C# – Read log file being used by another process

cfileremote desktop

Goal

I want to press a button on my GUI and read in the seclog.log file (symantec AV log) from a remote machine and display the contents of the log to a rich text box in my application.

Things That Work

everything but reading the log file

Error Message

System.IO.IOException was unhandled
Message=The process cannot access the file '\\HOSTNAME\C$\Program Files (x86)\Symantec\Symantec Endpoint Protection\seclog.log' because it is being used by another process.
Source=mscorlib

code

//possible seclog paths
        String seclogPath1 = @"\\\\" + target + "\\C$\\Program Files (x86)\\Symantec\\Symantec Endpoint Protection\\seclog.log";
        String seclogPath2 = @"\\\\" + target + "\\C$\\Program Files\\Symantec\\Symantec Endpoint Protection\\seclog.log";

        //if seclog exists
        if (File.Exists(seclogPath1))
        {
            //output.AppendText("file exists at " + seclogPath1);
            //var seclogContent = File.Open(seclogPath1, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);

            Stream stream = File.OpenRead(seclogPath1);
            StreamReader streamReader = new StreamReader(stream);
            string str = streamReader.ReadToEnd();
            output.AppendText(str);
            streamReader.Close();
            stream.Close();


        }

Things I've Tried

File is being used by another process

C# The process cannot access the file ''' because it is being used by another process

Googling the issue

using filestreams in multiple ways

Best Answer

//possible seclog paths
String seclogPath1 = @"\\\\" + target + "\\C$\\Program Files (x86)\\Symantec\\Symantec Endpoint Protection\\seclog.log";
String seclogPath2 = @"\\\\" + target + "\\C$\\Program Files\\Symantec\\Symantec Endpoint Protection\\seclog.log";

//if seclog exists
if (File.Exists(seclogPath1))
{
    //output.AppendText("file exists at " + seclogPath1);
    //var seclogContent = File.Open(seclogPath1, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);

    Stream stream = File.Open(seclogPath1, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
    //File.OpenRead(seclogPath1);
    StreamReader streamReader = new StreamReader(stream);
    string str = streamReader.ReadToEnd();
    output.AppendText(str);
    streamReader.Close();
    stream.Close();


}

what i had to change

i had to create a readwrite filestream

original code

Stream stream = File.OpenRead(seclogPath1);
StreamReader streamReader = new StreamReader(stream);

new code

Stream stream = File.Open(seclogPath1, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
//File.OpenRead(seclogPath1);
StreamReader streamReader = new StreamReader(stream);

ES6 Modules

ECMAScript (ES6) modules have been supported in Node.js since v8.5, with the --experimental-modules flag, and since at least Node.js v13.8.0 without the flag. To enable "ESM" (vs. Node.js's previous CommonJS-style module system ["CJS"]) you either use "type": "module" in package.json or give the files the extension .mjs. (Similarly, modules written with Node.js's previous CJS module can be named .cjs if your default is ESM.)

Using package.json:

{
    "type": "module"
}

Then module.js:

export function hello() {
  return "Hello";
}

Then main.js:

import { hello } from './module.js';
let val = hello();  // val is "Hello";

Using .mjs, you'd have module.mjs:

export function hello() {
  return "Hello";
}

Then main.mjs:

import { hello } from './module.mjs';
let val = hello();  // val is "Hello";

ECMAScript modules in browsers

Browsers have had support for loading ECMAScript modules directly (no tools like Webpack required) since Safari 10.1, Chrome 61, Firefox 60, and Edge 16. Check the current support at caniuse. There is no need to use Node.js' .mjs extension; browsers completely ignore file extensions on modules/scripts.

<script type="module">
  import { hello } from './hello.mjs'; // Or it could be simply `hello.js`
  hello('world');
</script>

// hello.mjs -- or it could be simply `hello.js`
export function hello(text) {
  const div = document.createElement('div');
  div.textContent = `Hello ${text}`;
  document.body.appendChild(div);
}

Dynamic imports in browsers

Dynamic imports let the script load other scripts as needed:

<script type="module">
  import('hello.mjs').then(module => {
      module.hello('world');
    });
</script>

Node.js require

The older CJS module style, still widely used in Node.js, is the module.exports/require system.

// mymodule.js
module.exports = {
   hello: function() {
      return "Hello";
   }
}

// server.js
const myModule = require('./mymodule');
let val = myModule.hello(); // val is "Hello"

There are other ways for JavaScript to include external JavaScript contents in browsers that do not require preprocessing.

