From d5928d48137bb52cfd61b7a363ed7e28defa9dac Mon Sep 17 00:00:00 2001
From: danieljbruce <danieljbruce@users.noreply.github.com>
Date: Tue, 18 Aug 2026 14:35:47 -0400
Subject: [PATCH 1/7] =?UTF-8?q?Revert=20"fix:=20validate=20path=20paramete?=
 =?UTF-8?q?rs=20and=20prevent=20traversal/injection=20in=20REST=E2=80=A6"?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

This reverts commit 0152a8ee36592d90f435336fda95993c9cbd227a.
---
 core/packages/gax/src/transcoding.ts          |  79 ++---------
 core/packages/gax/test/unit/transcoding.ts    |  58 --------
 .../test/transcoding_validation.ts            | 132 ------------------
 3 files changed, 9 insertions(+), 260 deletions(-)
 delete mode 100644 packages/google-cloud-dialogflow-cx/test/transcoding_validation.ts

diff --git a/core/packages/gax/src/transcoding.ts b/core/packages/gax/src/transcoding.ts
index 070612ec117c..3d27a86c4f74 100644
--- a/core/packages/gax/src/transcoding.ts
+++ b/core/packages/gax/src/transcoding.ts
@@ -118,30 +118,6 @@ export function deleteField(request: JSONObject, field: string): void {
   delete request[part];
 }
 
-// Validates a single path segment matched by a single wildcard (*).
-// Checks that the segment is not exactly '.' or '..' (directory traversal indicators).
-function validateUriPathSegment(propertyName: string, value: string): void {
-  if (value === '.' || value === '..') {
-    throw new Error(`Invalid value ${value} for ${propertyName}`);
-  }
-}
-
-// Validates a multi-segment path matched by a double wildcard (**).
-// Splitting by slash, it checks that no individual segment is exactly '.' or '..'.
-// This segment-by-segment check prevents directory traversal while allowing
-// legitimate resource names containing dots (e.g., domain-scoped project IDs).
-function validateUriPath(propertyName: string, value: string): void {
-  if (value) {
-    // Split by slash and check for exact segment matches of '.' or '..' rather
-    // than using a simple string.includes('.') check. This avoids rejecting
-    // valid domain-scoped resource segments (e.g. projects/example.com:project-id).
-    const segments = value.split('/');
-    if (segments.some(segment => segment === '.' || segment === '..')) {
-      throw new Error(`Value for ${propertyName} must not contain segments that are exactly . or ..`);
-    }
-  }
-}
-
 export function buildQueryStringComponents(
   request: JSONObject,
   prefix = '',
@@ -172,35 +148,18 @@ export function buildQueryStringComponents(
   return resultList;
 }
 
-/**
- * Percent-encodes a string according to RFC 3986, preserving only unreserved
- * characters (alpha-numeric, '-', '_', '.', and '~'). All other characters,
- * including slashes ('/'), are percent-encoded.
- *
- * This is necessary because encodeURIComponent natively encodes URL-unsafe
- * characters like ?, #, $, &, +, etc., but preserves !, ', (, ), and *.
- * To ensure strict compliance, we manually encode those preserved characters.
- *
- * @param {string} str - The input string to encode.
- * @returns {string} The percent-encoded string.
- */
 export function encodeWithSlashes(str: string): string {
-  return encodeURIComponent(str).replace(
-    /[!'()*]/g, // Characters preserved by encodeURIComponent
-    character => '%' + character.charCodeAt(0).toString(16).toUpperCase()
-  );
+  return str
+    .split('')
+    .map(c => (c.match(/[-_.~0-9a-zA-Z]/) ? c : encodeURIComponent(c)))
+    .join('');
 }
 
-/**
- * Percent-encodes a string according to RFC 3986, preserving unreserved
- * characters (alpha-numeric, '-', '_', '.', and '~') and slashes ('/'). All other
- * characters are percent-encoded.
- *
- * @param {string} str - The input string to encode.
- * @returns {string} The percent-encoded string with slashes preserved.
- */
 export function encodeWithoutSlashes(str: string): string {
-  return str.split('/').map(encodeWithSlashes).join('/');
+  return str
+    .split('')
+    .map(c => (c.match(/[-_.~0-9a-zA-Z/]/) ? c : encodeURIComponent(c)))
+    .join('');
 }
 
 function escapeRegExp(str: string) {
@@ -210,10 +169,8 @@ function escapeRegExp(str: string) {
 export function applyPattern(
   pattern: string,
   fieldValue: string,
-  propertyName = 'resource', // Used to provide precise error messages when path validation fails
 ): string | undefined {
   if (!pattern || pattern === '*') {
-    validateUriPathSegment(propertyName, fieldValue);
     return encodeWithSlashes(fieldValue);
   }
 
@@ -230,27 +187,10 @@ export function applyPattern(
       '$',
   );
 
-  const match = fieldValue.match(regex);
-  if (!match) {
+  if (!fieldValue.match(regex)) {
     return undefined;
   }
 
-  // Identify the segments and wildcards in pattern to perform validation in order of appearance
-  const wildcards: string[] = pattern.match(/\*\*|\*/g) || [];
-
-  // Check the captured group values
-  for (let i = 1; i < match.length; i++) {
-    const groupVal = match[i];
-    if (groupVal !== undefined && groupVal !== null) {
-      const wildcardType = wildcards[i - 1];
-      if (wildcardType === '*') {
-        validateUriPathSegment(propertyName, groupVal);
-      } else if (wildcardType === '**') {
-        validateUriPath(propertyName, groupVal);
-      }
-    }
-  }
-
   return encodeWithoutSlashes(fieldValue);
 }
 
@@ -285,7 +225,6 @@ export function match(
     const appliedPattern = applyPattern(
       pattern,
       fieldValue === null ? 'null' : fieldValue!.toString(),
-      camelCasedField,
     );
     if (appliedPattern === undefined) {
       return undefined;
diff --git a/core/packages/gax/test/unit/transcoding.ts b/core/packages/gax/test/unit/transcoding.ts
index 3d1d613adf1e..4c0d40395107 100644
--- a/core/packages/gax/test/unit/transcoding.ts
+++ b/core/packages/gax/test/unit/transcoding.ts
@@ -370,24 +370,6 @@ describe('gRPC to HTTP transcoding', () => {
     );
   });
 
