Atomically read the first token of a line when in the IDLE state

atomic.patch

diff --git a/MailKit/Net/Imap/ImapCommand.cs b/MailKit/Net/Imap/ImapCommand.cs
index 3d9f2b6..f6d9160 100644
--- a/MailKit/Net/Imap/ImapCommand.cs
+++ b/MailKit/Net/Imap/ImapCommand.cs
@@ -500,7 +500,7 @@ namespace MailKit.Net.Imap {
 					try {
 						Engine.Stream.ReadTimeout = -1;
 
-						token = Engine.ReadToken (idle.LinkedToken);
+						token = Engine.AtomicReadToken (idle.LinkedToken);
 						Engine.Stream.ReadTimeout = timeout;
 					} catch (OperationCanceledException) {
 						Engine.Stream.ReadTimeout = timeout;
diff --git a/MailKit/Net/Imap/ImapEngine.cs b/MailKit/Net/Imap/ImapEngine.cs
index e7c90e4..4b411c8 100644
--- a/MailKit/Net/Imap/ImapEngine.cs
+++ b/MailKit/Net/Imap/ImapEngine.cs
@@ -640,6 +640,28 @@ namespace MailKit.Net.Imap {
 		}
 
 		/// <summary>
+		/// Reads the next token atomically.
+		/// </summary>
+		/// <returns>The token.</returns>
+		/// <param name="cancellationToken">The cancellation token.</param>
+		/// <exception cref="System.InvalidOperationException">
+		/// The engine is not connected.
+		/// </exception>
+		/// <exception cref="System.OperationCanceledException">
+		/// The operation was canceled via the cancellation token.
+		/// </exception>
+		/// <exception cref="System.IO.IOException">
+		/// An I/O error occurred.
+		/// </exception>
+		/// <exception cref="ImapProtocolException">
+		/// An IMAP protocol error occurred.
+		/// </exception>
+		public ImapToken AtomicReadToken (CancellationToken cancellationToken)
+		{
+			return Stream.AtomicReadToken (cancellationToken);
+		}
+
+		/// <summary>
 		/// Peeks at the next token.
 		/// </summary>
 		/// <returns>The next token.</returns>
diff --git a/MailKit/Net/Imap/ImapStream.cs b/MailKit/Net/Imap/ImapStream.cs
index db1dc2c..f81a5dd 100644
--- a/MailKit/Net/Imap/ImapStream.cs
+++ b/MailKit/Net/Imap/ImapStream.cs
@@ -491,7 +491,7 @@ namespace MailKit.Net.Imap {
 			}
 		}
 
-		unsafe string ReadAtomString (byte* inbuf, bool flag, string specials, CancellationToken cancellationToken)
+		unsafe string ReadAtomString (byte* inbuf, string specials, bool atomic, bool flag, CancellationToken cancellationToken)
 		{
 			var builder = new StringBuilder ();
 			byte* inptr = inbuf + inputIndex;
@@ -512,7 +512,10 @@ namespace MailKit.Net.Imap {
 				if (inptr < inend)
 					break;
 
-				inputIndex = (int) (inptr - inbuf);
+				if (!atomic)
+					inputIndex = (int) (inptr - inbuf);
+				else
+					builder.Clear ();
 
 				ReadAhead (1, cancellationToken);
 
@@ -525,9 +528,9 @@ namespace MailKit.Net.Imap {
 			return builder.ToString ();
 		}
 
-		unsafe ImapToken ReadAtomToken (byte* inbuf, string specials, CancellationToken cancellationToken)
+		unsafe ImapToken ReadAtomToken (byte* inbuf, string specials, bool atomic, CancellationToken cancellationToken)
 		{
-			var atom = ReadAtomString (inbuf, false, specials, cancellationToken);
+			var atom = ReadAtomString (inbuf, specials, atomic, false, cancellationToken);
 
 			return atom == "NIL" ? new ImapToken (ImapTokenType.Nil, atom) : new ImapToken (ImapTokenType.Atom, atom);
 		}
@@ -536,7 +539,7 @@ namespace MailKit.Net.Imap {
 		{
 			inputIndex++;
 
