如何在 Node.js 0.10 中立即使用读取流链接写入流？
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How to chain write stream, immediately with a read stream in Node.js 0.10?
提问by Sahat Yalkabov
The following line will download an image file from a specified urlvariable:
以下行将从指定的url变量下载图像文件：
var filename = path.join(__dirname, url.replace(/^.*[\\/]/, ''));
request(url).pipe(fs.createWriteStream(filename));
And these lines will take that image and save to MongoDB GridFS:
这些行将获取该图像并保存到 MongoDB GridFS：
var gfs = Grid(mongoose.connection.db, mongoose.mongo);
var writestream = gfs.createWriteStream({ filename: filename });
fs.createReadStream(filename).pipe(writestream);
Chaining pipelike this throws Error: 500 Cannot Pipe. Not Pipeable.
pipe像这样的链接会引发错误：500 无法管道。不可管道。
request(url).pipe(fs.createWriteStream(filename)).pipe(writestream);
This happens because the image file is not ready to be read yet, right? What should I do to get around this problem?Error: 500 Cannot Pipe. Not Pipeable.
发生这种情况是因为图像文件还没有准备好被读取，对吗？我应该怎么做才能解决这个问题？错误：500 无法管道。不可管道。
Using the following: Node.js 0.10.10, mongoose, requestand gridfs-streamlibraries.
使用下面的：Node.js的0.10.10，猫鼬，要求和GridFS的流库。
回答by loganfsmyth
request(url).pipe(fs.createWriteStream(filename)).pipe(writestream);
is the same as this:
与此相同：
var fileStream = fs.createWriteStream(filename);
request(url).pipe(fileStream);
fileStream.pipe(writestream);
So the issue is that you are attempting to .pipeone WriteStreaminto another WriteStream.
所以问题是你正试图将.pipe一个WriteStream变成另一个WriteStream。
回答by BIJENDER KHATANA
// create 'fs' module variable
var fs = require("fs");
// open the streams
var readerStream = fs.createReadStream('inputfile.txt');
var writerStream = fs.createWriteStream('outputfile.txt');
// pipe the read and write operations
// read input file and write data to output file
readerStream.pipe(writerStream);
回答by mechanicious
I think the confusion in chaining the pipes is caused by the fact that the pipe method implicitly "makes choices" on it's own on what to return. That is:
我认为链接管道的混乱是由于管道方法隐式地“做出选择”，它自己决定返回什么。那是：
readableStream.pipe(writableStream) // Returns writable stream
readableStream.pipe(duplexStream) // Returns readable stream
But the general rule says that "You can only pipe a Writable Stream to a Readable Stream." In other words only Readable Streams have the pipe()method.
但一般规则是“您只能通过管道将 Writable Stream 传输到 Readable Stream”。换句话说，只有 Readable Streams 有这个pipe()方法。
