CryptoStream.ReadAsync Method (Byte[], Int32, Int32, CancellationToken)

.NET Framework (current version)

Reads a sequence of bytes from the current stream asynchronously, advances the position within the stream by the number of bytes read, and monitors cancellation requests.

Namespace:   System.Security.Cryptography
Assembly:  mscorlib (in mscorlib.dll)

public override Task<int> ReadAsync(
	byte[] buffer,
	int offset,
	int count,
	CancellationToken cancellationToken


Type: System.Byte[]

The buffer to write the data into.

Type: System.Int32

The byte offset in buffer at which to begin writing data from the stream.

Type: System.Int32

The maximum number of bytes to read.

Type: System.Threading.CancellationToken

The token to monitor for cancellation requests. The default value is None.

Return Value

Type: System.Threading.Tasks.Task<Int32>

A task that represents the asynchronous read operation. The value of the task object's TResult parameter contains the total number of bytes read into the buffer. The result can be less than the number of bytes requested if the number of bytes currently available is less than the requested number, or it can be 0 (zero) if the end of the stream has been reached.

Exception Condition

buffer is null.


offset or count is negative.


The sum of offset and count is larger than the buffer length.


The stream does not support reading.


The stream has been disposed.


The stream is currently in use by a previous read operation.

You must preface your call to ReadAsync with the await (C#) or Await (Visual Basic) operator to suspend execution of the method until the task is complete. For more information, see Asynchronous Programming with Async and Await (C# and Visual Basic).

If the operation is canceled before it completes, the returned task contains the Canceled value for the Status property.

.NET Framework
Available since 4.5
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