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elnode - ""

what is it? download elnode

The Emacs webserver.

by Unknown

how to install

M-x package-install [RET] elnode [RET]


= Elnode =

An evented IO webserver in Emacs Lisp.

== Requirements ==

Elnode will not run properly on anything less than Emacs 24.  Elnode
requires Emacs 24's lexical binding as it makes extensive use of

== Rationale ==

Elnode is a great for these things:

 * nice simple server with few dependancies (just Emacs and {{{cat}}} basically)
 * prototyping webapps
 * browser testing
 * asynchronous apps, like chat apps

== Installation ==

Elnode is 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

   '("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)

=== Install from this repository ===

Installing from the sources is complex and requires the dependancies
declared in the file {{{recipes/elnode}}}.

The recipe file is used by
[[|elpakit]] or other tools to
build the package.

elpakit can help build elnode, and help with running tests. Install
elpakit from [[|marmalade]]
and then you can build Elnode with elpakit by doing:

M-x elpakit-make-multi

in the Elnode directory.

You can build the Elnode package and run the Elnode tests on that
package with the following lisp:

(elpakit-test (list elnode-directory) 'elnode-tests 'elnode)

Where {{{elnode-directory}}} specifies your local Elnode repository

The list //can// include more repository directories which will be
combined into a single package archive.

== Out of the box ==

When Elnode initializes it automatically starts a webserver and a Wiki

If you:

M-x customize-group

you can alter a number of variables pertaining to the default
configuration, including the directory used to keep files.

By default the package installs files in your {{{.emacs.d}}} - it uses
a directory called {{{elnode}}} for the Wiki root and the
webroot. Both are configurable with Elnode config variables.

You can also just ignore the built in stuff completely and write your
own servers.

=== What Elnode servers are running? ===

Elnode tracks the servers an Emacs instance is running and you can see
the view of that with:

M-x list-elnode-servers

The list shows TCP ports and handlers and you can press return on a
handler and move to it's source code definition.

You can kill a server by hitting "k" on it.

== How does it work? ==

The simplest thing that Elnode does is let you start a webserver on a

M-x elnode-make-webserver [RET] 
Serve files from: [enter directory] [RET]
TCP Port (try something over 8000): 8009 [RET]

and there will be a webserver started on port 8009 serving files from
whatever directory you specified.

By default Elnode starts that server on the host specified by
{{{elnode-init-host}}} which is a variable you can customize:

M-x customize-variable [RET] elnode-init-host [RET]

Take care though, you don't want to expose your Emacs session to the

You can also use the prefix key to specify the host for just this one

C-u M-x elnode-make-webserver [RET] 
Docroot: [enter directory] [RET]
Port: 8009 [RET]

=== Basic Elnode for programmers ===

Elnode's power is most visible to programmers though.

You can define a handler function:

(defun my-test-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 'my-test-handler :port 8010 :host "localhost")

You can also start the server interactively... with:

M-x elnode-start

it interactively asks for the 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

== API ==

=== Mapping paths to handlers ===

{{{elnode-hostpath-dispatcher}}} takes a-list of path/handler mappings:

   '(("^\\(.*\\)" . elnode-wikiserver)
     ("^\\(.*\\)" . user-admin)
     ("^.*//\\(.*\\)" . elnode-webserver)))

(defun root-handler (httpcon)
  (elnode-hostpath-dispatcher httpcon my-app-routes))

(elnode-start 'root-handler :port 8009)

This will create a server on port 8009 being handled by
{{{root-handler}}} which will root the requests to the appropriate handler.

Any request for the host {{{}}} with the path
{{{/wiki/}}} will be sent to the Elnode Wiki engine.

Any request for the host {{{}}} with the path
{{{/admintool/}}} will be sent to the {{{user-admin}}} handler,
presumably that is defined somewhere.

Any other request will be sent to the default Elnode webserver.

Elnode itself uses a hostpath dispatcher on the default Elnode server.
This can actually be configured with the variable
{{{elnode-hostpath-default-table}}}, so you can actually change the
default behaviour of the Elnode default server just with Emacs config.

The use of regexs in Elnode's mapping is supported by other
tools. Sub-expressions are capturable in mapping support routines such
as {{{elnode-docroot-for}}}.

When a handler is called by {{{elnode-hostpath-dispatcher}}} then the
parts of the match are available through the function
{{{elnode-http-mapping}}}. So we could code the {{{user-admin}}}
handler like this:

##! emacs-lisp
(defun user-admin (httpcon)
  (let ((username (elnode-http-mapping httpcon 1)))
    (user-admin-send-admin-page httpcon username)))

The {{{(elnode-http-mapping httpcon 1)}}} accesses the first
sub-expression of the regex that caused the match:

     ("^\\(.*\\)" . user-admin)

so, everything AFTER the {{{admintool/}}}.

Some tools in Elnode do this for you, so you don't have to. Again,
look at {{{elnode-docroot-for}}}.

=== Serving files ===

There are several helpers for serving files with Elnode. You can serve
directories of files directly by making a webserver handler. A
function {{{elnode-webserver-handler-maker}}} can make webservers:

##! emacs-lisp

(setq my-webserver
      (elnode-webserver-handler-maker "~/my-webroot"))

(elnode-start my-webserver :port 8010)

The Elnode webserver also produces index pages and can be configured
with a number of variables:

* {{{elnode-webserver-index-page-template}}} defines the page template used for the index
* {{{elnode-webserver-index-file-template}}} defines the template for each file in the index, normally it's just an A tag ponting to the file.