-  it('should correctly handle Unicode surrogate pairs in encodeWithSlashes', () => {
-    // Emojis (like 😊) are surrogate pairs.
-    // They should be encoded successfully instead of throwing a URIError.
-    assert.strictEqual(encodeWithSlashes('😊'), '%F0%9F%98%8A');
-  });
-
-  it('should preserve unreserved characters while strictly percent-encoding all other characters in encodeWithSlashes', () => {
-    // Standard RFC unreserved characters: [-_.~0-9a-zA-Z]
-    const unreserved = 'abc-123_.~';
-    assert.strictEqual(encodeWithSlashes(unreserved), unreserved);
-
-    // Reserved and special characters: should be percent encoded, including !\'()*
-    const specialChars = "!\'()*";
-    const encoded = encodeWithSlashes(specialChars);
-    // ! -> %21, ' -> %27, ( -> %28, ) -> %29, * -> %2A
-    assert.strictEqual(encoded, '%21%27%28%29%2A');
-  });
-
   it('encodeWithoutSlashes', () => {
     assert.strictEqual(encodeWithoutSlashes('abcd'), 'abcd');
     assert.strictEqual(
@@ -402,12 +384,6 @@ describe('gRPC to HTTP transcoding', () => {
     );
   });
 
-  it('should correctly handle Unicode surrogate pairs in encodeWithoutSlashes', () => {
-    // Emojis (like 😊) are surrogate pairs.
-    // They should be encoded successfully instead of throwing a URIError.
-    assert.strictEqual(encodeWithoutSlashes('😊'), '%F0%9F%98%8A');
-  });
-
   it('applyPattern', () => {
     assert.strictEqual(applyPattern('*', 'test'), 'test');
     assert.strictEqual(applyPattern('test', 'test'), 'test');
@@ -435,40 +411,6 @@ describe('gRPC to HTTP transcoding', () => {
     );
   });
 
-  it('applyPattern should throw an error for double-asterisk segment traversal containing segments that are exactly ".."', () => {
-    assert.throws(() => {
-      applyPattern(
-        'projects/*/locations/*/agents/*/sessions/**',
-        'projects/p/locations/l/agents/a/sessions/agents/../subagent',
-        'session'
-      );
-    }, /Value for session must not contain segments that are exactly \. or \.\./);
-  });
-
-  it('applyPattern should throw an error for double-asterisk segment traversal containing segments that are exactly "."', () => {
-    assert.throws(() => {
-      applyPattern(
-        'projects/*/locations/*/agents/*/sessions/**',
-        'projects/p/locations/l/agents/a/sessions/agents/./subagent',
-        'session'
-      );
-    }, /Value for session must not contain segments that are exactly \. or \.\./);
-  });
-
-  it('applyPattern should percent-encode query injection attempt on double-asterisk without throwing traversal error', () => {
-    const res = applyPattern(
-      'projects/*/locations/*/agents/*/sessions/**',
-      'projects/p/locations/l/agents/a/sessions/..?$foo=BAR#',
-      'session'
-    );
-    assert.strictEqual(res, 'projects/p/locations/l/agents/a/sessions/..%3F%24foo%3DBAR%23');
-  });
-
-  it('applyPattern should handle optional unmatched groups gracefully without throwing TypeErrors', () => {
-    const res = applyPattern('projects/*', 'projects/p', 'session');
-    assert.strictEqual(res, 'projects/p');
-  });
-
   it('flattenObject', () => {
     assert.deepStrictEqual(flattenObject({}), {});
     assert.deepStrictEqual(flattenObject({field: 'value'}), {field: 'value'});
diff --git a/packages/google-cloud-dialogflow-cx/test/transcoding_validation.ts b/packages/google-cloud-dialogflow-cx/test/transcoding_validation.ts
deleted file mode 100644
index 9130c26a8e79..000000000000
--- a/packages/google-cloud-dialogflow-cx/test/transcoding_validation.ts
+++ /dev/null
@@ -1,132 +0,0 @@
-// Copyright 2026 Google LLC
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     https://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-import * as assert from 'assert';
-import { describe, it } from 'mocha';
-import { v3 } from '../src';
-
-const sinon = require('sinon');
-
-describe('Dialogflow CX Fallback Transcoding and Path Traversal Prevention', () => {
-  let client: v3.SessionsClient;
-  let fetchStub: any;
-
-  beforeEach(() => {
-    client = new v3.SessionsClient({
-      fallback: true,
-      credentials: { client_email: 'bogus@example.com', private_key: 'bogus' },
-      projectId: 'bogus',
-    });
-    fetchStub = sinon.stub().resolves({
-      ok: true,
-      status: 200,
-      arrayBuffer: () => Promise.resolve(Buffer.from('{}')),
-    });
-    client.auth.fetch = fetchStub;
-  });
-
-  // Test 1: Single Asterisk Dot Validation on client call
-  it.skip('1. should throw an error for single-asterisk segment traversal using exactly "." as session ID', async () => {
-    // TODO: Re-enable this test when the gax version with the new encoding is released.
-    await client.initialize();
-    await assert.rejects(
-      client.detectIntent({
-        session: 'projects/p/locations/l/agents/a/sessions/.',
-        queryInput: { text: { text: 'hello' }, languageCode: 'en' },
-      }),
-      /Invalid value \. for session/
-    );
-  });
-
-  // Test 2: Single Asterisk Dot-Dot Validation on client call
-  it.skip('2. should throw an error for single-asterisk segment traversal using exactly ".." as session ID', async () => {
-    // TODO: Re-enable this test when the gax version with the new encoding is released.
-    await client.initialize();
-    await assert.rejects(
-      client.detectIntent({
-        session: 'projects/p/locations/l/agents/a/sessions/..',
-        queryInput: { text: { text: 'hello' }, languageCode: 'en' },
-      }),
-      /Invalid value \.\. for session/
-    );
-  });
-
-
-
-  // Test 5: Standard Valid Path fallback REST call
-  it('5. should pass transcoding validation with a valid session path and construct the correct REST URL', async () => {
-    await client.initialize();
-    await client.detectIntent({
-      session: 'projects/p/locations/l/agents/a/sessions/valid-session-id',
-      queryInput: { text: { text: 'hello' }, languageCode: 'en' },
-    });
-    assert.strictEqual(fetchStub.callCount, 1);
-    const requestUrl = fetchStub.firstCall.args[0];
-    assert.ok(requestUrl.includes('/v3/projects/p/locations/l/agents/a/sessions/valid-session-id:detectIntent'));
-  });
-
-  // Test 6: Query Parameter Injection Prevention via percent-encoding
-  it('6. should protect against query parameter injection by percent-encoding "?" and "$" in the session ID', async () => {
-    await client.initialize();
-    await client.detectIntent({
-      session: 'projects/p/locations/l/agents/a/sessions/my-session?$httpMethod=DELETE#',
-      queryInput: { text: { text: 'hello' }, languageCode: 'en' },
-    });
-    assert.strictEqual(fetchStub.callCount, 1);
-    const requestUrl = fetchStub.firstCall.args[0];
-    // "?" -> %3F, "$" -> %24, "=" -> %3D, "#" -> %23
-    assert.ok(requestUrl.includes('my-session%3F%24httpMethod%3DDELETE%23'));
-  });
-
-  // Test 7: Combined Path Traversal and Query Parameter Injection
-  it('7. should protect against path traversal and query injection by percent-encoding combined patterns', async () => {
-    // This request is permitted because the template uses * instead of **
-    // * is supposed to match against exactly . or ..
-    // This is okay because we still percent encode the ? parameter.
-    // example: POST https://<location>-dialogflow.googleapis.com/v3/{session=projects/*/locations/*/agents/*/sessions/*}:detectIntent
-    await client.initialize();
-    await client.detectIntent({
-      session: 'projects/p/locations/l/agents/a/sessions/..?$httpMethod=DELETE#',
-      queryInput: { text: { text: 'hello' }, languageCode: 'en' },
-    });
-    assert.strictEqual(fetchStub.callCount, 1);
-    const requestUrl = fetchStub.firstCall.args[0];
-    assert.ok(requestUrl.includes('/v3/projects/p/locations/l/agents/a/sessions/..%3F%24httpMethod%3DDELETE%23:detectIntent'));
-  });
-
-  // Test 8: Combined Path Traversal (.) and Query Parameter Injection
-  it('8. should protect against path traversal and query injection by percent-encoding combined patterns using dot', async () => {
-    await client.initialize();
-    await client.detectIntent({
-      session: 'projects/p/locations/l/agents/a/sessions/.?$httpMethod=DELETE#',
-      queryInput: { text: { text: 'hello' }, languageCode: 'en' },
-    });
-    assert.strictEqual(fetchStub.callCount, 1);
-    const requestUrl = fetchStub.firstCall.args[0];
-    assert.ok(requestUrl.includes('/v3/projects/p/locations/l/agents/a/sessions/.%3F%24httpMethod%3DDELETE%23:detectIntent'));
-  });
-
-  // Test 9: Percent-encoding all other characters
-  it.skip('9. should percent-encode all other characters except unreserved ones', async () => {
-    // TODO: Re-enable this test when the gax version with the new encoding is released.
-    await client.initialize();
-    await client.detectIntent({
-      session: 'projects/p/locations/l/agents/a/sessions/ !@$&\'()*+,;=:%',
-      queryInput: { text: { text: 'hello' }, languageCode: 'en' },
-    });
-    assert.strictEqual(fetchStub.callCount, 1);
-    const requestUrl = fetchStub.firstCall.args[0];
-    assert.ok(requestUrl.includes('/v3/projects/p/locations/l/agents/a/sessions/%20%21%40%24%26%27%28%29%2A%2B%2C%3B%3D%3A%25:detectIntent'));
-  });
-});

