Lightweight C library for HTML5 websockets
Notes about generic-table

What is generic-table?

Generic-table is a JSON schema and client-side JS file that makes it easy to display live, table structured HTML over a ws link.

An example plugin and index.html using it are provided, but lwsgt itself doesn't have its own plugin, it's just a JSON schema and client-side JS that other plugins can use to simplify displaying live, table-based data without having to reinvent the wheel each time.

The ws protocol sends JSON describing the table, and then JSON updating the table contents when it chooses, the brower table is updated automatically, live.

Enabling for build

Enable the demo plugin at CMake with -DLWS_WITH_PLUGINS=1

Integrating with your html

  • In your HEAD section, include lwsgt.js
<script src="lwsgt.js"></script>
  • Also in your HEAD section, style the lwsgt CSS, eg
.lwsgt_title { font-size: 24; text-align:center }
.lwsgt_breadcrumbs { font-size: 18; text-align:left }
.lwsgt_table { font-size: 14; padding:12px; margin: 12px; align:center }
.lwsgt_hdr { font-size: 18; text-align:center;
background-color: rgba(40, 40, 40, 0.8); color: white }
.lwsgt_tr { padding: 10px }
.lwsgt_td { padding: 3px }

You can skip this but the result will be less beautiful until some CSS is provided.

  • In your body section, declare a div with an id (can be whatever you want)
<tr><td><div id="lwsgt1" class="group1"></div></td></tr>

lwsgt JS will put its content there.

  • Finally in a <script> at the end of your page, instantiate lwsgt and provide a custom callback for clickable links
var v1 = new lwsgt_initial("Dir listing demo",
"lwsgt1", "lwsgt_dir_click", "v1");
function lwsgt_dir_click(gt, u, col, row)
if (u[0] == '=') { /* change directory */
window[gt].lwsgt_ws.send(u.substring(1, u.length));
var win =, '_blank');

In the callback, you can recover the ws object by window[gt].lwsgt_ws.

Lwsgt constructor

To instantiate the ws link and lwsgt instance, your HTML must call a lwsgt constructor for each region on the page managed by lwsgt.

var myvar = new lwsgt_initial(title, ws_protocol, div_id, click_cb, myvar);

All of the arguments are strings.

Parameter Description
title Title string to go above the table
ws_protocol Protocol name string to use when making ws connection
div_id HTML id of div to fill with content
click_cb Callback function name string to handle clickable links
myvar Name of var used to hold this instantiation globally

Note "myvar" is needed so it can be passed to the click handling callback.

Lwsgt click handling function

When a clickable link produced by lwsgt is clicked, the function named in the click_cb parameter to lwsgt_initial is called.

That function is expected to take four parameters, eg

function lwsgt_dir_click(gt, u, col, row)

Parameter Description
gt Name of global var holding this lwsgt context (ie, myvar)
u Link "url" string
col Table column number link is from
row Table row number link is from

Generic-table JSON

Column layout

When the ws connection is established, the protocol should send a JSON message describing the table columns. For example

"cols": [
{ "name": "Date" },
{ "name": "Size", "align": "right" },
{ "name": "Icon" },
{ "name": "Name", "href": "uri"},
{ "name": "uri", "hide": "1" }
  • This describes 5 columns
  • Only four columns (not "uri") should be visible
  • "Name" should be presented as a clickable link using "uri" as the destination, when a "uri" field is presented.
  • "Size" field should be presented aligned to the right


When a view is hierarchical, it's useful to provide a "path" with links back in the "path", known as "breadcrumbs".

Elements before the last one should provide a "url" member as well as the displayable name, which is used to create the link destination.

The last element, being the current displayed page should not have a url member and be displayed without link style.

"breadcrumbs":[{"name":"top", "url": "/" }, {"name":"mydir"}]

Table data

The actual file data consists of an array of rows, containing the columns mentioned in the original "cols" section.

"Icon":" ",
"Date":"2015-Feb-06 03:08:35 +0000",

Setting up protocol-lws-table-dirlisting

The example protocol needs two mounts, one to provide the index.html, js and the protocol itself

"mountpoint": "/dirtest",
"origin": "file:///usr/share/libwebsockets-test-server/generic-table",
"origin": "callback://protocol-lws-table-dirlisting",
"default": "index.html",
"pmo": [{
"dir": "/usr/share/libwebsockets-test-server"

The protocol wants a per-mount option (PMO) to tell it the base directory it is serving from, named "dir".

The other mount is there to simply serve items that get clicked on from the table in a secure way

"mountpoint": "/dirtest/serve",
"origin": "file:///usr/share/libwebsockets-test-server",
"default": "index.html"

This last bit is not related to using lwsgt itself.