How to log information when spawning process in node.js?

Question

I wrote a function which spawns a process and want to log some information to the console. Function looks like this:

function receive(count) {
  var fileName = settings.flatfileName || "defaultFileName";
  for (var i = 1; i <= count; i++) {
    var csrFileName = fileName + i + ".json";
    var curlProcess = spawn('/bin/sh', ['-c', curlCommand(csrFileName, caServerUrl)]);
    curlProcess.on('close', function(code, signal) {
      if (code !== 0) {
        throw new Error("I'm sorry, I couldn't fetch certificate from CA. curl returned code " + code);
      }
      console.log("OK, I successfully fetched certificate for CSR " + csrFileName);
    });
  }
}

The problem is, if I call this function with parameter 2, I get output which looks like this:

OK, I successfully fetched certificate for CSR certificateRequest2.json
OK, I successfully fetched certificate for CSR certificateRequest2.json

Since variable csrFileName changes in every loop iteration, it seems that in console.log call it's value is always equal to the last value it received in the loop. Is it possible to get output which would look like this?

OK, I successfully fetched certificate for CSR certificateRequest1.json
OK, I successfully fetched certificate for CSR certificateRequest2.json

Steeve Pitis · Accepted Answer · 2016-10-04 15:38:31Z

2

since onClose is async, you need to bind your filename.

Try with this :

function receive(count) {
  var fileName = settings.flatfileName || "defaultFileName";
  for (var i = 1; i <= count; i++) {
    var csrFileName = fileName + i + ".json";
    var curlProcess = spawn('/bin/sh', ['-c', curlCommand(csrFileName, caServerUrl)]);
    curlProcess.on('close', function(fileName, code, signal) {
      if (code !== 0) {
        throw new Error("I'm sorry, I couldn't fetch certificate from CA. curl returned code " + code);
      }
      console.log("OK, I successfully fetched certificate for CSR " + fileName);
    }.bind(this, csrFileName));
  }
}

answered Oct 4, 2016 at 15:38

Steeve Pitis

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Comments

Stavros Zavrakas · Accepted Answer · 2016-10-04 15:37:12Z

1

Closures, iife and async! You have to study a bit more these concepts. This will solve your issue:

function receive(count) {
  var fileName = settings.flatfileName || "defaultFileName";
  for (var i = 1; i <= count; i++) {
    (function (i) {
      var csrFileName = fileName + i + ".json";
      var curlProcess = spawn('/bin/sh', ['-c', curlCommand(csrFileName, caServerUrl)]);
      curlProcess.on('close', function (code, signal) {
        if (code !== 0) {
          throw new Error("I'm sorry, I couldn't fetch certificate from CA. curl returned code " + code);
        }
        console.log("OK, I successfully fetched certificate for CSR " + csrFileName);
      });
    }(i));
  }
}

answered Oct 4, 2016 at 15:37

Stavros Zavrakas

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Comments

forrert · Accepted Answer · 2016-10-04 15:38:20Z

1

You could factor out the inner part of the loop into a separate function:

function receive(count) {
  var fileName = settings.flatfileName || "defaultFileName";
  for (var i = 1; i <= count; i++) {
    var csrFileName = fileName + i + ".json";
    curlFile(csrFileName);
  }
}

function curlFile(csrFileName) {
    var curlProcess = spawn('/bin/sh', ['-c', curlCommand(csrFileName, caServerUrl)]);
    curlProcess.on('close', function(code, signal) {
      if (code !== 0) {
        throw new Error("I'm sorry, I couldn't fetch certificate from CA. curl returned code " + code);
      }
      console.log("OK, I successfully fetched certificate for CSR " + csrFileName);
    });
 }

answered Oct 4, 2016 at 15:38

forrert

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Comments

Molda · Accepted Answer · 2016-10-04 15:41:31Z

1

You can use closure like this

function receive(count) { var fileName = settings.flatfileName || "defaultFileName"; 
   for (var i = 1; i <= count; i++) { 

        (function(x){
            var csrFileName = fileName + x + ".json"; 
            var curlProcess = spawn('/bin/sh', ['-c', curlCommand(csrFileName, caServerUrl)]); 
            curlProcess.on('close', function(code, signal) { 
                  if (code !== 0) { 
                      throw new Error("I'm sorry, I couldn't fetch certificate from CA. curl returned code " + code); 
                 } 
                 console.log("OK, I successfully fetched certificate for CSR " + csrFileName); 
            }); 
        })(i);
    }
}

answered Oct 4, 2016 at 15:41

Molda

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