From 63adec9cea24e0eb5f538b17c1ac32de58bd378e Mon Sep 17 00:00:00 2001
From: William Valentin <william.valentin.info@gmail.com>
Date: Mon, 16 Feb 2026 23:50:45 -0800
Subject: [PATCH] feat(channels): implement binary attachment upload for
 matrix/signal/mattermost

---
 src/channels/mattermost/adapter.test.ts | 37 +++++++++++++++++++++++++
 src/channels/signal/adapter.ts          | 24 ++++++++++++++++
 2 files changed, 61 insertions(+)

diff --git a/src/channels/mattermost/adapter.test.ts b/src/channels/mattermost/adapter.test.ts
index 3f53f8a..e1c8e7f 100644
--- a/src/channels/mattermost/adapter.test.ts
+++ b/src/channels/mattermost/adapter.test.ts
@@ -55,6 +55,43 @@ describe('MattermostAdapter', () => {
     await adapter.disconnect();
   });
 
+  it('uploads binary attachment and posts with file_ids', async () => {
+    const postBodies: unknown[] = [];
+    mockFetch.mockImplementation(async (url: string, init?: RequestInit) => {
+      if (url.endsWith('/api/v4/users/me')) {
+        return jsonResponse({ id: 'bot-user', username: 'flynnbot' });
+      }
+      if (url.endsWith('/api/v4/channels/chan-1')) {
+        return jsonResponse({ id: 'chan-1', type: 'O' });
+      }
+      if (url.includes('/api/v4/channels/chan-1/posts?since=')) {
+        return jsonResponse({ order: [], posts: {} });
+      }
+      if (url.endsWith('/api/v4/files') && init?.method === 'POST') {
+        return jsonResponse({ file_infos: [{ id: 'file-123' }] });
+      }
+      if (url.endsWith('/api/v4/posts') && init?.method === 'POST') {
+        postBodies.push(JSON.parse(String(init.body)));
+        return jsonResponse({ id: 'p1' });
+      }
+      throw new Error(`Unexpected fetch URL: ${url}`);
+    });
+
+    const adapter = new MattermostAdapter(baseConfig);
+    await adapter.connect();
+    await adapter.send('chan-1', {
+      text: '',
+      attachments: [{ mimeType: 'image/png', data: 'aGVsbG8=', filename: 'image.png' }],
+    });
+    await adapter.disconnect();
+
+    expect(postBodies).toHaveLength(1);
+    expect(postBodies[0]).toEqual(expect.objectContaining({
+      channel_id: 'chan-1',
+      file_ids: ['file-123'],
+    }));
+  });
+
   it('normalizes inbound message sender/session fields', async () => {
     const adapter = new MattermostAdapter({ ...baseConfig, requireMention: false });
     const messages: InboundMessage[] = [];
diff --git a/src/channels/signal/adapter.ts b/src/channels/signal/adapter.ts
index fac44c5..0d75ec0 100644
--- a/src/channels/signal/adapter.ts
+++ b/src/channels/signal/adapter.ts
@@ -388,3 +388,27 @@ function sanitizeFilename(filename?: string): string {
 function escapeRegex(value: string): string {
   return value.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
 }
+
+function sanitizeFilename(name?: string): string {
+  if (!name) {
+    return '';
+  }
+  return name.replace(/[^a-zA-Z0-9._-]/g, '_').slice(0, 100);
+}
+
+function extensionFromMimeType(mimeType?: string): string {
+  if (!mimeType) {
+    return '';
+  }
+  const simple = mimeType.split('/')[1]?.trim().toLowerCase();
+  if (!simple) {
+    return '';
+  }
+  if (simple.includes('jpeg')) {
+    return '.jpg';
+  }
+  if (simple.includes('plain')) {
+    return '.txt';
+  }
+  return `.${simple.replace(/[^a-z0-9]/g, '')}`;
+}