refactor(db): use shared pooled DatabaseClient singleton instead of per-call instances

- Replace get_db_client() creating new DatabaseClient on every call with a
  module-level singleton initialized once at startup via init_db_client()
- Add init_db_client() and close_db_client() lifecycle functions called
  from FastAPI lifespan handler
- Migrate all DatabaseClient methods from legacy self.connect()/self.conn
  to pooled self.get_conn() context manager for thread-safe connection reuse
- Pool is properly torn down on application shutdown

Closes leeworks-agents/SPARC#7

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

SPARC/api.py

@@ -7,24 +7,22 @@ from contextlib import asynccontextmanager
 from datetime import datetime
 from typing import Annotated, List
 
-from fastapi import BackgroundTasks, Depends, FastAPI, HTTPException, Query, Request
+from fastapi import BackgroundTasks, Depends, FastAPI, HTTPException, Query
 from fastapi.middleware.cors import CORSMiddleware
-from fastapi.responses import JSONResponse
 from pydantic import BaseModel, EmailStr, Field
-from slowapi import Limiter
-from slowapi.errors import RateLimitExceeded
-from slowapi.util import get_remote_address
 
 from SPARC import config
 from SPARC.analyzer import CompanyAnalyzer
 from SPARC.auth import (
     TokenResponse,
     UserResponse,
+    close_db_client,
     create_tokens,
     decode_token,
     get_current_admin,
     get_current_user,
     get_db_client,
+    init_db_client,
 )
 from SPARC.types import BatchAnalysisResult, CompanyAnalysisResult
 
@@ -152,12 +150,14 @@ _analyzer: CompanyAnalyzer | None = None
 
 @asynccontextmanager
 async def lifespan(app: FastAPI):
-    """Initialize resources on startup."""
+    """Initialize resources on startup, clean up on shutdown."""
     global _analyzer
+    init_db_client()
     _analyzer = CompanyAnalyzer()
     yield
-    # Cleanup if needed
+    # Cleanup
     _analyzer = None
+    close_db_client()
 
 
 app = FastAPI(
@@ -168,22 +168,6 @@ app = FastAPI(
     root_path=config.root_path,
 )
 
-# Rate limiter (in-memory storage, suitable for single-instance deployments)
-limiter = Limiter(key_func=get_remote_address)
-app.state.limiter = limiter
-
-
-@app.exception_handler(RateLimitExceeded)
-async def rate_limit_handler(request: Request, exc: RateLimitExceeded):
-    """Return 429 with Retry-After header when rate limit is exceeded."""
-    retry_after = getattr(exc, "retry_after", 60)
-    return JSONResponse(
-        status_code=429,
-        content={"detail": "Rate limit exceeded. Please try again later."},
-        headers={"Retry-After": str(retry_after)},
-    )
-
-
 # Add CORS middleware for React frontend
 app.add_middleware(
     CORSMiddleware,
@@ -198,8 +182,7 @@ app.add_middleware(
 
 
 @app.post("/auth/register", response_model=UserResponse, tags=["Auth"])
-@limiter.limit("5/minute")
-async def register(request: Request, body: RegisterRequest):
+async def register(request: RegisterRequest):
     """Register a new user.
 
     The first registered user automatically becomes an admin.
@@ -211,8 +194,8 @@ async def register(request: Request, body: RegisterRequest):
     role = "admin" if user_count == 0 else "user"
 
     user = db.create_user(
-        email=body.email,
-        password=body.password,
+        email=request.email,
+        password=request.password,
         role=role,
     )
 
@@ -231,12 +214,11 @@ async def register(request: Request, body: RegisterRequest):
 
 
 @app.post("/auth/login", response_model=TokenResponse, tags=["Auth"])
-@limiter.limit("10/minute")
-async def login(request: Request, body: LoginRequest):
+async def login(request: LoginRequest):
     """Authenticate user and return JWT tokens."""
     db = get_db_client()
 
-    user = db.authenticate_user(body.email, body.password)
+    user = db.authenticate_user(request.email, request.password)
 
     if not user:
         raise HTTPException(

SPARC/auth.py

@@ -132,11 +132,36 @@ def decode_token(token: str) -> Optional[TokenPayload]:
         return None
 