From 3c595c3b78745003d2696a45feb82bbc1b2163c5 Mon Sep 17 00:00:00 2001
From: Daniel Bruce <djbruce@google.com>
Date: Tue, 18 Aug 2026 15:08:49 -0400
Subject: [PATCH 2/7] reintroduce the transcoding changes for vulnerability

---
 core/packages/gax/src/transcoding.ts          |  85 +++++++++--
 core/packages/gax/test/unit/transcoding.ts    |  61 ++++++++
 .../gax/test/unit/transcoding_validation.ts   | 138 ++++++++++++++++++
 3 files changed, 274 insertions(+), 10 deletions(-)
 create mode 100644 core/packages/gax/test/unit/transcoding_validation.ts

diff --git a/core/packages/gax/src/transcoding.ts b/core/packages/gax/src/transcoding.ts
index 3d27a86c4f74..f855c8875ac8 100644
--- a/core/packages/gax/src/transcoding.ts
+++ b/core/packages/gax/src/transcoding.ts
@@ -118,6 +118,32 @@ export function deleteField(request: JSONObject, field: string): void {
   delete request[part];
 }
 
+// Validates a single path segment matched by a single wildcard (*).
+// Checks that the segment is not exactly '.' or '..' (directory traversal indicators).
+function validateUriPathSegment(propertyName: string, value: string): void {
+  if (value === '.' || value === '..') {
+    throw new Error(`Invalid value ${value} for ${propertyName}`);
+  }
+}
+
+// Validates a multi-segment path matched by a double wildcard (**).
+// Splitting by slash, it checks that no individual segment is exactly '.' or '..'.
+// This segment-by-segment check prevents directory traversal while allowing
+// legitimate resource names containing dots (e.g., domain-scoped project IDs).
+function validateUriPath(propertyName: string, value: string): void {
+  if (value) {
+    // Split by slash and check for exact segment matches of '.' or '..' rather
+    // than using a simple string.includes('.') check. This avoids rejecting
+    // valid domain-scoped resource segments (e.g. projects/example.com:project-id).
+    const segments = value.split('/');
+    if (segments.some(segment => segment === '.' || segment === '..')) {
+      throw new Error(
+        `Value for ${propertyName} must not contain segments that are exactly . or ..`,
+      );
+    }
+  }
+}
+
 export function buildQueryStringComponents(
   request: JSONObject,
   prefix = '',
@@ -140,7 +166,9 @@ export function buildQueryStringComponents(
     } else {
       resultList.push(
         `${prefix}${encodeWithoutSlashes(key)}=${encodeWithoutSlashes(
-          requestValue === null || requestValue === undefined ? 'null' : requestValue.toString(),
+          requestValue === null || requestValue === undefined
+            ? 'null'
+            : requestValue.toString(),
         )}`,
       );
     }
@@ -148,18 +176,35 @@ export function buildQueryStringComponents(
   return resultList;
 }
 
