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Algernon Tutorial

"Hello"

Goal

Display Hello Algernon! in your browser.

Steps

Create hello.lua

Create a hello.lua file that looks like this:

handle("/", function()
  content("text/plain")
  print("Hello Algernon!")
end)
  • handle is a built-in function that can serve an endpoint with a given function.
  • function() [...] end is an anonymous Lua function.
  • content is a built-in function for settting the content type / MIME type, such as text/plain, text/html or image/png.
  • print is a built-in function for outputting text to the HTTP client (typically a browser) that is visiting this page.

Start Algernon:

Run algernon hello.lua

View the result

Visit http://localhost:3000 in your favorite browser.

"Simple"

Goal

Use a directory structure instead of a single Lua file with handlers.

Steps

Create and enter a directory

mkdir simple
cd simple

Create an index.lua file

Create an index.lua file that looks like this:

print("the light")

Serve the current directory

Serve the current directory with Algernon:

algernon .

View the result

Visit http://localhost:3000 in a browser and see "the light".

"Eyes"

Goal

Serve an image by printing it from Lua, and then use it within an HTML page.

Steps

Create and enter a directory

mkdir eyes
cd eyes

Create eye.lua

Create an eye.lua file that looks like this:

content("image/svg+xml")

print [[
<?xml version="1.0" encoding="UTF-8"?>
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100">
  <circle cx="50" cy="50" r="40" fill="white" stroke="black" stroke-width="2" />
  <circle cx="38" cy="50" r="20" fill="black" />
  <circle cx="28" cy="42" r="5" fill="white" />
</svg>
]]

This outputs an SVG image.

Create index.lua

Create an index.lua file that looks like this:

content("text/html")

print [[
<!doctype html><html><body>
<img src="eye.lua" width="25em">
<img src="eye.lua" width="25em">
]]

This is the main/default handler for this directory, and outputs a simple HTML page that displays two images.

The browser does not care if the images end with an unusual file extension such as .lua, because the content-type / MIME type regulates this.

Serve the current directory

algernon -e .

Note that the -e flag is for "development mode", where error messages may appear directly in the browser, and pages are not cached.

View the result

  • Visit http://localhost:3000/eye.lua in a browser and observe the result of serving an SVG image.
  • Visit http://localhost:3000/ in a browser and observe the result of serving the HTML document (which uses eye.lua, twice).

Examine the network traffic

  • In ie. Firefox, press F12 (or fn+F12 on macOS). Select the Network tab and then reload the page.
  • Click the 200 | GET | localhost:3000 | eye.lua | ... row.
  • On the right hand side, observe that Content-Type is image/svg+xml and that the Server is Algernon and a version number.
  • There are also various security-related headers that have been set (that can be turned off with the --no-headers flag).

"Auto-Refresh"

Goal

Style a HTML page with CSS and try out the auto-refresh feature.

Steps

Create and enter a directory

mkdir style
cd style

Create the eye.svg image

Create an eye.svg file that looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100">
  <circle cx="50" cy="50" r="40" fill="white" stroke="black" stroke-width="4" />
  <circle cx="38" cy="50" r="20" fill="black" />
  <circle cx="28" cy="42" r="5" fill="white" />
</svg>

Create the mouth.svg image

Create a mouth.svg file that looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<svg xmlns="http://www.w3.org/2000/svg" width="100" height="50" viewBox="0 0 100 50">
  <path d="M 10,25 Q 50,50 90,25 Q 50,0 10,25 Z" fill="white" stroke="black" stroke-width="2"/>
</svg>

Create the HTML document

Create an index.html file that looks like this:

<!doctype html>
<html>
  <head>
    <title>Face</title>
    <link rel="stylesheet" href="style.css">
  </head>
  <body>
    <div id="face">
      <img src="eye.svg" id="left_eye">
      <img src="eye.svg" id="right_eye">
      <img src="mouth.svg" id="mouth">
    </div>
  </body>
</html>

Style the document with CSS

Create a style.css file that looks like this:

#face {
  position: relative;
  top: 4em;
  left: 4em;
  width: 12.5em;
  height: 12.5em;
  background: lightblue;
  border-radius: 1.25em;
}

#left_eye, #right_eye, #mouth {
  position: absolute;
}

#left_eye, #right_eye {
  animation: rotate 16s linear infinite;
}

#left_eye {
  top: 2em;
  left: 0.75em;
  width: 5.625em;
}

#right_eye {
  top: 2em;
  left: 6.125em;
  width: 5.625em;
}

#mouth {
  top: 7em;
  left: 3.125em;
  width: 6.25em;
}

@keyframes rotate {
  from { transform: rotate(0deg); }
  to { transform: rotate(360deg); }
}

Serve the page

Serve the page with:

algernon -a -e --no-headers .
  • Note that serving with algernon -a -e and visiting http://127.0.0.1:3000 instead of using --no-headers and visiting http://localhost:3000 also works.

View the result

Visit http://localhost:3000 to see an animated page.

Auto-refresh

Algernon comes with an auto-refresh feature that inserts a tiny bit of JavaScript into a page, watches files for changes and also serves file changed events as SSE (server sent events).

Here's one way to try it out (requires the -a flag):

  • While still serving the page, and displaying it in the browser, change the numbers in style.css, save the file and observe that the page in the browser instantly changes.
  • Also try changing numbers in eye.svg and mouth.svg, save the file and watch the page instantly being updated.

Next step

What should the next step in this tutorial be? Please submit an issue with a suggestion. Thanks for reading! :)