feat：新增大屏存取发布接口

app/core/body_limit.py

@@ -0,0 +1,71 @@
+"""限制请求体大小：声明的 Content-Length 超限直接 413，没声明（分块）或声明得不实的，边读边数
+
+FastAPI 会先把整个请求体收完再调用接口函数，超大的请求体已经占满了带宽和内存
+和数据文件上传的 UploadSizeLimit 同一出发点；限制随路径而不同，所以用规则表，第一条命中的生效
+"""
+
+import re
+from dataclasses import dataclass
+
+from fastapi.responses import JSONResponse
+from starlette.exceptions import HTTPException
+from starlette.types import ASGIApp, Message, Receive, Scope, Send
+
+from app.common.response import error_content
+
+
+class BodyTooLarge(HTTPException):
+    """边读边数时超限；message 由全局 HTTP 异常处理放进信封，和声明超限的响应文案一致"""
+
+    def __init__(self, message: str):
+        super().__init__(413)
+        self.message = message
+
+
+@dataclass(frozen=True)
+class BodyLimitRule:
+    methods: frozenset[str]
+    path: re.Pattern[str]
+    max_bytes: int
+    message: str
+
+
+class BodyLimit:
+    def __init__(self, app: ASGIApp, rules: list[BodyLimitRule]):
+        self.app = app
+        self.rules = rules
+
+    async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
+        rule = self._match(scope) if scope["type"] == "http" else None
+        if rule is None:
+            await self.app(scope, receive, send)
+            return
+        length = dict(scope["headers"]).get(b"content-length", b"")
+        if length.isdigit() and int(length) > rule.max_bytes:
+            response = JSONResponse(error_content(413, rule.message), 413)
+            await response(scope, receive, send)
+            return
+        received = 0
+
+        async def counted() -> Message:
+            nonlocal received
+            message = await receive()
+            if message["type"] == "http.request":
+                received += len(message.get("body", b""))
+                if received > rule.max_bytes:
+                    # 抛出的异常由应用里统一的 HTTP 异常处理转成 413 信封
+                    raise BodyTooLarge(rule.message)
+            return message
+
+        await self.app(scope, counted, send)
+
+    def _match(self, scope: Scope) -> BodyLimitRule | None:
+        return next(
+            (
+                rule
+                for rule in self.rules
+                if scope["method"] in rule.methods
+                and rule.path.fullmatch(scope["path"])
+            ),
+            None,
+        )

app/core/exceptions.py

@@ -50,6 +50,8 @@ async def handle_http_exception(_request: Request, exc: HTTPException) -> JSONRe
         message = HTTPStatus(exc.status_code).phrase
     except ValueError:
         message = "请求失败"
+    # 个别异常自带面向用户的文案，例如请求体超限
+    message = getattr(exc, "message", None) or message
     return JSONResponse(
         status_code=exc.status_code,
         content=error_content(exc.status_code, message),