https://github.com/MetaMask/json-rpc-engine
RpcEngine——
https://github.com/MetaMask/json-rpc-engine
a tool for processing JSON RPC
usage
const RpcEngine = require('json-rpc-engine')
let engine = new RpcEngine()
Build a stack of json rpc processors by pushing in RpcEngine middleware.
通过push RpcEngine中间件构建一个json rpc处理器堆栈，处理步骤为先进后出，handle时得到的结果是与push时作出的处理相关的
engine.push(function(req, res, next, end){
res.result = 42
end()
})
⚠️push是能够对之后handle传入的request（即json rpc的值进行处理，(req, res, next, end)中的req就是handle传入的request）的一些状态进行定义或作出一些相关处理，会在handle处理json rpc时对其造成影响。
比如如果在push中设置res.result = req.id，那么就是将json rpc中传进来的（id: 1）的值传出
res：返回的是在push中经过处理后的json rpc的值，如果push中什么都没有做，那么req与res的值是相同的
JSON RPC are handled asynchronously, stepping down the stack until complete.异步处理request，直到返回结果
let request = { id: 1, jsonrpc: '2.0', method: 'hello' } engine.handle(request, function(err, res){ // do something with res.result，res.result即为push中设置的true })
RpcEngine middleware has direct access to the request and response objects. It can let processing continue down the stack with next() or complete the request with end().RpcEngine中间件可以直接访问请求和响应对象。它可以使用next()继续处理堆栈，也可以使用end()完成请求
engine.push(function(req, res, next, end){
if (req.skipCache) return next()
res.result = getResultFromCache(req)
end()
})
By passing a 'return handler' to the next function, you can get a peek at the result before it returns.
通过将“返回处理程序”传递给下一个函数，您可以在结果返回之前看到它
engine.push(function(req, res, next, end){
next(function(cb){//就是先压入堆栈中，不进行处理，等到所以push都解决完后再返回处理
insertIntoCache(res, cb)
})
})
RpcEngines can be nested by converting them to middleware asMiddleware(engine)。rpcengine可以通过将它们转换为中间件(中间件)来嵌套
const asMiddleware = require('json-rpc-engine/lib/asMiddleware')
let engine = new RpcEngine() let subengine = new RpcEngine() engine.push(asMiddleware(subengine))
gotchas陷阱
Handle errors via end(err), NOT next(err).解决error使用的是end（），而不是next（）
/* INCORRECT */
engine.push(function(req, res, next, end){
next(new Error()) }) /* CORRECT */ engine.push(function(req, res, next, end){ end(new Error()) })
json-rpc-engine/test/basic.spec.js
举例说明：
/* eslint-env mocha */
'use strict' const assert = require('assert') const RpcEngine = require('../src/index.js') describe('basic tests', function () { it('basic middleware test', function (done) { let engine = new RpcEngine() engine.push(function (req, res, next, end) { req.method = 'banana' res.result = 42 end() }) let payload = { id: 1, jsonrpc: '2.0', method: 'hello' } engine.handle(payload, function (err, res) { assert.ifError(err, 'did not error') assert(res, 'has res') assert.equal(res.result, 42, 'has expected result') assert.equal(payload.method, 'hello', 'original request object is not mutated by middleware') //payload.method仍然是'hello'，而不会被改成'banana' done() }) }) it('interacting middleware test', function (done) { //两个push交互 let engine = new RpcEngine() engine.push(function (req, res, next, end) { req.resultShouldBe = 42 next() }) engine.push(function (req, res, next, end) { res.result = req.resultShouldBe end() }) let payload = { id: 1, jsonrpc: '2.0', method: 'hello' } engine.handle(payload, function (err, res) { assert.ifError(err, 'did not error') assert(res, 'has res') assert.equal(res.result, 42, 'has expected result') done() }) }) it('erroring middleware test', function (done) { let engine = new RpcEngine() engine.push(function (req, res, next, end) { end(new Error('no bueno'))//定义一个错误 }) let payload = { id: 1, jsonrpc: '2.0', method: 'hello' } engine.handle(payload, function (err, res) { assert(err, 'did error') //测试发现有错，push中定义的 assert(res, 'does have response') assert(res.error, 'does have error on response') done() }) }) it('empty middleware test', function (done) { let engine = new RpcEngine() let payload = { id: 1, jsonrpc: '2.0', method: 'hello' } //如果没有push ，handle将报错 engine.handle(payload, function (err, res) { assert(err, 'did error') done() }) }) it('handle batch payloads', function (done) { let engine = new RpcEngine() engine.push(function (req, res, next, end) { res.result = req.id end() }) let payloadA = { id: 1, jsonrpc: '2.0', method: 'hello' } let payloadB = { id: 2, jsonrpc: '2.0', method: 'hello' } let payload = [payloadA, payloadB] //可以一下子handle多个push engine.handle(payload, function (err, res) { assert.ifError(err, 'did not error') assert(res, 'has res') assert(Array.isArray(res), 'res is array') assert.equal(res[0].result, 1, 'has expected result') assert.equal(res[1].result, 2, 'has expected result') done() }) })
json-rpc-engine/test/asMiddleware.spec.js
/* eslint-env mocha */
'use strict' const assert = require('assert') const RpcEngine = require('../src/index.js') const asMiddleware = require('../src/asMiddleware.js') describe('asMiddleware', function () { //嵌套 it('basic', function (done) { let engine = new RpcEngine() let subengine = new RpcEngine() let originalReq subengine.push(function (req, res, next, end) { originalReq = req res.result = 'saw subengine' end() }) engine.push(asMiddleware(subengine))//将两种嵌套，那么engine就能够使用subengine在push时的定义 let payload = { id: 1, jsonrpc: '2.0', method: 'hello' } engine.handle(payload, function (err, res) { assert.ifError(err, 'did not error') assert(res, 'has res') assert.equal(originalReq.id, res.id, 'id matches') assert.equal(originalReq.jsonrpc, res.jsonrpc, 'jsonrpc version matches') assert.equal(res.result, 'saw subengine', 'response was handled by nested engine') done() }) }) })
json-rpc-engine/src/idRemapMiddleware.js
const getUniqueId = require('./getUniqueId')
module.exports = createIdRemapMiddleware function createIdRemapMiddleware() { return (req, res, next, end) => { const originalId = req.id const newId = getUniqueId() req.id = newId res.id = newId next((done) => { req.id = originalId res.id = originalId done() }) } }
测试：
json-rpc-engine/test/idRemapMiddleware.spec.js
/* eslint-env mocha */
'use strict' const assert = require('assert') const RpcEngine = require('../src/index.js') const createIdRemapMiddleware = require('../src/idRemapMiddleware.js') describe('idRemapMiddleware tests', function () { it('basic middleware test', function (done) { let engine = new RpcEngine() const observedIds = { before: {}, after: {}, } engine.push(function (req, res, next, end) { observedIds.before.req = req.id observedIds.before.res = res.id //设置使得handle时 res.id = req.id，两者结果相同 next() }) engine.push(createIdRemapMiddleware()) engine.push(function (req, res, next, end) { observedIds.after.req = req.id observedIds.after.res = res.id // set result so it doesnt error res.result = true end() }) let payload = { id: 1, jsonrpc: '2.0', method: 'hello' } const payloadCopy = Object.assign({}, payload) engine.handle(payload, function (err, res) { assert.ifError(err, 'did not error') assert(res, 'has res') // collected data assert(observedIds.before.req, 'captured ids') assert(observedIds.before.res, 'captured ids') assert(observedIds.after.req, 'captured ids') assert(observedIds.after.res, 'captured ids') // data matches expectations assert.equal(observedIds.before.req, observedIds.before.res, 'ids match') //一开始两个是相同的 assert.equal(observedIds.after.req, observedIds.after.res, 'ids match') //之后两个的结果也是相同的，但是变成了newId // correct behavior assert.notEqual(observedIds.before.req, observedIds.after.req, 'ids are different') //前后的req.id不同了 assert.equal(observedIds.before.req, res.id, 'result id matches original') //但是before和最后输出的结果res.id还是一样的 assert.equal(payload.id, res.id, 'result id matches original') assert.equal(payloadCopy.id, res.id, 'result id matches original') done() }) }) })
这里可以知道idRemapMiddleware的作用是在过程中间得到一个新的、比较复杂的Id进行一系列处理，但是最后输出的给用户看的表示结果还是一样的