Node.js：在对其 stdin 流进行大型写入操作期间突然关闭子进程时，会引发无法捕获的错误

编程问答 2022-05-06

问题描述

注意：我已经找到了解决此问题的方法，将其发布在此处以供后人使用。查看所选答案。

以下（简化的）代码抛出一个无法捕捉的“write EPIPE”（在某些情况下“write EOF”）错误：

const { exec } = require("child_process");

const veryLargeString = "x".repeat(10 * 1024 * 1024);

const p = exec("gibberishThatwillFailImmediately");

p.stdin.write(veryLargeString);

我在该问题上的失败尝试：

  • 在写入前检查 stdin.destroyed 标志
  • 在写入前检查 stdin.writeableEnded 标志
  • 分块输入并在每个块之前检查 stdin.writeableEnded。这会导致不确定的行为。
  • 用 try-catch 包裹 stdin.write(data) 行
  • 调用 stdin.end(data) 而不是 stdin.write(data)
  • 传递 stdin.write() 一个回调，应该得到发生的任何错误。回调得到了错误，但并没有阻止它被抛出。

解决方法

向 stdin 流注册“错误”处理程序似乎可以防止抛出错误。像这样：

const { exec } = require("child_process");

const veryLargeString = "x".repeat(10 * 1024 * 1024);

const p = exec("gibberishThatWillFailImmediately");

p.stdin.on('error',(error) => console.log("error caught: ",error));

p.stdin.write(veryLargeString);

这是一个返回包含错误的承诺的示例，如果没有发生错误，则返回 null：

const { exec } = require("child_process");

const veryLargeString = "x".repeat(10 * 1024 * 1024);

function safelyWriteDataToStdin(stdin,data) {
  // Register an awaitable callback that will capture any error occuring during the write operation
  const promise = new Promise((resolve,_reject) => {
    // Using once() and not on() to remove the listener after the first catch.
    stdin.once("error",(error) => resolve(error));

    // stdin.end(data,callback) can probably be used here,but I keep the `write()` just in case `end()`'s callback is called before the 'error' event,since the docs are not clear about that. (docs say: "The callback is invoked before 'finish' or on error." for node version 15.0.0. Is "on error" how node people say "after error"? idk.)
    stdin.write(
      data,(error) => {
        if (!error) resolve(null); // The condition is necessary because when an error occurs,the callback is called before the 'error' event handler
      } // Signal the promise to complete when the write operation is complete with no errors. I don't simply use this `error` parameter because the exception will still be thrown if I don't listen to the 'error' event,and the docs say: "If an error occurs,the callback may or may not be called with the error as its first argument. To reliably detect write errors,add a listener for the 'error' event.". Also,I tested it myself and got two different errors in this callback and in the 'error' event handler.
    );
  });

  return promise;
}

const p = exec("gibberishThatWillFailImmediately");

safelyWriteDataToStdin(p.stdin,veryLargeString).then((error)=>console.log("The error is:",error ));
child-processnode-streamsstdin