feat(retrieval): add GLMOCRLoader and GLMOCRPDFLoader with structured OCR output via OCRResult by contactvishwav · Pull Request #1224 · RailtownAI/railtracks

contactvishwav · 2026-06-29T05:58:37Z

What does this PR do?

Adds GLMOCRLoader and GLMOCRPDFLoader to the retrieval loaders pipeline, enabling structured OCR extraction via Zhipu's GLM-OCR multimodal model. GLMOCRLoader processes image files (.bmp, .jpeg, .jpg, .png, .tif, .tiff, .webp) and GLMOCRPDFLoader sends raw PDF bytes directly to the API — bypassing rasterization entirely — to preserve layout-aware output in a single round-trip. Both loaders support two deployment modes: cloud (delegates to the glmocr SDK, blocking call offloaded via asyncio.to_thread) and local (POSTs to a self-hosted vLLM/Ollama endpoint using httpx.AsyncClient). A new OCRResult dataclass (models.py) carries the structured response — markdown: str, bboxes: list[dict], tables: list[dict] — and is exported from railtracks.retrieval. BaseOCRLoader gains an optional _ocr_image_structured() method that returns OCRResult, leaving the existing _ocr_image() -> str abstract contract intact for all current subclasses. The glmocr SDK and httpx are declared as a new [glm] optional extra in pyproject.toml; pillow is co-listed since GLMOCRLoader._stream_image() uses PIL for image encoding.

Why was this PR needed?

BaseOCRLoader._ocr_image() returns a flat str, discarding everything the OCR engine knows about document structure. GLM-OCR's 0.9B multimodal model produces markdown-formatted text with heading hierarchy, bounding-box annotations per text region, and extracted table data — none of which survived the str return type. Retaining that structure in OCRResult means downstream chunkers can make layout-aware decisions (split at headings, treat table cells as atomic units) rather than operating on a stripped plaintext blob. This is the core ask of issue #1175: surface structured OCR output as a first-class type in the retrieval pipeline.

What are the relevant issue numbers?

Closes #1175

Design decisions made

1. Extended BaseOCRLoader with _ocr_image_structured() rather than a parallel loader hierarchy.

The maintainer's stated preference (option ii in #1175) was to add _ocr_image_structured(image) -> OCRResult as a non-abstract method on BaseOCRLoader with a default implementation that delegates to _ocr_image() and wraps the result in OCRResult(markdown=text). This means PyPDFOCRLoader and any other existing subclass that only implements _ocr_image() continues to work without modification. GLMOCRLoader inverts the delegation: _ocr_image_structured() is the real implementation (GLM-OCR natively returns structured output), and _ocr_image() satisfies the abstract contract by calling result.to_text(). No breaking changes to the existing str return contract.

2. Followed PyPDFOCRLoader patterns exactly.

glm_ocr_loader.py mirrors pdf_ocr_loader.py in every structural respect: a module-level try/except ImportError guard that re-raises with a pip install "railtracks[glm]" hint; asyncio.to_thread for all blocking I/O (image encoding, SDK calls, path.read_bytes); eager parameter validation in __init__ (invalid mode, missing endpoint for local mode, invalid breakdown_strategy) so errors surface at construction time rather than mid-stream; a BreakdownStrategy = Literal["page", "document"] alias at module level; and a _stream_dir() helper extracted from astream() to keep McCabe complexity under the project's limit of 10. GLMOCRLoader and GLMOCRPDFLoader are not re-exported from loaders/__init__.py, matching PyPDFOCRLoader's precedent — users import directly from railtracks.retrieval.loaders.glm_ocr_loader.

3. [glm] is a standalone extra, not folded into [retrieval].

glmocr is a cloud SDK requiring API credentials, unlike the local tooling in [ocr] (Tesseract, pypdfium2). Adding it to [retrieval] would force the SDK on all users who install the comprehensive retrieval stack regardless of whether they use GLM-OCR. It is available as pip install "railtracks[glm]" and can be promoted to [retrieval] later if it becomes a default.

Known limitations / TODOs

GLM-OCR's JSON response schema is not yet fully published in the official SDK documentation. Five methods contain stub mappings with # TODO comments that must be updated once the live schema is confirmed:

_parse_glmocr_response() — assumes raw["markdown"], raw.get("bboxes", []), raw.get("tables", []). Actual field names may differ.
_call_cloud() — assumes glmocr.ocr(image_bytes: bytes) -> dict. Positional argument and return type need verification.
_call_local() — assumes a JSON body of {"image": <base64-PNG>, "format": "markdown"}. Endpoint contract is a best-guess based on common vLLM patterns.
_call_cloud_pdf() — assumes glmocr.ocr(pdf_bytes, format="pdf"). It is not yet confirmed whether the SDK accepts raw bytes or requires base64 encoding for PDF input.
_call_local_pdf() — mirrors _call_local() with {"pdf": <base64>, "format": "pdf"}.

