Improve compatibility for re-dispatched servlet request

sentinel-adapter/sentinel-spring-webmvc-adapter/src/main/java/com/alibaba/csp/sentinel/adapter/spring/webmvc/AbstractSentinelInterceptor.java

@@ -34,6 +34,21 @@
 import org.springframework.web.servlet.ModelAndView;
 
 /**
+ * Since request may be reprocessed in flow if any forwarding or including or other action
+ * happened (see {@link javax.servlet.ServletRequest#getDispatcherType()}) we will only 
+ * deal with the initial request. So we use <b>reference count</b> to track in 
+ * dispathing "onion" though which we could figure out whether we are in initial type "REQUEST".
+ * That means the sub-requests which we rarely meet in practice will NOT be recorded in Sentinel.
+ * <p>
+ * How to implement a forward sub-request in your action:
+ * <pre>
+ * initalRequest() {
+ *     ModelAndView mav = new ModelAndView();
+ *     mav.setViewName("another");
+ *     return mav;
+ * }
+ * </pre>
+ * 
  * @author kaizi2009
  * @since 1.7.1
  */
@@ -49,20 +64,46 @@ public AbstractSentinelInterceptor(BaseWebMvcConfig config) {
         AssertUtil.assertNotBlank(config.getRequestAttributeName(), "requestAttributeName should not be blank");
         this.baseWebMvcConfig = config;
     }
-
+
+    /**
+     * @param request
+     * @param rcKey
+     * @param step
+     * @return reference count after increasing (initial value as zero to be increased) 
+     */
+    private Integer increaseReferece(HttpServletRequest request, String rcKey, int step) {
+        Object obj = request.getAttribute(rcKey);
+
+        if (obj == null) {
+            // initial
+            obj = Integer.valueOf(0);
+        }
+
+        Integer newRc = (Integer)obj + step;
+        request.setAttribute(rcKey, newRc);
+        return newRc;
+    }
+
     @Override
     public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
         throws Exception {
         try {
             String resourceName = getResourceName(request);
 
-            if (StringUtil.isNotEmpty(resourceName)) {
-                // Parse the request origin using registered origin parser.
-                String origin = parseOrigin(request);
-                String contextName = getContextName(request);
-                ContextUtil.enter(contextName, origin);
-                setEntryInRequest(request, baseWebMvcConfig.getRequestAttributeName(), resourceName);
+            if (StringUtil.isEmpty(resourceName)) {
+                return true;
             }
+
+            if (increaseReferece(request, this.baseWebMvcConfig.getRequestRefName(), 1) != 1) {
+                return true;
+            }
+
+            // Parse the request origin using registered origin parser.
+            String origin = parseOrigin(request);
+            String contextName = getContextName(request);
+            ContextUtil.enter(contextName, origin);
+            Entry entry = SphU.entry(resourceName, ResourceTypeConstants.COMMON_WEB, EntryType.IN);
+            request.setAttribute(baseWebMvcConfig.getRequestAttributeName(), entry);
             return true;
         } catch (BlockException e) {
             try {
@@ -95,11 +136,20 @@ protected String getContextName(HttpServletRequest request) {
     @Override
     public void afterCompletion(HttpServletRequest request, HttpServletResponse response,
                                 Object handler, Exception ex) throws Exception {
+        if (increaseReferece(request, this.baseWebMvcConfig.getRequestRefName(), -1) != 0) {
+            return;
+        }
+
         Entry entry = getEntryInRequest(request, baseWebMvcConfig.getRequestAttributeName());
-        if (entry != null) {
-            traceExceptionAndExit(entry, ex);
-            removeEntryInRequest(request);
+        if (entry == null) {
+            // should not happen
+            RecordLog.warn("[{}] No entry found in request, key: {}",
+                    getClass().getSimpleName(), baseWebMvcConfig.getRequestAttributeName());
+            return;
         }
+
+        traceExceptionAndExit(entry, ex);
+        removeEntryInRequest(request);
         ContextUtil.exit();
     }
 
@@ -108,26 +158,6 @@ public void postHandle(HttpServletRequest request, HttpServletResponse response,
                            ModelAndView modelAndView) throws Exception {
     }
 
