1 files changed, 51 insertions, 0 deletions
diff --git a/u/server/filter/json.ts b/u/server/filter/json.ts
new file mode 100644
index 0000000..4a2961e
--- /dev/null
+++ b/u/server/filter/json.ts
@@ -0,0 +1,51 @@
+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");
+export const jsonModel = <MessageT>(
+  jsonTransformer: JsonTransformer<MessageT>,
+): RequestFilter<MessageT> =>
+(r: ITraceable<PenguenoRequest, ServerTrace>) =>
+  r.bimap(TraceUtil.withMetricTrace(ParseJsonMetric))
+    .map((j) =>
+      Either.fromFailableAsync<Error, MessageT>(j.get().json())
+        .then((either) =>
+          either.mapLeft((errReason) => {
+            j.trace.addTrace(LogLevel.WARN).trace(`${errReason}`);
+            return new PenguenoError(
+              "seems to be invalid JSON (>//<) can you fix?",
+              400,
+            );
+          })
+        )
+    )
+    .peek(
+      TraceUtil.promiseify((traceableEither) =>
+        traceableEither.get().mapBoth(
+          () => traceableEither.trace.trace(ParseJsonMetric.failure),
+          () => traceableEither.trace.trace(ParseJsonMetric.success),
+        )
+      ),
+    )
+    .map(
+      TraceUtil.promiseify((traceableEitherJson) =>
+        traceableEitherJson.get()
+          .mapRight(traceableEitherJson.move)
+          .flatMap(jsonTransformer)
+      ),
+    )
+    .get();