events: simplify stack compare function

This simplifies the `longestSeqContainedIn()` logic by checking for the first identical occurance of at least three frames instead of the longest one. It also removes an unused argument. PR-URL: #24744 Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
nodejs · May 16, 2019 · aca5ed5563fb268b9ecc137e2bc557e0a38b363e · aca5ed5
1 parent ead4bb6
commit aca5ed5563fb268b9ecc137e2bc557e0a38b363e
Showing with 20 additions and 21 deletions.

+20 −21 lib/events.js
diff --git a/lib/events.js b/lib/events.js
@@ -104,30 +104,29 @@ EventEmitter.prototype.getMaxListeners = function getMaxListeners() {
   return $getMaxListeners(this);
 };
 
-// Returns the longest sequence of `a` that fully appears in `b`,
-// of length at least 3.
-// This is a lazy approach but should work well enough, given that stack
-// frames are usually unequal or otherwise appear in groups, and that
-// we only run this code in case of an unhandled exception.
-function longestSeqContainedIn(a, b) {
-  for (var len = a.length; len >= 3; --len) {
-    for (var i = 0; i < a.length - len; ++i) {
-      // Attempt to find a[i:i+len] in b
-      for (var j = 0; j < b.length - len; ++j) {
-        let matches = true;
-        for (var k = 0; k < len; ++k) {
-          if (a[i + k] !== b[j + k]) {
-            matches = false;
-            break;
-          }
+// Returns the length and line number of the first sequence of `a` that fully
+// appears in `b` with a length of at least 4.
+function identicalSequenceRange(a, b) {
+  for (var i = 0; i < a.length - 3; i++) {
+    // Find the first entry of b that matches the current entry of a.
+    const pos = b.indexOf(a[i]);
+    if (pos !== -1) {
+      const rest = b.length - pos;
+      if (rest > 3) {
+        let len = 1;
+        const maxLen = Math.min(a.length - i, rest);
+        // Count the number of consecutive entries.
+        while (maxLen > len && a[i + len] === b[pos + len]) {
+          len++;
+        }
+        if (len > 3) {
+          return [len, i];
         }
-        if (matches)
-          return [ len, i, j ];
       }
     }
   }
 
-  return [ 0, 0, 0 ];
+  return [0, 0];
 }
 
 function enhanceStackTrace(err, own) {
@@ -136,9 +135,9 @@ function enhanceStackTrace(err, own) {
   const errStack = err.stack.split('\n').slice(1);
   const ownStack = own.stack.split('\n').slice(1);
 
-  const [ len, off ] = longestSeqContainedIn(ownStack, errStack);
+  const [ len, off ] = identicalSequenceRange(ownStack, errStack);
   if (len > 0) {
-    ownStack.splice(off + 1, len - 1,
+    ownStack.splice(off + 1, len - 2,
                     '    [... lines matching original stack trace ...]');
   }
   // Do this last, because it is the only operation with side effects.