node.js - 如何在 koa 中发送 HTTP 响应之前等待 url 回调？

Question

我有一个 koa 路由器，我需要调用一个 api，异步返回结果。这意味着我无法立即获得结果，api 会在正常时调用我的 callback url。但现在我必须像同步 api 一样使用它，这意味着我必须等到回调 url 被调用。

我的路由器是这样的:

router.post("/voice", async (ctx, next) => {
    // call a API here
    const params = {
        data: "xxx",
        callback_url: "http//myhost/ret_callback",
    };
    const req = new Request("http://xxx/api", {
        method: "POST",
        body: JSON.stringify(params),
    });
    const resp = await fetch(req);
    const data = await resp.json();

    // data here is not the result I want, this api just return a task id, this api will call my url back
    const taskid = data.taskid;

    // now I want to wait here until I got "ret_callback"

    // .... wait .... wait
    // "ret_callback" is called now
    // get the answer in "ret_callback"
    ctx.body = {
        result: "ret_callback result here",
    }
})

我的回调 url 是这样的:

router.post("/ret_callback", async (ctx, next) => {
    const params = ctx.request.body;

    // taskid will tell me this answer to which question
    const taskid = params.taskid;
    // this is exactly what I want
    const result = params.text;

    ctx.body = {
        code: 0,
        message: "success",
    };
})

那么我怎样才能让这个 aync api 像一个 sync api 一样呢？

Answer 1

只需将 resolve() 传递给另一个函数。例如，您可以这样做:

// use a map to save a lot of resolve()
const taskMap = new Map();

router.post("/voice", async (ctx, next) => {
    // call a API here
    const params = {
        data: "xxx",
        callback_url: "http//myhost/ret_callback",
    };
    const req = new Request("http://xxx/api", {
        method: "POST",
        body: JSON.stringify(params),
    });
    const resp = await fetch(req);
    const data = await resp.json();

    const result = await waitForCallback(data.taskid);

    ctx.body = {
        result,
    } })

const waitForCallback = (taskId) => {
    return new Promise((resolve, reject) => {
        const task = {};
        task.id = taskId;
        task.onComplete = (data) => {
            resolve(data);
        };
        task.onError = () => {
            reject();
        };
        taskMap.set(task.id, task);
    });
};

router.post("/ret_callback", async (ctx, next) => {
    const params = ctx.request.body;

    // taskid will tell me this answer to which question
    const taskid = params.taskid;
    // this is exactly what I want
    const result = params.text;

    // here you continue the waiting response
    taskMap.get(taskid).onComplete(result);
    // not forget to clean rubbish
    taskMap.delete(taskid);

    ctx.body = {
        code: 0,
        message: "success",
    }; })

我没有测试它，但我认为它会起作用。