Add guardian helper functions to send/recv files

[cmickeyb]

Add send_file and recv_file to the guardian utility functions. These routines will use the keyvalue store for moving files to and from another service. While useful beyond the guardian, this is where they are most needed.

Eventually, it would be good to add comparable C++ routines that could be implemented within a contract.

Also improved the error handling and message generation for capability processing.

[Copilot]

Pull Request Overview

Adds helper routines for file transfer via the KeyValueStore and cleans up error handling in the guardian WSGI service.

• Converts error logging and responses in process_capability.py to use F-strings and adds a guard around missing operation fields.
• Introduces send_file and recv_file in common/utility.py for chunked file upload/download through the key-value store.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
common-contract/pdo/contracts/guardian/wsgi/process_capability.py	Standardize exception logging with f-strings and add missing-field guard for dispatch
common-contract/pdo/contracts/guardian/common/utility.py	Implement send_file/recv_file for chunked file operations in KVS

Comments suppressed due to low confidence (3)

common-contract/pdo/contracts/guardian/common/utility.py:36

• The constant uses double underscores which is reserved for Python internals; consider renaming to CHUNK_SIZE to follow PEP 8 conventions.

__CHUNK_SIZE__ = 1024

common-contract/pdo/contracts/guardian/common/utility.py:39

• New public functionality send_file lacks automated tests; consider adding unit tests that verify correct chunking, key generation, and KVS sync behavior.

def send_file(file_name, block_store = None, **kwargs):

common-contract/pdo/contracts/guardian/common/utility.py:59

• The input_encoding='str' flag may misinterpret raw bytes; confirm the store expects a string or switch to a raw/binary mode to avoid data corruption.

with kv : _ = kv.set(f'{key}_{chunk_number}', chunk, input_encoding='str', output_encoding='raw')