# ETagPlug
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This plug generates shallow [ETags](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag).
Shallow means that it uses the whole response to generate the ETag and does not care about the specific content of each response. It is not context sensitive. For a deep (speak context sensitive) generation of ETags you can take a look at [Phoenix ETag](https://github.com/michalmuskala/phoenix_etag).
## Installation
The plug can be installed by adding `etag_plug` to your list of dependencies in `mix.exs`:
```elixir
def deps do
[
{:etag_plug, "~> 0.1.0"}
]
end
```
Documentation can be generated with [ExDoc](https://github.com/elixir-lang/ex_doc) and published on [HexDocs](https://hexdocs.pm). Once published, the docs can be found at [https://hexdocs.pm/etag_plug](https://hexdocs.pm/etag_plug).
# Usage
You can simply use the plug without any configuration, it then defaults to the configuration as specified in the "Configuration" section.
```elixir
plug ETag.Plug
```
You can also provide a number of options, see the "Configuration" section for details.
```elixir
plug ETag.Plug,
generator: MyCustomGenerator,
methods: ["GET", "HEAD"],
status_codes: [:ok, 201, :not_modified]
```
## Configuration
A full configuration equal to the defaults could look like this:
```elixir
config :etag_plug,
generator: ETag.Generator.SHA1,
methods: ["GET"],
status_codes: [200]
```
Each of these options is explained in detail below.
### `generator`
Expects a module implementing the `ETag.Generator` behaviour. The plug ships with a number of "default" generators:
- `ETag.Generator.MD5`
- `ETag.Generator.SHA1`
- `ETag.Generator.SHA512`
__Default__: `Application.get_env(:etag_plug, :generator, ETag.Generator.SHA1)`
### `methods`
Expects a list of strings, describing the HTTP methods for which ETags should be generated and evaluated.
__Default__: `Application.get_env(:etag_plug, :methods, ["GET"])`
### `status_codes`
Expects an enumerable of integers (or status atoms) which define the statuses for which ETags should be handled and generated.
__Default__: `Application.get_env(:etag_plug, :status_codes, [200])`