# `Storehouse.Variants.Plug`
[🔗](https://github.com/hattoriai/storehouse/blob/v0.2.0/lib/storehouse/variants/plug.ex#L1)

Serves variants (`Storehouse.Variants`) at the URLs
`Storehouse.variant_url/3` gives, making each the first time it is
asked for: `GET <at>/<original key>/<preset>-<width>-<fingerprint>`.

In the endpoint, before the router:

    plug Storehouse.Variants.Plug

or in a router, where `forward` strips the path:

    forward "/variants", Storehouse.Variants.Plug, at: "/"

Only a preset's widths are made: any other size, preset or key gives
`404`, as does an original that is not there, or not an image. A
fingerprint of a preset since changed is redirected (`302`) to the
preset's current URL. The format of a preset of several is chosen by
the request's `Accept`, with `Vary: Accept`.

A variant is sent with `Cache-Control: public, max-age=31536000,
immutable`: its URL changes when its preset does, so a CDN in front
keeps it for a year.

## Options

  * `:at` - the request path. The default is the configured `:url`
    (`"/variants"`).
  * `:only` - which originals have variants: a list of key prefixes,
    or a function of the key. The default is every key with a preset's
    name, width and fingerprint: originals that must stay private
    (served only at signed URLs) are left out with it.
  * `:cache_tag` - `true` sends the original's `Cache-Tag`
    (`Storehouse.Purge.cache_tag/1`) with each of its variants, for a
    purge by tag.
  * `:adapter` - the store. The default is `Storehouse.adapter/0`.
  * The configuration's (`:presets`, `:renderer`, `:prefix`).

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*Consult [api-reference.md](api-reference.md) for complete listing*