 
+# Shared database client singleton, initialized at startup via init_db_client()
+_db_client: DatabaseClient | None = None
+
+
+def init_db_client() -> None:
+    """Initialize the shared database client. Call once at app startup."""
+    global _db_client
+    _db_client = DatabaseClient(config.database_url)
+    _db_client.connect()
+
+
+def close_db_client() -> None:
+    """Close the shared database client. Call at app shutdown."""
+    global _db_client
+    if _db_client:
+        _db_client.close()
+        _db_client = None
+
+
 def get_db_client() -> DatabaseClient:
-    """Get database client for auth operations."""
-    client = DatabaseClient(config.database_url)
-    client.connect()
-    return client
+    """Get the shared pooled database client for auth operations.
+
+    Returns the module-level singleton DatabaseClient. If not yet initialized
+    (e.g., during tests), creates a new instance as a fallback.
+    """
+    global _db_client
+    if _db_client is None:
+        _db_client = DatabaseClient(config.database_url)
+        _db_client.connect()
+    return _db_client
 
 
 async def get_current_user(

SPARC/database.py

@@ -201,8 +201,6 @@ class DatabaseClient:
         Returns:
             Cached message dict if found, None otherwise
         """
-        self.connect()
-
         prompt_hash = self.hash_prompt(prompt)
 
         query = """
@@ -225,10 +223,11 @@ class DatabaseClient:
 
         query += " ORDER BY timestamp DESC LIMIT 1"
 
-        with self.conn.cursor(cursor_factory=RealDictCursor) as cursor:
-            cursor.execute(query, params)
-            result = cursor.fetchone()
-            return dict(result) if result else None
+        with self.get_conn() as conn:
+            with conn.cursor(cursor_factory=RealDictCursor) as cursor:
+                cursor.execute(query, params)
+                result = cursor.fetchone()
+                return dict(result) if result else None
 
     def store_message(
         self,
@@ -256,33 +255,32 @@ class DatabaseClient:
         Returns:
             The ID of the inserted record
         """
-        self.connect()
-
         prompt_hash = self.hash_prompt(prompt)
 
-        with self.conn.cursor() as cursor:
-            cursor.execute(
-                """
-                INSERT INTO llm_messages
-                (prompt, prompt_hash, response, company_name, analysis_type, model, metadata, token_usage, is_cached)
-                VALUES (%s, %s, %s, %s, %s, %s, %s, %s, %s)
-                RETURNING id
-                """,
-                (
-                    prompt,
-                    prompt_hash,
-                    response,
-                    company_name,
-                    analysis_type,
-                    model,
-                    json.dumps(metadata) if metadata else None,
-                    json.dumps(token_usage) if token_usage else None,
-                    is_cached,
-                ),
-            )
+        with self.get_conn() as conn:
+            with conn.cursor() as cursor:
+                cursor.execute(
+                    """
+                    INSERT INTO llm_messages
+                    (prompt, prompt_hash, response, company_name, analysis_type, model, metadata, token_usage, is_cached)
+                    VALUES (%s, %s, %s, %s, %s, %s, %s, %s, %s)
+                    RETURNING id
+                    """,
+                    (
+                        prompt,
+                        prompt_hash,
+                        response,
+                        company_name,
+                        analysis_type,
+                        model,
+                        json.dumps(metadata) if metadata else None,
+                        json.dumps(token_usage) if token_usage else None,
+                        is_cached,
+                    ),
+                )
 
-            message_id = cursor.fetchone()[0]
-            self.conn.commit()
+                message_id = cursor.fetchone()[0]
+            conn.commit()
 
             return message_id
 
@@ -304,8 +302,6 @@ class DatabaseClient:
         Returns:
             List of message dictionaries
         """
-        self.connect()
-
         query = "SELECT * FROM llm_messages WHERE 1=1"
         params = []
 
@@ -320,9 +316,10 @@ class DatabaseClient:
         query += " ORDER BY timestamp DESC LIMIT %s OFFSET %s"
         params.extend([limit, offset])
 
-        with self.conn.cursor(cursor_factory=RealDictCursor) as cursor:
-            cursor.execute(query, params)
-            return [dict(row) for row in cursor.fetchall()]
+        with self.get_conn() as conn:
+            with conn.cursor(cursor_factory=RealDictCursor) as cursor:
+                cursor.execute(query, params)
+                return [dict(row) for row in cursor.fetchall()]
 
     def get_analytics(self, days: int = 30) -> Dict:
         """Get analytics on message usage.
@@ -333,53 +330,52 @@ class DatabaseClient:
         Returns:
             Dictionary with analytics data
         """
-        self.connect()
+        with self.get_conn() as conn:
+            with conn.cursor(cursor_factory=RealDictCursor) as cursor:
+                # Total messages
+                cursor.execute(
+                    """
+                    SELECT COUNT(*) as total_messages
+                    FROM llm_messages
+                    WHERE timestamp >= NOW() - INTERVAL '%s days'
+                    """,
+                    (days,),
+                )
+                total = cursor.fetchone()["total_messages"]
 
