Sillo Architecture Overview

System layers, boundaries, component relationships, dependency graph

1. System Layers and Boundaries

Sillo is a standalone ASGI web framework. It does not inherit from any base application class. SilloApp is a plain Python object that implements the ASGI protocol via __call__(scope, receive, send).

The codebase is organized into four concentric layers:

graph TD
    L4["<b>Layer 4 · User Application</b><br/>app = SilloApp(), route handlers, middleware, config"]
    L3["<b>Layer 3 · Framework Surface</b><br/>application.py · route_builder.py · exception_handler.py<br/>config/ · events/ · auth/ · mail/ · session/ · cache/<br/>templating/ · graphql/ · permissions/ · users/ · validation/"]
    L2["<b>Layer 2 · Core Engine</b><br/>core/routing/ · core/dependencies/ · core/encoding.py<br/>core/http/ · core/error/ · core/helpers/<br/>_internals/_middleware.py · middleware/"]
    L1["<b>Layer 1 · ASGI Primitives</b><br/>types.py · objects/ (Scope, Message, Receive, Send)<br/>websockets/"]

    L4 --> L3 --> L2 --> L1

Layer 1: ASGI Primitives defines the type aliases and data structures that map directly to the ASGI spec: Scope, Message, Receive, Send, ASGIApp. All higher layers depend on these types; they depend on nothing within sillo.

Layer 2: Core Engine implements the request/response cycle: routing, dependency injection, encoding, error handling, and the middleware bridge. These modules are framework-internal and are not part of the public API surface.

Layer 3. Framework Surface provides the features application developers interact with: configuration, events, authentication, sessions, mail, templates, GraphQL, permissions, and validation. These modules depend on the core engine.

Layer 4. User Application is the SilloApp instance and everything the developer writes. It composes layers 2 and 3.

Key Source Files

File	Layer	Purpose
`types.py`	1	Core type aliases (`Scope`, `Message`, `Receive`, `Send`, `ASGIApp`, `MiddlewareType`, `HandlerType`)
`objects/common.py`	1	`Address`, `Secret`, `State`
`objects/datastructures.py`	1	`ImmutableMultiDict`, `MultiDict`
`objects/http.py`	1	`QueryParams`, `Headers`, `MutableHeaders`, `UploadedFile`, `FormData`
`objects/routing.py`	1	`URL`, `URLPath`, `RouteParam`
`core/routing/`	2	`Router`, `Route`, `WebsocketRoute`, path matching
`core/dependencies/base.py`	2	`Depend`, `Dependant`, `solve_dependencies`, `_build_execution_plan`
`core/encoding.py`	2	`jsonable_encoder`, `CUSTOM_ENCODERS`, `ENCODERS_BY_TYPE`
`core/error/handler.py`	2	`ServerErrorMiddleware`, debug HTML error page
`core/http/`	2	`Request`, `Response` (Responder), `StreamingResponse`
`_internals/_middleware.py`	2	`ASGIRequestResponseBridge`, `DefineMiddleware`, `_CachedRequest`
`application.py`	3	`SilloApp`: the application entry point
`exception_handler.py`	3	`ExceptionMiddleware`, built-in exception handlers
`config/core.py`	3	`Config` base class (Pydantic + `.env` loading)
`events/`	3	`EventEmitter`, transports, event protocol
`encoding.py`	3	Re-export facade for `core.encoding`

2. Component Relationship Diagram

graph TB
    subgraph "ASGI Server (uvicorn / granian / daphne)"
        SERVER["ASGI Server"]
    end

    subgraph "SilloApp (application.py)"
        APP["SilloApp<br/>__call__(scope, receive, send)"]
        STATE["app.state: dict[str, Any]"]
        OAPI["openapi: APIDocumentation"]
        EVENTS["events: EventEmitter"]
        COMMANDS["commands: list[Command]"]
    end

