Shared reader for chunks of queued buffers #368

Overview

This task (milestone M2) moves the code that reads one chunk of queued buffers out of the network push operation. The result is one reader that the shared push operation uses for every connection type.

Background & Motivation

A push reads queued buffers in chunks and sends each chunk to the peer. Today this read is inside NetworkPushTransferOperation, and it uses the default database. The shared push operation in #374 needs the same read for network and disk peers.

Design: spec. Plan: implementation plan, Task 7.

Description & Expected Outcomes

A private function returns the serialized buffers of one transfer session for an offset and a chunk size. It orders the buffers by primary key, and each item includes its record max counter list. The function reads from the database handle that the caller gives. The network push operation uses this function with the context database.

Deliverables & Contracts

The task delivers:

• _serialize_buffer_chunk(transfer_session, offset, chunk_size, db), with db required.
• A network push operation that uses this function, with no change in behavior.

Acceptance Criteria

• With 5 buffers, an offset of 2, and a chunk size of 2, the function returns the 3rd and 4th buffers by primary key.
• Each returned item has an rmcb_list.
• The characterization suite passes without edits.

Technical Pointers & Architecture

• Target Components: morango/sync/operations.py:1480-1521 (NetworkPushTransferOperation.handle).
• Related Patterns: BufferSerializer in morango/api/serializers.py.
• Data Model & Schema Considerations: None.
• Resilience & Failure Modes: None.

Notes & Tradeoffs

• Dependencies: Blocked by: Explicit database handle for sync database access #365 (Explicit database handle for sync database access). Blocks: Sync stage operations work with any peer connection #374.
• Testing Requirements: This is a refactor. The characterization suite from Tests that pin today's async network push and pull behavior #363 and Tests that pin today's legacy network sync behavior #364 must pass without edits. Run tox -e postgres at the end of milestone M2.

Metadata

• Complexity: Low
• Target Branch: release-v0.9.x

AI Usage

Drafted with Claude (Claude Code) from the approved design spec and implementation plan. The author reviewed the requirements, and the code references were checked against the release-v0.9.x codebase.