Move common utility classes to wpiutil library. (#79)

This is a breaking change to dependencies that use the static ntcore
library.  Unless the wpiutil library is also linked, linker errors will
result.  This does not affect the shared ntcore library.

include/tcpsockets/NetworkStream.h

@@ -0,0 +1,43 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2015. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#ifndef WPIUTIL_TCPSOCKETS_NETWORKSTREAM_H_
+#define WPIUTIL_TCPSOCKETS_NETWORKSTREAM_H_
+
+#include <cstddef>
+
+#include "llvm/StringRef.h"
+
+namespace wpi {
+
+class NetworkStream {
+ public:
+  NetworkStream() = default;
+  virtual ~NetworkStream() = default;
+
+  enum Error {
+    kConnectionClosed = 0,
+    kConnectionReset = -1,
+    kConnectionTimedOut = -2
+  };
+
+  virtual std::size_t send(const char* buffer, std::size_t len, Error* err) = 0;
+  virtual std::size_t receive(char* buffer, std::size_t len, Error* err,
+                              int timeout = 0) = 0;
+  virtual void close() = 0;
+
+  virtual llvm::StringRef getPeerIP() const = 0;
+  virtual int getPeerPort() const = 0;
+  virtual void setNoDelay() = 0;
+
+  NetworkStream(const NetworkStream&) = delete;
+  NetworkStream& operator=(const NetworkStream&) = delete;
+};
+
+}  // namespace wpi
+
+#endif  // WPIUTIL_TCPSOCKETS_NETWORKSTREAM_H_