Specified method is not supported while using SeekOrigin.Begin on stream

Question

I have a StreamReader which I am using to deserialize my request later on as shown below -

Here s is Stream object -

using (var reader = new StreamReader(s))
{
    using (var jsonReader = new JsonTextReader(reader))
    {
        var ser = new JsonSerializer();
        return ser.Deserialize<T>(jsonReader);
    }
}

Everything works fine but now I am trying to print the actual request body on the console so I tried like this but it gives me an error -

using (var reader = new StreamReader(s))
{
    string body = reader.ReadToEnd();
    // print body on the console which is what I am trying to do
    // reset to start of stream
    // this line gives me error
    s.Seek(0, SeekOrigin.Begin);
    using (var jsonReader = new JsonTextReader(reader))
    {
        var ser = new JsonSerializer();
        return ser.Deserialize<T>(jsonReader);
    }
}

After this change, I am getting an error as - Specified method is not supported. I am not sure what wrong I am doing here.

Note: This is just for debugging purpose only that I want to print the body on console. After that I will remove reader.ReadToEnd(); stuff.

If you've already read the stream content in `body`, why don't you deserialize this string instead of reading the stream again? — Marco, Jun 08 '21 at 21:29
I am just trying to print the request body as a string on the console which is coming to this method so I came up with this quick way before it can be deserialized. I didn't realize we can that too. My main idea is to print the request body as a string on console and also deserialize it the way it is doing currently. — AndyP, Jun 08 '21 at 21:31
It's a nonsense: either you deserialize the stream OR you read the whole stream content and deserialize the string. Reading the stream twice is a waste of resources IMHO — Marco, Jun 08 '21 at 21:32
From the help on this exception: The stream does not support seeking, such as if the stream is constructed from a pipe or console output. So it looks like you will need to change your approach or construct the stream so it supports Seek() method. [link](https://learn.microsoft.com/en-us/dotnet/api/system.io.stream.seek?view=net-5.0) — David Glass, Jun 08 '21 at 21:33
This is just for debugging purpose only. After that I will remove `reader.ReadToEnd();` stuff. — AndyP, Jun 08 '21 at 21:34

score 5 · Accepted Answer · answered Jun 08 '21 at 21:35

Not all streams support seeking. Stream has the CanSeek property, which is probably false in this case.

In this specific case, since you're reading the whole message into a string anyway, you can create a StringReader from the string and pass that into JsonTextReader instead of the StreamReader.

In other cases, you may need to find a different solution. For example, if you're reading an ASP.NET Core request stream, you can enable buffering to allow the stream to be read multiple times.

Specified method is not supported while using SeekOrigin.Begin on stream

1 Answers1