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An attempt to make an EmacsLISP clone of node.js.


Elnode should be used for making small, personal web services or for developing a first draft of a web service you may later do in Clojure or Node.js or some other web framework.

Emacs is a very good LISP programming environment as well as a great editor. Now that Emacs 24 has lexical scope EmacsLISP is a very powerful language. A webserver framework inside such a powerful LISP environment therefore makes sense.


Elnode is now packaged in marmalade.

For dealing with package repositories check out the Emacs Wiki but the short version is to add the following to your .emacs or your .emacs.d/init.el:

   '("marmalade" . ""))

And then do:

M-x list-packages

find Elnode in the list and press i or ENTER to install it.

If you don't want to use packages you can just install elnode.el on your load-path somewhere and:

(require 'elnode)

Out of the box

When Elnode initializes it automatically starts a webserver.

If you:

M-x customize-group

you can alter a number of variables pertaining to the default configuration.

You can also just ignore it and write your own servers.

How does it work?

You can define a handler function:

(defun nicferrier-handler (httpcon)
  "Demonstration function"
  (elnode-http-start httpcon "200" '("Content-type" . "text/html"))
  (elnode-http-return httpcon "<html><b>HELLO!</b></html>")

And then start the server:

(elnode-start 'nicferrier-handler 8010 "localhost")

You can also start the server interactively... you still have to pass it a handler function and a port.

Stopping the server

If you can remember the port you started your server on then you'll be able to stop it, like:

(elnode-stop 8010)

You can also stop interactively:

M-x elnode-stop


elnode-child-process httpcon program &rest args

Run the specified process asynchronously and send it's output to the http connection.

program is the program to run. args is a list of arguments to pass to the program.

It is NOT POSSIBLE to run more than one process at a time directed at the same http connection.

elnode-defer-now handler

The function you call to defer processing of the current socket.

Pass in the current handler.

FIXME: We could capture the current handler somehow? I think the point is that whatever signals elnode-defer should be getting control back when the deferred is re-processed.

elnode-defer-or-do guard &rest body

Test the guard and defer if it suceeds and body if it doesn't.

elnode-dispatcher httpcon url-mapping-table &optional function-404

Dispatch the httpcon to the correct function based on the url-mapping-table.

url-mapping-table is an alist of:

 (url-regex . function-to-dispatch)

To map the root url you should use:


elnode-dispatcher uses elnode-normalize-path to ensure paths end in / so to map another url you should use:




elnode-error msg &rest args

Log msg with args as an error.

This function is available for handlers to call. It is also used by elnode iteslf.

There is only one error log, in the future there may be more.

elnode-hostpath-default-handler httpcon

A hostpath handler using the elnode-hostpath-default-table for the match table.

This simply calls elnode-hostpath-dispatcher with elnode-hostpath-default-table.

elnode-hostpath-dispatcher httpcon hostpath-mapping-table &optional function-404

Dispatch the httpcon to the correct handler based on the hostpath-mapping-table.

hostpath-mapping-table has a regex of the host and the path slash separated, thus:

 ("^localhost/pastebin.*" . pastebin-handler)

elnode-http-cookie httpcon name

Get the cookie value specified by the name.

elnode-http-header httpcon name

Get the header specified by name from the header.

elnode-http-method httpcon

Get the PATHINFO of the request.

elnode-http-param httpcon name

Get the named parameter from the request.

elnode-http-params httpcon

Get an alist of the parameters in the request.

If the method is a GET then the parameters are from the url. If the method is a POST then the parameters may come from either the url or the POST body or both:

 POST /path?a=b&x=y

would result in:

 '(([[a]] [[b]] [[c]])([[x]] . [[y]]))

elnode-http-pathinfo httpcon

Get the PATHINFO of the request.

elnode-http-query httpcon

Get the QUERY of the request.

elnode-http-return httpcon &optional data

End the response on httpcon optionally sending data first.

httpcon is the http connection which must have had the headers sent with elnode-http-start

data must be a string, it's just passed to elnode-http-send.

elnode-http-send-string httpcon str

Send the string to the HTTP connection.

