Feature (canvas): Add Api for download "message" component output's file (#11772)

### What problem does this PR solve?

-Add Api for download "message" component output's file 
-Change the attachment output type check from tuple to
dictionary,because 'attachement' is not instance of tuple
-Update the message type to message_end to avoid the problem that
content does not send an error message when the message type is ans
["data"] ["content"]

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)
- [x] New Feature (non-breaking change which adds functionality)

agent/canvas.py

@@ -534,10 +534,12 @@ class Canvas(Graph):
                         yield decorate("message", {"content": cpn_obj.output("content")})
                         cite = re.search(r"\[ID:[ 0-9]+\]",  cpn_obj.output("content"))
 
-                    if isinstance(cpn_obj.output("attachment"), tuple):
-                        yield decorate("message", {"attachment": cpn_obj.output("attachment")})
-
-                    yield decorate("message_end", {"reference": self.get_reference() if cite else None})
+                    message_end = {}
+                    if isinstance(cpn_obj.output("attachment"), dict):
+                        message_end["attachment"] = cpn_obj.output("attachment")
+                    if cite:
+                        message_end["reference"] = self.get_reference()
+                    yield decorate("message_end", message_end)
 
                     while partials:
                         _cpn_obj = self.get_component_obj(partials[0])

api/apps/sdk/files.py

@@ -14,7 +14,7 @@
 #  limitations under the License.
 #
 
-
+import asyncio
 import pathlib
 import re
 from quart import request, make_response
@@ -29,6 +29,7 @@ from api.db import FileType
 from api.db.services import duplicate_name
 from api.db.services.file_service import FileService
 from api.utils.file_utils import filename_type
+from api.utils.web_utils import CONTENT_TYPE_MAP
 from common import settings
 from common.constants import RetCode
 
@@ -629,6 +630,19 @@ async def get(tenant_id, file_id):
     except Exception as e:
         return server_error_response(e)
 
+@manager.route("/file/download/<attachment_id>", methods=["GET"])  # noqa: F821
+@token_required
+async def download_attachment(tenant_id,attachment_id):
+    try:
+        ext = request.args.get("ext", "markdown")
+        data = await asyncio.to_thread(settings.STORAGE_IMPL.get, tenant_id, attachment_id)
+        response = await make_response(data)
+        response.headers.set("Content-Type", CONTENT_TYPE_MAP.get(ext, f"application/{ext}"))
+
+        return response
+
+    except Exception as e:
+        return server_error_response(e)
 
 @manager.route('/file/mv', methods=['POST'])  # noqa: F821
 @token_required