libcutils/fastboot: improve multi-buffer write.

Fixes libcutils multi-buffer write interface to be more friendly and
hooks into it from the fastboot Socket class.

Bug: http://b/26558551
Change-Id: Ibb3a8428fc379755602de52722c1260f9e345bc0
diff --git a/libcutils/sockets_windows.cpp b/libcutils/sockets_windows.cpp
new file mode 100644
index 0000000..ed6b1a7
--- /dev/null
+++ b/libcutils/sockets_windows.cpp
@@ -0,0 +1,86 @@
+/*
+ * Copyright (C) 2015 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.
+ */
+
+#include <cutils/sockets.h>
+
+// https://msdn.microsoft.com/en-us/library/windows/desktop/ms741549(v=vs.85).aspx
+// claims WSACleanup() should be called before program exit, but general
+// consensus seems to be that it hasn't actually been necessary for a long time,
+// likely since Windows 3.1. Additionally, trying to properly use WSACleanup()
+// can be extremely tricky and cause deadlock when using threads or atexit().
+//
+// Both adb (1) and Chrome (2) purposefully avoid WSACleanup() with no issues.
+// (1) https://android.googlesource.com/platform/system/core.git/+/master/adb/sysdeps_win32.cpp
+// (2) https://code.google.com/p/chromium/codesearch#chromium/src/net/base/winsock_init.cc
+extern "C" bool initialize_windows_sockets() {
+    // There's no harm in calling WSAStartup() multiple times but no benefit
+    // either, we may as well skip it after the first.
+    static bool init_success = false;
+
+    if (!init_success) {
+        WSADATA wsaData;
+        init_success = (WSAStartup(MAKEWORD(2, 2), &wsaData) == 0);
+    }
+
+    return init_success;
+}
+
+int socket_close(cutils_socket_t sock) {
+    return closesocket(sock);
+}
+
+int socket_set_receive_timeout(cutils_socket_t sock, int timeout_ms) {
+    return setsockopt(sock, SOL_SOCKET, SO_RCVTIMEO,
+                      reinterpret_cast<char*>(&timeout_ms), sizeof(timeout_ms));
+}
+
+ssize_t socket_send_buffers(cutils_socket_t sock,
+                            const cutils_socket_buffer_t* buffers,
+                            size_t num_buffers) {
+    if (num_buffers > SOCKET_SEND_BUFFERS_MAX_BUFFERS) {
+        return -1;
+    }
+
+    WSABUF wsa_buffers[SOCKET_SEND_BUFFERS_MAX_BUFFERS];
+    for (size_t i = 0; i < num_buffers; ++i) {
+        // It's safe to cast away const here; WSABUF declares non-const
+        // void* because it's used for both send and receive, but since
+        // we're only sending, the data won't be modified.
+        wsa_buffers[i].buf =
+                reinterpret_cast<char*>(const_cast<void*>(buffers[i].data));
+        wsa_buffers[i].len = buffers[i].length;
+    }
+
+    DWORD bytes_sent = 0;
+    if (WSASend(sock, wsa_buffers, num_buffers, &bytes_sent, 0, nullptr,
+                nullptr) != SOCKET_ERROR) {
+        return bytes_sent;
+    }
+
+    return -1;
+}