+/**
+ * Percent-encodes a string according to RFC 3986, preserving only unreserved
+ * characters (alpha-numeric, '-', '_', '.', and '~'). All other characters,
+ * including slashes ('/'), are percent-encoded.
+ *
+ * This is necessary because encodeURIComponent natively encodes URL-unsafe
+ * characters like ?, #, $, &, +, etc., but preserves !, ', (, ), and *.
+ * To ensure strict compliance, we manually encode those preserved characters.
+ *
+ * @param {string} str - The input string to encode.
+ * @returns {string} The percent-encoded string.
+ */
 export function encodeWithSlashes(str: string): string {
-  return str
-    .split('')
-    .map(c => (c.match(/[-_.~0-9a-zA-Z]/) ? c : encodeURIComponent(c)))
-    .join('');
+  return encodeURIComponent(str).replace(
+    /[!'()*]/g, // Characters preserved by encodeURIComponent
+    character => '%' + character.charCodeAt(0).toString(16).toUpperCase(),
+  );
 }
 
+/**
+ * Percent-encodes a string according to RFC 3986, preserving unreserved
+ * characters (alpha-numeric, '-', '_', '.', and '~') and slashes ('/'). All other
+ * characters are percent-encoded.
+ *
+ * @param {string} str - The input string to encode.
+ * @returns {string} The percent-encoded string with slashes preserved.
+ */
 export function encodeWithoutSlashes(str: string): string {
-  return str
-    .split('')
-    .map(c => (c.match(/[-_.~0-9a-zA-Z/]/) ? c : encodeURIComponent(c)))
-    .join('');
+  return str.split('/').map(encodeWithSlashes).join('/');
 }
 
 function escapeRegExp(str: string) {
@@ -169,8 +214,10 @@ function escapeRegExp(str: string) {
 export function applyPattern(
   pattern: string,
   fieldValue: string,
+  propertyName = 'resource', // Used to provide precise error messages when path validation fails
 ): string | undefined {
   if (!pattern || pattern === '*') {
+    validateUriPathSegment(propertyName, fieldValue);
     return encodeWithSlashes(fieldValue);
   }
 
@@ -187,10 +234,27 @@ export function applyPattern(
       '$',
   );
 
-  if (!fieldValue.match(regex)) {
+  const match = fieldValue.match(regex);
+  if (!match) {
     return undefined;
   }
 
+  // Identify the segments and wildcards in pattern to perform validation in order of appearance
+  const wildcards: string[] = pattern.match(/\*\*|\*/g) || [];
+
+  // Check the captured group values
+  for (let i = 1; i < match.length; i++) {
+    const groupVal = match[i];
+    if (groupVal !== undefined && groupVal !== null) {
+      const wildcardType = wildcards[i - 1];
+      if (wildcardType === '*') {
+        validateUriPathSegment(propertyName, groupVal);
+      } else if (wildcardType === '**') {
+        validateUriPath(propertyName, groupVal);
+      }
+    }
+  }
+
   return encodeWithoutSlashes(fieldValue);
 }
 
@@ -225,6 +289,7 @@ export function match(
     const appliedPattern = applyPattern(
       pattern,
       fieldValue === null ? 'null' : fieldValue!.toString(),
+      camelCasedField,
     );
     if (appliedPattern === undefined) {
       return undefined;
diff --git a/core/packages/gax/test/unit/transcoding.ts b/core/packages/gax/test/unit/transcoding.ts
index 4c0d40395107..5eb901223f2c 100644
--- a/core/packages/gax/test/unit/transcoding.ts
+++ b/core/packages/gax/test/unit/transcoding.ts
@@ -370,6 +370,24 @@ describe('gRPC to HTTP transcoding', () => {
     );
   });
 
+  it('should correctly handle Unicode surrogate pairs in encodeWithSlashes', () => {
+    // Emojis (like 😊) are surrogate pairs.
+    // They should be encoded successfully instead of throwing a URIError.
+    assert.strictEqual(encodeWithSlashes('😊'), '%F0%9F%98%8A');
+  });
+
+  it('should preserve unreserved characters while strictly percent-encoding all other characters in encodeWithSlashes', () => {
+    // Standard RFC unreserved characters: [-_.~0-9a-zA-Z]
+    const unreserved = 'abc-123_.~';
+    assert.strictEqual(encodeWithSlashes(unreserved), unreserved);
+
+    // Reserved and special characters: should be percent encoded, including !\'()*
+    const specialChars = "!'()*";
+    const encoded = encodeWithSlashes(specialChars);
+    // ! -> %21, ' -> %27, ( -> %28, ) -> %29, * -> %2A
+    assert.strictEqual(encoded, '%21%27%28%29%2A');
+  });
+
   it('encodeWithoutSlashes', () => {
     assert.strictEqual(encodeWithoutSlashes('abcd'), 'abcd');
     assert.strictEqual(
@@ -384,6 +402,12 @@ describe('gRPC to HTTP transcoding', () => {
     );
   });
 
+  it('should correctly handle Unicode surrogate pairs in encodeWithoutSlashes', () => {
+    // Emojis (like 😊) are surrogate pairs.
+    // They should be encoded successfully instead of throwing a URIError.
+    assert.strictEqual(encodeWithoutSlashes('😊'), '%F0%9F%98%8A');
+  });
+
   it('applyPattern', () => {
     assert.strictEqual(applyPattern('*', 'test'), 'test');
     assert.strictEqual(applyPattern('test', 'test'), 'test');
@@ -411,6 +435,43 @@ describe('gRPC to HTTP transcoding', () => {
     );
   });
 
