diff --git a/src/sink.h b/src/sink.h
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+/*
+  Copyright © 2018 Hasan Yavuz Özderya
+
+  This file is part of serialplot.
+
+  serialplot is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  serialplot is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with serialplot.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef SINK_H
+#define SINK_H
+
+#include <QList>
+#include "samplepack.h"
+
+class Source;
+
+class Sink
+{
+public:
+    /// Placeholder virtual destructor
+    virtual ~Sink() {};
+
+    /// Connects a sink to get any data that this sink
+    /// gets. Connecting an already connected sink is an error.
+    void connectFollower(Sink* sink);
+
+    /// Disconnects a follower. Disconnecting an unconnected sink is
+    /// an error.
+    void disconnectFollower(Sink* sink);
+
+    /// Returns the connected source. `nullptr` if it's not connected.
+    const Source* connectedSource() const;
+    Source* connectedSource();
+
+protected:
+    /// Entry point for incoming data. Re-implementations should
+    /// call this function to feed followers.
+    virtual void feedIn(const SamplePack& data);
+
+    /// Is set by connected source. Re-implementations should call
+    /// this function to update followers.
+    virtual void setNumChannels(unsigned nc, bool x);
+
+    /// Set by the connected source when its connected. When
+    /// disconnecting it's set to `nullptr`.
+    ///
+    /// @note Previous source is disconnected.
+    ///
+    /// @important Trying to connect a source while its already
+    /// connected is an error.
+    void setSource(Source* s);
+
+    friend Source;
+
+private:
+    QList<Sink*> followers;
+    Source* source = nullptr;   ///< source that this sink is connected to
+    bool _hasX;
+    unsigned _numChannels;
+};
+
+#endif // SINK_H