    subgraph "Middleware Chain"
        SEM["ServerErrorMiddleware<br/>(outer)"]
        BRIDGE1["ASGIRequestResponseBridge"]
        USER_MW["User Middleware<br/>(app.use())"]
        BRIDGE2["ASGIRequestResponseBridge"]
        EXCMW["ExceptionMiddleware<br/>(inner)"]
        BRIDGE3["ASGIRequestResponseBridge"]
    end

    subgraph "Router (core/routing/)"
        ROUTER["Router"]
        ROUTES["list[Route]"]
        WS_ROUTES["list[WebsocketRoute]"]
    end

    subgraph "Dependency Injection"
        DEPEND["Depend"]
        DEPENDANT["Dependant"]
        SOLVER["solve_dependencies()"]
        PLAN["_build_execution_plan()"]
    end

    subgraph "Request / Response"
        REQ["Request"]
        RESP["Responder (Response)"]
        STREAM["StreamingResponse"]
    end

    subgraph "Objects Layer"
        URL["URL"]
        HEADERS["Headers / MutableHeaders"]
        QP["QueryParams"]
        FORM["FormData / UploadedFile"]
        MD["MultiDict / ImmutableMultiDict"]
        STATE_OBJ["State"]
        SECRET["Secret"]
        ADDR["Address"]
    end

    subgraph "Encoding"
        JSON_ENC["jsonable_encoder()"]
        CUSTOM["CUSTOM_ENCODERS"]
        BY_TYPE["ENCODERS_BY_TYPE"]
    end

    subgraph "Exception Handling"
        EXCM["ExceptionMiddleware"]
        HANDLERS["_exception_handlers<br/>_status_handlers"]
        LOOKUP["_lookup_exception_handler()"]
    end

    SERVER -->|"scope, receive, send"| APP
    APP -->|"lifespan"| SERVER
    APP -->|"http / websocket"| SEM
    SEM --> BRIDGE1
    BRIDGE1 --> USER_MW
    USER_MW --> BRIDGE2
    BRIDGE2 --> EXCMW
    EXCMW --> BRIDGE3
    BRIDGE3 --> ROUTER

    APP --- STATE
    APP --- OAPI
    APP --- EVENTS
    APP --- COMMANDS

    ROUTER --> ROUTES
    ROUTER --> WS_ROUTES
    ROUTES -->|"match path"| REQ
    ROUTES --> SOLVER
    SOLVER --> DEPENDANT
    DEPENDANT --> PLAN
    DEPENDANT -->|"extract params"| REQ

    REQ --> URL
    REQ --> HEADERS
    REQ --> QP
    REQ --> FORM

    RESP --> JSON_ENC
    JSON_ENC --> CUSTOM
    JSON_ENC --> BY_TYPE

    EXCM --> LOOKUP
    LOOKUP --> HANDLERS

Request Flow (Simplified)

sequenceDiagram
    participant S as ASGI Server
    participant A as SilloApp
    participant SEM as ServerErrorMiddleware
    participant UMW as User Middleware
    participant EXC as ExceptionMiddleware
    participant R as Router
    participant H as Handler

    S->>A: __call__(scope, receive, send)
    A->>A: Inject scope["app"], scope["base_app"], scope["global_state"]
    alt scope["type"] == "lifespan"
        A->>A: handle_lifespan(receive, send)
    else scope["type"] == "http"
        A->>A: handle_request(scope, receive, send)
        A->>SEM: Build middleware chain (reversed)
        SEM->>UMW: Forward request
        UMW->>EXC: Forward request
        EXC->>R: Forward request
        R->>R: Match route by path + method
        R->>R: solve_dependencies()
        R->>H: Call handler(request, response, **deps)
        H-->>R: Return response
        R-->>EXC: Return response
        EXC-->>UMW: Return response
        UMW-->>SEM: Return response
        SEM-->>S: Send ASGI messages
    end

