# `Image.Plug.SourceResolver`
[🔗](https://github.com/elixir-image/image_plug/blob/v0.1.0/lib/image/plug/source_resolver.ex#L1)

Behaviour for source resolvers.

A resolver turns a `t:Image.Plug.Source.t/0` into an open
`Vix.Vips.Image` plus a small bag of metadata used for HTTP cache
headers (`content_type`, `etag_seed`, optionally `last_modified` and
`byte_size`).

A resolver typically handles one `Image.Plug.Source` kind. The
default `Image.Plug.SourceResolver.Composite` dispatches by kind to
a configured set of per-kind resolvers.

# `meta`

```elixir
@type meta() :: %{
  :content_type => String.t(),
  :etag_seed => binary(),
  optional(:last_modified) => DateTime.t(),
  optional(:byte_size) => non_neg_integer(),
  optional(:cache_control) => String.t(),
  optional(:immutable?) => boolean()
}
```

Metadata about the resolved source. The plug uses these values to
build cache headers and to fingerprint the response for ETag
computation.

* `:content_type` — the MIME type of the source bytes.

* `:etag_seed` — any stable per-source binary. `Image.Plug.Cache`
  hashes this together with the pipeline fingerprint to compute the
  response ETag.

* `:last_modified` — optional `DateTime` to emit as `Last-Modified`.

* `:byte_size` — optional integer; informational.

* `:cache_control` — optional `Cache-Control` directive to forward
  on the response.

* `:immutable?` — if `true`, the cache layer may add `immutable`.

# `load`

```elixir
@callback load(Image.Plug.Source.t(), options :: keyword()) ::
  {:ok, Vix.Vips.Image.t(), meta()} | {:error, Image.Plug.Error.t()}
```

Loads the source bytes referenced by `source` and opens them as a
`Vix.Vips.Image`.

Returns the open image plus a `t:meta/0` map.

---

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