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diff --git a/src/lib/asiolink/io_socket.h b/src/lib/asiolink/io_socket.h
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+// Copyright (C) 2010-2017 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef IO_SOCKET_H
+#define IO_SOCKET_H 1
+
+// IMPORTANT NOTE: only very few ASIO headers files can be included in
+// this file.  In particular, asio.hpp should never be included here.
+// See the description of the namespace below.
+#include <unistd.h>             // for some network system calls
+
+#include <functional>
+#include <string>
+
+#include <exceptions/exceptions.h>
+
+namespace isc {
+namespace asiolink {
+
+/// \brief The \c IOSocket class is an abstract base class to represent
+/// various types of network sockets.
+///
+/// This class is a wrapper for the ASIO socket classes such as
+/// \c ip::tcp::socket and \c ip::udp::socket.
+///
+/// Derived class implementations are completely hidden within the
+/// implementation.  User applications only get access to concrete
+/// \c IOSocket objects via the abstract interfaces.
+///
+/// We may revisit this decision when we generalize the wrapper and more
+/// modules use it.  Also, at that point we may define a separate (visible)
+/// derived class for testing purposes rather than providing factory methods
+/// (i.e., getDummy variants below).
+class IOSocket {
+public:
+
+    /// @name Types of objects encapsulating socket options.
+    //@{
+
+    /// @brief Represents SO_REUSEADDR socket option.
+    typedef boost::asio::socket_base::reuse_address ReuseAddress;
+
+    //@}
+
+    ///
+    /// \name Constructors and Destructor
+    ///
+    /// Note: The copy constructor and the assignment operator are
+    /// intentionally defined as private, making this class non-copyable.
+    //@{
+private:
+    IOSocket(const IOSocket& source);
+    IOSocket& operator=(const IOSocket& source);
+protected:
+    /// \brief The default constructor.
+    ///
+    /// This is intentionally defined as \c protected as this base class
+    /// should never be instantiated (except as part of a derived class).
+    IOSocket() {}
+public:
+    /// The destructor.
+    virtual ~IOSocket() {}
+    //@}
+
+    /// \brief Return the "native" representation of the socket.
+    ///
+    /// In practice, this is the file descriptor of the socket for
+    /// UNIX-like systems so the current implementation simply uses
+    /// \c int as the type of the return value.
+    /// We may have to need revisit this decision later.
+    ///
+    /// In general, the application should avoid using this method;
+    /// it essentially discloses an implementation specific "handle" that
+    /// can change the internal state of the socket (consider the
+    /// application closes it, for example).
+    /// But we sometimes need to perform very low-level operations that
+    /// requires the native representation.  Passing the file descriptor
+    /// to a different process is one example.
+    /// This method is provided as a necessary evil for such limited purposes.
+    ///
+    /// This method never throws an exception.
+    ///
+    /// \return The native representation of the socket.  This is the socket
+    /// file descriptor for UNIX-like systems.
+    virtual int getNative() const = 0;
+
+    /// \brief Return the transport protocol of the socket.
+    ///
+    /// Currently, it returns \c IPPROTO_UDP for UDP sockets, and
+    /// \c IPPROTO_TCP for TCP sockets.
+    ///
+    /// This method never throws an exception.
+    ///
+    /// \return IPPROTO_UDP for UDP sockets
+    /// \return IPPROTO_TCP for TCP sockets
+    virtual int getProtocol() const = 0;
+
+    /// \brief Return a non-usable "dummy" UDP socket for testing.
+    ///
+    /// This is a class method that returns a "mock" of UDP socket.
+    /// This is not associated with any actual socket, and its only
+    /// responsibility is to return \c IPPROTO_UDP from \c getProtocol().
+    /// The only feasible usage of this socket is for testing so that
+    /// the test code can prepare some "UDP data" even without opening any
+    /// actual socket.
+    ///
+    /// This method never throws an exception.
+    ///
+    /// \return A reference to an \c IOSocket object whose \c getProtocol()
+    /// returns \c IPPROTO_UDP.
+    static IOSocket& getDummyUDPSocket();
+
+    /// \brief Return a non-usable "dummy" TCP socket for testing.
+    ///
+    /// See \c getDummyUDPSocket().  This method is its TCP version.
+    ///
+    /// \return A reference to an \c IOSocket object whose \c getProtocol()
+    /// returns \c IPPROTO_TCP.
+    static IOSocket& getDummyTCPSocket();
+};
+
+} // namespace asiolink
+} // namespace isc
+
+#endif // IO_SOCKET_H