在https://stackoverflow.com/a/18658613/779159中是一个如何使用内置加密库和流来计算文件的md5的示例。
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);
但是可以将其转换为使用ES8 async / await而不是如上所述使用回调,但是仍然保持使用流的效率吗?
答案 0 :(得分:66)
async
/ await
仅适用于承诺,而不适用于流。有一些想法可以创建一个类似于流的数据类型,它可以获得自己的语法,但是如果有的话,这些都是高度实验的,我不会详细介绍。
无论如何,你的回调只等待流的结束,这非常适合承诺。你只需要包装流:
var fd = fs.createReadStream('/some/file/name.txt');
var hash = crypto.createHash('sha1');
hash.setEncoding('hex');
// read all file and pipe it (write it) to the hash object
fd.pipe(hash);
var end = new Promise(function(resolve, reject) {
hash.on('end', () => resolve(hash.read()));
fd.on('error', reject); // or something like that. might need to close `hash`
});
现在你可以等待这个承诺:
(async function() {
let sha1sum = await end;
console.log(sha1sum);
}());
答案 1 :(得分:17)
Node V15 现在在 stream/promises 中有一个 promisfiy 管道。 这是最干净、最正式的方式。
const { pipeline } = require('stream/promises');
async function run() {
await pipeline(
fs.createReadStream('archive.tar'),
zlib.createGzip(),
fs.createWriteStream('archive.tar.gz')
);
console.log('Pipeline succeeded.');
}
run().catch(console.error);
我们都应该感谢它在这里完成了多少工作:
这个管道是 Node.JS 最强大的特性之一。使其完全异步并不容易。现在我们有了。
答案 2 :(得分:6)
如果您使用的节点版本> = v10.0.0,则可以使用stream.pipeline和util.promisify。
const fs = require('fs');
const crypto = require('crypto');
const util = require('util');
const stream = require('stream');
const pipeline = util.promisify(stream.pipeline);
const hash = crypto.createHash('sha1');
hash.setEncoding('hex');
async function run() {
await pipeline(
fs.createReadStream('/some/file/name.txt'),
hash
);
console.log('Pipeline succeeded');
}
run().catch(console.error);
答案 3 :(得分:2)
类似的作品:
for (var res of fetchResponses){ //node-fetch package responses
const dest = fs.createWriteStream(filePath,{flags:'a'});
totalBytes += Number(res.headers.get('content-length'));
await new Promise((resolve, reject) => {
res.body.pipe(dest);
res.body.on("error", (err) => {
reject(err);
});
dest.on("finish", function() {
resolve();
});
});
}
答案 4 :(得分:1)
我会发表评论,但没有足够的声誉。
警告: 如果您的应用程序正在传递流并执行异步/等待,请在等待之前非常小心地连接所有管道。您最终可能会得到不包含您认为它们所做的事情的流。这是最小的例子
const { PassThrough } = require('stream');
async function main() {
const initialStream = new PassThrough();
const otherStream = new PassThrough();
const data = [];
otherStream.on('data', dat => data.push(dat));
const resultOtherStreamPromise = new Promise(resolve => otherStream.on('end', () => { resolve(Buffer.concat(data)) }));
const yetAnotherStream = new PassThrough();
const data2 = [];
yetAnotherStream.on('data', dat => data2.push(dat));
const resultYetAnotherStreamPromise = new Promise(resolve => yetAnotherStream.on('end', () => { resolve(Buffer.concat(data2)) }));
initialStream.pipe(otherStream);
initialStream.write('some ');
await Promise.resolve(); // Completely unrelated await
initialStream.pipe(yetAnotherStream);
initialStream.end('data');
const [resultOtherStream, resultYetAnotherStream] = await Promise.all([
resultOtherStreamPromise,
resultYetAnotherStreamPromise,
]);
console.log('other stream:', resultOtherStream.toString()); // other stream: some data
console.log('yet another stream:', resultYetAnotherStream.toString()); // yet another stream: data
}
main();
答案 5 :(得分:1)
2021 年更新:
Node 文档中的新示例:
async function print(readable) {
readable.setEncoding('utf8');
let data = '';
for await (const chunk of readable) {
data += chunk;
}
console.log(data);
}
见https://nodejs.org/api/stream.html#stream_readable_symbol_asynciterator