-    /**
-     * Note:
-     * If the attribute key already exists in request, don't create new {@link Entry},
-     * to guarantee the order of {@link Entry} in pair and avoid {@link com.alibaba.csp.sentinel.ErrorEntryFreeException}.
-     *
-     * Refer to:
-     * https://github.com/alibaba/Sentinel/issues/1531
-     * https://github.com/alibaba/Sentinel/issues/1482
-     */
-    protected void setEntryInRequest(HttpServletRequest request, String name, String resourceName) throws BlockException {
-        Object attrVal = request.getAttribute(name);
-        if (attrVal != null) {
-            RecordLog.warn("[{}] The attribute key '{}' already exists in request, please set `requestAttributeName`",
-                getClass().getSimpleName(), name);
-        } else {
-            Entry entry = SphU.entry(resourceName, ResourceTypeConstants.COMMON_WEB, EntryType.IN);
-            request.setAttribute(name, entry);
-        }
-    }
-
     protected Entry getEntryInRequest(HttpServletRequest request, String attrKey) {
         Object entryObject = request.getAttribute(attrKey);
         return entryObject == null ? null : (Entry)entryObject;

sentinel-adapter/sentinel-spring-webmvc-adapter/src/main/java/com/alibaba/csp/sentinel/adapter/spring/webmvc/config/BaseWebMvcConfig.java

@@ -17,7 +17,6 @@
 
 import com.alibaba.csp.sentinel.adapter.spring.webmvc.callback.BlockExceptionHandler;
 import com.alibaba.csp.sentinel.adapter.spring.webmvc.callback.RequestOriginParser;
-import com.alibaba.csp.sentinel.util.AssertUtil;
 
 /**
  * Common base configuration for Spring Web MVC adapter.
@@ -28,6 +27,7 @@
 public abstract class BaseWebMvcConfig {
 
     protected String requestAttributeName;
+    protected String requestRefName;
     protected BlockExceptionHandler blockExceptionHandler;
     protected RequestOriginParser originParser;
 
@@ -37,6 +37,16 @@ public String getRequestAttributeName() {
 
     public void setRequestAttributeName(String requestAttributeName) {
         this.requestAttributeName = requestAttributeName;
+        this.requestRefName = this.requestAttributeName + "-rc";
+    }
+
+    /**
+     * Paired with attr name used to track reference count.
+     * 
+     * @return
+     */
+    public String getRequestRefName() {
+        return requestRefName;
     }
 
     public BlockExceptionHandler getBlockExceptionHandler() {

sentinel-demo/sentinel-demo-spring-webmvc/src/main/java/com/alibaba/csp/sentinel/demo/spring/webmvc/controller/WebMvcTestController.java

@@ -17,40 +17,53 @@
 
 import java.util.Random;
 import java.util.concurrent.TimeUnit;
+import org.springframework.stereotype.Controller;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PathVariable;
-import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.bind.annotation.ResponseBody;
+import org.springframework.web.servlet.ModelAndView;
 
 /**
  * Test controller
  * @author kaizi2009
  */
-@RestController
+@Controller
 public class WebMvcTestController {
 
     @GetMapping("/hello")
+    @ResponseBody
     public String apiHello() {
         doBusiness();
         return "Hello!";
     }
 
     @GetMapping("/err")
+    @ResponseBody
     public String apiError() {
         doBusiness();
         return "Oops...";
     }
 
     @GetMapping("/foo/{id}")
+    @ResponseBody
     public String apiFoo(@PathVariable("id") Long id) {
         doBusiness();
         return "Hello " + id;
     }
 
     @GetMapping("/exclude/{id}")
+    @ResponseBody
     public String apiExclude(@PathVariable("id") Long id) {
         doBusiness();
         return "Exclude " + id;
     }
+
+    @GetMapping("/forward")
+    public ModelAndView apiForward() {
+        ModelAndView mav = new ModelAndView();
+        mav.setViewName("hello");
+        return mav;
+    }
 
     private void doBusiness() {
         Random random = new Random(1);