From 64dfe6432e26713df7ac29f2e480061c19f8a66a Mon Sep 17 00:00:00 2001
From: trevor-signal <131492920+trevor-signal@users.noreply.github.com>
Date: Mon, 11 Aug 2025 15:21:21 -0400
Subject: [PATCH] Treat 403 from CDN0 the same as a 404 from others CDNs

---
 .../util/downloadAttachment_test.ts           | 61 +++++++++++++++++++
 ts/util/downloadAttachment.ts                 |  7 +++
 2 files changed, 68 insertions(+)

diff --git a/ts/test-electron/util/downloadAttachment_test.ts b/ts/test-electron/util/downloadAttachment_test.ts
index 7da302aeb3..301a048047 100644
--- a/ts/test-electron/util/downloadAttachment_test.ts
+++ b/ts/test-electron/util/downloadAttachment_test.ts
@@ -122,6 +122,67 @@ describe('utils/downloadAttachment', () => {
     ]);
   });
 
+  it('throw permanently missing error if attachment fails with 403 from cdn 0 and no backup information', async () => {
+    const stubDownload = sinon
+      .stub()
+      .onFirstCall()
+      .throws(new HTTPError('not found', { code: 403, headers: {} }));
+
+    const attachment = { ...baseAttachment, cdnNumber: 0 };
+    await assert.isRejected(
+      downloadAttachment({
+        attachment,
+        options: {
+          hasMediaBackups: true,
+          onSizeUpdate: noop,
+          abortSignal: abortController.signal,
+        },
+        dependencies: {
+          downloadAttachmentFromLocalBackup: stubDownload,
+          downloadAttachmentFromServer: stubDownload,
+        },
+      }),
+      AttachmentPermanentlyUndownloadableError
+    );
+
+    assert.equal(stubDownload.callCount, 1);
+    assertDownloadArgs(stubDownload.getCall(0).args, [
+      fakeServer,
+      { attachment, mediaTier: MediaTier.STANDARD },
+      {
+        variant: AttachmentVariant.Default,
+        onSizeUpdate: noop,
+        abortSignal: abortController.signal,
+        logPrefix: '[REDACTED]est',
+      },
+    ]);
+  });
+
+  it('throw permanently missing error if attachment fails with 403 with no cdn number and no backup information', async () => {
+    const stubDownload = sinon
+      .stub()
+      .onFirstCall()
+      .throws(new HTTPError('not found', { code: 403, headers: {} }));
+
+    // nullish cdn number gets converted to 0
+    const attachment = { ...baseAttachment, cdnNumber: undefined };
+    await assert.isRejected(
+      downloadAttachment({
+        attachment,
+        options: {
+          hasMediaBackups: true,
+          onSizeUpdate: noop,
+          abortSignal: abortController.signal,
+        },
+        dependencies: {
+          downloadAttachmentFromLocalBackup: stubDownload,
+          downloadAttachmentFromServer: stubDownload,
+        },
+      }),
+      AttachmentPermanentlyUndownloadableError
+    );
+  });
+
   it('downloads from backup tier first if there is backup information', async () => {
     const stubDownload = sinon.stub();
     const attachment = backupableAttachment;
diff --git a/ts/util/downloadAttachment.ts b/ts/util/downloadAttachment.ts
index 725fb4c066..fd020edc63 100644
--- a/ts/util/downloadAttachment.ts
+++ b/ts/util/downloadAttachment.ts
@@ -138,6 +138,13 @@ export async function downloadAttachment({
     // then start returning 404
     if (error instanceof HTTPError && error.code === 404) {
       throw new AttachmentPermanentlyUndownloadableError(`HTTP ${error.code}`);
+    } else if (
+      error instanceof HTTPError &&
+      // CDN 0 can return 403 which means the same as 404 from other CDNs
+      error.code === 403 &&
+      (attachment.cdnNumber == null || attachment.cdnNumber === 0)
+    ) {
+      throw new AttachmentPermanentlyUndownloadableError(`HTTP ${error.code}`);
     } else {
       throw error;
     }