+  it('applyPattern should throw an error for double-asterisk segment traversal containing segments that are exactly ".."', () => {
+    assert.throws(() => {
+      applyPattern(
+        'projects/*/locations/*/agents/*/sessions/**',
+        'projects/p/locations/l/agents/a/sessions/agents/../subagent',
+        'session',
+      );
+    }, /Value for session must not contain segments that are exactly \. or \.\./);
+  });
+
+  it('applyPattern should throw an error for double-asterisk segment traversal containing segments that are exactly "."', () => {
+    assert.throws(() => {
+      applyPattern(
+        'projects/*/locations/*/agents/*/sessions/**',
+        'projects/p/locations/l/agents/a/sessions/agents/./subagent',
+        'session',
+      );
+    }, /Value for session must not contain segments that are exactly \. or \.\./);
+  });
+
+  it('applyPattern should percent-encode query injection attempt on double-asterisk without throwing traversal error', () => {
+    const res = applyPattern(
+      'projects/*/locations/*/agents/*/sessions/**',
+      'projects/p/locations/l/agents/a/sessions/..?$foo=BAR#',
+      'session',
+    );
+    assert.strictEqual(
+      res,
+      'projects/p/locations/l/agents/a/sessions/..%3F%24foo%3DBAR%23',
+    );
+  });
+
+  it('applyPattern should handle optional unmatched groups gracefully without throwing TypeErrors', () => {
+    const res = applyPattern('projects/*', 'projects/p', 'session');
+    assert.strictEqual(res, 'projects/p');
+  });
+
   it('flattenObject', () => {
     assert.deepStrictEqual(flattenObject({}), {});
     assert.deepStrictEqual(flattenObject({field: 'value'}), {field: 'value'});
diff --git a/core/packages/gax/test/unit/transcoding_validation.ts b/core/packages/gax/test/unit/transcoding_validation.ts
new file mode 100644
index 000000000000..7d4a09e48266
--- /dev/null
+++ b/core/packages/gax/test/unit/transcoding_validation.ts
@@ -0,0 +1,138 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import * as assert from 'assert';
+import { describe, it } from 'mocha';
+import * as path from 'path';
+
+const dialogflowPath = path.resolve(
+  __dirname,
+  '../../../../../../packages/google-cloud-dialogflow-cx'
+);
+const { v3 } = require(dialogflowPath);
+
+const sinon = require('sinon');
+
+describe('Dialogflow CX Fallback Transcoding and Path Traversal Prevention', () => {
+  let client: any;
+  let fetchStub: any;
+
+  beforeEach(() => {
+    client = new v3.SessionsClient({
+      fallback: true,
+      credentials: { client_email: 'bogus@example.com', private_key: 'bogus' },
+      projectId: 'bogus',
+    });
+    fetchStub = sinon.stub().resolves({
+      ok: true,
+      status: 200,
+      arrayBuffer: () => Promise.resolve(Buffer.from('{}')),
+    });
+    client.auth.fetch = fetchStub;
+  });
+
+  // Test 1: Single Asterisk Dot Validation on client call
+  it.skip('1. should throw an error for single-asterisk segment traversal using exactly "." as session ID', async () => {
+    // TODO: Re-enable this test when the gax version with the new encoding is released.
+    await client.initialize();
+    await assert.rejects(
+      client.detectIntent({
+        session: 'projects/p/locations/l/agents/a/sessions/.',
+        queryInput: { text: { text: 'hello' }, languageCode: 'en' },
+      }),
+      /Invalid value \. for session/
+    );
+  });
+
+  // Test 2: Single Asterisk Dot-Dot Validation on client call
+  it.skip('2. should throw an error for single-asterisk segment traversal using exactly ".." as session ID', async () => {
+    // TODO: Re-enable this test when the gax version with the new encoding is released.
+    await client.initialize();
+    await assert.rejects(
+      client.detectIntent({
+        session: 'projects/p/locations/l/agents/a/sessions/..',
+        queryInput: { text: { text: 'hello' }, languageCode: 'en' },
+      }),
+      /Invalid value \.\. for session/
+    );
+  });
+
+
+
+  // Test 5: Standard Valid Path fallback REST call
+  it('5. should pass transcoding validation with a valid session path and construct the correct REST URL', async () => {
+    await client.initialize();
+    await client.detectIntent({
+      session: 'projects/p/locations/l/agents/a/sessions/valid-session-id',
+      queryInput: { text: { text: 'hello' }, languageCode: 'en' },
+    });
+    assert.strictEqual(fetchStub.callCount, 1);
+    const requestUrl = fetchStub.firstCall.args[0];
+    assert.ok(requestUrl.includes('/v3/projects/p/locations/l/agents/a/sessions/valid-session-id:detectIntent'));
+  });
+
+  // Test 6: Query Parameter Injection Prevention via percent-encoding
+  it('6. should protect against query parameter injection by percent-encoding "?" and "$" in the session ID', async () => {
+    await client.initialize();
+    await client.detectIntent({
+      session: 'projects/p/locations/l/agents/a/sessions/my-session?$httpMethod=DELETE#',
+      queryInput: { text: { text: 'hello' }, languageCode: 'en' },
+    });
+    assert.strictEqual(fetchStub.callCount, 1);
+    const requestUrl = fetchStub.firstCall.args[0];
+    // "?" -> %3F, "$" -> %24, "=" -> %3D, "#" -> %23
+    assert.ok(requestUrl.includes('my-session%3F%24httpMethod%3DDELETE%23'));
+  });
+
+  // Test 7: Combined Path Traversal and Query Parameter Injection
+  it('7. should protect against path traversal and query injection by percent-encoding combined patterns', async () => {
+    // This request is permitted because the template uses * instead of **
+    // * is supposed to match against exactly . or ..
+    // This is okay because we still percent encode the ? parameter.
+    // example: POST https://<location>-dialogflow.googleapis.com/v3/{session=projects/*/locations/*/agents/*/sessions/*}:detectIntent
+    await client.initialize();
+    await client.detectIntent({
+      session: 'projects/p/locations/l/agents/a/sessions/..?$httpMethod=DELETE#',
+      queryInput: { text: { text: 'hello' }, languageCode: 'en' },
+    });
+    assert.strictEqual(fetchStub.callCount, 1);
+    const requestUrl = fetchStub.firstCall.args[0];
+    assert.ok(requestUrl.includes('/v3/projects/p/locations/l/agents/a/sessions/..%3F%24httpMethod%3DDELETE%23:detectIntent'));
+  });
+
+  // Test 8: Combined Path Traversal (.) and Query Parameter Injection
+  it('8. should protect against path traversal and query injection by percent-encoding combined patterns using dot', async () => {
+    await client.initialize();
+    await client.detectIntent({
+      session: 'projects/p/locations/l/agents/a/sessions/.?$httpMethod=DELETE#',
+      queryInput: { text: { text: 'hello' }, languageCode: 'en' },
+    });
+    assert.strictEqual(fetchStub.callCount, 1);
+    const requestUrl = fetchStub.firstCall.args[0];
+    assert.ok(requestUrl.includes('/v3/projects/p/locations/l/agents/a/sessions/.%3F%24httpMethod%3DDELETE%23:detectIntent'));
+  });
+
+  // Test 9: Percent-encoding all other characters
+  it.skip('9. should percent-encode all other characters except unreserved ones', async () => {
+    // TODO: Re-enable this test when the gax version with the new encoding is released.
+    await client.initialize();
+    await client.detectIntent({
+      session: 'projects/p/locations/l/agents/a/sessions/ !@$&\'()*+,;=:%',
+      queryInput: { text: { text: 'hello' }, languageCode: 'en' },
+    });
+    assert.strictEqual(fetchStub.callCount, 1);
+    const requestUrl = fetchStub.firstCall.args[0];
+    assert.ok(requestUrl.includes('/v3/projects/p/locations/l/agents/a/sessions/%20%21%40%24%26%27%28%29%2A%2B%2C%3B%3D%3A%25:detectIntent'));
+  });
+});

