added application error catcher filter

docs/custom-error-pages.adoc

@@ -29,3 +29,25 @@ spring:
 3. In the datadir create a folder from the root directory: "gateway/templates/error"
 4. Place your error page files named as per the status code. For example for 404: 404.html
 5. Restart georchestra gateway.
+
+== Using custom error pages for applications errors
+
+Custom error pages can also be used when an application behind the gateways returns an error.
+
+To enable it globally, add this to application.yaml :
+[application.yaml]
+----
+spring:
+  cloud:
+    gateway:
+      default-filters:
+        - ServiceError
+----
+
+To enable it only on some routes, add this to concerned routes in routes.yaml :
+[routes.yaml]
+----
+        filters:
+        - name: ServiceError
+----
+

gateway/src/main/java/org/georchestra/gateway/autoconfigure/app/FiltersAutoConfiguration.java

@@ -20,6 +20,7 @@
 
 import org.georchestra.gateway.filter.global.ResolveTargetGlobalFilter;
 import org.georchestra.gateway.filter.headers.HeaderFiltersConfiguration;
+import org.georchestra.gateway.filter.global.ServiceErrorGatewayFilterFactory;
 import org.georchestra.gateway.model.GatewayConfigProperties;
 import org.georchestra.gateway.model.GeorchestraTargetConfig;
 import org.geoserver.cloud.gateway.filter.RouteProfileGatewayFilterFactory;
@@ -64,4 +65,8 @@ public class FiltersAutoConfiguration {
     public @Bean StripBasePathGatewayFilterFactory stripBasePathGatewayFilterFactory() {
         return new StripBasePathGatewayFilterFactory();
     }
+
+    public @Bean ServiceErrorGatewayFilterFactory serviceErrorGatewayFilterFactory() {
+        return new ServiceErrorGatewayFilterFactory();
+    }
 }

gateway/src/main/java/org/georchestra/gateway/filter/global/ServiceErrorGatewayFilterFactory.java

@@ -0,0 +1,38 @@
+package org.georchestra.gateway.filter.global;
+
+import org.springframework.cloud.gateway.filter.GatewayFilter;
+import org.springframework.cloud.gateway.filter.GatewayFilterChain;
+import org.springframework.cloud.gateway.filter.factory.AbstractGatewayFilterFactory;
+import org.springframework.core.Ordered;
+import org.springframework.http.HttpStatus;
+import org.springframework.web.server.ResponseStatusException;
+import org.springframework.web.server.ServerWebExchange;
+import reactor.core.publisher.Mono;
+
+public class ServiceErrorGatewayFilterFactory extends AbstractGatewayFilterFactory<Object> {
+    public ServiceErrorGatewayFilterFactory() {
+        super(Object.class);
+    }
+
+    @Override
+    public GatewayFilter apply(final Object config) {
+        return new ServiceErrorGatewayFilter();
+    }
+
+    private static class ServiceErrorGatewayFilter implements GatewayFilter, Ordered {
+
+        public @Override Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
+            return chain.filter(exchange).then(Mono.fromRunnable(() -> {
+                HttpStatus statusCode = exchange.getResponse().getStatusCode();
+                if (statusCode.is4xxClientError() || statusCode.is5xxServerError()) {
+                    throw new ResponseStatusException(statusCode);
+                }
+            }));
+        }
+
+        @Override
+        public int getOrder() {
+            return ResolveTargetGlobalFilter.ORDER + 1;
+        }
+    }
+}