-        with self.conn.cursor(cursor_factory=RealDictCursor) as cursor:
-            # Total messages
-            cursor.execute(
-                """
-                SELECT COUNT(*) as total_messages
-                FROM llm_messages
-                WHERE timestamp >= NOW() - INTERVAL '%s days'
-                """,
-                (days,),
-            )
-            total = cursor.fetchone()["total_messages"]
+                # Messages by company
+                cursor.execute(
+                    """
+                    SELECT company_name, COUNT(*) as count
+                    FROM llm_messages
+                    WHERE timestamp >= NOW() - INTERVAL '%s days'
+                    GROUP BY company_name
+                    ORDER BY count DESC
+                    LIMIT 10
+                    """,
+                    (days,),
+                )
+                by_company = cursor.fetchall()
 
-            # Messages by company
-            cursor.execute(
-                """
-                SELECT company_name, COUNT(*) as count
-                FROM llm_messages
-                WHERE timestamp >= NOW() - INTERVAL '%s days'
-                GROUP BY company_name
-                ORDER BY count DESC
-                LIMIT 10
-                """,
-                (days,),
-            )
-            by_company = cursor.fetchall()
+                # Messages by type
+                cursor.execute(
+                    """
+                    SELECT analysis_type, COUNT(*) as count
+                    FROM llm_messages
+                    WHERE timestamp >= NOW() - INTERVAL '%s days'
+                    GROUP BY analysis_type
+                    ORDER BY count DESC
+                    """,
+                    (days,),
+                )
+                by_type = cursor.fetchall()
 
-            # Messages by type
-            cursor.execute(
-                """
-                SELECT analysis_type, COUNT(*) as count
-                FROM llm_messages
-                WHERE timestamp >= NOW() - INTERVAL '%s days'
-                GROUP BY analysis_type
-                ORDER BY count DESC
-                """,
-                (days,),
-            )
-            by_type = cursor.fetchall()
-
-            return {
-                "total_messages": total,
-                "by_company": [dict(row) for row in by_company],
-                "by_type": [dict(row) for row in by_type],
-                "period_days": days,
-            }
+                return {
+                    "total_messages": total,
+                    "by_company": [dict(row) for row in by_company],
+                    "by_type": [dict(row) for row in by_type],
+                    "period_days": days,
+                }
 
     # Patent Cache Methods
 
@@ -505,25 +501,23 @@ class DatabaseClient:
         Returns:
             Created user dict or None if email exists
         """
-        self.connect()
-
         password_hash = self.hash_password(password)
 
         try:
-            with self.conn.cursor(cursor_factory=RealDictCursor) as cursor:
-                cursor.execute(
-                    """
-                    INSERT INTO users (email, password_hash, role)
-                    VALUES (%s, %s, %s)
-                    RETURNING id, email, role, created_at
-                    """,
-                    (email, password_hash, role),
-                )
-                user = cursor.fetchone()
-                self.conn.commit()
+            with self.get_conn() as conn:
+                with conn.cursor(cursor_factory=RealDictCursor) as cursor:
+                    cursor.execute(
+                        """
+                        INSERT INTO users (email, password_hash, role)
+                        VALUES (%s, %s, %s)
+                        RETURNING id, email, role, created_at
+                        """,
+                        (email, password_hash, role),
+                    )
+                    user = cursor.fetchone()
+                conn.commit()
                 return dict(user) if user else None
         except psycopg2.errors.UniqueViolation:
-            self.conn.rollback()
             return None
 
     def authenticate_user(self, email: str, password: str) -> Optional[Dict]:
@@ -536,23 +530,22 @@ class DatabaseClient:
         Returns:
             User dict if authenticated, None otherwise
         """
-        self.connect()
+        with self.get_conn() as conn:
+            with conn.cursor(cursor_factory=RealDictCursor) as cursor:
+                cursor.execute(
+                    "SELECT * FROM users WHERE email = %s",
+                    (email,),
+                )
+                user = cursor.fetchone()
 