3. Dependency Graph

Module-Level Dependencies

graph TD
    types.py -->|"no internal deps"| objects/common.py

    objects/common.py -->|"no internal deps"| ASGI_SPEC["ASGI Spec Types"]
    objects/datastructures.py -->|"no internal deps"| PYTHON["Python stdlib"]
    objects/http.py --> objects/datastructures.py
    objects/http.py --> utils/concurrency.py
    objects/routing.py --> objects/common.py
    objects/routing.py --> objects/datastructures.py

    core/encoding.py -->|"Pydantic, stdlib"| PYTHON
    core/dependencies/base.py --> validation/
    core/http/request.py --> objects/
    core/http/response.py --> objects/
    core/error/handler.py --> core/http/
    core/error/handler.py --> middleware/base.py
    core/routing/base.py --> core/dependencies/
    core/routing/base.py --> core/http/

    _internals/_middleware.py --> core/http/
    _internals/_middleware.py --> types.py

    exception_handler.py --> exceptions.py
    exception_handler.py --> core/http/
    exception_handler.py --> validation/

    application.py --> _internals/_middleware.py
    application.py --> core/routing/
    application.py --> core/dependencies/
    application.py --> core/encoding.py
    application.py --> core/error/
    application.py --> exception_handler.py
    application.py --> events/
    application.py --> openapi/
    application.py --> types.py
    application.py --> objects/routing.py

The 7 Core Dependencies of `SilloApp`

Every SilloApp instance depends on exactly seven subsystems at construction time:

Router (core/routing/): route registration, path matching, request dispatch
ExceptionMiddleware (exception_handler.py): exception-to-response mapping
OpenAPI / APIDocumentation (openapi/): schema generation, docs UI mounting
EventEmitter (events/): application-level event broadcasting
Middleware Stack (_internals/_middleware.py): ASGIRequestResponseBridge wrapping
Config (config/): configuration management (used by subsystems, not directly by SilloApp)
Dependencies (core/dependencies/): Depend / Dependant / solve_dependencies

graph LR
    APP["SilloApp"]
    APP --> R["Router"]
    APP --> EXC["ExceptionMiddleware"]
    APP --> OAPI["APIDocumentation"]
    APP --> EE["EventEmitter"]
    APP --> MW["Middleware Stack"]
    APP --> CFG["Config subsystem"]
    APP --> DI["Dependency Injection"]

4. Architectural Patterns

4.1 Middleware Chain

Sillo uses a dispatch-style middleware pattern, not raw ASGI middleware. User middleware follows the signature:

async def my_middleware(
    request: Request,
    response: Response,
    call_next: Callable[..., Awaitable[Response]],
) -> Response:
    # Pre-processing
    result = await call_next()
    # Post-processing
    return result

The ASGIRequestResponseBridge (_internals/_middleware.py) converts this dispatch-style middleware into proper ASGI middleware. It:

Creates a _CachedRequest from the ASGI scope
Creates a Responder (Response) object
Sets up an anyio.MemoryObjectStream for response body streaming
Runs the inner app in a background task, streaming response chunks through the memory channel
Calls the dispatch function with (request, response, call_next)

Middleware ordering (outermost first, as seen by the request):

graph TD
    SEM["ServerErrorMiddleware"] --> UN["User Middleware (N)"]
    UN --> UN1["User Middleware (N-1)"]
    UN1 --> DOTS["..."]
    DOTS --> U1["User Middleware (1)"]
    U1 --> EM["ExceptionMiddleware"]
    EM --> R["Router"]

    SEM -.- SEMN["catches unhandled exceptions, serves debug pages"]
    UN -.- UNN["app.use() calls, LIFO order"]
    EM -.- EMN["catches HTTPException, ValidationError"]
    R -.- RN["route matching, handler execution"]

    classDef note fill:none,stroke:none;
    class SEMN,UNN,EMN,RN note;

app.use() insertion order: Each app.use(middleware) call does:

self.http_middleware.insert(0, Middleware(ASGIRequestResponseBridge, dispatch=middleware))

This means middleware added later wraps middleware added earlier, inside-out application. The first middleware added is closest to the router; the last middleware added is outermost (closest to ServerErrorMiddleware).

