Preview

The client gets the content of each preview from one endpoint. The code lives in sources/server/Preview/. The route, the schema contract and the middlewares come from the REST library.

Classes

Class	Role
Module	Publishes Config, Rest\Repository and Rest\Controller. Registers the route.
Rest\Schema	The schema of the request. WordPress validates the request with it.
Rest\Controller	Finds the post of the URL and answers with the payload.
Rest\Repository	Builds the payload and keeps it in the object cache.
Rest\Excerpt	Makes the fallback excerpt from the content.

Request

GET /wp-json/rinkukado/v1/preview?url=<absolute-url>

The url parameter is the absolute URL of a post of this site.

Response

The endpoint answers 200 with id, title, excerpt, permalink and thumbnail. The thumbnail field is null, or an object with src, srcset, width, height and alt.

{
  "id": 42,
  "title": "Hello world",
  "excerpt": "The first words of the post…",
  "permalink": "https://example.com/hello-world/",
  "thumbnail": {
    "src": "https://example.com/wp-content/uploads/hello.jpg",
    "srcset": "…",
    "width": 300,
    "height": 200,
    "alt": ""
  }
}

The rinkukado.rest.payload filter can change the payload. See Filters.

Errors

Every rejection answers 404 with the code not_found. The response never says which check failed.

Cache

Request	Header
anonymous	Cache-Control: public, max-age=300
from a logged-in user	Cache-Control: no-store

The Caching middleware of the REST library sets the header.

The client also caches each settled result for the page session. See Preview.

Filters

Filter	Default	Purpose
rinkukado.rest.post-types	every public type except attachment	The types that the endpoint accepts.
rinkukado.rest.excerpt-length	30	The word count of the fallback excerpt.
rinkukado.rest.payload	the payload	The last change before the response.

Post types

The default list of post types excludes attachment, so a media page shows no preview. Add attachment back through rinkukado.rest.post-types when a site wants a preview for its media pages.

Payload

rinkukado.rest.payload receives the payload array and the WP_Post object, just before the endpoint sends the response.