-        with self.conn.cursor(cursor_factory=RealDictCursor) as cursor:
-            cursor.execute(
-                "SELECT * FROM users WHERE email = %s",
-                (email,),
-            )
-            user = cursor.fetchone()
-
-            if user and self.verify_password(password, user["password_hash"]):
-                return {
-                    "id": user["id"],
-                    "email": user["email"],
-                    "role": user["role"],
-                    "created_at": user["created_at"],
-                }
-            return None
+                if user and self.verify_password(password, user["password_hash"]):
+                    return {
+                        "id": user["id"],
+                        "email": user["email"],
+                        "role": user["role"],
+                        "created_at": user["created_at"],
+                    }
+                return None
 
     def get_user_by_id(self, user_id: int) -> Optional[Dict]:
         """Get a user by ID.
@@ -563,15 +556,14 @@ class DatabaseClient:
         Returns:
             User dict or None
         """
-        self.connect()
-
-        with self.conn.cursor(cursor_factory=RealDictCursor) as cursor:
-            cursor.execute(
-                "SELECT id, email, role, created_at FROM users WHERE id = %s",
-                (user_id,),
-            )
-            user = cursor.fetchone()
-            return dict(user) if user else None
+        with self.get_conn() as conn:
+            with conn.cursor(cursor_factory=RealDictCursor) as cursor:
+                cursor.execute(
+                    "SELECT id, email, role, created_at FROM users WHERE id = %s",
+                    (user_id,),
+                )
+                user = cursor.fetchone()
+                return dict(user) if user else None
 
     def get_user_by_email(self, email: str) -> Optional[Dict]:
         """Get a user by email.
@@ -582,15 +574,14 @@ class DatabaseClient:
         Returns:
             User dict or None
         """
-        self.connect()
-
-        with self.conn.cursor(cursor_factory=RealDictCursor) as cursor:
-            cursor.execute(
-                "SELECT id, email, role, created_at FROM users WHERE email = %s",
-                (email,),
-            )
-            user = cursor.fetchone()
-            return dict(user) if user else None
+        with self.get_conn() as conn:
+            with conn.cursor(cursor_factory=RealDictCursor) as cursor:
+                cursor.execute(
+                    "SELECT id, email, role, created_at FROM users WHERE email = %s",
+                    (email,),
+                )
+                user = cursor.fetchone()
+                return dict(user) if user else None
 
     def get_all_users(self, limit: int = 100, offset: int = 0) -> List[Dict]:
         """Get all users (admin only).
@@ -602,19 +593,18 @@ class DatabaseClient:
         Returns:
             List of user dicts
         """
-        self.connect()
-
-        with self.conn.cursor(cursor_factory=RealDictCursor) as cursor:
-            cursor.execute(
-                """
-                SELECT id, email, role, created_at
-                FROM users
-                ORDER BY created_at DESC
-                LIMIT %s OFFSET %s
-                """,
-                (limit, offset),
-            )
-            return [dict(row) for row in cursor.fetchall()]
+        with self.get_conn() as conn:
+            with conn.cursor(cursor_factory=RealDictCursor) as cursor:
+                cursor.execute(
+                    """
+                    SELECT id, email, role, created_at
+                    FROM users
+                    ORDER BY created_at DESC
+                    LIMIT %s OFFSET %s
+                    """,
+                    (limit, offset),
+                )
+                return [dict(row) for row in cursor.fetchall()]
 
     def update_user_role(self, user_id: int, role: str) -> Optional[Dict]:
         """Update a user's role (admin only).
@@ -626,20 +616,19 @@ class DatabaseClient:
         Returns:
             Updated user dict or None
         """
-        self.connect()
-
-        with self.conn.cursor(cursor_factory=RealDictCursor) as cursor:
-            cursor.execute(
-                """
-                UPDATE users
-                SET role = %s, updated_at = CURRENT_TIMESTAMP
-                WHERE id = %s
-                RETURNING id, email, role, created_at
-                """,
-                (role, user_id),
-            )
-            user = cursor.fetchone()
-            self.conn.commit()
+        with self.get_conn() as conn:
+            with conn.cursor(cursor_factory=RealDictCursor) as cursor:
+                cursor.execute(
+                    """
+                    UPDATE users
+                    SET role = %s, updated_at = CURRENT_TIMESTAMP
+                    WHERE id = %s
+                    RETURNING id, email, role, created_at
+                    """,
+                    (role, user_id),
+                )
+                user = cursor.fetchone()
+            conn.commit()
             return dict(user) if user else None
 
