Expresso.Assets (expresso v0.1.0)

Keeps one copy of each large file that the document holds more than one time

A deck is one file, so an image or a track goes into the document as a data URI. An SVG file of a diagram or of an icon can also hold an image as a data URI in an href or an xlink:href attribute. Each view of the slide holds its own copy: the present view, each page of the handout view and the picture in the menu. An image of 250 KB in a slide of two steps was then in the document six times.

dedupe/1 runs on the HTML of the document. For each value of a src, an href or an xlink:href attribute that is a data URI of 1024 characters or more, and that occurs more than one time:

the first element keeps the attribute, and gets data-asset-N with the name of that attribute, such as data-asset-0="src";
each other element loses the attribute, and gets data-asset-src="0" or data-asset-href="0" in its place. An xlink:href gets data-asset-href, because SVG 2 reads href in place of xlink:href, and a selector cannot hold the : of the name.

The presenter script copies the value back into each element when the document loads. assets/src/assets.ts gives the rules.

Summary

Functions

dedupe(html)

Replace each copy of a large data URI after its first with a reference to the first

Functions

dedupe(html)

@spec dedupe(String.t()) :: String.t()

Replace each copy of a large data URI after its first with a reference to the first

iex> uri = "data:image/png;base64," <> String.duplicate("A", 1100)
iex> html = ~s(<img src="#{uri}"><img src="#{uri}">)
iex> Expresso.Assets.dedupe(html)
~s(<img data-asset-0="src" src="#{uri}"><img data-asset-src="0">)

A data URI that occurs one time, or that is short, stays as it is.