如果可能的话,我想通过管道将两个Node.js流合并为一个流。我使用的是Transform streams。
换句话说,我希望我的库返回myStream
供人们使用。例如,他们可以这样写:
process.stdin.pipe(myStream).pipe(process.stdout);
在内部,我使用了一个插入到myInternalStream
中我自己的逻辑中的第三方vendorStream
来完成一些工作。因此,上面的内容将转化为:
process.stdin.pipe(vendorStream).pipe(myInternalStream).pipe(process.stdout);
我能做这样的事吗?我尝试过var myStream = vendorStream.pipe(myInternalStream)
,但显然不起作用。
为了与bash
进行类比,假设我想编写一个程序来检查某个流(tail -n 1 | grep h
)的最后一行中是否存在字母h
,我可以创建一个shell脚本:
# myscript.sh
tail -n 1 | grep h
如果人们这样做了:
$ printf "abc\ndef\nghi" | . myscript.sh
它就是这样的。
这就是我到目前为止所知道的:
// Combine a pipe of two streams into one stream
var util = require('util')
, Transform = require('stream').Transform;
var chunks1 = [];
var stream1 = new Transform();
var soFar = '';
stream1._transform = function(chunk, encoding, done) {
chunks1.push(chunk.toString());
var pieces = (soFar + chunk).split('\n');
soFar = pieces.pop();
for (var i = 0; i < pieces.length; i++) {
var piece = pieces[i];
this.push(piece);
}
return done();
};
var chunks2 = [];
var count = 0;
var stream2 = new Transform();
stream2._transform = function(chunk, encoding, done) {
chunks2.push(chunk.toString());
count = count + 1;
this.push(count + ' ' + chunk.toString() + '\n');
done();
};
var stdin = process.stdin;
var stdout = process.stdout;
process.on('exit', function () {
console.error('chunks1: ' + JSON.stringify(chunks1));
console.error('chunks2: ' + JSON.stringify(chunks2));
});
process.stdout.on('error', process.exit);
// stdin.pipe(stream1).pipe(stream2).pipe(stdout);
// $ (printf "abc\nd"; sleep 1; printf "ef\nghi\n") | node streams-combine.js
// Outputs:
// 1 abc
// 2 def
// 3 ghi
// chunks1: ["abc\nd","ef\nghi\n"]
// chunks2: ["abc","def","ghi"]
// Best working solution I could find
var stream3 = function(src) {
return src.pipe(stream1).pipe(stream2);
};
stream3(stdin).pipe(stdout);
// $ (printf "abc\nd"; sleep 1; printf "ef\nghi\n") | node streams-combine.js
// Outputs:
// 1 abc
// 2 def
// 3 ghi
// chunks1: ["abc\nd","ef\nghi\n"]
// chunks2: ["abc","def","ghi"]
这有可能吗?如果我要做的事情不清楚,请让我知道。
谢谢!
发布于 2013-07-05 02:48:34
您可以查看要通过管道传输到流的内容,然后使用unpipe
将其传输到您感兴趣的流:
var PassThrough = require('stream').PassThrough;
var stream3 = new PassThrough();
// When a source stream is piped to us, undo that pipe, and save
// off the source stream piped into our internally managed streams.
stream3.on('pipe', function(source) {
source.unpipe(this);
this.transformStream = source.pipe(stream1).pipe(stream2);
});
// When we're piped to another stream, instead pipe our internal
// transform stream to that destination.
stream3.pipe = function(destination, options) {
return this.transformStream.pipe(destination, options);
};
stdin.pipe(stream3).pipe(stdout);
您可以将此功能提取到您自己的可构造流类中:
var util = require('util');
var PassThrough = require('stream').PassThrough;
var StreamCombiner = function() {
this.streams = Array.prototype.slice.apply(arguments);
this.on('pipe', function(source) {
source.unpipe(this);
for(i in this.streams) {
source = source.pipe(this.streams[i]);
}
this.transformStream = source;
});
};
util.inherits(StreamCombiner, PassThrough);
StreamCombiner.prototype.pipe = function(dest, options) {
return this.transformStream.pipe(dest, options);
};
var stream3 = new StreamCombiner(stream1, stream2);
stdin.pipe(stream3).pipe(stdout);
发布于 2016-08-05 18:35:05
一种选择可能是使用multipipe,它允许您将多个转换链接在一起,包装为单个转换流:
// my-stream.js
var multipipe = require('multipipe');
module.exports = function createMyStream() {
return multipipe(vendorStream, myInternalStream);
};
然后您可以执行以下操作:
var createMyStream = require('./my-stream');
var myStream = createMyStream();
process.stdin.pipe(myStream).pipe(process.stdout);
澄清:这使标准输入经过vendorStream,然后是myInternalStream,最后是标准输出。
https://stackoverflow.com/questions/17471659
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