=== More controlled serving ===

If you need more control over serving files you can write handlers
with {{{elnode-docroot-for}}}. This does a lot of complex work for you
to map a directory tree to a webserver namespace.

This example shows how to use {{{elnode-docroot-for}}}

##! emacs-lisp

(defun elnode-org-handler (httpcon)
  (elnode-docroot-for "~/work/org"
      with org-file
      on httpcon
      do (with-current-buffer (find-file-noselect org-file)
           (let ((org-html
                  ;; This might throw errors so you could condition-case it
                  (org-export-as-html 3 nil nil 'string)))
             (elnode-send-html httpcon org-html)))))

The first argument is the directory of files which you want to serve,
then {{{with variable}}} specifies the name of a variable to use in
the body of the code which will be bound to the filename of the file
the user wants. Then {{{on httpcon}}} specifies the HTTP connection to
use and then {{{do ....}}} specifies the code to use.

{{{elnode-docroot-for}}} processes incomming requests on the
{{{httpcon}}} you specify by checking the request matches a file in
the directory you specify (it sends a 404 if it does not find one). 

It also does last modified caching on the file and sends an HTTP 304
response if the file has not been updated since the last request.

If a matching file exists and the it is not cached then
{{{elnode-docroot-for}}} runs the {{{do}}} code to send the response

=== Sending files ===

Elnode also has {{{elnode-send-file}}} for sending files to the response,
along with {{{elnode-docroot-for}}} this makes a powerful simple
webserver tool.  {{{elnode-send-file}}} can be used to send any
arbitary file:

##! emacs-lisp
(defun my-status-page (httpcon)
  (elnode-http-start httpcon 200 '("Content-type" . "text/html"))
  (elnode-send-file httpcon "~/static-status-file.html"))

A handler that will only ever respond with one static file.  Of
course, this isn't very interesting, combined with
{{{elnode-docroot-for}}} it can be used to serve directories and the
like, or you could work out the filename to be sent with some other

There is another use for {{{elnode-send-file}}} which is simple
templating.  You can pass parameters to {{{elnode-send-file}}} and it
will template them into the file:

(defun my-templater(httpcon)
  (let ((hash (make-hash-table 
                 :test 'equal 
                 :data "username" "nicferrier")))
     (elnode-http-start httpcon 200 '("Content-type" . "text/html"))
         httpcon "~/my-template.html" 
         :replacements hash)))

The template file must have sections marked up like:

<!##E username E##!>

for each of the variables.

This makes for simple but quite powerful templating.

=== Really Really simple file sending ===

It's also possible to make send file functions automatically so if you
want to map a handler that serves just one file in a dispatcher that's

##! emacs-lisp
`(("^\\(.*\\)" . elnode-wikiserver)
  ("^.*//styles.css" . ,(elnode-make-send-file "~/mainstyles.css"))
  ("^.*//\\(.*\\)" . elnode-webserver))

It's also possible to use templating with this style of programming by
passing a function returning the alist variable map as

##! emacs-lisp
(defun my-templater ()
  '(("username" . "william occam")))

`(("^\\(.*\\)" . elnode-wikiserver)
  ("^.*//styles.css" . ,(elnode-make-send-file 
                           :replacements 'my-templater))
  ("^.*//\\(.*\\)" . elnode-webserver))

This makes templating and setting up very simple websites very easy

=== Accessing data in the HTTP request ===

There are a bunch of functions that do what you would expect about
data in the HTTP request:

##! emacs-lisp

(elnode-http-method httpcon)
=> "POST"

(elnode-http-pathinfo httpcon)
=> "/wiki/blah.creole"

(elnode-http-query httpcon)
=> "a=10&b=20&c=the+quick+brown+fox"

(elnode-http-params httpcon)
=> (("a" . "10")("b" . "20")("c" . "the quick brown fox"))

(elnode-http-param httpcon "username")
=> "nicferrier"

(elnode-http-cookie httpcon "session-id")
=> "1213313"

(elnode-http-header httpcon "Date")
=> "Mon, Feb 27 2012 22:10:21 GMT"

(elnode-http-header httpcon 'date)
=> "Mon, Feb 27 2012 22:10:21 GMT"

(elnode-http-header httpcon 'date :time) ;; with convert flag set to :time
=> (20299 65357)

Note that Elnode generally can accept symbol's as well as strings to
name things, if it can't it's a bug, 
[[|please report it]].

Also, Elnode can handle some conversions sometimes. I would like to
respond to user demand about when and where to do that and what to
do. Please give me feedback.

=== Elnode's raw data ===

Elnode stores most of it's internal state on the connection object and
it's all accessible via a macro {{{elnode/con-get}}}. 

Some interesting properties and how to access them:

##! emacs-lisp

(elnode/con-get httpcon :elnode-http-status)
=> "GET / HTTP/1.1"

(elnode/con-get httpcon :elnode-http-resource)
=> "/"

(elnode/con-get httpcon :elnode-http-version)
=> "1.1"

These are not supported by Elnode at all, there is no guarantee that
the names of these properties won't change. If you feel that you want
official support (ie: a function) then make an issue on the Elnode

== To Do? ==

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

* make an elnode param handler that sanitzes input
** one way to do that was found by aidalgol:

(require 'htmlize)
 "<a href='/blah?a=10&b=2'></a><script>call_func()</script>")

* 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
** //why?// because then a single Emacs could have just 1 server socket open for all sorts of different roles
* 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 started server