fix: correctly raise file not found errors in File GET endpoints

[jordanrfrazier]

Checks for file existence before streaming response is returned so the proper error is raised.

Summary by CodeRabbit

• Bug Fixes

  • Improved file download robustness with enhanced error handling that detects missing files and returns detailed 404 responses, providing clearer feedback when files are unavailable.

• Refactor

  • Consolidated file streaming implementation across storage systems to improve consistency and eliminate redundant branching logic.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

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Walkthrough

File streaming logic is unified by introducing a new abstract get_file_stream method in the storage service layer, implementing it with async iterator typing in local storage, and refactoring the API endpoint to use this consolidated method with prior existence verification via get_file_size.

Changes

Cohort / File(s)	Summary
Storage service abstraction src/backend/base/langflow/services/storage/service.py, src/backend/base/langflow/services/storage/local.py	Added abstract method get_file_stream to base StorageService class with return type AsyncIterator[bytes]. Implemented in LocalStorageService with explicit AsyncIterator[bytes] return type annotation; runtime logic unchanged.
API file streaming endpoint src/backend/base/langflow/api/v2/files.py	Refactored streaming logic to use unified flow: verifies file existence via get_file_size (catches FileNotFoundError for 404 response), obtains stream via unified get_file_stream, wraps with byte_stream_generator for chunking, and sends StreamingResponse. Replaces prior storage-type branching.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

• Review new abstract method contract and implementation consistency across storage backends
• Verify refactored API streaming logic correctly handles file existence checks and error cases
• Confirm async iterator typing and chunking behavior align with unified streaming approach

Pre-merge checks and finishing touches

Important

Pre-merge checks failed

Please resolve all errors before merging. Addressing warnings is optional.

❌ Failed checks (1 error, 4 warnings)

Check name	Status	Explanation	Resolution
Test Coverage For New Implementations	❌ Error	PR modifies file streaming API and storage service implementations but includes no new test files to validate error handling or functionality.	Add test files covering file not found errors, successful streaming, and storage backend implementations to ensure regression prevention.
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.
Test Quality And Coverage	⚠️ Warning	PR modifies critical file streaming and error handling functionality across three source files but includes no corresponding test files for AsyncIterator behavior, file existence checking, or 404 error handling.	Add unit tests for get_file_stream() AsyncIterator behavior, integration tests for download_file endpoint success/error cases, and async tests for LocalStorageService file existence checking with pytest.mark.asyncio.
Test File Naming And Structure	⚠️ Warning	PR modifies file streaming endpoints but includes no test files following pytest patterns or covering new functionality.	Add test_*.py files with pytest structure covering: successful file streaming for S3/local storage, FileNotFoundError handling with 404 responses, edge cases, and integration tests for API endpoints.
Excessive Mock Usage Warning	⚠️ Warning	v2_files_test has 87 mocks across 31 tests (~2.8 per test), obscuring real component interactions, while local_storage_test and s3_storage_test effectively use real objects with minimal mocks.	Refactor v2_files_test to use real database fixtures, actual storage operations, and integration tests instead of excessive mocking to better verify real component interactions.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main objective: ensuring proper 'file not found' error handling in File GET endpoints, which aligns with the changes consolidating streaming logic with an existence check.

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[codecov]

Codecov Report

❌ Patch coverage is 70.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 32.53%. Comparing base (3681cb2) to head (6341ae6).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
src/backend/base/langflow/api/v2/files.py	66.66%	2 Missing ⚠️
.../backend/base/langflow/services/storage/service.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10908      +/-   ##
==========================================
- Coverage   32.56%   32.53%   -0.03%     
==========================================
  Files        1371     1371              
  Lines       63493    63544      +51     
  Branches     9383     9397      +14     
==========================================
  Hits        20675    20675              
- Misses      41778    41829      +51     
  Partials     1040     1040              

Flag	Coverage Δ
backend	51.52% <70.00%> (-0.01%)	⬇️
frontend	14.31% <ø> (ø)
lfx	39.95% <ø> (-0.10%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...rc/backend/base/langflow/services/storage/local.py	85.88% <100.00%> (ø)
.../backend/base/langflow/services/storage/service.py	77.77% <66.66%> (-1.02%)	⬇️
src/backend/base/langflow/api/v2/files.py	62.80% <66.66%> (+0.43%)	⬆️

... and 18 files with indirect coverage changes

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[coderabbitai]

Actionable comments posted: 2

📜 Review details

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 6cedc28 and d08efcf.

⛔ Files ignored due to path filters (1)

• uv.lock is excluded by !**/*.lock

📒 Files selected for processing (3)

• src/backend/base/langflow/api/v2/files.py (1 hunks)
• src/backend/base/langflow/services/storage/local.py (2 hunks)
• src/backend/base/langflow/services/storage/service.py (2 hunks)

🧰 Additional context used

📓 Path-based instructions (2)

src/backend/**/*.py

📄 CodeRabbit inference engine (.cursor/rules/backend_development.mdc)

src/backend/**/*.py: Use FastAPI async patterns with await for async operations in component execution methods
Use asyncio.create_task() for background tasks and implement proper cleanup with try/except for asyncio.CancelledError
Use queue.put_nowait() for non-blocking queue operations and asyncio.wait_for() with timeouts for controlled get operations

Files:

• src/backend/base/langflow/api/v2/files.py
• src/backend/base/langflow/services/storage/local.py
• src/backend/base/langflow/services/storage/service.py

src/backend/base/langflow/api/**/*.py

📄 CodeRabbit inference engine (.cursor/rules/backend_development.mdc)

Backend API endpoints should be organized by version (v1/, v2/) under src/backend/base/langflow/api/ with specific modules for features (chat.py, flows.py, users.py, etc.)

