# `Plug.RequestId`
[🔗](https://github.com/elixir-plug/plug/blob/v1.20.1/lib/plug/request_id.ex#L1)

A plug for generating a unique request ID for each request.

The generated request ID will be in the format:

```
GEBMr97eLMHtGWsAAAVj
```

If a request ID already exists in a configured HTTP request header (see options below),
then this plug will use that value, *assuming it is between 20 and 200 characters*.
If such header is not present, this plug will generate a new request ID.

The request ID is added to the `Logger` metadata as `:request_id`, and to the
response as the configured HTTP response header (see options below). To see the
request ID in your log output, configure your logger formatter to include the `:request_id`
metadata. For example:

    config :logger, :default_formatter, metadata: [:request_id]

We recommend to include this metadata configuration in your production
configuration file.

> #### Programmatic access to the request ID {: .tip}
>
> To access the request ID programmatically, use the `:assign_as` option (see below)
> to assign the request ID to a key in `conn.assigns`, and then fetch it from there.

## Usage

To use this plug, just plug it into the desired module:

    plug Plug.RequestId

## Options

  * `:http_header` - The name of the HTTP *request* header to check for
    existing request IDs. This is also the HTTP *response* header that will be
    set with the request id. Default value is `"x-request-id"`.

        plug Plug.RequestId, http_header: "custom-request-id"

  * `:assign_as` - The name of the key that will be used to store the
    discovered or generated request id in `conn.assigns`. If not provided,
    the request id will not be stored. *Available since v1.16.0*.

        plug Plug.RequestId, assign_as: :plug_request_id

  * `:logger_metadata_key` - The name of the key that will be used to store the
    discovered or generated request id in `Logger` metadata. If not provided,
    the request ID Logger metadata will be stored as `:request_id`. *Available
    since v1.18.0*.

        plug Plug.RequestId, logger_metadata_key: :my_request_id

  * `:generator` - The function used to generate the request ID, defaults to
    `Plug.RequestId.generate/0`. When setting up a custom function, it is recommended
    to be in the `&MyApp.custom_request_id/0` format, so it can be stored at compile-time.
    The generated value must also have size between 20 and 200 bytes.

        plug Plug.RequestId, generator: &MyApp.custom_request_id/0

# `generate`

```elixir
@spec generate() :: binary()
```

Generates a random Base64 encoded request ID.

---

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