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/json.ts | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)
 create mode 100644 lib/server/filter/json.ts

(limited to 'lib/server/filter/json.ts')

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();
-- 
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