Fix multipart/form-data boundary issue in HTTP Call node (#23903)

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

api/core/workflow/nodes/http_request/executor.py

@@ -279,14 +279,22 @@ class Executor:
                 headers[authorization.config.header] = authorization.config.api_key or ""
 
         # Handle Content-Type for multipart/form-data requests
-        # Fix for issue #22880: Missing boundary when using multipart/form-data
+        # Fix for issue #23829: Missing boundary when using multipart/form-data
         body = self.node_data.body
         if body and body.type == "form-data":
-            # For multipart/form-data with files, let httpx handle the boundary automatically
+            # For multipart/form-data with files (including placeholder files),
-            # by not setting Content-Type header when files are present
+            # remove any manually set Content-Type header to let httpx handle
-            if not self.files or all(f[0] == "__multipart_placeholder__" for f in self.files):
+            # For multipart/form-data, if any files are present (including placeholder files),
-                # Only set Content-Type when there are no actual files
+            # we must remove any manually set Content-Type header. This is because httpx needs to
-                # This ensures httpx generates the correct boundary
+            # automatically set the Content-Type and boundary for multipart encoding whenever files
+            # are included, even if they are placeholders, to avoid boundary issues and ensure correct
+            # file upload behaviour. Manually setting Content-Type can cause httpx to fail to set the
+            # boundary, resulting in invalid requests.
+            if self.files:
+                # Remove Content-Type if it was manually set to avoid boundary issues
+                headers = {k: v for k, v in headers.items() if k.lower() != "content-type"}
+            else:
+                # No files at all, set Content-Type manually
                 if "content-type" not in (k.lower() for k in headers):
                     headers["Content-Type"] = "multipart/form-data"
         elif body and body.type in BODY_TYPE_TO_CONTENT_TYPE:

api/tests/unit_tests/core/workflow/nodes/http_request/test_http_request_executor.py

@@ -243,8 +243,6 @@ def test_executor_with_form_data():
     # Check the executor's data
     assert executor.method == "post"
     assert executor.url == "https://api.example.com/upload"
-    assert "Content-Type" in executor.headers
-    assert "multipart/form-data" in executor.headers["Content-Type"]
     assert executor.params is None
     assert executor.json is None
     # '__multipart_placeholder__' is expected when no file inputs exist,
@@ -252,6 +250,11 @@ def test_executor_with_form_data():
     assert executor.files == [("__multipart_placeholder__", ("", b"", "application/octet-stream"))]
     assert executor.content is None
 
+    # After fix for #23829: When placeholder files exist, Content-Type is removed
+    # to let httpx handle Content-Type and boundary automatically
+    headers = executor._assembling_headers()
+    assert "Content-Type" not in headers or "multipart/form-data" not in headers.get("Content-Type", "")
+
     # Check that the form data is correctly loaded in executor.data
     assert isinstance(executor.data, dict)
     assert "text_field" in executor.data