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Hosting C2PA assets

Cross-origin (CORS) support​

Processing images from a URL or DOM selector requires the client to download the source image for processing. If the image is not on the same origin as the site running the JavaScript library, the server hosting the images must return the following HTTP response headers for cross-origin resource sharing (CORS):

The vast majority of major CDNs and hosting providers allow customizing these headers.

Range requests​

Since images can be quite large, the JavaScript library uses HTTP range requests to download the first part of the file (by default, the first 64KB). It then tests if C2PA manifest data exists in this downloaded fragment; if it does, the download proceeds and the JavaScript library processes the rest of the file. This avoids downloading potentially large amounts of data if an image does not contain a manifest.

For this feature to work, the server hosting the images must support HTTP range requests. To check, open your terminal and enter the following command (assuming you have curl installed):

curl -I http://assets.mycdn.com/images/image01.jpg

HTTP/1.1 200 OK
...
Accept-Ranges: bytes
Content-Length: 86405

If the response contains Accept-Ranges: bytes, then your server is set up to take advantage of this feature.

If the response contains Accept-Ranges: none or no Accept-Ranges field in the header, the JavaScript library will automatically re-request the image without the Range header, forcing a full download of the file.

Library assets​

To reduce the initial bundle size, serve both the Web Worker script and the WebAssembly binary as separate requests. If you are using a build system, this means you must export them as static assets. For examples of configuring popular build systems, see the Quick start guide.

To host the library yourself, expose the static asset files with the following response headers to avoid errors with some browsers:

  • c2pa/dist/assets/wasm/toolkit_bg.wasm: Serve with Content-Type: application/wasm reponse header.
  • c2pa/dist/c2pa.worker.min.js: Serve with Content-Type: text/javascript response header.

Then pass these URLs to the createC2pa function; for example:

const c2pa = await createC2pa({
    wasmSrc: 'https://your_static_asset_uri/toolkit_bg.wasm',
    workerSrc: 'https://your_static_asset_uri/c2pa.worker.min.js',
  })

Where your_static_asset_uri is the URI where you're serving the library asset files.

caution

When hosting the library files, make sure you are using the correct version number that aligns with the version of the library you're using.