chore (REF352): open_session enhancement.

[k82cn]

fix #352

[gemini-code-assist]

Summary of Changes

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This pull request significantly enhances the open_session RPC by introducing 'get-or-create' functionality. Previously, users had to manage separate open_session and create_session calls, leading to complex logic and potential race conditions. With this change, open_session can now atomically retrieve an existing session or create a new one if a SessionSpec is provided. It also incorporates spec validation to prevent configuration drift for existing sessions. This streamlines the session management workflow across Rust and Python SDKs, simplifying client-side logic and improving API usability.

Highlights

• Atomic Get-or-Create for Sessions: The open_session RPC now supports atomic 'get-or-create' functionality, allowing clients to retrieve an existing session or create a new one if it doesn't exist, all within a single call.
• Optional Session Specification: The OpenSessionRequest protobuf message has been enhanced with an optional SessionSpec field. This spec is used for creating new sessions or for validating the configuration of existing ones.
• Spec Validation for Existing Sessions: When an existing session is opened with a provided SessionSpec, the system now performs strict validation to ensure the requested spec matches the existing session's configuration, preventing configuration drift.
• Backward Compatibility: The enhancement maintains full backward compatibility, meaning existing clients that call open_session without providing a SessionSpec will continue to function as before.

Changelog

• docs/designs/RFE352-open-session-enhancement/FS.md
  • New design document added, detailing the enhancement of the OpenSession RPC to support atomic get-or-create semantics and spec validation.
• rpc/protos/frontend.proto
  • Modified OpenSessionRequest message to include an optional SessionSpec session field.
• sdk/python/src/flamepy/core/client.py
  • Updated open_session function signatures (module-level and Connection class) to accept an optional spec parameter, enabling session creation or validation.
• sdk/rust/src/client/mod.rs
  • Added a new open_session method to the Connection struct, allowing Rust clients to utilize the enhanced RPC with optional session specifications.
  • Imported OpenSessionRequest for use in the new open_session method.
• session_manager/src/apiserver/frontend.rs
  • Modified the open_session gRPC handler to correctly parse and forward the optional SessionSpec from incoming requests to the controller.
• session_manager/src/controller/mod.rs
  • Updated the open_session method to accept an optional SessionAttributes and delegate the core logic to the storage layer.
• session_manager/src/storage/engine/mod.rs
  • Extended the Engine trait with a new open_session method signature to accommodate the optional session specification.
• session_manager/src/storage/engine/sqlite.rs
  • Implemented the open_session method for the SqliteEngine, providing atomic get-or-create functionality, including internal helper functions (_get_session, _create_session) and a compare_specs function for validation.
  • Refactored existing get_session and create_session methods to utilize the new internal helper functions for transactional operations.
• session_manager/src/storage/mod.rs
  • Introduced a new open_session method that orchestrates the call to the underlying engine and updates the in-memory session cache.

Activity

• A new design document was created to formally propose and detail the open_session enhancement.
• The core gRPC protocol was updated to allow optional session specifications in OpenSessionRequest.
• The session manager's backend logic was significantly refactored to support atomic session retrieval or creation, including robust spec validation.
• Both the Python and Rust SDKs were updated to expose this new, more convenient API to developers.
• Helper functions were introduced in the SQLite engine to streamline transactional operations and ensure data consistency.

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[gemini-code-assist]

Code Review

This pull request introduces a valuable "get-or-create" enhancement to the open_session RPC, simplifying client logic and preventing potential race conditions. The changes are well-architected, consistently applied from the Protobuf definitions through the backend storage engine to the client SDKs. The use of a database transaction for atomicity is a key strength of this implementation. The accompanying design document is thorough and clear. I have provided a few minor suggestions to further improve the clarity of the design document and simplify a small portion of the Python SDK code.