Chain assembly in handle_request():

app = self.app  # Router
middleware = (
    [ServerErrorMiddleware(app, handler=..., debug=...)]
    + self.http_middleware                                    # user middleware
    + [Middleware(ASGIRequestResponseBridge, dispatch=self.exceptions_handler)]
)
for cls, args, kwargs in reversed(middleware):
    app = cls(app, *args, **kwargs)
return app(scope, receive, send)

The reversed() iteration builds the chain from innermost to outermost, so the first element in the list (ServerErrorMiddleware) becomes the outermost wrapper.

4.2 Dependency Injection Resolution

Sillo’s DI system is tree-based and iteratively resolved:

Registration phase (at route registration time):

def get_dependant(call, name=None, *, strict_validation=False) -> Dependant:
    sig = signature(call)
    deps = []
    markers = []

    for param_name, param in sig.parameters.items():
        default = param.default
        if isinstance(default, Depend):
            # Recursively build sub-dependency tree
            sub = get_dependant(default.dependency, param_name, ...)
            deps.append(sub)
        elif isinstance(default, ParameterExtractor):
            markers.append((param_name, default))

    # Build flat execution plan
    dependant = Dependant(call=call, dependencies=deps, ...)
    dependant._execution_plan = _build_execution_plan(dependant)
    return dependant

Resolution phase (at request time):

async def solve_dependencies(dependant, request, ...) -> dict[str, Any]:
    values = {}
    validated = await resolve_validated_params(dependant, request)

    for step in dependant._execution_plan:  # flat iteration, no recursion
        sub = step.dependant
        if sub.use_cache and sub.cache_key and sub.cache_key in cache:
            values[sub.name] = cache[sub.cache_key]
            continue

        kwargs = _collect_kwargs(sub, values, request, validated)

        if step.is_root:
            return kwargs  # Return handler kwargs, don't execute

        result = await _execute_dependency(sub, kwargs, cleanups)
        values[sub.name] = result

    return {}

Execution plan is a depth-first post-order traversal:

Dependency Tree:          Execution Plan:
    A                      1. C (child)
   / \                     2. D (child)
  B   C                    3. B (parent of C, D)
 / \                       4. A (root — collect kwargs only)
D   E                      5. E (child of A)

Supported callable types:

async def → await func(**kwargs)
def → func(**kwargs)
async def gen() → await agen.__anext__() + register aclose() cleanup
def gen() → next(gen) + register close() cleanup

4.3 Scope System

The ASGI scope dictionary is the primary communication channel between subsystems during request processing. Sillo injects three keys at the __call__ entry point:

async def __call__(self, scope, receive, send):
    scope["app"] = self          # The SilloApp instance
    scope["base_app"] = self     # Same reference, for mounted sub-apps
    scope["global_state"] = self.state  # app-level shared state dict

Downstream middleware and handlers access these via request.scope:

request.scope["app"]           # SilloApp instance
request.scope["base_app"]      # Root SilloApp (preserved across mounts)
request.scope["global_state"]  # app.state dict
request.scope["root_path"]     # ASGI mount prefix
request.scope["path"]          # Request path
request.scope["method"]        # HTTP method
request.scope["headers"]       # Raw header byte tuples
request.scope["query_string"]  # Raw query bytes
request.scope["path_params"]   # Route parameters (injected by Router)

4.4 Transport Abstraction

Sillo is transport-agnostic at the ASGI level. The SilloApp.__call__ method handles three scope types:

"lifespan" → handle_lifespan(receive, send): startup/shutdown lifecycle
"http" → handle_request(scope, receive, send): HTTP request processing
"websocket" → handle_request(scope, receive, send): WebSocket upgrade

The transport layer is fully abstracted by the ASGI protocol. Sillo works with any ASGI server: uvicorn, granian, daphne, hypercorn, etc.

# The entire transport interface:
Scope   = MutableMapping[str, Any]
Message = MutableMapping[str, Any]
Receive = Callable[[], Awaitable[Message]]
Send    = Callable[[Message], Awaitable[None]]
ASGIApp = Callable[[Scope, Receive, Send], Awaitable[Any]]

5. Inter-Subsystem Communication

5.1 Scope Dictionary

The ASGI scope dict is the primary per-request communication bus. It flows through every middleware layer and is accessible from any handler via request.scope.

