Uploading Attachments to SharePoint Lists Using REST

In a previous post, I walked through Uploading Attachments to SharePoint Lists Using SPServices. Well, in the “modern” world, I want to use REST whenever I can, especially with SharePoint Online.

I ran into a challenge figuring out how to make an attachment upload work in an AngularJS project. There are dozens of blog posts and articles out there about uploading files to SharePoint, and some of them even mention attachments. But I found that not a single one of the worked for me. It was driving me nuts. I could upload a file, but it was corrupt when it got there. Images didn’t look like images, Excel couldn’t open XLSX files, etc.

I reached out to Julie Turner (@jfj1997) and asked for help, but as is often the case, when you’re not as immersed in something it’s tough to get the context right. She gave me some excellent pointers, but I ended up traversing some of the same unfruitful ground with her.

Finally I decided to break things down into the simplest example possible, much like I did in my earlier post with SOAP. I created a test page called UploadTEST with a Content Editor Web Part pointing to UploadText.html, below:

<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.2.3/jquery.js"></script>

<input id="my-attachments" type="file" fileread="run.AttachmentData" fileinfo="run.AttachmentInfo" />

<script type="text/javascript" src="/sites/MySiteCollection/_catalogs/masterpage/_MyProject/js/UploadTEST.js"></script>

Like I said, I wanted to keep it simple. Here’s what I’m doing:

• In line 1, I load a recent version of jQuery from cdnjs. On the theory that Angular just adds another layer of complexity, I wanted to try just jQuery, which is useful for its $.ajax function, among many other things.
• In line 3, I’ve got an input field with type=”file”. In “modern” browsers, this gives us a familiar file picker.
• In line 5, I’m loading my script file called UploadTest.js, below:

$(document).ready(function() {

 var ID = 1;
 var listname = "UploadTEST";

 $("#my-attachments").change(function() {

  var file = $(this)[0].files[0];

  var getFileBuffer = function(file) {

   var deferred = $.Deferred();
   var reader = new FileReader();

   reader.onload = function(e) {
    deferred.resolve(e.target.result);
   }

   reader.onerror = function(e) {
    deferred.reject(e.target.error);
   }

   reader.readAsArrayBuffer(file);

   return deferred.promise();
  };

  getFileBuffer(file).then(function(buffer) {

   $.ajax({
    url: _spPageContextInfo.webAbsoluteUrl +
     "/_api/web/lists/getbytitle('" + listname + "')/items(" + ID + ")/AttachmentFiles/add(FileName='" + file.name + "')",
    method: 'POST',
    data: buffer,
    processData: false,
    headers: {
     "Accept": "application/json; odata=verbose",
     "content-type": "application/json; odata=verbose",
     "X-RequestDigest": document.getElementById("__REQUESTDIGEST").value,
     "content-length": buffer.byteLength
    }
   });

  });

 });
});

Here’s how this works – and yes, it does work!

• I’ve got everything wrapped in a $(document).ready() to ensure the page is fully loaded before my script runs.
• Lines 3-4 just set up some variables I could use for testing to keep things simple.
• In line 6, I bind to the change event for the input field. Whenever the user chooses a file in the dialog, this event will fire.
• In line 8, I’m getting the information about the file selected from the input element.
• Lines 10-26 is the same getFileBuffer function I used with SOAP; it’s where we use a FileReader to get the contents of the selected file into a buffer.
• The function in lines 28-42 runs when the file contents have been fully read. The getFileBuffer function returns a promise, and that promise is resolved when the function has gotten all of the file contents. With a large file, this could take a little while, and by using a promise we avoid getting ahead of ourselves. Here we make the REST call that uploads the attachment.
  • The URL ends up looking something like: “/my/site/path/_api/web/lists/getbytitle(‘UploadTEST’)/items(1)/AttachmentFiles/add(FileName=’boo.txt’)”
  • The method is a POST because we’re writing data to SharePoint
  • The data parameter contains the “payload”, which is the buffer returned from the getFileBuffer function.
  • The headers basically tell the server what we’re up to:
    • Accept doesn’t really come into play here unless we get a result back, but it says “send me back json and be verbose”
    • content-type is similar, but tells the server what it is getting from us
    • X-RequestDigest is the magic string from the page that tells the server we are who it thinks we are
    • content-length tells the server how many bytes it should expect

This worked for me on a basic Custom List (UploadTEST). So now I knew it was possible to upload an attachment using REST.

I took my logic and shoved it back into my AngularJS page, and it still worked! However, when I switched from $.ajax to AngularJS’s $http, I was back to corrupt files again. I’m still not sure why that is the case, but since I’m loading jQuery for some other things, anyway, I’ve decided to stick with $.ajax for now instead. If anyone reading this has an idea why $http would cause a problem, I’d love to hear about it.

Once again, I’m hoping my beating my head against this saves some folks some time. Ideally there would be actual documentation for the REST endpoints that would explain how to do things. Unfortunately, if there is for this, I can’t find it. I’d also love to know if /add allows any other parameters, particularly whether I can overwrite the attachment if one of the same name is already there. Maybe another day.