node.js – 为什么fs.createReadStream只管道一次？

fs.createReadStream('pdf-sample1.pdf')
  .pipe(fs.createWriteStream('pdf-sample2.pdf'))
  .pipe(fs.createWriteStream('pdf-sample3.pdf'))

但我遇到了一个错误：

Error: Cannot pipe. Not readable.
    at WriteStream.Writable.pipe (_stream_writable.js:162:22)
    at repl:1:86
    at REPLServer.defaultEval (repl.js:132:27)
    at bound (domain.js:254:14)
    at REPLServer.runBound [as eval] (domain.js:267:12)
    at REPLServer.<anonymous> (repl.js:279:12)
    at REPLServer.emit (events.js:107:17)
    at REPLServer.Interface._onLine (readline.js:214:10)
    at REPLServer.Interface._line (readline.js:553:8)
    at REPLServer.Interface._ttyWrite (readline.js:830:14)

谁能告诉我原因？

readable.pipe(writable);

在这种情况下,可写的可以是：

> a Writable Stream;
> a Duplex Stream;
>或Transform Stream.

因此,如果您尝试读取多个文件并将它们传输到可写流,则必须将每个文件传递给可写流,并在执行时传递end：false,因为默认情况下,可读流结束可写流什么时候没有更多的数据需要阅读.这是一个例子：

var ws = fs.createWriteStream('output.pdf');

fs.createReadStream('pdf-sample1.pdf').pipe(ws, { end: false });
fs.createReadStream('pdf-sample2.pdf').pipe(ws, { end: false });
fs.createReadStream('pdf-sample3.pdf').pipe(ws);

当然,这不是最好的方法,你可以实现一个函数来以更通用的方式包装这个逻辑,可能有一个循环或recursive solution.

更简单的解决方案是使用已解决此问题的模块,如this one here.