feat: add configurable JsonClient class for dependency injection

[ngjunsiang]

Feature Request: Configurable JsonClient Class for Dependency Injection

Problem

When testing Campus services that use campus_python.Campus, we need to replace the default CampusRequest with a test-compatible version that routes to Flask test clients instead of making real HTTP requests.

Current Workaround: Monkey-Patching

Currently, we have to monkey-patch the CampusRequest class:

import campus_python
from tests.flask_test import TestCampusRequest

# Replace CampusRequest globally
campus_python.json_client.CampusRequest = TestCampusRequest
campus_python.CampusRequest = TestCampusRequest  # Also patch module reference

Problems with this approach:

• ❌ Fragile - requires patching multiple module-level references
• ❌ Hard to debug - changes global state
• ❌ Confusing - not obvious that CampusRequest has been replaced
• ❌ Brittle - may break if campus-api-python internals change

Proposed Solution

Add a configurable class attribute to allow dependency injection of the JsonClient class:

class Campus:
    """Unified Campus client interface."""
    
    # Configurable JsonClient class
    json_client_class: type[JsonClient] = CampusRequest
    
    @property
    def auth(self) -> AuthRoot:
        if not hasattr(self, "_auth"):
            # Use json_client_class instead of hardcoded CampusRequest
            self._auth = AuthRoot(
                json_client=self.json_client_class(
                    base_url=base_url,
                    timeout=self.timeout,
                )
            )
        return self._auth
    
    @property
    def api(self) -> ApiRoot:
        if not hasattr(self, "_api"):
            self._api = ApiRoot(
                json_client=self.json_client_class(
                    base_url=base_url,
                    timeout=self.timeout,
                )
            )
        return self._api

Usage in Tests

import campus_python
from tests.flask_test import TestCampusRequest

def setup():
    # Configure campus_python to use test client
    campus_python.Campus.json_client_class = TestCampusRequest
    
    # Now all Campus instances use TestCampusRequest
    campus = campus_python.Campus(timeout=60)
    campus.auth.root.authenticate(...)  # Uses Flask test clients!

Benefits

1. ✅ Clean dependency injection - No monkey-patching required
2. ✅ Explicit configuration - Clear what JsonClient is being used
3. ✅ Backward compatible - Defaults to CampusRequest
4. ✅ Test-friendly - Easy to inject test doubles
5. ✅ Flexible - Allows custom JsonClient implementations for:
   • Testing (Flask test clients)
   • Mocking (for unit tests)
   • Custom HTTP backends (async, retry logic, etc.)

Implementation Details

Changes Required

File: campus_python/__init__.py

1. Add class attribute:

   class Campus:
       json_client_class: type[JsonClient] = CampusRequest

2. Replace hardcoded CampusRequest(...) with self.json_client_class(...):

   • In auth property (line ~81)
   • In api property (line ~107)

Example Custom JsonClient

from campus_python.json_client.interface import JsonClient, JsonResponse

class CustomJsonClient(JsonClient):
    """Custom JsonClient with special behavior."""
    
    def __init__(self, base_url: str | None = None, **kwargs):
        self.base_url = base_url or ""
        # ... custom initialization ...
    
    def get(self, path: str, query: dict | None = None) -> JsonResponse:
        # ... custom implementation ...
        pass
    
    # ... implement other methods ...

# Use it
campus_python.Campus.json_client_class = CustomJsonClient

Backward Compatibility

✅ Fully backward compatible - Default value is CampusRequest, so existing code continues to work without changes.

Related

• Campus services repo: https://github.com/nyjc-computing/campus
• Issue #485: Inconsistent HTTP client patterns in tests
• Current workaround in: tests/flask_test/campus_request.py

Alternatives Considered

1. Constructor parameter (Campus(json_client_class=...))

   • ❌ Doesn't work for services that instantiate Campus() internally (campus.auth, campus.api)

2. Global function (set_json_client_class())

   • ❌ More verbose than class attribute
   • ❌ Requires additional function to maintain

3. Keep monkey-patching

   • ❌ Fragile and confusing

Implementation Checklist

• Add json_client_class class attribute to Campus
• Update auth property to use self.json_client_class
• Update api property to use self.json_client_class
• Add docstring explaining the configuration option
• Add example to README or documentation
• Release as minor version bump (e.g., v2.1.0)