Upload file content from API to sharepoint list item attachment

Question

So I'm trying to upload a file, or multiple files, to a sharepoint as attachments to a list item. I have the code to upload the actual files but they're corrupt/unopenable when trying to access them in sharepoint.

I receive these files from an outside API in the form of:

{
    "File": {
        "contentType": ~~~~
        "fileContent": ~~~~
        "name": ~~~~.docx/.pdf
    }
}

I currently am trying to upload it like this:

spClient.DefaultRequestHeaders.Add("Accept", "application/json;odata=verbose");

foreach (var file in data["files"])
{
    var requestString = $"{siteUrl}/lists('{listID}')/items('{siteResponseObject["id"]}')/AttachmentFiles/add(FileName='{file["File"]["name"]}')";
    StringContent filePostData = new StringContent(file["File"]["fileContent"].ToString(), Encoding.UTF8, file["File"]["contentType"].ToString());
    var filePost = await spClient.PostAsync(requestString, filePostData);
}

The contentType of each file varies, while testing for example, I get back these file types:

application/vnd.openxmlformats-officedocument.spreadsheetml.sheet
application/vnd.openxmlformats-officedocument.wordprocessingml.document
application/pdf

siteResponseObject is the response from creating the listItem which contains it's ID and everything.

Does the sharepoint API expect to like a byte array? Am I encoding the StringContent object wrong?

Dmitry Kozlov · Accepted Answer · 2019-09-12 15:05:05Z

1

Most likely, you receive the fileContent as base64 string from the external service. So first, you must convert it into a stream and then post the stream in the body:

spClient.DefaultRequestHeaders.Add("Accept", "application/json;odata=verbose");

foreach (var file in data["files"])
{
    var bytes = Convert.FromBase64String(file["File"]["fileContent"]);
    var content = new StreamContent(new MemoryStream(bytes));

    var requestString = $"{siteUrl}/lists('{listID}')/items('{siteResponseObject["id"]}')/AttachmentFiles/add(FileName='{file["File"]["name"]}')";
    var filePost = await spClient.PostAsync(requestString, content);
}

answered Sep 12, 2019 at 15:05

Dmitry Kozlov

1,4988 silver badges13 bronze badges

That worked perfectly. Thank you.

KFrancis
– KFrancis

2019-09-12 16:57:01 +00:00
Commented Sep 12, 2019 at 16:57

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