From ba9cfca7d6828be88eb0ed2a06183ca5ca86ad01 Mon Sep 17 00:00:00 2001
From: Thomas Watson <w@tson.dk>
Date: Sat, 1 Feb 2025 08:05:26 +0100
Subject: [PATCH] [DI] Probe file path matching algo should prefer shorter
 paths

---
 .../src/debugger/devtools_client/state.js     |  7 +++--
 .../debugger/devtools_client/state.spec.js    | 31 ++++++++++++++++---
 2 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/packages/dd-trace/src/debugger/devtools_client/state.js b/packages/dd-trace/src/debugger/devtools_client/state.js
index 30f4d2c879b..d165996dd92 100644
--- a/packages/dd-trace/src/debugger/devtools_client/state.js
+++ b/packages/dd-trace/src/debugger/devtools_client/state.js
@@ -43,8 +43,8 @@ module.exports = {
         // If both are boundaries, or if characters match exactly
         if (isBoundary || urlChar === pathChar) {
           if (isBoundary) {
-            lastBoundaryPos = matchLength
             atBoundary = true
+            lastBoundaryPos = matchLength
           } else {
             atBoundary = false
           }
@@ -71,7 +71,10 @@ module.exports = {
       }
 
       // If we found a valid match and it's better than our previous best
-      if (atBoundary && lastBoundaryPos !== -1 && lastBoundaryPos > maxMatchLength) {
+      if (atBoundary && (
+        lastBoundaryPos > maxMatchLength ||
+        (lastBoundaryPos === maxMatchLength && url.length < bestMatch[0].length) // Prefer shorter paths
+      )) {
         maxMatchLength = lastBoundaryPos
         bestMatch[0] = url
         bestMatch[1] = scriptId
diff --git a/packages/dd-trace/test/debugger/devtools_client/state.spec.js b/packages/dd-trace/test/debugger/devtools_client/state.spec.js
index ff4455e7b7c..3533b3367c0 100644
--- a/packages/dd-trace/test/debugger/devtools_client/state.spec.js
+++ b/packages/dd-trace/test/debugger/devtools_client/state.spec.js
@@ -25,6 +25,13 @@ describe('findScriptFromPartialPath', function () {
             // Test case for when there's multiple partial matches
             listener({ params: { scriptId: 'should-match', url: 'file:///server/index.js' } })
             listener({ params: { scriptId: 'should-not-match', url: 'file:///index.js' } })
+
+            // Test case for when there's two equal length partial matches
+            listener({ params: { scriptId: 'should-not-match-longest-a', url: 'file:///node_modules/foo/index.js' } })
+            listener({ params: { scriptId: 'should-match-shortest-a', url: 'file:///foo/index.js' } })
+            // The same, but in reverse order to ensure this doesn't influence the result
+            listener({ params: { scriptId: 'should-match-shortest-b', url: 'file:///bar/index.js' } })
+            listener({ params: { scriptId: 'should-not-match-longest-b', url: 'file:///node_modules/bar/index.js' } })
           }
         }
       }
@@ -117,14 +124,30 @@ describe('findScriptFromPartialPath', function () {
       const result = state.findScriptFromPartialPath('server/index.js')
       expect(result).to.deep.equal(['file:///server/index.js', 'should-match', undefined])
     })
+
+    it('should match the shorter of two equal length partial matches', function () {
+      const result1 = state.findScriptFromPartialPath('foo/index.js')
+      expect(result1).to.deep.equal(['file:///foo/index.js', 'should-match-shortest-a', undefined])
+
+      const result2 = state.findScriptFromPartialPath('bar/index.js')
+      expect(result2).to.deep.equal(['file:///bar/index.js', 'should-match-shortest-b', undefined])
+    })
   })
 
-  describe('circuit breakers', function () {
-    it('should abort if the path is unknown', testPathNoMatch('this/path/does/not/exist.js'))
+  describe('should abort if the path is', function () {
+    it('unknown', testPathNoMatch('this/path/does/not/exist.js'))
+
+    it('undefined', testPathNoMatch(undefined))
+
+    it('an empty string', testPathNoMatch(''))
+
+    it('a slash', testPathNoMatch('/'))
+
+    it('a backslash', testPathNoMatch('\\'))
 
-    it('should abort if the path is undefined', testPathNoMatch(undefined))
+    it('a Windows drive letter', testPathNoMatch('c:'))
 
-    it('should abort if the path is an empty string', testPathNoMatch(''))
+    it('a Windows drive letter with a backslash', testPathNoMatch('c:\\'))
   })
 
   function testPathNoMatch (path) {