From 61f485531733427a848c7cdb3e6198efa9e89bf7 Mon Sep 17 00:00:00 2001
From: Philipp Langer <philipp.langer@typeform.com>
Date: Wed, 30 Oct 2024 17:18:19 +0100
Subject: [PATCH] fix(instrumentation-http): skip malformed forwarded headers

---
 experimental/CHANGELOG.md                          |  2 ++
 .../src/utils.ts                                   | 12 ++++++++++--
 .../test/integrations/http-enable.test.ts          | 14 ++++++++++++++
 3 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/experimental/CHANGELOG.md b/experimental/CHANGELOG.md
index aad560d8fc..bb08a41082 100644
--- a/experimental/CHANGELOG.md
+++ b/experimental/CHANGELOG.md
@@ -11,6 +11,8 @@ All notable changes to experimental packages in this project will be documented
 
 ### :bug: (Bug Fix)
 
+* fix(instrumentation-http): skip malformed forwarded headers. [#5095](https://github.com/open-telemetry/opentelemetry-js/issues/5095) @pmlanger
+
 ### :books: (Refine Doc)
 
 ### :house: (Internal)
diff --git a/experimental/packages/opentelemetry-instrumentation-http/src/utils.ts b/experimental/packages/opentelemetry-instrumentation-http/src/utils.ts
index a03600dfd4..ffbdeff675 100644
--- a/experimental/packages/opentelemetry-instrumentation-http/src/utils.ts
+++ b/experimental/packages/opentelemetry-instrumentation-http/src/utils.ts
@@ -572,7 +572,7 @@ function getServerAddress(
 ): { host: string; port?: string } | null {
   const forwardedHeader = request.headers['forwarded'];
   if (forwardedHeader) {
-    for (const entry of forwardedParse(forwardedHeader)) {
+    for (const entry of parseForwardedHeader(forwardedHeader)) {
       if (entry.host) {
         return parseHostHeader(entry.host, entry.proto);
       }
@@ -635,7 +635,7 @@ export function getRemoteClientAddress(
 ): string | null {
   const forwardedHeader = request.headers['forwarded'];
   if (forwardedHeader) {
-    for (const entry of forwardedParse(forwardedHeader)) {
+    for (const entry of parseForwardedHeader(forwardedHeader)) {
       if (entry.for) {
         return entry.for;
       }
@@ -916,3 +916,11 @@ function normalizeMethod(method?: string | null) {
 
   return '_OTHER';
 }
+
+function parseForwardedHeader(header: string): Record<string, string>[] {
+  try {
+    return forwardedParse(header);
+  } catch {
+    return [];
+  }
+}
diff --git a/experimental/packages/opentelemetry-instrumentation-http/test/integrations/http-enable.test.ts b/experimental/packages/opentelemetry-instrumentation-http/test/integrations/http-enable.test.ts
index ef42ced2e9..558bbcb8ff 100644
--- a/experimental/packages/opentelemetry-instrumentation-http/test/integrations/http-enable.test.ts
+++ b/experimental/packages/opentelemetry-instrumentation-http/test/integrations/http-enable.test.ts
@@ -277,6 +277,20 @@ describe('HttpInstrumentation Integration tests', () => {
       assert.ok(result.reqHeaders[DummyPropagation.SPAN_CONTEXT_KEY]);
     });
 
+    it('should succeed even with malformed Forwarded header', async () => {
+      const spans = memoryExporter.getFinishedSpans();
+      assert.strictEqual(spans.length, 0);
+
+      const headers = { 'x-foo': 'foo', forwarded: 'malformed' };
+      const result = await httpRequest.get(
+        new url.URL(`${protocol}://localhost:${mockServerPort}/?query=test`),
+        { headers }
+      );
+
+      assert.ok(result.reqHeaders[DummyPropagation.TRACE_CONTEXT_KEY]);
+      assert.ok(result.reqHeaders[DummyPropagation.SPAN_CONTEXT_KEY]);
+    });
+
     it('should create a span for GET requests and add propagation headers with Expect headers', async () => {
       let spans = memoryExporter.getFinishedSpans();
       assert.strictEqual(spans.length, 0);