YamlDotNet "Expected 'StreamEnd', got 'DocumentStart'"when reading string - yaml

Question

I'm using YamlDotNet with an Azure Function v2 to serialise YAML from a markdown file (hosted on GitHub) to a .net object. I'm struggling with this error when attempting to deserialize the YAML string
Expected 'StreamEnd', got 'DocumentStart
I'm getting the markdown file content using HttpClient with a GET request to https://github.com/martinkearn/Content/raw/fd83bf8218b7c5e01f8b498e8a831bcd3fc3c961/Blogs/Test.md which returns a raw markdown file in the response body.
My Model is
public class Article
{
public string Title { get; set; }
public string Author { get; set; }
public List<string> Categories { get; set; }
}
My YAML is
---
title: Test File
author: Martin Kearn
categories:
- Test
- GitHubCMS
- One More Tag
- another tag
---
Here is my code
// get url from request body
var url = "https://raw.githubusercontent.com/martinkearn/Content/fd83bf8218b7c5e01f8b498e8a831bcd3fc3c961/Blogs/Test.md";
// get raw file and extract YAML
using (var client = new HttpClient())
{
//setup HttpClient
client.BaseAddress = new Uri(url);
client.DefaultRequestHeaders.Add("User-Agent", "ExtractYAML Function");
//setup httpContent object
var response = await client.GetAsync(url);
string rawFile = await response.Content.ReadAsStringAsync();
using (var r = new StringReader(rawFile))
{
var deserializer = new DeserializerBuilder()
.WithNamingConvention(new CamelCaseNamingConvention())
.Build();
//This line is causing Expected 'StreamEnd', got 'DocumentStart'
var article = deserializer.Deserialize<Article>(r);
}
}

Answer 1

Your actual downloaded file contains:
---
title: Test File
author: Martin Kearn
categories:
- Test
- GitHubCMS
- One More Tag
- another tag
---
# Test file
The --- is the end-of-directives marker, which is optional if you don't have any directives ( %YAML 1.2, %TAG .... ).
Since you have an empty line after the second directive, this is counted as if your second document contained
---
null
# Test file
You should at least get rid of that empty line and possible remove the second end-of-directives marker, putting the comment at the end of the first document
The end-of-document indicator in YAML is ... at the beginning of a line.
Make your file read:
title: Test File
author: Martin Kearn
categories:
- Test
- GitHubCMS
- One More Tag
- another tag
# Test file
or at most:
---
title: Test File
author: Martin Kearn
categories:
- Test
- GitHubCMS
- One More Tag
- another tag
# Test file