905 words (approximately 5 mins)

Overview

A stream is a sequence of bytes that can be read from and written to.

Streams involve three fundamental operations:

  • Read – The transfer of data from a stream into a data structure.
  • Write – The transfer or data from a data structure into a stream.
  • Seek – Querying and modifying the current position within a stream.

Depending on a stream’s underlying data source, a stream may only support some subset of these operations. This can be tested with CanRead, CanWrite, and CanSeek properties.

Overview of Types for Streams

See here.

Composing Streams [ Documentation] [ Documentation]

Stream is the abstract base class of all streams. All streams implement IDisposable.

A backing store is a storage medium such as disk or memory. Each backing store implements its own stream as an implementation of the Stream class.
A base stream is a stream that connect to a backing store. They have constructors with the necessary parameters to connect the stream to the backing store.

Base streams can be attached to one or more pass-through streams that provide specific functionality. In this example, the base stream is a FileStream and the pass-through stream is a StreamReader composed of that base stream:

using System;
using System.IO;

public class CompBuf
{
    private const string FILE_NAME = "MyFile.txt";

    public static void Main()
    {
        if (!File.Exists(FILE_NAME))
			throw new Exception();

        FileStream fsIn = new FileStream(FILE_NAME, FileMode.Open, FileAccess.Read, FileShare.Read);
        
		using (StreamReader sr = new StreamReader(fsIn))
        {
            string input;
            // While not at the end of the file, read lines from the file.
            while (sr.Peek() > -1)
            {
                input = sr.ReadLine();
                Console.WriteLine(input);
            }
        }
    }
}

Bit Bucket

A stream with no backing store. To create this, use the Null field to retrieve an instance of a stream.

Readers and Writers

The System.IO namespace contains types for reading encoded characters from and writing to streams. These types handle conversion of encoded characters to and from bytes. Each reader and writer class is associated with a stream accessible via its BaseStream property.

Helper ClassUse
BinaryReader and BinaryWriterReading and writing primitive data types as binary values
StreamReader and StreamWriterReading and writing characters by using an encoding value to convert the characters to/from bytes
StringReader and StringWriterReading and writing characters to/from strings
TextReader and TextWriterThe abstract base class for other readers and writers of text data (but not binary data)

Stream Helpers

StreamReader

A TextReader that reads characters (not bytes) from a stream in a particular encoding (like UTF-8).

  • Implements IDisposable.
  • Warning: Not thread safe. See TextReader.Synchronized.
StreamWriter tw = File.CreateText(PATH_TO_TEXT_FILE); // TextWriter
tw.WriteLine("*some text*");
tw.Close(); // Close the file and release resources.

StreamWriter

A TextWriter that writes characters (not bytes) from a stream in a particular encoding (like UTF-8).

  • Implements IDisposable.
  • Warning: Not thread safe. See TextWriter.Synchronized.
StreamReader tr = File.OpenText(PATH_TO_TEXT_FILE); // TextReader
WriteLine(tr.ReadToEnd());
tr.Close();

Writing to XML Streams

Use WriteStartElement and WriteEndElement when an element may have child elements.
Use WriteElementString when an element does not have children.

FileStream? xmlFileStream = null;
XMLWriter? xml = null;

using (xmlFileStream = File.Create(file.xml)) // The using statement automatically generates a finally statement
{							// that calls Dispose on any object that implements IDisposable.
	using (xml = XmlWriter.Create(xmlFileStream, // Wrap the file stream in an XML writer stream helper.
	  new XmlWriterSettings { Indent = true} ))  // Automatically indent nested elements.
	{
		try 
		{
			xml.WriteStartDocument(); // Write the XML declaration.
			
			xml.WriteStartElement("callsigns"); // Write a root element.
			xml.WriteElementString("callsign", "Maverick");
			xml.WriteElementString("callsign", "Iceman");
			
			xml.WriteEndElement(); // Write the close root element.
			
			xml.Close(); // Close the helper.
			xmlFileStream.Close(); // Close the file stream.
		}
		catch (Exception ex) {
			…
		}
	} // Automatically calls xml.Dispose() if the object is not null.
} // Automatically calls xmlFileStream.Dispose() if the object is not null.

Output:

<?xml version="1.0" encoding="utf-8"?>
<callsigns>
	<callsign>Maverick</callsign>
	<callsign>Iceman</callsign>
</callsigns>

Reading from XML Streams

using (XmlReader reader = XmlReader.Create(xmlFilestream))
{
	while (reader.Read()) // Read the nextXML node.
	{
		if ((reader.NodeType = XmlNodeType.Element) // Check if we are on an element node named "callsign".
		  && (read.Name == "callsign"))
		{
			reader.Read(); // Move to the text inside the element.
			Console.WriteLine($"{reader.Value}"); // Read this element's value.
		}
	}
}

Compressing Streams

using System.IO.Compression; // BrotliStream, GZipStream, CompressionMode 
// Performance-wise, Brotli is like GZip/Deflate but 20% denser.
FileStream file = File.Create(filePath);

Stream compressor = new GZipStream(file, CompressionMode.Compress); // Compress file.

using (compressor)
{
	using (XmlWriter xml = XmlWriter.Create(compressor))
	{
		xml.WriteStartDocument();
		xml.WriteStartElement("callsigns");
		xml.WriteElementString("callsign", "Maverick");
		xml.WriteElementString("callsign", "Iceman");
		
		// Due to the using statement on XmlWriter, the normal call to WriteEndElement is not necessary.  When
		// XmlWriter disposes, it will automatically end all elements of any depth.
	}
}

Encoding / Decoding Streams

Example

StreamReader r = new(stream, Encoding.Encoding); // Text will be decoded as bytes are read from the stream.
StreamWriter w = new(stream, Encoding.Encoding); // Text will be encoded as bytes are written to the stream.

ReadExactly and ReadAtLeast

Stream.Read() may return less data than what is available in the stream and less data than the buffer being passed in. ReadExactly and ReadAtLeast address this limitation.

ReadExactly

Guaranteed to read exactly the number of bytes requested:

using FileStream f = File.Open("readme.md");
byte[] buffer = new byte[100];
f.ReadExactly(buffer); // guaranteed to read 100 bytes from the file

ReadAtLeast

Guaranteed to read at least the number of bytes requested:

using FileStream f = File.Open("readme.md");
byte[] buffer = new byte[100];
int bytesRead = f.ReadAtLeast(buffer, 10);
// 10 <= bytesRead <= 10

Warning: Throws an EndOfStreamException if the stream ends before the requested bytes have been read.