6. Global Filters
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# 6. Global Filters

The `GlobalFilter` interface has the same signature as `GatewayFilter`. These are special filters that are conditionally applied to all routes. (This interface and usage are subject to change in future milestones).

## 6.1 Combined Global Filter and GatewayFilter Ordering

TODO: document ordering

## 6.2 Forward Routing Filter

The `ForwardRoutingFilter` looks for a URI in the exchange attribute `ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR`. If the url has a `forward` scheme (ie `forward:///localendpoint`), it will use the Spring `DispatcherHandler` to handler the request. The unmodified original url is appended to the list in the `ServerWebExchangeUtils.GATEWAY_ORIGINAL_REQUEST_URL_ATTR` attribute.

## 6.3 LoadBalancerClient Filter

The `LoadBalancerClientFilter` looks for a URI in the exchange attribute `ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR`. If the url has a `lb` scheme (ie `lb://myservice`), it will use the Spring Cloud `LoadBalancerClient` to resolve the name (`myservice` in the previous example) to an actual host and port and replace the URI in the same attribute. The unmodified original url is appended to the list in the `ServerWebExchangeUtils.GATEWAY_ORIGINAL_REQUEST_URL_ATTR` attribute.

## 6.4 Netty Routing Filter

The Netty Routing Filter runs if the url located in the `ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR` exchange attribute has a `http` or `https` scheme. It uses the Netty `HttpClient` to make the downstream proxy request. The response is put in the `ServerWebExchangeUtils.CLIENT_RESPONSE_ATTR` exchange attribute for use in a later filter. (There is an experimental `WebClientHttpRoutingFilter` that performs the same function, but does not require netty)

## 6.5 Netty Write Response Filter

The `NettyWriteResponseFilter` runs if there is a Netty `HttpClientResponse` in the `ServerWebExchangeUtils.CLIENT_RESPONSE_ATTR` exchange attribute. It is run after all other filters have completed and writes the proxy response back to the gateway client response. (There is an experimental `WebClientWriteResponseFilter` that performs the same function, but does not require netty)

## 6.6 RouteToRequestUrl Filter

The `RouteToRequestUrlFilter` runs if there is a `Route` object in the `ServerWebExchangeUtils.GATEWAY_ROUTE_ATTR` exchange attribute. It creates a new URI, based off of the request URI, but updated with the URI attribute of the `Route` object. The new URI is placed in the ``ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR` exchange attribute`.

## 6.7 Websocket Routing Filter

The Websocket Routing Filter runs if the url located in the `ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR` exchange attribute has a `ws` or `wss` scheme. It uses the Spring Web Socket infrastructure to forward the Websocket request downstream.

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