C#idiomatic C#
ca2024fundamentals/code-analysis/quality-rules

Code analysis

CA2024: Do not use StreamReader.EndOfStream in async methods

Learn about code analysis rule CA2024 - Do not use StreamReader.EndOfStream in async methods

CA2024 Reliability enabled by default in .NET 10: As warning
Fix is breaking or non-breaking Non-breakingApplicable languages C# and Visual Basic

Cause

A call to System.IO.StreamReader.EndOfStream is made inside an async method.

Rule description

The property System.IO.StreamReader.EndOfStream can cause unintended synchronous blocking when no data is buffered. Instead, use System.IO.StreamReader.ReadLineAsync directly, which returns null when reaching the end of the stream.

How to fix violations

To fix a violation, directly call System.IO.StreamReader.ReadLineAsync and check the return value for null.

Example

The following code snippet shows a violation of CA2024:

csharp
public async Task Example(StreamReader streamReader)
{
    while (!streamReader.EndOfStream)
    {
        string? line = await streamReader.ReadLineAsync();
        // Do something with line.
    }
}
vb
Public Async Function Example(streamReader As StreamReader) As Task
    While Not streamReader.EndOfStream
        Dim line As String = Await streamReader.ReadLineAsync()
        ' Do something with line.
    End While
End Function

The following code snippet fixes the violation:

csharp
public async Task Example(StreamReader streamReader)
{
    string? line;
    while ((line = await streamReader.ReadLineAsync()) is not null)
    {
        // Do something with line.
    }
}
vb
Public Async Function Example(streamReader As StreamReader) As Task
    Dim line As String = Await streamReader.ReadLineAsync()
    While line IsNot Nothing
        ' Do something with line.
        line = Await streamReader.ReadLineAsync()
    End While
End Function

When to suppress warnings

You shouldn't suppress warnings from this rule, as your app might hang if you don't fix the violations.

Suppress a warning

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

csharp
#pragma warning disable CA2024
// The code that's violating the rule is on this line.
#pragma warning restore CA2024

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

ini
[*.{cs,vb}]
dotnet_diagnostic.CA2024.severity = none

For more information, see How to suppress code analysis warnings.