From d57bdfaace6da36aa038edd740d622b0ed18176a Mon Sep 17 00:00:00 2001
From: Linus Rath <139418639+rathlinus@users.noreply.github.com>
Date: Thu, 29 Oct 2026 03:12:41 +0100
Subject: [PATCH] fix: send writes only once after a dropped connection, retry
 only batches of reads

---
 .../__tests__/jmap-client-hardening.test.ts   | 34 +++++++++++++++++++
 src/api/jmap-client.ts                        | 16 ++++-----
 2 files changed, 42 insertions(+), 8 deletions(-)

diff --git a/src/api/__tests__/jmap-client-hardening.test.ts b/src/api/__tests__/jmap-client-hardening.test.ts
index a3c732b9..cda342eb 100644
--- a/src/api/__tests__/jmap-client-hardening.test.ts
+++ b/src/api/__tests__/jmap-client-hardening.test.ts
@@ -318,6 +318,40 @@ describe('JMAPClient hardening', () => {
     expect(fetch).toHaveBeenCalledTimes(2);
   });
 
+  // A write the server may already have applied must not run twice.
+  it.each([
+    [[['Email/set', { accountId: 'acc-1', destroy: ['e1'] }, '0']]],
+    [[['ContactCard/set', { accountId: 'acc-1', create: { c: {} } }, '0']]],
+    [[['Mailbox/get', { accountId: 'acc-1' }, '0'], ['Email/copy', { accountId: 'acc-1' }, '1']]],
+    [[['SieveScript/set', { accountId: 'acc-1' }, '0']]],
+  ])('does not replay a batch with a write after a network error (%j)', async (calls) => {
+    const client = await connected();
+    const fetch = mockFetch([
+      { status: 200, throw: new TypeError('Network request failed') },
+      { status: 200, json: { methodResponses: [] } },
+    ]);
+    const err = await client.request(calls as never).catch((e) => e);
+    expect(err).toBeInstanceOf(NetworkError);
+    expect(fetch).toHaveBeenCalledTimes(1);
+  });
+
+  it('replays a batch made only of reads', async () => {
+    vi.useFakeTimers();
+    const client = await connected();
+    const fetch = mockFetch([
+      { status: 200, throw: new TypeError('Network request failed') },
+      { status: 200, json: { methodResponses: [['Email/query', { ids: [] }, '0'], ['Email/get', { list: [] }, '1']] } },
+    ]);
+    const p = client.request([
+      ['Email/query', { accountId: 'acc-1' }, '0'],
+      ['Email/get', { accountId: 'acc-1', '#ids': { resultOf: '0', name: 'Email/query', path: '/ids' } }, '1'],
+      ['Email/changes', { accountId: 'acc-1', sinceState: 's' }, '2'],
+    ]);
+    await vi.advanceTimersByTimeAsync(1100);
+    await p;
+    expect(fetch).toHaveBeenCalledTimes(2);
+  });
+
   it('does not retry a submission after a network error and wraps it as NetworkError', async () => {
     const client = await connected();
     const fetch = mockFetch([{ status: 200, throw: new TypeError('Network request failed') }]);
diff --git a/src/api/jmap-client.ts b/src/api/jmap-client.ts
index 09457c31..bdf27a16 100644
--- a/src/api/jmap-client.ts
+++ b/src/api/jmap-client.ts
@@ -98,15 +98,15 @@ export function parseRetryAfter(header: string | null): number {
   return 60_000;
 }
 
-// Methods whose bodies must never be replayed automatically: a retried
-// EmailSubmission/set would send the mail twice.
+const READ_ONLY_METHOD = /\/(?:get|query|changes|queryChanges|parse)$|^Core\/echo$/;
+
+// Whether a batch must not be sent again after the connection failed without
+// an answer. The server may already have acted on it, so only batches made of
+// read methods are replayed (webmail isReplaySafeRequest): a retried /set,
+// /copy, /import or submission would be done twice - one Send delivering two
+// messages, one move or delete applied on top of its own result.
 function hasNonIdempotentMethod(methodCalls: ReadonlyArray<JMAPMethodCall>): boolean {
-  return methodCalls.some(
-    ([name]) =>
-      name === 'EmailSubmission/set' ||
-      name === 'Email/import' ||
-      name === 'Blob/upload',
-  );
+  return methodCalls.length === 0 || methodCalls.some(([name]) => !READ_ONLY_METHOD.test(name));
 }
 
 function fetchSessionDescribes(session: unknown): session is JMAPSession {