From d17aa365c73efdf8586e13bbe82c7ca02dc39deb Mon Sep 17 00:00:00 2001
From: Daniel Bruce <djbruce@google.com>
Date: Tue, 18 Aug 2026 16:02:21 -0400
Subject: [PATCH 3/7] reintroduce changes verbatim that AI missed

---
 core/packages/gax/src/transcoding.ts       | 66 ++++++++++++++++------
 core/packages/gax/test/unit/transcoding.ts | 35 ++++--------
 2 files changed, 60 insertions(+), 41 deletions(-)

diff --git a/core/packages/gax/src/transcoding.ts b/core/packages/gax/src/transcoding.ts
index 61ab518f48ff..40928240c66a 100644
--- a/core/packages/gax/src/transcoding.ts
+++ b/core/packages/gax/src/transcoding.ts
@@ -137,9 +137,7 @@ function validateUriPath(propertyName: string, value: string): void {
     // valid domain-scoped resource segments (e.g. projects/example.com:project-id).
     const segments = value.split('/');
     if (segments.some(segment => segment === '.' || segment === '..')) {
-      throw new Error(
-        `Value for ${propertyName} must not contain segments that are exactly . or ..`,
-      );
+      throw new Error(`Value for ${propertyName} must not contain segments that are exactly . or ..`);
     }
   }
 }
@@ -150,25 +148,22 @@ export function buildQueryStringComponents(
 ): string[] {
   const resultList = [];
   for (const key in request) {
-    const requestValue = request[key];
-    if (Array.isArray(requestValue)) {
-      for (const value of requestValue as JSONObject[]) {
+    if (Array.isArray(request[key])) {
+      for (const value of request[key] as JSONObject[]) {
         resultList.push(
           `${prefix}${encodeWithoutSlashes(key)}=${encodeWithoutSlashes(
             value.toString(),
           )}`,
         );
       }
-    } else if (typeof requestValue === 'object' && requestValue !== null) {
+    } else if (typeof request[key] === 'object' && request[key] !== null) {
       resultList.push(
-        ...buildQueryStringComponents(requestValue as JSONObject, `${key}.`),
+        ...buildQueryStringComponents(request[key] as JSONObject, `${key}.`),
       );
     } else {
       resultList.push(
         `${prefix}${encodeWithoutSlashes(key)}=${encodeWithoutSlashes(
-          requestValue === null || requestValue === undefined
-            ? 'null'
-            : requestValue.toString(),
+          request[key] === null ? 'null' : request[key]!.toString(),
         )}`,
       );
     }
@@ -176,18 +171,35 @@ export function buildQueryStringComponents(
   return resultList;
 }
 
+/**
+ * Percent-encodes a string according to RFC 3986, preserving only unreserved
+ * characters (alpha-numeric, '-', '_', '.', and '~'). All other characters,
+ * including slashes ('/'), are percent-encoded.
+ *
+ * This is necessary because encodeURIComponent natively encodes URL-unsafe
+ * characters like ?, #, $, &, +, etc., but preserves !, ', (, ), and *.
+ * To ensure strict compliance, we manually encode those preserved characters.
+ *
+ * @param {string} str - The input string to encode.
+ * @returns {string} The percent-encoded string.
+ */
 export function encodeWithSlashes(str: string): string {
   return encodeURIComponent(str).replace(
     /[!'()*]/g, // Characters preserved by encodeURIComponent
-    character => '%' + character.charCodeAt(0).toString(16).toUpperCase(),
+    character => '%' + character.charCodeAt(0).toString(16).toUpperCase()
   );
 }
 
+/**
+ * Percent-encodes a string according to RFC 3986, preserving unreserved
+ * characters (alpha-numeric, '-', '_', '.', and '~') and slashes ('/'). All other
+ * characters are percent-encoded.
+ *
+ * @param {string} str - The input string to encode.
+ * @returns {string} The percent-encoded string with slashes preserved.
+ */
 export function encodeWithoutSlashes(str: string): string {
-  return str
-    .split('')
-    .map(c => (c.match(/[-_.~0-9a-zA-Z/]/) ? c : encodeURIComponent(c)))
-    .join('');
+  return str.split('/').map(encodeWithSlashes).join('/');
 }
 
 function escapeRegExp(str: string) {
@@ -197,8 +209,10 @@ function escapeRegExp(str: string) {
 export function applyPattern(
   pattern: string,
   fieldValue: string,
+  propertyName = 'resource', // Used to provide precise error messages when path validation fails
 ): string | undefined {
   if (!pattern || pattern === '*') {
+    validateUriPathSegment(propertyName, fieldValue);
     return encodeWithSlashes(fieldValue);
   }
 
@@ -215,10 +229,27 @@ export function applyPattern(
       '$',
   );
 
-  if (!fieldValue.match(regex)) {
+  const match = fieldValue.match(regex);
+  if (!match) {
     return undefined;
   }
 
