Preserve bound args for upload handlers

[puneetdixit200]

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Type of change

• Bug fix (non-breaking change which fixes an issue)

Changes To Core Features:

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Description

Fixes #5290.

EventHandler.__call__ returned immediately when it saw rx.upload_files(...) or rx.upload_files_chunk(...), so any other bound arguments supplied to the same event handler were dropped. This keeps the upload client-handler spec, but appends normal bound handler arguments to the resulting EventSpec so on_drop=State.handle_upload(rx.upload_files(...), field) preserves field.

AI-assisted: OpenAI Codex, with local review and verification.

Testing

• Red before fix: uv run pytest tests/units/components/core/test_upload.py::test_upload_files_preserves_bound_event_args -q failed because field was missing from the upload event args.
• uv run pytest tests/units/components/core/test_upload.py -q
• uv run pytest tests/units/test_event.py -q
• uv run pytest tests/units/test_app.py -q -k 'upload and not compile_writes_upload_files_provider_app_wrap'
• uv run ruff check packages/reflex-base/src/reflex_base/event/__init__.py tests/units/components/core/test_upload.py
• uv run pyright packages/reflex-base/src/reflex_base/event/__init__.py tests/units/components/core/test_upload.py (0 errors, 1 existing warning in event/__init__.py)
• git diff --check

Note: uv run pytest tests/units/test_app.py -q -k upload currently fails in unrelated test_compile_writes_upload_files_provider_app_wrap with AttributeError: 'DynamicState' object has no attribute 'dynamic'; the remaining 18 upload-selected app tests pass with that case excluded.

[greptile-apps]

Greptile Summary

This PR fixes issue #5290 by threading extra bound handler arguments all the way through the upload pipeline — from the Python compile-time EventSpec, through the JavaScript uploadFiles client, and into the backend event dispatch for both buffered and streaming upload paths.

• Python (event/__init__.py): EventHandler.__call__ now collects non-upload bound args into payload, detects reserved-name clashes and duplicate FileUpload args at build time, and appends a __reflex_event_arg_names manifest key so the JS client knows exactly which payload keys to forward.
• JavaScript (state.js, upload.js): applyRestEvent reads the manifest and assembles extra_args; uploadFiles prepends them as a JSON form field before the file parts.
• Backend (_upload.py): _decode_event_args validates the form field as a JSON object (400 on malformed/non-object); both the buffered and streaming paths parse and forward the args into the dispatched Event.payload.

Confidence Score: 5/5

Safe to merge; the fix is complete end-to-end with both unit and integration test coverage.

The Python compile-time path, the JS client, and both backend upload paths are all updated consistently. The previously flagged gaps are fully addressed. No regressions in the normal no-extra-args path.

No files require special attention.

Important Files Changed

Filename	Overview
packages/reflex-base/src/reflex_base/event/init.py	Core fix: EventHandler.call now collects extra bound args alongside the upload EventSpec, adds a __reflex_event_arg_names manifest key, and detects reserved-name clashes and duplicate upload args at build time.
packages/reflex-components-core/src/reflex_components_core/core/_upload.py	Backend updated for both buffered and streaming paths: _decode_event_args validates JSON dict, _buffered_upload_args reads the form field for non-chunked uploads, and _UploadChunkMultipartParser gains on_args_ready callback + size-bounded buffering for the streaming path.
packages/reflex-base/src/reflex_base/.templates/web/utils/state.js	applyRestEvent now reads __reflex_event_arg_names from the event payload and collects only those keys into extra_args before passing them to uploadFiles.
packages/reflex-base/src/reflex_base/.templates/web/utils/helpers/upload.js	uploadFiles accepts new extra_args parameter and, when non-empty, prepends a __reflex_event_args JSON form field to the multipart body before the file parts.
tests/units/components/core/test_upload.py	Comprehensive new unit tests covering compile-time EventSpec preservation, reserved-name clash, _decode_event_args validation, and streaming parser edge cases.
tests/integration/test_upload.py	Two new integration test paths verifying end-to-end delivery of bound args for both buffered and streaming upload handlers.

_{Reviews (3): Last reviewed commit: "fix: carry upload bound args as a form f..." | Re-trigger Greptile}

[codspeed-hq]

Merging this PR will not alter performance

✅ 26 untouched benchmarks
⏩ 8 skipped benchmarks¹

---

_{Comparing puneetdixit200:fix/upload-bound-event-args (4ce6406) with main (31f785e)}

Footnotes

1. 8 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[puneetdixit200]

The runtime upload path is covered on the current head now: the compiled event carries __reflex_event_arg_names, applyRestEvent forwards those keys to uploadFiles, uploadFiles sends them as Reflex-Event-Args, and the backend upload handlers merge that header into both buffered and chunk upload events.

Focused verification: uv run pytest tests/units/components/core/test_upload.py -k "upload_files_preserves_bound_event_args or upload_files_multiple_upload_args_raises or upload_files_bound_arg_reserved_name_raises" -q -> 3 passed, 12 deselected.

[FarhanAliRaza]

@greptile please rereview.

[FarhanAliRaza]

@greptile please rereview.