Question

How could you use HTML to open a file on the client’s machine as plaintext (i.e., a .cpp, .txt, or even a .html file)? I want to extract the plain textfile from the user’s machine into an HTML <textarea>. Just FYI, I am using hiccup, clojure, and webnoir to generate the HTML and server so those are all other options to use to help the process along.

Answer 1

You have two main options: upload the file to your server to be served as HTML content or use HTML 5’s File API. This question also addresses a few more options (like applets, enabling drag-and-drop with the File API, etc.)

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Upload the file

1. Have the users choose the file using an <input type="file" .../> on one page
2. Upload the file contents to your server.
3. Redirect to a different page to show the file contents
4. Serve the uploaded file’s contents in a textarea on that page.

Pros:

• This method is pretty simple and straightforward.
• You can scan the file and do some heavy processing on the server

Cons:

• Trips to the server can be time consuming.

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HTML 5 Solution

1. Have the user choose the file using an <input type="file" .../>
2. Instead of posting the contents, use JavaScript to load the file into your HTML 5 local storage (see code below)
3. Use JavaScript to insert the contents of the file into your DOM.

Pros:

• No trip to the server (faster)

Cons:

• Any and all validation/processing must be done on the client side in JavaScript. This makes your client heavier and allows users to see/modify your code (which you might not need to care about).

I grabbed this code snippet from this site, which has some good examples of using the File API:

function onInitFs(fs) {

  fs.root.getFile('log.txt', {}, function(fileEntry) {

    // Get a File object representing the file,
    // then use FileReader to read its contents.
    fileEntry.file(function(file) {
       var reader = new FileReader();

       reader.onloadend = function(e) {
           // Do something with the contents, which are stored in 'this.result'
       };

       reader.readAsText(file);
    }, errorHandler);

  }, errorHandler);

}

window.requestFileSystem(window.TEMPORARY, 1024*1024, onInitFs, errorHandler);