This is really only a placeholder function for doing transfer-encoding.

elnode-http-start httpcon status &rest header

Start the http response on the specified http connection.

httpcon is the HTTP connection being handled. status is the HTTP status, eg: 200 or 404 header is a sequence of (header-name . value) pairs.

For example:

 (elnode-http-start //httpcon// "200" '("Content-type" . "text/html"))

elnode-http-version httpcon

Get the PATHINFO of the request.


Bootstraps the elnode environment when the Lisp is loaded.

It's useful to have elnode start automatically... on Lisp load. If the variable elnode-init-port is set then this function will launch a server on it.

The server is started with elnode-hostpath-default-handler as the handler and listening on elnode-init-host


List the current buffers being managed by elnode.

elnode-normalize-path httpcon handler

A decorator for handler that normalizes paths to have a trailing slash.

This checks the httpcon path for a trailing slash and sends a 302 to the slash trailed url if there is none.

Otherwise it calls handler.

elnode-send-400 httpcon

A generic 400 handler.

elnode-send-404 httpcon

A generic 404 handler.

elnode-send-redirect httpcon location

Sends a redirect to the specified location.

elnode-start request-handler port host

Start the elnode server so that request-handler handles requests on port on host.

Most of the work done by the server is actually done by functions, the sentinel function, the log function and a filter function.

request-handler is a function which is called with the request. The function is called with one argument, the http-connection.

You can use functions such as elnode-http-start and elnode-http-send-body to send the http response.


 (defun nic-server (httpcon)
   (elnode-http-start 200 '(("Content-Type": "text/html")))
   (elnode-http-return "<html><b>BIG!</b></html>")
 (elnode-start 'nic-server 8000)
 ;; End

You must also specify the port to start the server on.

You can optionally specify the hostname to start the server on, this must be bound to a local IP. Some names are special:

  local//host//  means
  * means

specifying an IP is also possible.

Note that although host can be specified, elnode does not disambiguate on running servers by host. So you cannot start 2 different elnode servers on the same port on different hosts.

elnode-stop port

Stop the elnode server attached to port.

elnode-test-path httpcon docroot handler &optional 404-handler

Check that the path requested is above the docroot specified.

Call 404-handler (or default 404 handler) on failure and handler on success.

handler is called: httpcon docroot targetfile

This is used by elnode--webserver-//handler//-proc in the webservers that it creates... but it's also meant to be generally useful for other handler writers.

elnode-webserver httpcon

A simple webserver that serves documents out of `elnode-webserver-docroot'.

This is just an example of an elnode webserver, but it may be all that is needed most of the time.

See elnode-webserver-handler-maker for more possibilities for making webserver functions.

httpcon is the HTTP connection to the user agent.

elnode-webserver-handler-maker &optional docroot extra-mime-types

Make a webserver handler possibly with the docroot and extra-mime-types.

Returns a proc which is the handler. The handler serves files out of the docroot and marks them with the content types that Emacs knows about. You can add extra content types for the webserver just by supplying an alist of mime-types and extensions for extra-mime-types.

The webserver handler also creates file indexes.

The webserver uses elnode-test-path to make sure that the request does not go above the docroot.


There's always a but.

Here's a list of buts:

  • the HTTP parsing isn't great, it uses too many regexs
  • we don't parse any data sent through POST other than form-data
  • the error handling is absolute rubbish

To Do?

If you're playing with elnode but you can't think of anything to do with it...

  • an elpa repository written with elnode
    • turn the package list into html
    • allow packages to be downloaded from elnode
    • upload of packages will require fixing the request management a little
  • an emacsclient with elnode
    • write a command line client that submits data to the server over HTTP
    • it should interact with the emacs user in the same way that emacs server does
  • a simple wiki engine with elnode
    • maybe using a command line wiki templating tool
  • alter elnode-webserver-handler-maker to do indexing better
    • take an optional index producing function?
    • take keyword flags that set the behaviour?
    • eg: :doindexes 't
  • browse-current-buffer
    • start an elnode server on some random port exposing the current buffer
    • automatically open a browser on the server
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