Add String Formatting Util

(Merged from http://go/wvgerrit/160042.)

Since we don't have access to std::format yet, this patch adds a
function to wvutil to format text into a std::string.

Bug: 255466913
Test: x86-64
Test: raven
Change-Id: I28043da76af5b4772a29fa7e7241343caf9b54a1

libwvdrmengine/cdm/util/test/string_format_unittest.cpp

@@ -0,0 +1,64 @@
+// Copyright 2022 Google LLC. All Rights Reserved. This file and proprietary
+// source code may only be used and distributed under the Widevine License
+// Agreement.
+
+#include "string_format.h"
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+
+#include <string>
+
+namespace wvutil {
+
+TEST(StringFormatTest, SignedInteger) {
+  constexpr char kFormat[] = "Version %d";
+  constexpr char kResult[] = "Version -123";
+  std::string result;
+  EXPECT_TRUE(FormatString(&result, kFormat, -123));
+  EXPECT_EQ(result, kResult);
+}
+
+TEST(StringFormatTest, UnsignedInteger) {
+  constexpr char kFormat[] = "Version %u";
+  constexpr char kResult[] = "Version 27";
+  std::string result;
+  EXPECT_TRUE(FormatString(&result, kFormat, 27));
+  EXPECT_EQ(result, kResult);
+}
+
+TEST(StringFormatTest, HexInteger) {
+  constexpr char kFormat[] = "Version %X";
+  constexpr char kResult[] = "Version FF";
+  std::string result;
+  EXPECT_TRUE(FormatString(&result, kFormat, 0xFF));
+  EXPECT_EQ(result, kResult);
+}
+
+TEST(StringFormatTest, Strings) {
+  constexpr char kFormat[] = "Hello, %s.";
+  constexpr char kResult[] = "Hello, DRM.";
+  std::string result;
+  EXPECT_TRUE(FormatString(&result, kFormat, "DRM"));
+  EXPECT_EQ(result, kResult);
+}
+
+TEST(StringFormatTest, Nothing) {
+  constexpr char kString[] = "No format fields.";
+  std::string result;
+  EXPECT_TRUE(FormatString(&result, kString));
+  EXPECT_EQ(result, kString);
+}
+
+TEST(StringFormatTest, NullOutput) {
+  constexpr char kString[] = "This will never be referenced.";
+  EXPECT_FALSE(FormatString(nullptr, kString));
+}
+
+TEST(StringFormatTest, NullFormat) {
+  std::string result;
+  EXPECT_FALSE(FormatString(&result, nullptr));
+  EXPECT_TRUE(result.empty());
+}
+
+}  // namespace wvutil