add README guide to handle server error

Author: YieldRay

README.md

@@ -6,7 +6,7 @@
 [![codecov](https://codecov.io/gh/YieldRay/json-rpc-ts/graph/badge.svg?token=BabjRkI8jk)](https://codecov.io/gh/YieldRay/json-rpc-ts)
 [![ci](https://github.com/yieldray/json-rpc-ts/actions/workflows/ci.yml/badge.svg)](https://github.com/yieldray/json-rpc-ts/actions/workflows/ci.yml)
 
-A strictly typed json-rpc(2.0) implementation, zero dependency, minimal abstraction, with simple api.
+A strictly typed json-rpc(2.0) implementation, zero dependency, minimal abstraction, with a simple API.
 
 > Specification <https://www.jsonrpc.org/specification>
 
@@ -28,9 +28,11 @@ deno add jsr:@yieldray/json-rpc-ts
 
 # Examples
 
-Example to use the client
+Example to use the client:
 
 ```ts
+import { JSONRPCClient } from '@yieldray/json-rpc-ts'
+
 const requestForResponse = (json: string) =>
     fetch('http://localhost:6800/jsonrpc', {
         method: 'POST',
@@ -54,9 +56,11 @@ const resultGid: string = await client.request('aria2.addUri', [
 ])
 ```
 
-Example to use the server
+Example to use the server:
 
 ```ts
+import { JSONRPCServer } from '@yieldray/json-rpc-ts'
+
 const server = new JSONRPCServer({
     upper: (str: string) => str.toUpperCase(),
     lower: (str: string) => str.toLowerCase(),
@@ -69,14 +73,73 @@ server.setMethod('trim', (str: string) => str.trim())
 server.setMethod('trimStart', (str: string) => str.trimStart())
 server.setMethod('trimEnd', (str: string) => str.trimEnd())
 
-const httpServer = Deno.serve(
-    async (request) => {
-        // server.handleRequest() accept string and returns Promise<string>
-        const jsonString = await server.handleRequest(await request.text())
+const handler = async (request: Request): Promise<Response> => {
+    // server.handleRequest() accept string and returns Promise<string>
+    const jsonString = await server.handleRequest(await request.text())
 
-        return new Response(jsonString, {
-            headers: { 'content-type': 'application/json' },
-        })
+    return new Response(jsonString, {
+        headers: { 'content-type': 'application/json' },
+    })
+}
+
+const httpServer = Deno.serve(handler)
+```
+
+When a server function fails, the server does not throw an exception but instead sends a JSONRPCError to the client, making the error unobservable by default. To handle server errors, you can wrap the server function as follows:
+
+```ts
+import {
+    JSONRPCInvalidParamsError,
+    type JSONRPCMethod,
+    type JSONRPCMethods,
+    JSONRPCServer,
+} from '@yieldray/json-rpc-ts'
+
+function wrapMethod<T, U>(fn: JSONRPCMethod<T, U>): JSONRPCMethod<T, U> {
+    return async (arg) => {
+        try {
+            console.log('Request', arg, fn)
+            const result = await fn(arg)
+            console.log('Response', result)
+            return result
+        } catch (e) {
+            console.error('Error', e)
+            throw e
+        }
+    }
+}
+
+function wrapMethods(methods: JSONRPCMethods): JSONRPCMethods {
+    return Object.fromEntries(
+        Object.entries(methods).map(([name, fn]) => [
+            name,
+            typeof fn === 'function' ? wrapMethod(fn.bind(methods)) : fn,
+        ]),
+    )
+}
+
+const methods: JSONRPCMethods = {
+    upper: (str: string) => {
+        if (typeof str !== 'string') {
+            throw new JSONRPCInvalidParamsError(
+                'Invalid argument type, expected string',
+            )
+        }
+        // if not JSONRPCxxxError, the client will receive an Internal Error
+        return str.toUpperCase()
     },
-)
+    lower: (str: string) => str.toLowerCase(),
+    plus: ([a, b]: [number, number]) => a + b,
+    minus: ([a, b]: [number, number]) => a - b,
+}
+
+const server = new JSONRPCServer(wrapMethods(methods))
+
+// or:
+const setMethod = <T, U>(name: string, method: JSONRPCMethod<T, U>) =>
+    server.setMethod(name, wrapMethod(method))
+
+setMethod('trim', (str: string) => str.trim())
+setMethod('trimStart', (str: string) => str.trimStart())
+setMethod('trimEnd', (str: string) => str.trimEnd())
 ```