Files:

• src/backend/base/langflow/api/v2/files.py

🧠 Learnings (1)

📓 Common learnings

Learnt from: CR
Repo: langflow-ai/langflow PR: 0
File: .cursor/rules/testing.mdc:0-0
Timestamp: 2025-11-24T19:47:28.997Z
Learning: Applies to src/backend/tests/**/*.py : Use `aiofiles` and `anyio.Path` for async file operations in tests; create temporary test files using `tmp_path` fixture and verify file existence and content

🧬 Code graph analysis (3)

src/backend/base/langflow/api/v2/files.py (3)

src/backend/base/langflow/services/storage/service.py (2)

• get_file_size (65-66)
• get_file_stream (44-58)

src/lfx/src/lfx/base/data/storage_utils.py (1)

• get_file_size (139-174)

src/lfx/src/lfx/services/storage/local.py (1)

• get_file_size (156-181)

src/backend/base/langflow/services/storage/local.py (3)

src/backend/base/langflow/services/storage/service.py (1)

• get_file_stream (44-58)

src/backend/base/langflow/services/storage/s3.py (1)

• get_file_stream (185-223)

src/lfx/src/lfx/services/storage/service.py (1)

• get_file_stream (106-126)

src/backend/base/langflow/services/storage/service.py (3)

src/backend/base/langflow/services/storage/local.py (1)

• get_file_stream (113-126)

src/backend/base/langflow/services/storage/s3.py (1)

• get_file_stream (185-223)

src/lfx/src/lfx/services/storage/service.py (1)

• get_file_stream (106-126)

🪛 GitHub Actions: Ruff Style Check

src/backend/base/langflow/services/storage/local.py

[error] 5-5: Ruff lint error TC003: Move standard library import collections.abc.AsyncIterator into a type-checking block.

🪛 GitHub Check: Ruff Style Check (3.13)

src/backend/base/langflow/services/storage/local.py

[failure] 5-5: Ruff (TC003)
src/backend/base/langflow/services/storage/local.py:5:29: TC003 Move standard library import collections.abc.AsyncIterator into a type-checking block

src/backend/base/langflow/services/storage/service.py

[failure] 6-6: Ruff (TC003)
src/backend/base/langflow/services/storage/service.py:6:29: TC003 Move standard library import collections.abc.AsyncIterator into a type-checking block

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (16)

• GitHub Check: Lint Backend / Run Mypy (3.11)
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• GitHub Check: Lint Backend / Run Mypy (3.13)
• GitHub Check: Run Backend Tests / Unit Tests - Python 3.10 - Group 5
• GitHub Check: Run Backend Tests / Unit Tests - Python 3.10 - Group 3
• GitHub Check: Run Backend Tests / Unit Tests - Python 3.10 - Group 1
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• GitHub Check: Run Backend Tests / Unit Tests - Python 3.10 - Group 2
• GitHub Check: Run Backend Tests / Unit Tests - Python 3.10 - Group 4
• GitHub Check: Run Backend Tests / LFX Tests - Python 3.10
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🔇 Additional comments (1)

src/backend/base/langflow/api/v2/files.py (1)

586-597: Pre‑flight size check and unified streaming look correct

The new get_file_size pre‑check cleanly converts missing files into a 404 before creating the StreamingResponse, and reusing get_file_stream wrapped in byte_stream_generator gives a consistent async stream across backends. Given that all current StorageService.get_file_stream implementations are async generators, calling it without await here is appropriate. I don’t see functional or error‑handling issues in this block.

[coderabbitai]

⚠️ Potential issue | 🟡 Minor

Move AsyncIterator import into TYPE_CHECKING to fix Ruff TC003

AsyncIterator is only used in type annotations here, and Ruff is flagging the top‑level import. With from __future__ import annotations already in place, it’s safe to import it only for type checking. You can fix the lint by moving the import into the existing TYPE_CHECKING block:

-from abc import abstractmethod
-from collections.abc import AsyncIterator
-from typing import TYPE_CHECKING
+from abc import abstractmethod
+from typing import TYPE_CHECKING
@@
-from langflow.services.base import Service
-
-if TYPE_CHECKING:
-    from langflow.services.session.service import SessionService
-    from langflow.services.settings.service import SettingsService
+from langflow.services.base import Service
+
+if TYPE_CHECKING:
+    from collections.abc import AsyncIterator
+    from langflow.services.session.service import SessionService
+    from langflow.services.settings.service import SettingsService

The get_file_stream abstract method and its docstring otherwise look good and align with the concrete implementations.

Also applies to: 43-59

🧰 Tools

🪛 GitHub Check: Ruff Style Check (3.13)

[failure] 6-6: Ruff (TC003)
src/backend/base/langflow/services/storage/service.py:6:29: TC003 Move standard library import collections.abc.AsyncIterator into a type-checking block

🤖 Prompt for AI Agents

In src/backend/base/langflow/services/storage/service.py around line 6 (and
similarly for the type-only uses in lines 43-59), the top-level import "from
collections.abc import AsyncIterator" is only used in annotations and triggers
Ruff TC003; move this import into the existing TYPE_CHECKING block (i.e., wrap
it in "if TYPE_CHECKING: from collections.abc import AsyncIterator") so the
import is only evaluated during static type checking while keeping "from
__future__ import annotations" and leaving the get_file_stream abstract method
and its docstring unchanged.

[erichare]

LGTM! Thanks @jordanrfrazier

[github-actions]

Frontend Unit Test Coverage Report

Coverage Summary

Lines	Statements	Branches	Functions
	15.45% (4253/27512)	8.63% (1815/21019)	9.74% (591/6064)

Unit Test Results

Tests	Skipped	Failures	Errors	Time
1671	0 💤	0 ❌	0 🔥	20.825s ⏱️