Keys injected by SilloApp.call:

Key	Type	Source	Description
`"app"`	`SilloApp`	`application.py:1232`	Current application instance
`"base_app"`	`SilloApp`	`application.py:1233`	Root application (preserved across mounts)
`"global_state"`	`dict`	`application.py:1234`	Reference to `app.state`

Keys injected by ASGI server:

Key	Type	Description
`"type"`	`str`	`"lifespan"`, `"http"`, or `"websocket"`
`"path"`	`str`	Request path
`"method"`	`str`	HTTP method
`"headers"`	`list[tuple[bytes, bytes]]`	Raw headers
`"query_string"`	`bytes`	Raw query string
`"root_path"`	`str`	ASGI mount prefix
`"server"`	`tuple[str, int]`	Server host and port
`"scheme"`	`str`	`"http"` or `"https"`

Keys injected by Router:

Key	Type	Description
`"path_params"`	`dict[str, str]`	Extracted route parameters

5.2 app.state

app.state is a plain dict[str, Any] shared across all requests. It is injected into every scope as scope["global_state"]. Handlers access it via:

request.scope["global_state"]["db_pool"]
# or through the State object wrapper:
request.state  # State object wrapping per-request state

The State class (objects/common.py) provides attribute-style access:

class State:
    def __setattr__(self, key, value):
        self._state[key] = value

    def __getattr__(self, key):
        try:
            return self._state[key]
        except KeyError:
            return None  # Never raises AttributeError

5.3 request.scope

Request objects wrap the ASGI scope and provide typed accessors:

class Request:
    def __init__(self, scope, receive):
        self.scope = scope
        self._receive = receive

    @property
    def url(self) -> URL: ...
    @property
    def method(self) -> str: ...
    @property
    def headers(self) -> Headers: ...
    @property
    def query_params(self) -> QueryParams: ...
    @property
    def path_params(self) -> RouteParam: ...
    @property
    def state(self) -> State: ...

5.4 ContextVar

Sillo does not use contextvars.ContextVar for request-scoped data in its core. The framework relies on the ASGI scope dictionary as the request-scoped storage mechanism. This is a deliberate design choice:

The scope dict is explicitly passed through the call chain
No implicit global state that could leak between requests
Sub-applications and mounted routers see the same scope

However, subsystems like authentication may use ContextVar internally for convenience (e.g., caching the current user for the duration of a request).

6. Trust Boundaries

6.1 Request Processing Pipeline

graph LR
    CLIENT["Client"] -->|"Untrusted"| SERVER["ASGI Server"]
    SERVER -->|"scope dict"| SEM["ServerErrorMiddleware"]
    SEM -->|"scope dict"| USER_MW["User Middleware"]
    USER_MW -->|"scope dict"| EXCMW["ExceptionMiddleware"]
    EXCMW -->|"scope dict"| ROUTER["Router"]
    ROUTER -->|"validated params"| HANDLER["Handler"]

6.2 Boundary Definitions

Boundary	Trust Level	Validation
Client → ASGI Server	Untrusted	Server-level (HTTP parsing, size limits)
ASGI Server → SilloApp	Semi-trusted	Scope dict structure assumed correct
Scope → Request	Semi-trusted	Lazy parsing, type coercion
Request → Handler	Untrusted	Pydantic validation, ParameterExtractor
Handler → Response	Trusted	jsonable_encoder, response_model validation
Response → Client	Trusted	ASGI message format

6.3 Validation Points

Parameter extraction (core/dependencies/base.py): ParameterExtractor subclasses (Query, Header, Cookie, Body, Form, File) extract values from specific request locations.
Pydantic validation (validation/): compile_validator() builds per-location Pydantic models at registration time. At request time, resolve_validated_params() validates all parameters in one pass.
Request body validation (request_model=): Route-level Pydantic models validate the request body before the handler runs.
Response validation (response_model=): The response is validated against the declared model before sending to the client.
Exception handling (exception_handler.py): ExceptionMiddleware catches all exceptions and converts them to appropriate HTTP responses. The _lookup_exception_handler() function walks the exception’s MRO to find the most specific handler.

