.
If optional third argument progress is non-nil, then the response
will include x-file and x-open headers to allow continuation of editing."
  (interactive)
  (edit-server-log proc "sending edit-server response")
  (if (processp proc)
      (let ((response-header (concat
			      "HTTP/1.0 200 OK\n"
			      (format "Server: Emacs/%s\n" emacs-version)
			      "Date: "
			      (format-time-string
			       "%a, %d %b %Y %H:%M:%S GMT\n"
			       (current-time))
                              "Access-Control-Allow-Origin: *\n"
			      (when progress
				(format "x-file: %s\nx-open: true\n" (buffer-name))))))
	(process-send-string proc response-header)
	(process-send-string proc "\n")
	(cond
	 ((stringp body)
	  (process-send-string proc (encode-coding-string body 'utf-8)))
	 ((not body) nil)
	 (t
	  (encode-coding-region (point-min) (point-max) 'utf-8)
	  (process-send-region proc (point-min) (point-max))))
	(process-send-eof proc)
	(edit-server-log proc "Editing done, sent HTTP OK response."))
    (message "edit-server-send-response: invalid proc (bug?)")))

Alternately one could also provide an edit-server-extra-http-headers param in config.