fix(mattermost): truncate draft previews on code-point boundaries (#97472)

ly-wang19 · claude · clawsweeper[bot] · web-flow · commit 881ec2f93f37 · 2026-06-28T18:20:33.000Z
Summary: - The PR replaces Mattermost draft preview raw UTF-16 slicing with the existing SDK `sliceUtf16Safe` helper and adds a regression test for an emoji that straddles the preview limit. - PR surface: Source +1, Tests +26. Total +27 across 2 files. - Reproducibility: yes. Source inspection shows current main raw-slices at `maxChars - 3`; driving `createMatt ... at UTF-16 indices 8-9 reaches the lone-surrogate path, though I did not run tests in this read-only sweep. Automerge notes: - PR branch already contained follow-up commit before automerge: fix(mattermost): truncate draft previews on code-point boundaries Validation: - ClawSweeper review passed for head 86d0dd2. - Required merge gates passed before the squash merge. Prepared head SHA: 86d0dd2 Review: #97472 (comment) Co-authored-by: ly-wang19 <ly-wang19@users.noreply.github.com> Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Co-authored-by: clawsweeper <274271284+clawsweeper[bot]@users.noreply.github.com> Approved-by: takhoffman
diff --git a/extensions/mattermost/src/mattermost/draft-stream.test.ts b/extensions/mattermost/src/mattermost/draft-stream.test.ts
@@ -205,6 +205,32 @@ describe("createMattermostDraftStream", () => {
     expect(stream.postId()).toBeUndefined();
   });
 
+  it("truncates on a code-point boundary so a straddling emoji is dropped whole", async () => {
+    const { client, calls } = createMockClient();
+    // maxChars=12 => cut point is maxChars-3=9. The emoji 😀 occupies UTF-16
+    // indices 8-9, so a raw slice(0,9) would keep the lone high surrogate at
+    // index 8 and drop its low surrogate at index 9, leaking a dangling half.
+    const stream = createMattermostDraftStream({
+      client,
+      channelId: "channel-1",
+      throttleMs: 0,
+      maxChars: 12,
+    });
+
+    const input = `${"a".repeat(8)}\u{1F600}${"b".repeat(5)}`;
+    stream.update(input);
+    await stream.flush();
+
+    expect(calls).toHaveLength(1);
+    const message = parseRequestJson(calls[0]?.init).message;
+    expect(typeof message).toBe("string");
+    const sent = message as string;
+    // The straddling emoji must be dropped whole, leaving no dangling surrogate half.
+    expect(/[\uD800-\uDFFF]/u.test(sent)).toBe(false);
+    expect(sent.length).toBeLessThanOrEqual(12);
+    expect(sent).toBe("aaaaaaaa...");
+  });
+
   it("does not resend after an update failure followed by stop", async () => {
     const warn = vi.fn();
     const calls: RequestRecord[] = [];
diff --git a/extensions/mattermost/src/mattermost/draft-stream.ts b/extensions/mattermost/src/mattermost/draft-stream.ts
@@ -1,5 +1,6 @@
 // Mattermost plugin module implements draft stream behavior.
 import { createFinalizableDraftLifecycle } from "openclaw/plugin-sdk/channel-outbound";
+import { sliceUtf16Safe } from "openclaw/plugin-sdk/text-utility-runtime";
 import {
   createMattermostPost,
   deleteMattermostPost,
@@ -29,7 +30,7 @@ function normalizeMattermostDraftText(text: string, maxChars: number): string {
   if (trimmed.length <= maxChars) {
     return trimmed;
   }
-  return `${trimmed.slice(0, Math.max(0, maxChars - 3)).trimEnd()}...`;
+  return `${sliceUtf16Safe(trimmed, 0, Math.max(0, maxChars - 3)).trimEnd()}...`;
 }
 
 export function createMattermostDraftStream(params: {

Original file line number	Diff line number	Diff line change
`@@ -1,5 +1,6 @@`
`1`	`1`	`// Mattermost plugin module implements draft stream behavior.`
`2`	`2`	`import { createFinalizableDraftLifecycle } from "openclaw/plugin-sdk/channel-outbound";`
	`3`	`+import { sliceUtf16Safe } from "openclaw/plugin-sdk/text-utility-runtime";`
`3`	`4`	`import {`
`4`	`5`	`createMattermostPost,`
`5`	`6`	`deleteMattermostPost,`
`@@ -29,7 +30,7 @@ function normalizeMattermostDraftText(text: string, maxChars: number): string {`
`29`	`30`	`if (trimmed.length <= maxChars) {`
`30`	`31`	`return trimmed;`
`31`	`32`	`}`
`32`		- return `${trimmed.slice(0, Math.max(0, maxChars - 3)).trimEnd()}...`;
	`33`	+ return `${sliceUtf16Safe(trimmed, 0, Math.max(0, maxChars - 3)).trimEnd()}...`;
`33`	`34`	`}`
`34`	`35`
`35`	`36`	`export function createMattermostDraftStream(params: {`