Improve OEMCrypto unit tests

This change updates the unit tests to have more comments so that it is
more clear what went wrong if a test fails.

Also, some utility code has been changed to make it easier to support
new platforms and read/write locks.

Also, the reference code has had some refactoring added to make it
easier for Widevine to test CDM code.  There should be no
functionality differences in the reference code.

Also, in the main API doc, there was an obsolete paragraph in the
description of the threading model.  This paragraph has been removed.

util/include/file_store.h

@@ -7,12 +7,13 @@
 #ifndef WVCDM_UTIL_FILE_STORE_H_
 #define WVCDM_UTIL_FILE_STORE_H_
 
-#include <unistd.h>
+#include <cstdint>
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "disallow_copy_and_assign.h"
+#include "platform.h"
 #include "util_common.h"
 
 namespace wvcdm {

util/include/platform.h

@@ -0,0 +1,33 @@
+// Copyright 2018 Google LLC. All Rights Reserved. This file and proprietary
+// source code may only be used and distributed under the Widevine Master
+// License Agreement.
+//
+// Platform - Abstracts some utilities between platforms.
+//
+#ifndef WVCDM_UTIL_PLATFORM_H_
+#define WVCDM_UTIL_PLATFORM_H_
+
+#include "util_common.h"
+
+#ifdef _WIN32
+# include <wtypes.h>
+# include <BaseTsd.h>
+# include <winsock2.h>  // For htonl and ntohl.
+# define __PRETTY_FUNCTION__ __FUNCTION__
+# undef NO_ERROR
+# undef GetCurrentTime
+# undef DeleteFile
+
+using ssize_t = SSIZE_T;
+
+inline void sleep(int seconds) {
+  Sleep(seconds * 1000);
+}
+CORE_UTIL_EXPORT int setenv(const char* key, const char* value, int overwrite);
+#else
+# include <arpa/inet.h>
+# include <sys/types.h>
+# include <unistd.h>
+#endif
+
+#endif  // WVCDM_UTIL_PLATFORM_H_

util/include/rw_lock.h

@@ -0,0 +1,65 @@
+// Copyright 2019 Google LLC. All Rights Reserved. This file and proprietary
+// source code may only be used and distributed under the Widevine Master
+// License Agreement.
+
+#ifndef WVCDM_UTIL_RW_LOCK_H_
+#define WVCDM_UTIL_RW_LOCK_H_
+
+#include <stdint.h>
+
+#include <condition_variable>
+#include <mutex>
+
+#include "disallow_copy_and_assign.h"
+#include "util_common.h"
+
+namespace wvcdm {
+
+// A simple reader-writer mutex implementation that mimics the one from C++17
+class CORE_UTIL_EXPORT shared_mutex {
+ public:
+  shared_mutex() : reader_count_(0), has_writer_(false) {}
+  ~shared_mutex();
+
+  // These methods take the mutex as a reader. They do not fulfill the
+  // SharedMutex requirement from the C++14 STL, but they fulfill enough of it
+  // to be used with |shared_lock| below.
+  void lock_shared();
+  void unlock_shared();
+
+  // These methods take the mutex as a writer. They fulfill the Mutex
+  // requirement from the C++11 STL so that this mutex can be used with
+  // |std::unique_lock|.
+  void lock() { lock_implementation(false); }
+  bool try_lock() { return lock_implementation(true); }
+  void unlock();
+
+ private:
+  bool lock_implementation(bool abort_if_unavailable);
+
+  uint32_t reader_count_;
+  bool has_writer_;
+
+  std::mutex mutex_;
+  std::condition_variable condition_variable_;
+
+  CORE_DISALLOW_COPY_AND_ASSIGN(shared_mutex);
+};
+
+// A simple reader lock implementation that mimics the one from C++14
+template <typename Mutex>
+class shared_lock {
+ public:
+  explicit shared_lock(Mutex& lock) : lock_(&lock) { lock_->lock_shared(); }
+  explicit shared_lock(Mutex* lock) : lock_(lock) { lock_->lock_shared(); }
+  ~shared_lock() { lock_->unlock_shared(); }
+
+ private:
+  Mutex* lock_;
+
+  CORE_DISALLOW_COPY_AND_ASSIGN(shared_lock);
+};
+
+}  // namespace wvcdm
+
+#endif  // WVCDM_UTIL_RW_LOCK_H_