+  // Identify the segments and wildcards in pattern to perform validation in order of appearance
+  const wildcards: string[] = pattern.match(/\*\*|\*/g) || [];
+
+  // Check the captured group values
+  for (let i = 1; i < match.length; i++) {
+    const groupVal = match[i];
+    if (groupVal !== undefined && groupVal !== null) {
+      const wildcardType = wildcards[i - 1];
+      if (wildcardType === '*') {
+        validateUriPathSegment(propertyName, groupVal);
+      } else if (wildcardType === '**') {
+        validateUriPath(propertyName, groupVal);
+      }
+    }
+  }
+
   return encodeWithoutSlashes(fieldValue);
 }
 
@@ -253,6 +284,7 @@ export function match(
     const appliedPattern = applyPattern(
       pattern,
       fieldValue === null ? 'null' : fieldValue!.toString(),
+      camelCasedField,
     );
     if (appliedPattern === undefined) {
       return undefined;
diff --git a/core/packages/gax/test/unit/transcoding.ts b/core/packages/gax/test/unit/transcoding.ts
index 85d4a1f7b4b5..cdb02048a7fa 100644
--- a/core/packages/gax/test/unit/transcoding.ts
+++ b/core/packages/gax/test/unit/transcoding.ts
@@ -382,7 +382,7 @@ describe('gRPC to HTTP transcoding', () => {
     assert.strictEqual(encodeWithSlashes(unreserved), unreserved);
 
     // Reserved and special characters: should be percent encoded, including !\'()*
-    const specialChars = "!'()*";
+    const specialChars = "!\'()*";
     const encoded = encodeWithSlashes(specialChars);
     // ! -> %21, ' -> %27, ( -> %28, ) -> %29, * -> %2A
     assert.strictEqual(encoded, '%21%27%28%29%2A');
@@ -402,6 +402,12 @@ describe('gRPC to HTTP transcoding', () => {
     );
   });
 
+  it('should correctly handle Unicode surrogate pairs in encodeWithoutSlashes', () => {
+    // Emojis (like 😊) are surrogate pairs.
+    // They should be encoded successfully instead of throwing a URIError.
+    assert.strictEqual(encodeWithoutSlashes('😊'), '%F0%9F%98%8A');
+  });
+
   it('applyPattern', () => {
     assert.strictEqual(applyPattern('*', 'test'), 'test');
     assert.strictEqual(applyPattern('test', 'test'), 'test');
@@ -434,7 +440,7 @@ describe('gRPC to HTTP transcoding', () => {
       applyPattern(
         'projects/*/locations/*/agents/*/sessions/**',
         'projects/p/locations/l/agents/a/sessions/agents/../subagent',
-        'session',
+        'session'
       );
     }, /Value for session must not contain segments that are exactly \. or \.\./);
   });
@@ -444,7 +450,7 @@ describe('gRPC to HTTP transcoding', () => {
       applyPattern(
         'projects/*/locations/*/agents/*/sessions/**',
         'projects/p/locations/l/agents/a/sessions/agents/./subagent',
-        'session',
+        'session'
       );
     }, /Value for session must not contain segments that are exactly \. or \.\./);
   });
@@ -453,12 +459,9 @@ describe('gRPC to HTTP transcoding', () => {
     const res = applyPattern(
       'projects/*/locations/*/agents/*/sessions/**',
       'projects/p/locations/l/agents/a/sessions/..?$foo=BAR#',
-      'session',
-    );
-    assert.strictEqual(
-      res,
-      'projects/p/locations/l/agents/a/sessions/..%3F%24foo%3DBAR%23',
+      'session'
     );
+    assert.strictEqual(res, 'projects/p/locations/l/agents/a/sessions/..%3F%24foo%3DBAR%23');
   });
 
   it('applyPattern should handle optional unmatched groups gracefully without throwing TypeErrors', () => {
@@ -616,22 +619,6 @@ describe('gRPC to HTTP transcoding', () => {
       ],
     );
   });
-
-  it('should gracefully handle undefined property values without throwing', () => {
-    const request = {
-      definedField: 'value',
-      undefinedField: undefined,
-    };
-
-    // Prior to PR 9150, this threw: TypeError: Cannot read properties of undefined (reading 'toString')
-    // With PR 9150, it gracefully serializes the undefined property to 'null'
-    const result = buildQueryStringComponents(request as any);
-
-    assert.deepStrictEqual(result, [
-      'definedField=value',
-      'undefinedField=null',
-    ]);
-  });
 });
 
 describe('override the HTTP rules in protoJson', () => {

From 192fa6fa1e57522dfb0c6d7c4629cdbc18dbbf5c Mon Sep 17 00:00:00 2001
From: Daniel Bruce <djbruce@google.com>
Date: Tue, 18 Aug 2026 16:05:32 -0400
Subject: [PATCH 4/7] Undo the buildQueryStringComponents changes

---
 core/packages/gax/src/transcoding.ts | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/core/packages/gax/src/transcoding.ts b/core/packages/gax/src/transcoding.ts
index 40928240c66a..070612ec117c 100644
--- a/core/packages/gax/src/transcoding.ts
+++ b/core/packages/gax/src/transcoding.ts
@@ -148,22 +148,23 @@ export function buildQueryStringComponents(
 ): string[] {
   const resultList = [];
   for (const key in request) {
-    if (Array.isArray(request[key])) {
-      for (const value of request[key] as JSONObject[]) {
+    const requestValue = request[key];
+    if (Array.isArray(requestValue)) {
+      for (const value of requestValue as JSONObject[]) {
         resultList.push(
           `${prefix}${encodeWithoutSlashes(key)}=${encodeWithoutSlashes(
             value.toString(),
           )}`,
         );
       }
-    } else if (typeof request[key] === 'object' && request[key] !== null) {
+    } else if (typeof requestValue === 'object' && requestValue !== null) {
       resultList.push(
-        ...buildQueryStringComponents(request[key] as JSONObject, `${key}.`),
+        ...buildQueryStringComponents(requestValue as JSONObject, `${key}.`),
       );
     } else {
       resultList.push(
         `${prefix}${encodeWithoutSlashes(key)}=${encodeWithoutSlashes(
-          request[key] === null ? 'null' : request[key]!.toString(),
+          requestValue === null || requestValue === undefined ? 'null' : requestValue.toString(),
         )}`,
       );
     }

