How do I generate a stream from a string?

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I need to write a unit test for a method that takes a stream which comes from a text file. I would like to do do something like this:

Stream s = GenerateStreamFromString("a,b \n c,d");
unit-testing stream string c#
12 Answers

If you need to change the encoding I vote for @ShaunBowe's solution. But every answer here copies the whole string in memory at least once. The answers with ToCharArray + BlockCopy combo do it twice.

If that matters here is a simple Stream wrapper for the raw UTF-16 string. If used with a StreamReader select Encoding.Unicode for it:

public class StringStream : Stream
{
    private readonly string str;

    public override bool CanRead => true;
    public override bool CanSeek => true;
    public override bool CanWrite => false;
    public override long Length => str.Length * 2;
    public override long Position { get; set; } // TODO: bounds check

    public StringStream(string s) => str = s ?? throw new ArgumentNullException(nameof(s));

    public override long Seek(long offset, SeekOrigin origin)
    {
        switch (origin)
        {
            case SeekOrigin.Begin:
                Position = offset;
                break;
            case SeekOrigin.Current:
                Position += offset;
                break;
            case SeekOrigin.End:
                Position = Length - offset;
                break;
        }

        return Position;
    }

    private byte this[int i] => (i & 1) == 0 ? (byte)(str[i / 2] & 0xFF) : (byte)(str[i / 2] >> 8);

    public override int Read(byte[] buffer, int offset, int count)
    {
        // TODO: bounds check
        var len = Math.Min(count, Length - Position);
        for (int i = 0; i < len; i++)
            buffer[offset++] = this[(int)(Position++)];
        return (int)len;
    }

    public override int ReadByte() => Position >= Length ? -1 : this[(int)Position++];
    public override void Flush() { }
    public override void SetLength(long value) => throw new NotSupportedException();
    public override void Write(byte[] buffer, int offset, int count) => throw new NotSupportedException();
    public override string ToString() => str; // ;)     
}

And here is a more complete solution with necessary bound checks (derived from MemoryStream so it has ToArray and WriteTo methods as well).

user_51147840
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