fastboot: socket testing improvements.

(This code was originally part of a huge fastboot CL but has been split
out to try to make the CLs a little more manageable).

More prep for fastboot TCP and UDP implementations. This CL adds a
SocketMock class that makes it easy to mock out network behavior so we
can unit test the TCP and UDP protocols.

Also uses the new libcutils socket_get_local_port() to avoid hardcoding
a server port in unit tests.

Bug: http://b/26157893.
Change-Id: I1ba10f31e98d7349313fc15f240383d63378a8db
diff --git a/fastboot/socket_mock.h b/fastboot/socket_mock.h
new file mode 100644
index 0000000..3e62b33
--- /dev/null
+++ b/fastboot/socket_mock.h
@@ -0,0 +1,97 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef SOCKET_MOCK_H_
+#define SOCKET_MOCK_H_
+
+#include <memory>
+#include <queue>
+#include <string>
+
+#include <android-base/macros.h>
+
+#include "socket.h"
+
+// A mock Socket implementation to be used for testing. Tests can set expectations for messages
+// to be sent and provide messages to be received in order to verify protocol behavior.
+//
+// Example: testing sending "foo" and receiving "bar".
+//   SocketMock mock;
+//   mock.ExpectSend("foo");
+//   mock.AddReceive("bar");
+//   EXPECT_TRUE(DoFooBar(&mock));
+//
+// Example: testing sending "foo" and expecting "bar", but receiving "baz" instead.
+//   SocketMock mock;
+//   mock.ExpectSend("foo");
+//   mock.AddReceive("baz");
+//   EXPECT_FALSE(DoFooBar(&mock));
+class SocketMock : public Socket {
+  public:
+    SocketMock();
+    ~SocketMock() override;
+
+    ssize_t Send(const void* data, size_t length) override;
+    ssize_t Receive(void* data, size_t length, int timeout_ms) override;
+    int Close() override;
+    virtual std::unique_ptr<Socket> Accept();
+
+    // Adds an expectation for Send().
+    void ExpectSend(std::string message);
+
+    // Adds an expectation for Send() that returns -1.
+    void ExpectSendFailure(std::string message);
+
+    // Adds data to provide for Receive().
+    void AddReceive(std::string message);
+
+    // Adds a Receive() failure.
+    void AddReceiveFailure();
+
+    // Adds a Socket to return from Accept().
+    void AddAccept(std::unique_ptr<Socket> sock);
+
+  private:
+    enum class EventType { kSend, kReceive, kAccept };
+
+    struct Event {
+        Event(EventType _type, std::string _message, ssize_t _return_value,
+              std::unique_ptr<Socket> _sock);
+
+        EventType type;
+        std::string message;
+        ssize_t return_value;
+        std::unique_ptr<Socket> sock;
+    };
+
+    std::queue<Event> events_;
+
+    DISALLOW_COPY_AND_ASSIGN(SocketMock);
+};
+
+#endif  // SOCKET_MOCK_H_