Implementing a WebDAV Client in .NET

In a project I had to download files from a Nextcloud. I decided to use WebDAV, as it also allows to switch to another file cloud solution in the future.

I didn’t found a nice WebDAV package on NuGET, so I decided to implement the WebDAV by myself. And honestly? It is really no big deal.

tl;dr: The C# code can be found on my GitHub.

Basic Usage

It’s just a single HTTP Request where the URL decides which file or folder is queried. Downloading a file with a GET request just works. If a folder content should be listed, the not so usual PROPFIND request has to be used.

propfind.txt:

<?xml version="1.0"?>
<d:propfind xmlns:d="DAV:">
    <d:prop>
        <d:resourcetype/>
        <d:getlastmodified/>
        <d:getcontentlength/>
        <d:getcontenttype/>
        <d:resourcetype/>
        <d:getetag/>
    </d:prop>
</d:propfind>

Depending on the WebDAV Server, there are different elements supported in the <d:prop> list. This list was made using the Nextcloud documentation.

Request:

curl -v \
    --user user:apppassword \
    -X PROPFIND \
    -H "Depth: 1"
    --data @propfind.txt \
    "https://cloud.example.com/remote.php/dav/files/user/"

Simplified Response:

<?xml version="1.0"?>
<d:multistatus>
    <d:response>
        <d:href>/remote.php/dav/files/test2.png</d:href>
        <d:propstat>
            <d:prop>
                <d:resourcetype/>
                <d:getlastmodified>Thu, 01 Jun 2023 08:56:36 GMT</d:getlastmodified>
                <d:getcontentlength>300234</d:getcontentlength>
                <d:getcontenttype>image/png</d:getcontenttype>
                <d:getetag>&quot;33cc1e16c5b589e9476e7ff81a7bcacc&quot;</d:getetag>
            </d:prop>
            <d:status>HTTP/1.1 200 OK</d:status>
        </d:propstat>
    </d:response>
</d:multistatus>

The list contains all files and folders. The Depth header controls how many levels should be included in the response.

Bonus: Check if file was modified

When the files are cached somewhere in the .NET application, it is maybe interesting to check if the original file was changed. Depending on the WebDAV Server, this is possible by using the ETag/If-None-Match mechanic:

curl -v \
    --user user:apppassword \
    -H "If-None-Match: \"4b1f2c01dda174d60dfdc2d203d78c1a\"" \
    "https://cloud.example.com/remote.php/dav/files/user/test2.png"

Every GET/HEAD request returns an ETag header, which contains the checksum for the requested resource. This has to be stored somehow in the .NET application. As soon as a check if the file was modified must be done, the request above can be sent.

If the file was modified, the server will return the content of that file. If not, the server will respond with a status 304 Not Modified with no body.

The Code

https://github.com/perryflynn/perrys-webdav-client