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=====================
Developer Usage Guide
=====================
This guide explains how developers can use the moz-cached-ohttp protocol in Firefox code.
Basic Usage
===========
The moz-cached-ohttp protocol is designed to be used like any other resource loading mechanism in Firefox,
with the key differences being that it provides privacy-preserving OHTTP-based loading with automatic caching,
and cannot be used for regular content, so only privileged contexts can use the scheme.
Creating Resource Requests
==========================
To load a resource via the moz-cached-ohttp protocol, construct a URL in the following format:
.. code-block:: javascript
const targetImageURL = "https://example.com/image.jpg";
const encodedURL = encodeURIComponent(targetImageURL);
const ohttpImageURL = `moz-cached-ohttp://newtab-image/?url=${encodedURL}`;
**Important**: The host must be ``newtab-image`` - other hosts are not currently supported and will result in an error.
.. note::
Target URLs must use the HTTPS protocol. HTTP URLs will be rejected.
Using with Image Elements
-------------------------
The protocol can be used directly in HTML image elements within privileged contexts.
.. code-block:: html
<img src="moz-cached-ohttp://newtab-image/?url=https%3A%2F%2Fexample.com%2Fimage.jpg" />
Using with Fetch API
---------------------
In privileged contexts, you can use the Fetch API:
.. code-block:: javascript
try {
const response = await fetch(ohttpImageURL);
if (response.ok) {
const blob = await response.blob();
// Use the image blob
}
} catch (error) {
console.error("Failed to load image:", error);
}
Performance Best Practices
===========================
Cache Utilization
------------------
The protocol automatically handles caching, but you can optimize usage:
* **Consistent URLs**: Use the same encoded URL format for the same target resource
* **Have the server provide appropriate cache lifetimes**: The longer the lifetime, the less we may need to refetch the resource on the same client.
* **Respect cache headers**: Don't bypass cache unnecessarily with cache-busting parameters
* **Monitor cache hits**: In development, verify that repeated requests hit the cache
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