-			var flag = "\\" + ReadAtomString (inbuf, true, AtomSpecials, cancellationToken);
+			var flag = "\\" + ReadAtomString (inbuf, AtomSpecials, false, true, cancellationToken);
 
 			return new ImapToken (ImapTokenType.Flag, flag);
 		}
@@ -638,6 +641,7 @@ namespace MailKit.Net.Imap {
 		/// </summary>
 		/// <returns>The token.</returns>
 		/// <param name="specials">A list of characters that are not legal in bare string tokens.</param>
+		/// <param name="atomic"><value>true</value> if atom tokens should be read atomically; otherwise, <value>false</value>.</param>
 		/// <param name="cancellationToken">The cancellation token.</param>
 		/// <exception cref="System.ObjectDisposedException">
 		/// The stream has been disposed.
@@ -648,7 +652,7 @@ namespace MailKit.Net.Imap {
 		/// <exception cref="System.IO.IOException">
 		/// An I/O error occurred.
 		/// </exception>
-		public ImapToken ReadToken (string specials, CancellationToken cancellationToken)
+		public ImapToken ReadToken (string specials, bool atomic, CancellationToken cancellationToken)
 		{
 			CheckDisposed ();
 
@@ -696,7 +700,7 @@ namespace MailKit.Net.Imap {
 						return ReadFlagToken (inbuf, cancellationToken);
 
 					if (c != '+' && IsAtom (*inptr, specials))
-						return ReadAtomToken (inbuf, specials, cancellationToken);
+						return ReadAtomToken (inbuf, specials, atomic, cancellationToken);
 
 					// special character token
 					inputIndex++;
@@ -710,6 +714,26 @@ namespace MailKit.Net.Imap {
 		/// Reads the next available token from the stream.
 		/// </summary>
 		/// <returns>The token.</returns>
+		/// <param name="specials">A list of characters that are not legal in bare string tokens.</param>
+		/// <param name="cancellationToken">The cancellation token.</param>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The stream has been disposed.
+		/// </exception>
+		/// <exception cref="System.OperationCanceledException">
+		/// The operation was canceled via the cancellation token.
+		/// </exception>
+		/// <exception cref="System.IO.IOException">
+		/// An I/O error occurred.
+		/// </exception>
+		public ImapToken ReadToken (string specials, CancellationToken cancellationToken)
+		{
+			return ReadToken (specials, false, cancellationToken);
+		}
+
+		/// <summary>
+		/// Reads the next available token from the stream.
+		/// </summary>
+		/// <returns>The token.</returns>
 		/// <param name="cancellationToken">The cancellation token.</param>
 		/// <exception cref="System.ObjectDisposedException">
 		/// The stream has been disposed.
@@ -722,7 +746,26 @@ namespace MailKit.Net.Imap {
 		/// </exception>
 		public ImapToken ReadToken (CancellationToken cancellationToken)
 		{
-			return ReadToken (AtomSpecials, cancellationToken);
+			return ReadToken (AtomSpecials, false, cancellationToken);
+		}
+
+		/// <summary>
+		/// Reads the next available token from the stream atomically.
+		/// </summary>
+		/// <returns>The token.</returns>
+		/// <param name="cancellationToken">The cancellation token.</param>
+		/// <exception cref="System.ObjectDisposedException">
+		/// The stream has been disposed.
+		/// </exception>
+		/// <exception cref="System.OperationCanceledException">
+		/// The operation was canceled via the cancellation token.
+		/// </exception>
+		/// <exception cref="System.IO.IOException">
+		/// An I/O error occurred.
+		/// </exception>
+		public ImapToken AtomicReadToken (CancellationToken cancellationToken)
+		{
+			return ReadToken (AtomSpecials, true, cancellationToken);
 		}
 
 		/// <summary>