jstedfast/MailKit · error · ArgumentOutOfRangeException

ArgumentOutOfRangeException

Error message

ArgumentOutOfRangeException

What it means

ValidateArguments guards DuplexStream.Read/ReadAsync/Write/WriteAsync. It throws ArgumentOutOfRangeException when offset is negative or beyond buffer.Length, or when count is negative or exceeds buffer.Length - offset. It ensures read/write operations never access memory outside the supplied buffer.

Solutions

1. Clamp or validate offset and count against buffer.Length before the call: 0 <= offset <= buffer.Length and 0 <= count <= buffer.Length - offset.
2. Fix the arithmetic that computes offset/count (check for subtraction underflow producing negatives).
3. If values come from external input, validate them at the boundary with a clear error message.

Example fix

// before
stream.Read (buffer, offset, count);
// after
if (offset < 0 || offset > buffer.Length) throw new ArgumentException (nameof (offset));
if (count < 0 || count > buffer.Length - offset) throw new ArgumentException (nameof (count));
stream.Read (buffer, offset, count);

static bool IsValidWindow (byte[] buffer, int offset, int count) =>
    buffer != null && offset >= 0 && offset <= buffer.Length && count >= 0 && count <= buffer.Length - offset;

bool ValidBufferArgs (byte[] b, int off, int cnt) => b != null && off >= 0 && off <= b.Length && cnt >= 0 && cnt <= b.Length - off;

try { stream.Read (buffer, offset, count); } catch (ArgumentOutOfRangeException ex) { /* log ex.ParamName: offset or count */ }

When it happens

Trigger: Calling Read/Write (or their async forms) on a DuplexStream with a negative offset, offset > buffer.Length, negative count, or count > buffer.Length - offset.

Common situations: Off-by-one buffer math; reusing buffer-size constants after changing buffer allocation; passing a user-supplied offset/count straight through without clamping.

Related errors

• ObjectDisposedException
• NotSupportedException
• Specified argument was out of range of valid values…
• Specified argument was out of range of valid values…
• arrayIndex

AI-assisted analysis of jstedfast/MailKit@9d3859a785 (2026-09-15). Data as JSON: /api/errors/b99049be3f9f45e4. Report an issue: GitHub.

Appendix: source

Thrown at MailKit/DuplexStream.cs:164

		/// <returns>A long value representing the length of the stream in bytes.</returns>
		/// <value>The length of the stream.</value>
		/// <exception cref="System.NotSupportedException">
		/// The stream does not support seeking.
		/// </exception>
		public override long Length {
			get { throw new NotSupportedException (); }
		}

		static void ValidateArguments (byte[] buffer, int offset, int count)
		{
			if (buffer == null)
				throw new ArgumentNullException (nameof (buffer));

			if (offset < 0 || offset > buffer.Length)
				throw new ArgumentOutOfRangeException (nameof (offset));

			if (count < 0 || count > (buffer.Length - offset))
				throw new ArgumentOutOfRangeException (nameof (count));
		}

		void CheckDisposed ()
		{
			if (disposed)
				throw new ObjectDisposedException (nameof (DuplexStream));
		}

		/// <summary>
		/// Reads a sequence of bytes from the stream and advances the position
		/// within the stream by the number of bytes read.
		/// </summary>
		/// <returns>The total number of bytes read into the buffer. This can be less than the number of bytes requested if that many
		/// bytes are not currently available, or zero (0) if the end of the stream has been reached.</returns>
		/// <param name="buffer">The buffer.</param>
		/// <param name="offset">The buffer offset.</param>
		/// <param name="count">The number of bytes to read.</param>
		/// <exception cref="System.ArgumentNullException">

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