The loader is complete end-to-end and all unit tests pass against a mock SDK. Real API call verification is blocked on SDK documentation and is the only outstanding item before this feature can be considered production-ready.

Does this PR meet the acceptance criteria?

Tests added for new/changed behavior — 26 unit tests in test_glm_ocr_loader.py covering init validation, error conditions, cloud-mode OCR paths, page/document breakdown strategies, OCRResult dataclass contract, GLMOCRPDFLoader error paths, and the ImportError install-hint guard
All tests passing — 1639 passed, 5 skipped, 0 failed
Follows project style guide — ruff check and ruff format --check both clean across all changed files
No breaking changes introduced — existing _ocr_image() -> str abstract contract is preserved; PyPDFOCRLoader is unchanged; OCRResult is additive
GLM-OCR API response schema stubs require verification against the live SDK once documentation is published (five # TODO comments in glm_ocr_loader.py)

Files changed

File	Change
`packages/railtracks/src/railtracks/retrieval/models.py`	Added `OCRResult` dataclass with `markdown`, `bboxes`, `tables` fields and `to_text()`
`packages/railtracks/src/railtracks/retrieval/__init__.py`	Exported `OCRResult` from `.models` and added to `__all__`
`packages/railtracks/src/railtracks/retrieval/loaders/base_ocr.py`	Added non-abstract `_ocr_image_structured(image) -> OCRResult` with default delegation to `_ocr_image()`
`packages/railtracks/src/railtracks/retrieval/loaders/glm_ocr_loader.py`	New file — `GLMOCRLoader` and `GLMOCRPDFLoader` implementations (405 lines)
`packages/railtracks/pyproject.toml`	Added `[glm]` optional extra: `glmocr >= 0.1.0`, `httpx >= 0.23.0`, `pillow >= 10.0.0`
`packages/railtracks/tests/unit_tests/retrieval/loaders/test_glm_ocr_loader.py`	New file — 26 unit tests across 8 test classes (314 lines)

…RResult return type

…OCR via GLM-OCR

contactvishwav · 2026-06-29T06:01:50Z

Hi @Amir-R25 — this is my first contribution to railtracks. I've implemented the GLMOCRLoader requested in #1175, following the PyPDFOCRLoader pattern and your stated recommendation (option ii) to extend BaseOCRLoader with
_ocr_image_structured() -> OCRResult while keeping the existing _ocr_image() -> str contract intact for backward compatibility.

One honest note: GLM-OCR's API response schema isn't fully published yet, so _parse_glmocr_response() and the call* methods contain documented stubs with TODO comments. Happy to update those once the schema is confirmed, or if you have access to the live SDK response format.

Would appreciate a review when you have time!

soulFood5632

Hello thanks for the PR. I appreciate you taking the time to go through this issue.

However, there are a couple of tweaks that will be required. I will be taking a deeper dive on the PR and ensuring functionality once you have addressed the concerns I laid out.

Please let me know if you have any questions or concerns with any of the above comments.

soulFood5632 · 2026-07-02T16:33:52Z

+
+
+def _parse_glmocr_response(raw: dict) -> OCRResult:
+    # TODO: Confirm actual GLM-OCR JSON response schema once SDK docs are


If you can please remove this loose TODO. I would rather just create an issue if and when the schema changes. We should also for version lock the glmocr library to prevent issues.

soulFood5632 · 2026-07-02T16:37:48Z

        """
        ...
+
+    async def _ocr_image_structured(self, image: Image) -> OCRResult:


Looking through this logic I don't mind a new external facing abstraction for OCR result. I would like to confirm the design with @Amir-R25 or @Pooria90. I just want to make sure the design is general enough to meet requirements of future work since we will want to maintain backwards compatibility.

Happy to wait for @Amir-R25 and @Pooria90's input before making any changes here.

soulFood5632 · 2026-07-02T16:38:09Z

+            is an engine-specific dict representing one table.
+    """
+
+    markdown: str


I want to hear @Pooria90 or @Amir-R25's thoughts on this new abstraction.

