only run SendErrorFilter once (fixes recursive forwarding if /error fails)

spring-cloud-netflix-core/src/main/java/org/springframework/cloud/netflix/zuul/filters/post/SendErrorFilter.java

@@ -14,6 +14,8 @@ import javax.servlet.RequestDispatcher;
 @Slf4j
 public class SendErrorFilter extends ZuulFilter {
 
+    protected static final String SEND_ERROR_FILTER_RAN = "sendErrorFilter.ran";
+
     @Value("${error.path:/error}")
     private String errorPath;
 
@@ -30,7 +32,8 @@ public class SendErrorFilter extends ZuulFilter {
     @Override
     public boolean shouldFilter() {
         RequestContext ctx = RequestContext.getCurrentContext();
-        return ctx.containsKey("error.status_code");
+        //only forward to errorPath if it hasn't been forwarded to already
+        return ctx.containsKey("error.status_code") && !ctx.getBoolean(SEND_ERROR_FILTER_RAN, false);
     }
 
     @Override
@@ -46,6 +49,7 @@ public class SendErrorFilter extends ZuulFilter {
             ctx.getRequest().setAttribute("javax.servlet.error.status_code", statusCode);
 			RequestDispatcher dispatcher = ctx.getRequest().getRequestDispatcher(errorPath);
 			if (dispatcher != null) {
+				ctx.set(SEND_ERROR_FILTER_RAN, true);
 				dispatcher.forward(ctx.getRequest(), ctx.getResponse());
 			}
         } catch (Exception e) {

spring-cloud-netflix-core/src/test/java/org/springframework/cloud/netflix/zuul/filters/post/SendErrorFilterTests.java

@@ -48,4 +48,13 @@ public class SendErrorFilterTests {
 		assertTrue("shouldFilter returned false", filter.shouldFilter());
 		filter.run();
 	}
+
+	@Test
+	public void doesNotRunTwice() {
+		SendErrorFilter filter = createSendErrorFilter(new MockHttpServletRequest());
+
+		assertTrue("shouldFilter returned false", filter.shouldFilter());
+		filter.run();
+		assertFalse("shouldFilter returned true", filter.shouldFilter());
+	}
 }