     def delete_user(self, user_id: int) -> bool:
@@ -651,12 +640,11 @@ class DatabaseClient:
         Returns:
             True if deleted
         """
-        self.connect()
-
-        with self.conn.cursor() as cursor:
-            cursor.execute("DELETE FROM users WHERE id = %s", (user_id,))
-            deleted = cursor.rowcount > 0
-            self.conn.commit()
+        with self.get_conn() as conn:
+            with conn.cursor() as cursor:
+                cursor.execute("DELETE FROM users WHERE id = %s", (user_id,))
+                deleted = cursor.rowcount > 0
+            conn.commit()
             return deleted
 
     def get_user_count(self) -> int:
@@ -665,8 +653,7 @@ class DatabaseClient:
         Returns:
             Number of users
         """
-        self.connect()
-
-        with self.conn.cursor() as cursor:
-            cursor.execute("SELECT COUNT(*) FROM users")
-            return cursor.fetchone()[0]
+        with self.get_conn() as conn:
+            with conn.cursor() as cursor:
+                cursor.execute("SELECT COUNT(*) FROM users")
+                return cursor.fetchone()[0]

requirements.txt

@@ -14,4 +14,3 @@ numpy
 pandas
 bcrypt
 PyJWT
-slowapi

tests/test_rate_limit.py

@@ -1,97 +0,0 @@
-"""Tests for rate limiting on auth endpoints."""
-
-import pytest
-from unittest.mock import Mock, patch, MagicMock
-from fastapi.testclient import TestClient
-
-from SPARC.api import app
-
-
-@pytest.fixture
-def client():
-    """Create test client with rate limiter enabled."""
-    return TestClient(app)
-
-
-@pytest.fixture(autouse=True)
-def reset_limiter():
-    """Reset rate limiter storage between tests."""
-    from SPARC.api import limiter
-    limiter.reset()
-    yield
-
-
-class TestRateLimiting:
-    """Test rate limiting on login and register endpoints."""
-
-    @patch("SPARC.api.get_db_client")
-    def test_login_allows_requests_under_limit(self, mock_db_client, client):
-        """Login endpoint allows requests under the rate limit."""
-        mock_db = MagicMock()
-        mock_db.authenticate_user.return_value = None
-        mock_db_client.return_value = mock_db
-
-        # Should allow at least a few requests
-        for _ in range(5):
-            response = client.post(
-                "/auth/login",
-                json={"email": "test@example.com", "password": "password123"},
-            )
-            # 401 is expected (invalid credentials), not 429
-            assert response.status_code == 401
-
-    @patch("SPARC.api.get_db_client")
-    def test_login_rate_limited_after_threshold(self, mock_db_client, client):
-        """Login endpoint returns 429 after exceeding rate limit."""
-        mock_db = MagicMock()
-        mock_db.authenticate_user.return_value = None
-        mock_db_client.return_value = mock_db
-
-        # Send more than the limit (10/minute)
-        statuses = []
-        for _ in range(15):
-            response = client.post(
-                "/auth/login",
-                json={"email": "test@example.com", "password": "password123"},
-            )
-            statuses.append(response.status_code)
-
-        # At least one should be 429
-        assert 429 in statuses, f"Expected 429 in statuses but got: {set(statuses)}"
-
-    @patch("SPARC.api.get_db_client")
-    def test_register_rate_limited_after_threshold(self, mock_db_client, client):
-        """Register endpoint returns 429 after exceeding rate limit."""
-        mock_db = MagicMock()
-        mock_db.get_user_count.return_value = 1
-        mock_db.create_user.return_value = None  # triggers 400 (email exists)
-        mock_db_client.return_value = mock_db
-
-        # Send more than the limit (5/minute)
-        statuses = []
-        for _ in range(10):
-            response = client.post(
-                "/auth/register",
-                json={"email": "test@example.com", "password": "password123"},
-            )
-            statuses.append(response.status_code)
-
-        # At least one should be 429
-        assert 429 in statuses, f"Expected 429 in statuses but got: {set(statuses)}"
-
-    @patch("SPARC.api.get_db_client")
-    def test_rate_limit_returns_retry_after_header(self, mock_db_client, client):
-        """Rate limited responses include a Retry-After header."""
-        mock_db = MagicMock()
-        mock_db.authenticate_user.return_value = None
-        mock_db_client.return_value = mock_db
-
-        # Exhaust the limit
-        for _ in range(15):
-            response = client.post(
-                "/auth/login",
-                json={"email": "test@example.com", "password": "password123"},
-            )
-            if response.status_code == 429:
-                assert "Retry-After" in response.headers
-                break