feat: add additional processing tools

adapters/http.ts

@@ -1,4 +1,5 @@
 import type { RelayAdapter, RelayRequestInput, RelayResponse } from "../libraries/adapter.ts";
+import { RelayError, UnprocessableContentError } from "../libraries/errors.ts";
 
 export class HttpAdapter implements RelayAdapter {
   #id: number = 0;
@@ -6,10 +7,28 @@ export class HttpAdapter implements RelayAdapter {
   constructor(readonly url: string) {}
 
   async send({ method, params }: RelayRequestInput): Promise<RelayResponse> {
-    const res = await fetch(this.url, { method: "POST", headers: { "content-type": "application/json" }, body: JSON.stringify({ method, params, id: this.#id++ }) });
-    if (res.headers.get("content-type")?.includes("application/json") === false) {
-      throw new Error("Unexpected return type");
+    const id = this.#id++;
+    const res = await fetch(this.url, {
+      method: "POST",
+      headers: { "content-type": "application/json" },
+      body: JSON.stringify({ relay: "1.0", method, params, id }),
+    });
+    const contentType = res.headers.get("content-type");
+    if (contentType !== "application/json") {
+      return {
+        relay: "1.0",
+        error: new UnprocessableContentError(`Invalid 'content-type' in header header, expected 'application/json', received '${contentType}'`),
+        id,
+      };
     }
-    return res.json();
+    const json = await res.json();
+    if ("error" in json) {
+      return {
+        relay: "1.0",
+        error: RelayError.fromJSON(json.error),
+        id,
+      };
+    }
+    return json;
   }
 }