From 9970036d203ba2d0a46b35ba6fad21d49441cdd4 Mon Sep 17 00:00:00 2001
From: Elizabeth Hunt <me@liz.coffee>
Date: Sun, 27 Jul 2025 17:03:10 -0700
Subject: hai

---
 lib/server/filter/index.ts  | 34 ++++++++++++++++++++++++++++++++++
 lib/server/filter/json.ts   | 42 ++++++++++++++++++++++++++++++++++++++++++
 lib/server/filter/method.ts | 30 ++++++++++++++++++++++++++++++
 3 files changed, 106 insertions(+)
 create mode 100644 lib/server/filter/index.ts
 create mode 100644 lib/server/filter/json.ts
 create mode 100644 lib/server/filter/method.ts

(limited to 'lib/server/filter')

diff --git a/lib/server/filter/index.ts b/lib/server/filter/index.ts
new file mode 100644
index 0000000..509deb3
--- /dev/null
+++ b/lib/server/filter/index.ts
@@ -0,0 +1,34 @@
+import {
+    type IEither,
+    type ITraceable,
+    LogLevel,
+    type PenguenoRequest,
+    type ServerTrace,
+} from '@emprespresso/pengueno';
+
+export enum ErrorSource {
+    USER = LogLevel.WARN,
+    SYSTEM = LogLevel.ERROR,
+}
+
+export class PenguenoError extends Error {
+    public readonly source: ErrorSource;
+    constructor(
+        override readonly message: string,
+        public readonly status: number,
+    ) {
+        super(message);
+        this.source = Math.floor(status / 100) === 4 ? ErrorSource.USER : ErrorSource.SYSTEM;
+    }
+}
+
+export interface RequestFilter<
+    T,
+    Err extends PenguenoError = PenguenoError,
+    RIn = ITraceable<PenguenoRequest, ServerTrace>,
+> {
+    (req: RIn): IEither<Err, T> | Promise<IEither<Err, T>>;
+}
+
+export * from './method';
+export * from './json';
diff --git a/lib/server/filter/json.ts b/lib/server/filter/json.ts
new file mode 100644
index 0000000..bc53d47
--- /dev/null
+++ b/lib/server/filter/json.ts
@@ -0,0 +1,42 @@
+import {
+    Either,
+    type IEither,
+    type ITraceable,
+    LogLevel,
+    Metric,
+    PenguenoError,
+    type PenguenoRequest,
+    type RequestFilter,
+    type ServerTrace,
+    TraceUtil,
+} from '@emprespresso/pengueno';
+
+export interface JsonTransformer<R, ParsedJson = unknown> {
+    (json: ITraceable<ParsedJson, ServerTrace>): IEither<PenguenoError, R>;
+}
+
+const ParseJsonMetric = Metric.fromName('JsonParse').asResult();
+export const jsonModel =
+    <MessageT>(jsonTransformer: JsonTransformer<MessageT>): RequestFilter<MessageT> =>
+    (r: ITraceable<PenguenoRequest, ServerTrace>) =>
+        r
+            .flatMap(TraceUtil.withFunctionTrace(jsonModel))
+            .flatMap(TraceUtil.withMetricTrace(ParseJsonMetric))
+            .map((j) =>
+                Either.fromFailableAsync<Error, MessageT>(<Promise<MessageT>>j.get().req.json()).then((either) =>
+                    either.mapLeft((errReason) => {
+                        j.trace.traceScope(LogLevel.WARN).trace(errReason);
+                        return new PenguenoError('seems to be invalid JSON (>//<) can you fix?', 400);
+                    }),
+                ),
+            )
+            .flatMapAsync(TraceUtil.promiseify(TraceUtil.traceResultingEither(ParseJsonMetric)))
+            .map(
+                TraceUtil.promiseify((traceableEitherJson) =>
+                    traceableEitherJson
+                        .get()
+                        .mapRight((j) => traceableEitherJson.move(j))
+                        .flatMap(jsonTransformer),
+                ),
+            )
+            .get();
diff --git a/lib/server/filter/method.ts b/lib/server/filter/method.ts
new file mode 100644
index 0000000..7d6aa76
--- /dev/null
+++ b/lib/server/filter/method.ts
@@ -0,0 +1,30 @@
+import {
+    Either,
+    HttpMethod,
+    IEither,
+    type ITraceable,
+    LogLevel,
+    PenguenoError,
+    type PenguenoRequest,
+    type RequestFilter,
+    type ServerTrace,
+    TraceUtil,
+} from '@emprespresso/pengueno';
+
+export const requireMethod =
+    (methods: Array<HttpMethod>): RequestFilter<HttpMethod> =>
+    (req: ITraceable<PenguenoRequest, ServerTrace>) =>
+        req
+            .flatMap(TraceUtil.withFunctionTrace(requireMethod))
+            .map((t): IEither<PenguenoError, HttpMethod> => {
+                const {
+                    req: { method },
+                } = t.get();
+                if (!methods.includes(method)) {
+                    const msg = "that's not how you pet me (⋟﹏⋞)~";
+                    t.trace.traceScope(LogLevel.WARN).trace(msg);
+                    return Either.left(new PenguenoError(msg, 405));
+                }
+                return Either.right(method);
+            })
+            .get();
-- 
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