AJAX Loading

You could load an additional script with an AJAX call and then use eval to run it. This is the most straightforward way, but it is limited to your domain because of the JavaScript sandbox security model. Using eval also opens the door to bugs, hacks and security issues.

Fetch Loading

Like Dynamic Imports you can load one or many scripts with a fetch call using promises to control order of execution for script dependencies using the Fetch Inject library:

fetchInject([
  'https://cdn.jsdelivr.net/momentjs/2.17.1/moment.min.js'
]).then(() => {
  console.log(`Finish in less than ${moment().endOf('year').fromNow(true)}`)
})

jQuery Loading

The jQuery library provides loading functionality in one line:

$.getScript("my_lovely_script.js", function() {
   alert("Script loaded but not necessarily executed.");
});

Dynamic Script Loading

You could add a script tag with the script URL into the HTML. To avoid the overhead of jQuery, this is an ideal solution.

The script can even reside on a different server. Furthermore, the browser evaluates the code. The <script> tag can be injected into either the web page <head>, or inserted just before the closing </body> tag.

Here is an example of how this could work:

function dynamicallyLoadScript(url) {
    var script = document.createElement("script");  // create a script DOM node
    script.src = url;  // set its src to the provided URL

    document.head.appendChild(script);  // add it to the end of the head section of the page (could change 'head' to 'body' to add it to the end of the body section instead)
}

This function will add a new <script> tag to the end of the head section of the page, where the src attribute is set to the URL which is given to the function as the first parameter.

Both of these solutions are discussed and illustrated in JavaScript Madness: Dynamic Script Loading.

Detecting when the script has been executed

Now, there is a big issue you must know about. Doing that implies that you remotely load the code. Modern web browsers will load the file and keep executing your current script because they load everything asynchronously to improve performance. (This applies to both the jQuery method and the manual dynamic script loading method.)

It means that if you use these tricks directly, you won't be able to use your newly loaded code the next line after you asked it to be loaded, because it will be still loading.

For example: my_lovely_script.js contains MySuperObject:

var js = document.createElement("script");

js.type = "text/javascript";
js.src = jsFilePath;

document.body.appendChild(js);

var s = new MySuperObject();

Error : MySuperObject is undefined

Then you reload the page hitting F5. And it works! Confusing...

So what to do about it ?

Well, you can use the hack the author suggests in the link I gave you. In summary, for people in a hurry, he uses an event to run a callback function when the script is loaded. So you can put all the code using the remote library in the callback function. For example:

function loadScript(url, callback)
{
    // Adding the script tag to the head as suggested before
    var head = document.head;
    var script = document.createElement('script');
    script.type = 'text/javascript';
    script.src = url;

    // Then bind the event to the callback function.
    // There are several events for cross browser compatibility.
    script.onreadystatechange = callback;
    script.onload = callback;

    // Fire the loading
    head.appendChild(script);
}

Then you write the code you want to use AFTER the script is loaded in a lambda function:

var myPrettyCode = function() {
   // Here, do whatever you want
};

Then you run all that:

loadScript("my_lovely_script.js", myPrettyCode);

Note that the script may execute after the DOM has loaded, or before, depending on the browser and whether you included the line script.async = false;. There's a great article on Javascript loading in general which discusses this.

Source Code Merge/Preprocessing

As mentioned at the top of this answer, many developers use build/transpilation tool(s) like Parcel, Webpack, or Babel in their projects, allowing them to use upcoming JavaScript syntax, provide backward compatibility for older browsers, combine files, minify, perform code splitting etc.

Python – How to read a file line-by-line into a list

This code will read the entire file into memory and remove all whitespace characters (newlines and spaces) from the end of each line:

with open(filename) as file:
    lines = file.readlines()
    lines = [line.rstrip() for line in lines]

If you're working with a large file, then you should instead read and process it line-by-line:

with open(filename) as file:
    for line in file:
        print(line.rstrip())

In Python 3.8 and up you can use a while loop with the walrus operator like so:

with open(filename) as file:
    while (line := file.readline().rstrip()):
        print(line)

Depending on what you plan to do with your file and how it was encoded, you may also want to manually set the access mode and character encoding:

with open(filename, 'r', encoding='UTF-8') as file:
    while (line := file.readline().rstrip()):
        print(line)