From f79e824d8ed761fb47192778e269aa288501833d Mon Sep 17 00:00:00 2001
From: Aran Yogesh <yogesh.mahendran@langchain.dev>
Date: Fri, 20 Mar 2026 14:34:14 -0700
Subject: [PATCH] feat: add Slack image support with url_private auth and
 content-type validation [closes: OPE-23] (#1073)

* feat: add Slack image support with url_private auth and content-type validation

* fix: simplify Slack image fetch by removing manual redirect logic

* fix: use urlparse hostname check to resolve CodeQL URL sanitization warning

* Update agent/utils/multimodal.py

Co-authored-by: Brace Sproul <braceasproul@gmail.com>

* fix: simplify host matching conditions in multimodal image fetching

* reverting changes

---------

Co-authored-by: Brace Sproul <braceasproul@gmail.com>
---
 agent/utils/multimodal.py | 24 ++++++++++++++++++++++--
 agent/webapp.py           | 19 +++++++++++++++++++
 2 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/agent/utils/multimodal.py b/agent/utils/multimodal.py
index bc2b7ff6..0cbc885c 100644
--- a/agent/utils/multimodal.py
+++ b/agent/utils/multimodal.py
@@ -8,6 +8,7 @@ import mimetypes
 import os
 import re
 from typing import Any
+from urllib.parse import urlparse
 
 import httpx
 from langchain_core.messages.content import create_image_block
@@ -44,7 +45,8 @@ async def fetch_image_block(
     try:
         logger.debug("Fetching image from %s", image_url)
         headers = None
-        if "uploads.linear.app" in image_url:
+        host = (urlparse(image_url).hostname or "").lower()
+        if host == "uploads.linear.app" or host.endswith(".uploads.linear.app"):
             linear_api_key = os.environ.get("LINEAR_API_KEY", "")
             if linear_api_key:
                 headers = {"Authorization": linear_api_key}
@@ -53,7 +55,16 @@ async def fetch_image_block(
                     "LINEAR_API_KEY not set; cannot authenticate image fetch for %s",
                     image_url,
                 )
-        response = await client.get(image_url, headers=headers)
+        elif host == "files.slack.com" or host.endswith(".files.slack.com"):
+            slack_bot_token = os.environ.get("SLACK_BOT_TOKEN", "")
+            if slack_bot_token:
+                headers = {"Authorization": f"Bearer {slack_bot_token}"}
+            else:
+                logger.warning(
+                    "SLACK_BOT_TOKEN not set; cannot authenticate image fetch for %s",
+                    image_url,
+                )
+        response = await client.get(image_url, headers=headers, follow_redirects=True)
         response.raise_for_status()
         content_type = response.headers.get("Content-Type", "").split(";")[0].strip()
         if not content_type:
@@ -66,6 +77,15 @@ async def fetch_image_block(
                 return None
             content_type = guessed
 
+        supported_types = {"image/jpeg", "image/png", "image/gif", "image/webp"}
+        if content_type not in supported_types:
+            logger.warning(
+                "Unsupported content type '%s' for %s; skipping image",
+                content_type,
+                image_url,
+            )
+            return None
+
         encoded = base64.b64encode(response.content).decode("ascii")
         logger.info(
             "Fetched image %s (%s, %d bytes)",
diff --git a/agent/webapp.py b/agent/webapp.py
index c8a7f958..6eda31f3 100644
--- a/agent/webapp.py
+++ b/agent/webapp.py
@@ -771,6 +771,25 @@ async def process_slack_mention(event_data: dict[str, Any], repo_config: dict[st
     )
     content_blocks: list[dict[str, Any]] = [create_text_block(prompt)]
 
+    image_urls = dedupe_urls(
+        [url for msg in context_messages for url in extract_image_urls(msg.get("text", ""))]
+        + [
+            f["url_private"]
+            for msg in context_messages
+            for f in msg.get("files", [])
+            if isinstance(f, dict)
+            and f.get("mimetype", "").startswith("image/")
+            and f.get("url_private")
+        ]
+    )
+    if image_urls:
+        logger.info("Preparing %d image(s) for Slack mention", len(image_urls))
+        async with httpx.AsyncClient() as http_client:
+            for image_url in image_urls:
+                image_block = await fetch_image_block(image_url, http_client)
+                if image_block:
+                    content_blocks.append(image_block)
+
     configurable: dict[str, Any] = {
         "repo": repo_config,
         "slack_thread": {