6.4 Security Middleware

Security-related middleware is applied via app.use():

AuthenticationMiddleware (auth/middleware.py): Validates credentials and populates request.user. Configured via SilloApp(auth=[...]).
CORSMiddleware (middleware/security.py): CORS headers.
CSRFMiddleware (configurable): CSRF token validation.
RateLimitMiddleware (configurable): Request rate limiting.

7. The Coherence Claim

Sillo’s architecture is coherent: every subsystem is reachable from every other subsystem through a small number of well-defined channels, and no subsystem duplicates the responsibility of another.

7.1 Single Source of Truth per Concern

Concern	Single Owner	Access Path
Route matching	`Router`	`app.router` / `app.app`
Dependency injection	`core/dependencies/`	`Depend()` markers in signatures
JSON encoding	`core/encoding.py`	`jsonable_encoder()` + `CUSTOM_ENCODERS`
Exception handling	`exception_handler.py`	`ExceptionMiddleware`
Configuration	`config/core.py`	`Config` base class
Event broadcasting	`events/`	`app.events`
OpenAPI generation	`openapi/`	`app.openapi` / `app.openapi_config`
Middleware bridging	`_internals/_middleware.py`	`ASGIRequestResponseBridge`
Request/Response	`core/http/`	`Request`, `Responder`
Data structures	`objects/`	All `MultiDict`, `URL`, `Headers` etc.

7.2 No Circular Dependencies

The dependency flow is strictly acyclic:

types.py ← objects/ ← core/ ← application.py ← subsystems (auth, mail, etc.)

Higher layers import lower layers; lower layers never import higher layers. The encoding.py re-export facade (sillo.encoding) exists specifically to provide a stable public import path without creating a circular dependency between application.py and core/encoding.py.

7.3 Middleware Chain Integrity

The middleware chain is assembled once per request in handle_request(). The assembly is deterministic:

ServerErrorMiddleware (outermost: catches everything)
User middleware (in app.use() insertion order, LIFO)
ExceptionMiddleware (innermost before router: catches handler exceptions)
Router (route matching + handler execution)

Each middleware layer wraps the next via ASGIRequestResponseBridge, which converts dispatch-style (request, response, call_next) into proper ASGI (scope, receive, send). Non-HTTP scopes (websocket, lifespan) pass through directly without bridging.

7.4 DI Tree Immutability

The dependency tree is built once at route registration time (get_dependant()) and never modified afterward. The execution plan is flattened into a list of ExecutionStep objects at the same time. This means:

No tree walking at request time
No recursive resolution
Cache keys are pre-computed
Validator plans are pre-flattened

The only mutable state during resolution is the values dict and the dependency_cache dict, both of which are per-request and per-request only.

7.5 Encoding Coherence

All JSON encoding flows through a single function: jsonable_encoder(). It consults three registries in priority order:

Custom encoders (CUSTOM_ENCODERS + per-call custom_encoder dict)
Built-in type encoders (ENCODERS_BY_TYPE: direct type match)
Isinstance-based encoders (encoders_by_class_tuples: inverted index)

Application-level custom encoders are registered via:

app.add_encoder(type_, encoder) → updates both app.custom_encoders and global CUSTOM_ENCODERS
register_encoder(type_, encoder) → updates global CUSTOM_ENCODERS only

Both paths converge on the same CUSTOM_ENCODERS dict, so encoders registered either way are visible to jsonable_encoder().