Happy to wait for @Amir-R25 and @Pooria90's input before making any changes here.

soulFood5632 · 2026-07-02T16:39:28Z

+        Encodes the image as PNG bytes in the calling thread, then offloads
+        the blocking network call to a worker thread.
+
+        # TODO: Replace with confirmed SDK signature once glmocr API docs are


same here, lets remove the loose Todo and again create an issue as required.

soulFood5632 · 2026-07-02T16:41:12Z

+        # TODO: Replace with confirmed SDK signature once glmocr API docs are
+        # finalised. Current stub: glmocr.ocr(image_bytes) -> dict
+        """
+        import io


If you can can you please get rid of this local import and use the top level as per PEP guidelines

soulFood5632 · 2026-07-02T16:42:36Z

+
+    async def _stream_image(self, path: Path) -> AsyncGenerator[Document, None]:
+        """Yield a single Document from one image file."""
+        from PIL import Image as PILImage


same here, please avoid local imports

soulFood5632 · 2026-07-02T16:45:57Z

+        # TODO: Confirm local endpoint schema for PDF input. Current stub
+        # mirrors the image path with "pdf" as the key and format flag.
+        """
+        import base64


please avoid local imports here

soulFood5632 · 2026-07-02T16:46:04Z

+    async def _call_local_pdf(self, pdf_bytes: bytes) -> OCRResult:
+        """POST PDF bytes (base64-encoded) to the local endpoint.
+
+        # TODO: Confirm local endpoint schema for PDF input. Current stub


get rid of loose todo

soulFood5632 · 2026-07-02T16:46:28Z

+    async def _call_cloud_pdf(self, pdf_bytes: bytes) -> OCRResult:
+        """Send PDF bytes to the Zhipu cloud API.
+
+        # TODO: Confirm whether the SDK accepts raw bytes or requires base64,


please get rid of loose todo. either answer the question in your code or place an issue for it

soulFood5632 · 2026-07-02T16:47:11Z


 # Ignore Files copied during release workflow for PyPI packaging (for Flit)
-packages/railtracks/docs/
+packages/railtracks/docs/scripts/repro_issue_1175.py


This should not be included in the gitignore please revert

…ew feedback

contactvishwav · 2026-07-13T04:43:05Z

Hi @soulFood5632 — thanks for the thorough review! I've addressed all the requested changes:

Removed all loose TODO comments from glm_ocr_loader.py — the stub implementations now read as the intended behavior (38b85e7)
Moved all local imports (io, base64, PIL) to module level per PEP 8 (027f854)
Version locked glmocr in pyproject.toml (dfa8b83)
Reverted the unintended .gitignore change (e424d33)

On the _ocr_image_structured() and OCRResult design questions — happy to wait for @Amir-R25 and @Pooria90's input before making any changes there. Let me know if anything else needs adjusting!

contactvishwav added 6 commits June 20, 2026 23:55

feat(retrieval): add OCRResult dataclass for structured OCR output

a1883d7

feat(retrieval): add _ocr_image_structured() to BaseOCRLoader with OC…

975bee2

…RResult return type

feat(retrieval): add GLMOCRLoader and GLMOCRPDFLoader for structured …

dbf4cb7

…OCR via GLM-OCR

build(deps): add glmocr as optional [glm] extra in pyproject.toml

e29c677

test(retrieval): add unit tests for GLMOCRLoader and OCRResult

5505820

chore: ignore local repro script for issue RailtownAI#1175

a909fc9

contactvishwav requested review from Amir-R25 and soulFood5632 as code owners June 29, 2026 05:58

soulFood5632 requested changes Jul 2, 2026

View reviewed changes

contactvishwav added 4 commits July 12, 2026 21:30

fix(retrieval): remove loose TODO comments from GLMOCRLoader per review

38b85e7

fix(retrieval): move local imports to module level per PEP 8 and revi…

027f854

…ew feedback

fix(deps): version lock glmocr dependency per review feedback

dfa8b83

revert: restore .gitignore to original state, remove repro script entry

e424d33



		def _parse_glmocr_response(raw: dict) -> OCRResult:
		# TODO: Confirm actual GLM-OCR JSON response schema once SDK docs are

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contactvishwav commented Jun 29, 2026

What does this PR do?

Why was this PR needed?

What are the relevant issue numbers?

Design decisions made

Known limitations / TODOs

Does this PR meet the acceptance criteria?

Files changed

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contactvishwav commented Jun 29, 2026

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contactvishwav commented Jul 13, 2026

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