From 60586c789e9a5b859103ac1ed052ffdf541fdb15 Mon Sep 17 00:00:00 2001
From: Daniel Bruce <djbruce@google.com>
Date: Tue, 18 Aug 2026 16:13:35 -0400
Subject: [PATCH 5/7] re-add the transcoding test

---
 core/packages/gax/test/unit/transcoding.ts | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/core/packages/gax/test/unit/transcoding.ts b/core/packages/gax/test/unit/transcoding.ts
index cdb02048a7fa..3d1d613adf1e 100644
--- a/core/packages/gax/test/unit/transcoding.ts
+++ b/core/packages/gax/test/unit/transcoding.ts
@@ -619,6 +619,22 @@ describe('gRPC to HTTP transcoding', () => {
       ],
     );
   });
+
+  it('should gracefully handle undefined property values without throwing', () => {
+    const request = {
+      definedField: 'value',
+      undefinedField: undefined,
+    };
+
+    // Prior to PR 9150, this threw: TypeError: Cannot read properties of undefined (reading 'toString')
+    // With PR 9150, it gracefully serializes the undefined property to 'null'
+    const result = buildQueryStringComponents(request as any);
+
+    assert.deepStrictEqual(result, [
+      'definedField=value',
+      'undefinedField=null',
+    ]);
+  });
 });
 
 describe('override the HTTP rules in protoJson', () => {

From 7dcf95409af3b82e6d0fbd0fea02c9951a6ea30d Mon Sep 17 00:00:00 2001
From: danieljbruce <danieljbruce@users.noreply.github.com>
Date: Tue, 18 Aug 2026 16:15:28 -0400
Subject: [PATCH 6/7] Apply suggestions from code review

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
---
 core/packages/gax/test/unit/transcoding_validation.ts | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/core/packages/gax/test/unit/transcoding_validation.ts b/core/packages/gax/test/unit/transcoding_validation.ts
index 7d4a09e48266..50796e57f396 100644
--- a/core/packages/gax/test/unit/transcoding_validation.ts
+++ b/core/packages/gax/test/unit/transcoding_validation.ts
@@ -14,13 +14,7 @@
 
 import * as assert from 'assert';
 import { describe, it } from 'mocha';
-import * as path from 'path';
-
-const dialogflowPath = path.resolve(
-  __dirname,
-  '../../../../../../packages/google-cloud-dialogflow-cx'
-);
-const { v3 } = require(dialogflowPath);
+const { v3 } = require('../../../../../../packages/google-cloud-dialogflow-cx');
 
 const sinon = require('sinon');
 

From 79ce8d562283caceb0436e64ee3d2b651223794f Mon Sep 17 00:00:00 2001
From: Daniel Bruce <djbruce@google.com>
Date: Tue, 18 Aug 2026 16:33:28 -0400
Subject: [PATCH 7/7] obscure the tests like we did for transcoding test

---
 .../packages/gax/test/unit/transcoding_validation.ts | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/core/packages/gax/test/unit/transcoding_validation.ts b/core/packages/gax/test/unit/transcoding_validation.ts
index 7d4a09e48266..86e8647eff41 100644
--- a/core/packages/gax/test/unit/transcoding_validation.ts
+++ b/core/packages/gax/test/unit/transcoding_validation.ts
@@ -86,13 +86,13 @@ describe('Dialogflow CX Fallback Transcoding and Path Traversal Prevention', ()
   it('6. should protect against query parameter injection by percent-encoding "?" and "$" in the session ID', async () => {
     await client.initialize();
     await client.detectIntent({
-      session: 'projects/p/locations/l/agents/a/sessions/my-session?$httpMethod=DELETE#',
+      session: 'projects/p/locations/l/agents/a/sessions/my-session?$foo=BAR#',
       queryInput: { text: { text: 'hello' }, languageCode: 'en' },
     });
     assert.strictEqual(fetchStub.callCount, 1);
     const requestUrl = fetchStub.firstCall.args[0];
     // "?" -> %3F, "$" -> %24, "=" -> %3D, "#" -> %23
-    assert.ok(requestUrl.includes('my-session%3F%24httpMethod%3DDELETE%23'));
+    assert.ok(requestUrl.includes('my-session%3F%24foo%3DBAR%23'));
   });
 
   // Test 7: Combined Path Traversal and Query Parameter Injection
@@ -103,24 +103,24 @@ describe('Dialogflow CX Fallback Transcoding and Path Traversal Prevention', ()
     // example: POST https://<location>-dialogflow.googleapis.com/v3/{session=projects/*/locations/*/agents/*/sessions/*}:detectIntent
     await client.initialize();
     await client.detectIntent({
-      session: 'projects/p/locations/l/agents/a/sessions/..?$httpMethod=DELETE#',
+      session: 'projects/p/locations/l/agents/a/sessions/..?$foo=BAR#',
       queryInput: { text: { text: 'hello' }, languageCode: 'en' },
     });
     assert.strictEqual(fetchStub.callCount, 1);
     const requestUrl = fetchStub.firstCall.args[0];
-    assert.ok(requestUrl.includes('/v3/projects/p/locations/l/agents/a/sessions/..%3F%24httpMethod%3DDELETE%23:detectIntent'));
+    assert.ok(requestUrl.includes('/v3/projects/p/locations/l/agents/a/sessions/..%3F%24foo%3DBAR%23:detectIntent'));
   });
 
   // Test 8: Combined Path Traversal (.) and Query Parameter Injection
   it('8. should protect against path traversal and query injection by percent-encoding combined patterns using dot', async () => {
     await client.initialize();
     await client.detectIntent({
-      session: 'projects/p/locations/l/agents/a/sessions/.?$httpMethod=DELETE#',
+      session: 'projects/p/locations/l/agents/a/sessions/.?$foo=BAR#',
       queryInput: { text: { text: 'hello' }, languageCode: 'en' },
     });
     assert.strictEqual(fetchStub.callCount, 1);
     const requestUrl = fetchStub.firstCall.args[0];
-    assert.ok(requestUrl.includes('/v3/projects/p/locations/l/agents/a/sessions/.%3F%24httpMethod%3DDELETE%23:detectIntent'));
+    assert.ok(requestUrl.includes('/v3/projects/p/locations/l/agents/a/sessions/.%3F%24foo%3DBAR%23:detectIntent'));
   });
 
   // Test 9: Percent-encoding all other characters