From 15c3acd7791d1c85bf838f30a6ff767dd2ef95b7 Mon Sep 17 00:00:00 2001
From: Linus Rath <139418639+rathlinus@users.noreply.github.com>
Date: Thu, 15 Oct 2026 06:05:22 +0200
Subject: [PATCH] perf: open large HTML messages with one request instead of
 two

---
 lib/__tests__/jmap-truncated-body.test.ts | 22 ++++++++++++++++++++++
 lib/jmap/client.ts                        |  6 +++++-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/lib/__tests__/jmap-truncated-body.test.ts b/lib/__tests__/jmap-truncated-body.test.ts
index 75b89923d..dbfef35b5 100644
--- a/lib/__tests__/jmap-truncated-body.test.ts
+++ b/lib/__tests__/jmap-truncated-body.test.ts
@@ -172,4 +172,26 @@ describe('JMAPClient truncated body refetch (#884)', () => {
     expect(emails.find((e) => e.id === 'email-1')?.bodyValues?.html1.value).toBe('full-1');
     expect(emails.find((e) => e.id === 'email-2')?.bodyValues?.html1.value).toBe('full-2');
   });
+
+  it('getEmail fetches a body just over the list cap in one request', async () => {
+    // Opening one message needs all of its body; at the list-sized 256 kB cap
+    // a 300 kB newsletter came back truncated and was fetched twice.
+    const client = await createConnectedClient();
+    const html = '<html>' + 'x'.repeat(300_000) + '</html>';
+    fetchSpy.mockImplementation(async (_input, init) => {
+      const call = JSON.parse((init as RequestInit).body as string).methodCalls[0][1];
+      const cap = call.maxBodyValueBytes as number;
+      return mockFetchResponse(200, {
+        methodResponses: [['Email/get', { list: [{
+          ...truncatedEmail(),
+          bodyValues: { html1: { value: html.slice(0, cap), isTruncated: html.length > cap } },
+        }] }, '0']],
+      });
+    });
+
+    const email = await client.getEmail('email-1');
+
+    expect(fetchSpy).toHaveBeenCalledTimes(1);
+    expect(email?.bodyValues?.html1.value).toBe(html);
+  });
 });
diff --git a/lib/jmap/client.ts b/lib/jmap/client.ts
index 47cb56c2d..92db5f63c 100644
--- a/lib/jmap/client.ts
+++ b/lib/jmap/client.ts
@@ -27,6 +27,10 @@ import { toInertBlob } from "@/lib/file-preview";
 // / #884). Bounded well above the default so it stays rare in practice while
 // still guarding against unbounded memory use on a malicious/oversized body.
 const TRUNCATED_BODY_REFETCH_MAX_BYTES = 8_000_000;
+// Opening one message needs its whole body, so its fetch takes more than the
+// list-sized cap: a newsletter just over 256 kB came back truncated and was
+// fetched a second time. Larger bodies still take the refetch above.
+const OPEN_EMAIL_MAX_BODY_BYTES = 1_000_000;
 
 // Names of nodes created over WebDAV come back percent-encoded from
 // FileNode/get (see decodeFileNodeName / #869). Normalize at the boundary so
@@ -2369,7 +2373,7 @@ export class JMAPClient implements IJMAPClient {
           fetchTextBodyValues: true,
           fetchHTMLBodyValues: true,
           fetchAllBodyValues: true,
-          maxBodyValueBytes: 256000,
+          maxBodyValueBytes: OPEN_EMAIL_MAX_BODY_BYTES,
         }, "0"],
       ]);