Appendix A: File Inventory

Layer 1: ASGI Primitives

core/sillo/types.py                    — 41 lines   — Type aliases
core/sillo/objects/__init__.py         — 38 lines   — Public re-exports
core/sillo/objects/common.py           — 209 lines  — Address, Secret, State
core/sillo/objects/datastructures.py   — 438 lines  — ImmutableMultiDict, MultiDict
core/sillo/objects/http.py             — 1070 lines — QueryParams, Headers, MutableHeaders, UploadedFile, FormData
core/sillo/objects/routing.py          — 780 lines  — URL, URLPath, RouteParam
core/sillo/websockets/                 — WebSocket support

Layer 2: Core Engine

core/sillo/core/routing/               — Router, Route, WebsocketRoute, path matching
core/sillo/core/dependencies/base.py   — 589 lines  — DI system
core/sillo/core/encoding.py            — 393 lines  — jsonable_encoder
core/sillo/core/http/                  — Request, Response, StreamingResponse
core/sillo/core/error/handler.py       — 1604 lines — ServerErrorMiddleware, debug pages
core/sillo/_internals/_middleware.py   — 546 lines  — ASGIRequestResponseBridge
core/sillo/middleware/                  — BaseMiddleware, gzip, security utilities

Layer 3: Framework Surface

core/sillo/application.py              — 2800+ lines — SilloApp
core/sillo/exception_handler.py        — 407 lines  — ExceptionMiddleware
core/sillo/config/core.py              — 115 lines  — Config base class
core/sillo/events/                     — Event system
core/sillo/auth/                       — Authentication
core/sillo/mail/                       — Email sending
core/sillo/session/                    — Session management
core/sillo/cache/                      — Caching
core/sillo/templating/                 — Template rendering
core/sillo/graphql/                    — GraphQL support
core/sillo/permissions/                — Authorization
core/sillo/users/                      — User model
core/sillo/validation/                 — Parameter validation
core/sillo/openapi/                    — OpenAPI generation
core/sillo/console/                    — CLI commands
core/sillo/security/                   — Security utilities
core/sillo/record/                     — Record/ORM support
core/sillo/work/                       — Background tasks

Appendix B: Key Design Decisions

Standalone ASGI app. SilloApp does not inherit from any base class. It implements __call__(scope, receive, send) directly.
Dispatch-style middleware: User middleware follows (request, response, call_next) -> Response rather than raw ASGI (scope, receive, send). The ASGIRequestResponseBridge handles the conversion.
Tree-based DI: Dependencies are declared via Depend() markers in function signatures. The tree is built once at registration and flattened into an execution plan for iterative resolution.
Scope dict as communication bus: All per-request context flows through the ASGI scope dictionary. No global state, no ContextVar for core features.
Config per subsystem. Each subsystem (database, session, mail, etc.) owns its own Config subclass. The base Config class provides .env loading and secret masking.
Single encoding path: All JSON serialization flows through jsonable_encoder(), which consults a prioritized chain of encoder registries.
OpenAPI built at startup. The OpenAPI document is generated once during _startup() and cached per mount prefix. Serving it writes a stored string.
Event system is pluggable. The EventEmitter supports multiple transport backends (in-memory, Redis, database) via a pluggable transport registry. Events carry priority, phase, and cancellation semantics.
Console commands are co-registered: Application commands are registered on SilloApp.commands and discovered by the sillo CLI at import time, eliminating the need for a separate command registry file.

Appendix C: Glossary

Term	Definition
ASGI	Asynchronous Server Gateway Interface: the async successor to WSGI
Scope	A mutable dict carrying per-connection metadata through the ASGI stack
Dispatch middleware	Middleware following `(request, response, call_next) -> Response`
ASGI middleware	Middleware following raw `(scope, receive, send) -> None`
Dependant	A node in the DI dependency tree, wrapping a callable and its sub-dependencies
Execution plan	A flat, depth-first, post-order list of `ExecutionStep` objects for iterative DI resolution
ParameterExtractor	A marker (`Query`, `Header`, `Cookie`, `Body`, `Form`, `File`) that pulls a value from a specific request location
jsonable_encoder	The single serialization function that converts any Python object to JSON-compatible types
CUSTOM_ENCODERS	The global dict mapping types to user-defined encoder functions
ENCODERS_BY_TYPE	The built-in dict mapping 25+ standard Python types to their JSON encoders
Lifespan	The ASGI protocol phase for application startup/shutdown, before any requests are served
Mount prefix	A URL path prefix under which a sub-application or the same application is served