Convert negative paramIdx of ParamFlowRule in ParamFlowSlot

Signed-off-by: Carpenter Lee <hooleeucas@163.com>

sentinel-extension/sentinel-parameter-flow-control/src/main/java/com/alibaba/csp/sentinel/slots/block/flow/param/ParamFlowChecker.java

@@ -52,7 +52,7 @@ final class ParamFlowChecker {
         }
 
         // Get parameter value. If value is null, then pass.
-        Object value = valueAt(args, paramIdx);
+        Object value = args[paramIdx];
         if (value == null) {
             return true;
         }
@@ -64,18 +64,6 @@ final class ParamFlowChecker {
         return passLocalCheck(resourceWrapper, rule, count, value);
     }
 
-    private static Object valueAt(Object[] args, int paramIdx) {
-        Object value = null;
-        if (paramIdx < 0) {
-            if (-paramIdx <= args.length) {
-                return args[args.length + paramIdx];
-            }
-        } else {
-            value = args[paramIdx];
-        }
-        return value;
-    }
-
     private static boolean passLocalCheck(ResourceWrapper resourceWrapper, ParamFlowRule rule, int count,
                                           Object value) {
         try {

sentinel-extension/sentinel-parameter-flow-control/src/main/java/com/alibaba/csp/sentinel/slots/block/flow/param/ParamFlowSlot.java

@@ -47,9 +47,8 @@ public class ParamFlowSlot extends AbstractLinkedProcessorSlot<DefaultNode> {
     private final Object LOCK = new Object();
 
     @Override
-    public void entry(Context context, ResourceWrapper resourceWrapper, DefaultNode node, int count, boolean prioritized, Object... args)
-        throws Throwable {
-
+    public void entry(Context context, ResourceWrapper resourceWrapper, DefaultNode node, int count,
+                      boolean prioritized, Object... args) throws Throwable {
         if (!ParamFlowRuleManager.hasRules(resourceWrapper.getName())) {
             fireEntry(context, resourceWrapper, node, count, prioritized, args);
             return;
@@ -73,6 +72,16 @@ public class ParamFlowSlot extends AbstractLinkedProcessorSlot<DefaultNode> {
             }
 
             for (ParamFlowRule rule : rules) {
+                int paramIdx = rule.getParamIdx();
+                if (paramIdx < 0) {
+                    if (-paramIdx <= args.length) {
+                        rule.setParamIdx(args.length + paramIdx);
+                    } else {
+                        // illegal index, give it a illegal positive value, latter rule check will pass
+                        rule.setParamIdx(-paramIdx);
+                    }
+                }
+
                 // Initialize the parameter metrics.
                 initHotParamMetricsFor(resourceWrapper, rule.getParamIdx());
 
@@ -105,7 +114,7 @@ public class ParamFlowSlot extends AbstractLinkedProcessorSlot<DefaultNode> {
      * Package-private for test.
      *
      * @param resourceWrapper resource to init
-     * @param index index to initialize, which must be valid
+     * @param index           index to initialize, which must be valid
      */
     void initHotParamMetricsFor(ResourceWrapper resourceWrapper, /*@Valid*/ int index) {
         ParameterMetric metric;

sentinel-extension/sentinel-parameter-flow-control/src/test/java/com/alibaba/csp/sentinel/slots/block/flow/param/ParamFlowSlotTest.java

@@ -39,6 +39,28 @@ public class ParamFlowSlotTest {
 
     private final ParamFlowSlot paramFlowSlot = new ParamFlowSlot();
 
+    @Test
+    public void testNegativeParamIdx() throws Throwable {
+        String resourceName = "testNegativeParamIdx";
+        ResourceWrapper resourceWrapper = new StringResourceWrapper(resourceName, EntryType.IN);
+        ParamFlowRule rule = new ParamFlowRule(resourceName)
+            .setCount(1)
+            .setParamIdx(-1);
+        ParamFlowRuleManager.loadRules(Collections.singletonList(rule));
+        paramFlowSlot.entry(null, resourceWrapper, null, 1, false, "abc", "def", "ghi");
+        assertEquals(2, rule.getParamIdx().longValue());
+
+        rule.setParamIdx(-100);
+        ParamFlowRuleManager.loadRules(Collections.singletonList(rule));
+        paramFlowSlot.entry(null, resourceWrapper, null, 1, false, "abc", "def", "ghi");
+        assertEquals(100, rule.getParamIdx().longValue());
+
+        rule.setParamIdx(0);
+        ParamFlowRuleManager.loadRules(Collections.singletonList(rule));
+        paramFlowSlot.entry(null, resourceWrapper, null, 1, false, "abc", "def", "ghi");
+        assertEquals(0, rule.getParamIdx().longValue());
+    }
+
     @Test
     public void testEntryWhenParamFlowRuleNotExists() throws Throwable {
         String resourceName = "testEntryWhenParamFlowRuleNotExists";