如何使用异步ES7 /等待与流？ [英] How to use ES7 async/await with streams?

问题描述

在 http://stackoverflow.com/a/18658613/779159 是如何计算的MD5为例使用文件的内置加密库和溪流。

In http://stackoverflow.com/a/18658613/779159 is an example of how to calculate the md5 of a file using the built-in crypto library and streams.

var fs = require('fs');
var crypto = require('crypto');

// the file you want to get the hash    
var fd = fs.createReadStream('/some/file/name.txt');
var hash = crypto.createHash('sha1');
hash.setEncoding('hex');

fd.on('end', function() {
    hash.end();
    console.log(hash.read()); // the desired sha1sum
});

// read all file and pipe it (write it) to the hash object
fd.pipe(hash);

但是，它可以将其转换为使用ES7异步/等待，而不是使用回调如上可见，但同时仍保持使用流的效率？

But is it possible to convert this to using ES7 async/await instead of using the callback as seen above, but while still keeping the efficiency of using streams?

推荐答案

异步 / 等待只适用于诺言，不与流。有想法，使额外的流式数据类型将获得它自己的语法，但这些都是高度，如果实验在所有我不会赘述了。

async/await only works with promises, not with streams. There are ideas to make an extra stream-like data type that would get its own syntax, but those are highly experimental if at all and I won't go into details.

总之，你的回调只是等待流，这是一个承诺的完美契合的结束。你只需要换流：

Anyway, your callback is only waiting for the end of the stream, which is a perfect fit for a promise. You'd just have to wrap the stream:

var fd = fs.createReadStream('/some/file/name.txt');
var hash = crypto.createHash('sha1');
hash.setEncoding('hex');
fd.on('end', function() {
    hash.end();
});
// read all file and pipe it (write it) to the hash object
fd.pipe(hash);

var end = new Promise(function(resolve, reject) {
    fd.on('end', ()=>resolve(hash.read()));
    fd.on('error', reject); // or something like that
});

现在，你可以等待这个承诺：

Now you can await that promise:

(async function() {
    let sha1sum = await end;
    console.log(sha1sum);
}());

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