From a1367e9cdd2773ef27da8c307342f904875e8aa8 Mon Sep 17 00:00:00 2001
From: Sehoon Shon <sshon@google.com>
Date: Fri, 27 Feb 2026 18:57:32 -0500
Subject: [PATCH] fix(core): parse raw ASCII buffer strings in Gaxios errors
 (#20626)

---
 .../src/core/loggingContentGenerator.test.ts  | 72 +++++++++++++++++++
 .../core/src/core/loggingContentGenerator.ts  | 32 +++++++++
 2 files changed, 104 insertions(+)

diff --git a/packages/core/src/core/loggingContentGenerator.test.ts b/packages/core/src/core/loggingContentGenerator.test.ts
index fc9103491c..5c0db58353 100644
--- a/packages/core/src/core/loggingContentGenerator.test.ts
+++ b/packages/core/src/core/loggingContentGenerator.test.ts
@@ -243,6 +243,78 @@ describe('LoggingContentGenerator', () => {
         expect(errorEvent.error_type).toBe('FatalAuthenticationError');
       });
     });
+
+    describe('Gaxios error parsing', () => {
+      it('should parse raw ASCII buffer strings in Gaxios errors', async () => {
+        const req = { contents: [], model: 'gemini-pro' };
+
+        // Simulate a Gaxios error with comma-separated ASCII codes
+        const asciiData = '72,101,108,108,111'; // "Hello"
+        const gaxiosError = Object.assign(new Error('Gaxios Error'), {
+          response: { data: asciiData },
+        });
+
+        vi.mocked(wrapped.generateContent).mockRejectedValue(gaxiosError);
+
+        await expect(
+          loggingContentGenerator.generateContent(
+            req,
+            'prompt-123',
+            LlmRole.MAIN,
+          ),
+        ).rejects.toSatisfy((error: unknown) => {
+          const gError = error as { response: { data: unknown } };
+          expect(gError.response.data).toBe('Hello');
+          return true;
+        });
+      });
+
+      it('should leave data alone if it is not a comma-separated string', async () => {
+        const req = { contents: [], model: 'gemini-pro' };
+
+        const normalData = 'Normal error message';
+        const gaxiosError = Object.assign(new Error('Gaxios Error'), {
+          response: { data: normalData },
+        });
+
+        vi.mocked(wrapped.generateContent).mockRejectedValue(gaxiosError);
+
+        await expect(
+          loggingContentGenerator.generateContent(
+            req,
+            'prompt-123',
+            LlmRole.MAIN,
+          ),
+        ).rejects.toSatisfy((error: unknown) => {
+          const gError = error as { response: { data: unknown } };
+          expect(gError.response.data).toBe(normalData);
+          return true;
+        });
+      });
+
+      it('should leave data alone if parsing fails', async () => {
+        const req = { contents: [], model: 'gemini-pro' };
+
+        const invalidAscii = '72,invalid,101';
+        const gaxiosError = Object.assign(new Error('Gaxios Error'), {
+          response: { data: invalidAscii },
+        });
+
+        vi.mocked(wrapped.generateContent).mockRejectedValue(gaxiosError);
+
+        await expect(
+          loggingContentGenerator.generateContent(
+            req,
+            'prompt-123',
+            LlmRole.MAIN,
+          ),
+        ).rejects.toSatisfy((error: unknown) => {
+          const gError = error as { response: { data: unknown } };
+          expect(gError.response.data).toBe(invalidAscii);
+          return true;
+        });
+      });
+    });
   });
 
   describe('generateContentStream', () => {
diff --git a/packages/core/src/core/loggingContentGenerator.ts b/packages/core/src/core/loggingContentGenerator.ts
index 5679c03a52..027a3a24ad 100644
--- a/packages/core/src/core/loggingContentGenerator.ts
+++ b/packages/core/src/core/loggingContentGenerator.ts
@@ -274,6 +274,32 @@ export class LoggingContentGenerator implements ContentGenerator {
     logApiResponse(this.config, event);
   }
 
+  private _fixGaxiosErrorData(error: unknown): void {
+    // Fix for raw ASCII buffer strings appearing in dev with the latest
+    // Gaxios updates.
+    if (
+      typeof error === 'object' &&
+      error !== null &&
+      'response' in error &&
+      typeof error.response === 'object' &&
+      error.response !== null &&
+      'data' in error.response
+    ) {
+      const response = error.response as { data: unknown };
+      const data = response.data;
+      if (typeof data === 'string' && data.includes(',')) {
+        try {
+          const charCodes = data.split(',').map(Number);
+          if (charCodes.every((code) => !isNaN(code))) {
+            response.data = String.fromCharCode(...charCodes);
+          }
+        } catch (_e) {
+          // If parsing fails, just leave it alone
+        }
+      }
+    }
+  }
+
   private _logApiError(
     durationMs: number,
     error: unknown,
@@ -380,6 +406,9 @@ export class LoggingContentGenerator implements ContentGenerator {
         } catch (error) {
           spanMetadata.error = error;
           const durationMs = Date.now() - startTime;
+
+          this._fixGaxiosErrorData(error);
+
           this._logApiError(
             durationMs,
             error,
@@ -447,6 +476,9 @@ export class LoggingContentGenerator implements ContentGenerator {
           );
         } catch (error) {
           const durationMs = Date.now() - startTime;
+
+          this._fixGaxiosErrorData(error);
+
           this._logApiError(
             durationMs,
             error,