发送多个 HTTP 请求

我需要编写使用项目 ID 查找有关项目的信息的程序。

该 API 一次仅获取一项，因此我只能对每项执行一次查询。 API 仅限于五个同时请求。任何额外的结果都会给出 HTTP 429 错误。

如果有一个 JavaScript 对象，其中包含所有带有 ID 的项目

如何检索所有给定 ID 的信息而不触发同时请求限制，并且不对已看到的项目 ID 执行不必要的查询。

import fetch from "node-fetch";

let itemObject = [
  { itemName: "", itemID: "" },
  { itemName: "", itemID: "" },
  { itemName: "", itemID: "" },
  { itemName: "", itemID: "" },
];

async function sendIDRequests() {
  try {
    const response = await fetch("https://url/items/:ID", {
      headers: {
        Authorization: "",
      },
    });
    if (!response.ok) {
      throw new Error(`${response.status} ${response.statusText}`);
    }
    response
      .text()
      .then((res) => console.log(res))
      .catch((err) => {
        throw new Error(err);
      });
  } catch (error) {
    console.error(error);
  }
}

sendRequests()

为此，我想到了两种方法。批处理和滑动窗口方法。批处理可能更容易，但使用滑动窗口将是更有效的实现。

使用 Promise.all() 进行批处理

此方法创建批量请求，最多达到指定的batchSize只有当一批请求全部完成后，才会发出下一批请求。

您需要在此处添加一些错误处理，以防请求失败。

import fetch from "node-fetch";

// list of items that you might want to use to compose your URL (not actually used here)
let itemObject = [
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
];


(async () => {
    // number of concurrent requests in one batch
    const batchSize = 4;
    // request counter
    let curReq = 0;
    // as long as there are items in the list continue to form batches
    while (curReq < itemObject.length) {
        // a batch is either limited by the batch size or it is smaller than the batch size when there are less items required
        const end = itemObject.length < curReq + batchSize ? itemObject.length: curReq + batchSize;
        // we know the number of concurrent request so reserve memory for this
        const concurrentReq = new Array(batchSize);
        // issue one request for each item in the batch
        for (let index = curReq; index < end; index++) {
            concurrentReq.push(fetch("https://postman-echo.com/get"))
            console.log(`sending request ${curReq}...`)
            curReq++;
        }
        // wait until all promises are done or one promise is rejected
        await Promise.all(concurrentReq);
        console.log(`requests ${curReq - batchSize}-${curReq} done.`)
    }
})();

预期结果：

sending request 0...
sending request 1...
sending request 2...
sending request 3...
requests 0-4 done.
sending request 4...
sending request 5...
sending request 6...
sending request 7...
requests 4-8 done.
sending request 8...
sending request 9...
sending request 10...
sending request 11...
requests 8-12 done.

带信号量的滑动窗口

这种方法使用了一个滑动窗口 https://en.wikipedia.org/wiki/Sliding_window_protocol并在另一个请求完成后立即安排一个新请求，同时始终保持请求计数低于或等于最大数量n任意时刻的并发请求。 你需要实现的是信号 https://en.wikipedia.org/wiki/Semaphore_(programming).

JavaScript 中有一个用于此目的的库，名为异步互斥体 https://github.com/DirtyHairy/async-mutex.

下面是使用该库向 Postman Echo API 同时发送 2 个请求的示例程序。在信号量允许的情况下，永远不会有更多的请求同时运行（在您的情况下，限制为 5，这里是 2）。

import { Semaphore } from "async-mutex";
import fetch from "node-fetch";

// list of items that you might want to use to compose your URL (not actually used here)
let itemObject = [
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
    { itemName: "", itemID: "" },
];

(async () => {
    // allow two concurrent requests (adjust for however many are required)
    const semaphore = new Semaphore(2);

    itemObject.forEach(async (item, idx) => {
        // acquire the semaphore
        const [value, release] = await semaphore.acquire();
        // at this point the semaphore has been acquired and the job needs to be done 
        try {
            console.log(`sending request ${idx}...`)
            const response = await fetch("https://postman-echo.com/get")
            if(!response.ok){
                console.log(`request failed with status code ${response.status}`)
            }
        }
        catch (error) {
            console.log("request failed.")
        }
        finally {
            console.log(`request ${idx} done...`)
            // release the semaphore again so a new request can be issued 
            release();
        }
    })
})();

预期输出（顺序可能有所不同）：

sending request 0...
sending request 1...
request 1 done...
sending request 2...
request 2 done...
sending request 3...
request 3 done...
sending request 4...
request 0 done...
sending request 5...
request 4 done...
sending request 6...
request 5 done...
sending request 7...
request 6 done...
sending request 8...
request 7 done...
sending request 9...
request 8 done...
sending request 10...
request 9 done...
sending request 11...
request 10 done...
request 11 done...