dotnet/maui · error · NotSupportedException

The streams can't be read for comparison

Error message

The streams can't be read for comparison

What it means

The AreStreamsEqual utility compares two streams byte-for-byte but first checks that both CanRead. If either stream cannot be read, it throws NotSupportedException because the comparison is impossible. This is a precondition guard, not a recoverable runtime fault.

Source

Thrown at src/Compatibility/Core/src/WPF/Microsoft.Windows.Shell/Standard/Utilities.cs:166

			return (short)(i & 0xFFFF);
		}

		[SuppressMessage("Microsoft.Performance", "CA1811:AvoidUncalledPrivateCode")]
		[SuppressMessage("Microsoft.Security", "CA2122:DoNotIndirectlyExposeMethodsWithLinkDemands")]
		public static bool AreStreamsEqual(Stream left, Stream right)
		{
			if (null == left)
			{
				return right == null;
			}
			if (null == right)
			{
				return false;
			}

			if (!left.CanRead || !right.CanRead)
			{
				throw new NotSupportedException("The streams can't be read for comparison");
			}

			if (left.Length != right.Length)
			{
				return false;
			}

			var length = (int)left.Length;

			// seek to beginning
			left.Position = 0;
			right.Position = 0;

			// total bytes read
			int totalReadLeft = 0;
			int totalReadRight = 0;

			// bytes read on this iteration

View on GitHub (pinned to f377ff1c5e)

Solutions

1. Verify left.CanRead && right.CanRead before calling AreStreamsEqual.
2. Open file streams with FileAccess.Read or ReadWrite when they will be compared.
3. If comparing data, copy both streams into MemoryStreams first if read access is uncertain.

Example fix

// before
bool same = Utilities.AreStreamsEqual(left, right);

// after
if (!left.CanRead || !right.CanRead)
{
    throw new InvalidOperationException("Both streams must be readable for comparison.");
}
bool same = Utilities.AreStreamsEqual(left, right);

// Before comparing streams
if (left == null || right == null)
{
    // null comparison is valid in AreStreamsEqual (null == null is true)
}
if (left != null && right != null && (!left.CanRead || !right.CanRead))
{
    throw new InvalidOperationException("Both streams must be readable for comparison.");
}
bool equal = Utilities.AreStreamsEqual(left, right);

When it happens

Trigger: Calling Utilities.AreStreamsEqual(left, right) where left.CanRead or right.CanRead is false — e.g. passing a write-only FileStream or a closed stream whose CanRead has become false.

Common situations: Comparing a stream that was opened with write-only access; passing a stream that was already disposed (some implementations report CanRead=false after Close); comparing against a network stream whose read side has been shut down.

Related errors

• The stream doesn't support modifications.
• Bad value for origin
• Invalid enumeration value
• No file exists at "{0}"
• Unexpected platform (expected: android) in device: {deviceDe

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/384f9dd9fb81918e. Report an issue: GitHub.