fix: allow multipart/form-data boundary to end with a newline (#5660)

The RFC 7578 spec for multipart/form-data requests does not require the
body of a request to end with a CRLF, only that each section begins with
a CRLF. While many clients implement multipart requests with the
trailing CRLF, the implementation for fetch in Node.js version 22 and
below does not.

This caused my a good number of hours debugging!

It does turn out that in September 2024 the Node.js fetch implementation
added the CRLF (https://github.com/nodejs/undici/pull/3625), though this
hasn't made it to a Node.js release yet.

This change allows the boundary to end with a newline or
not, as long as the boundary is followed by the end of the request body.

src/backend/base/langflow/main.py

@@ -193,9 +193,12 @@ def create_app():
             body = await request.body()
 
             boundary_start = f"--{boundary}".encode()
+            # The multipart/form-data spec doesn't require a newline after the boundary, however many clients do
+            # implement it that way
             boundary_end = f"--{boundary}--\r\n".encode()
+            boundary_end_no_newline = f"--{boundary}--".encode()
 
-            if not body.startswith(boundary_start) or not body.endswith(boundary_end):
+            if not body.startswith(boundary_start) or not body.endswith((boundary_end, boundary_end_no_newline)):
                 return JSONResponse(
                     status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
                     content={"detail": "Invalid multipart formatting"},