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/Android.bp

@@ -309,6 +309,7 @@ cdm_util_src_files = [
     "cdm/util/src/platform.cpp",
     "cdm/util/src/rw_lock.cpp",
     "cdm/util/src/string_conversions.cpp",
+    "cdm/util/src/string_format.cpp",
 ]
 
 cc_library_static {

libwvdrmengine/cdm/test/coverage-test.mk

@@ -41,6 +41,7 @@ LOCAL_SRC_FILES := \
   ../util/test/cdm_random_unittest.cpp \
   ../util/test/file_store_unittest.cpp \
   ../util/test/file_utils_unittest.cpp \
+  ../util/test/string_format_unittest.cpp \
   ../util/test/test_sleep.cpp \
   ../../oemcrypto/test/oec_device_features.cpp \
   ../../oemcrypto/test/oec_key_deriver.cpp \

libwvdrmengine/cdm/util/include/string_format.h

@@ -0,0 +1,18 @@
+// Copyright 2022 Google LLC. All Rights Reserved. This file and proprietary
+// source code may only be used and distributed under the Widevine License
+// Agreement.
+#ifndef WVCDM_UTIL_STRING_FORMAT_H_
+#define WVCDM_UTIL_STRING_FORMAT_H_
+
+#include <string>
+
+namespace wvutil {
+
+#ifdef __GNUC__
+[[gnu::format(printf, 2, 3)]]
+#endif
+bool FormatString(std::string* out, const char* fmt, ...);
+
+}  // namespace wvutil
+
+#endif  // WVCDM_UTIL_STRING_FORMAT_H_

libwvdrmengine/cdm/util/src/string_format.cpp

@@ -0,0 +1,40 @@
+// 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 <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <memory>
+
+namespace wvutil {
+
+bool FormatString(std::string* out, const char* fmt, ...) {
+  if (out == nullptr || fmt == nullptr) return false;
+
+  va_list ap1;
+  va_start(ap1, fmt);
+  const int desired_size = vsnprintf(nullptr, 0, fmt, ap1);
+  va_end(ap1);
+
+  if (desired_size < 0) return false;
+  const size_t buffer_size =
+      static_cast<size_t>(desired_size) + 1;  // +1 for null
+  std::unique_ptr<char[]> buffer(new char[buffer_size]);
+
+  va_list ap2;
+  va_start(ap2, fmt);
+  const int actual_size = vsnprintf(buffer.get(), buffer_size, fmt, ap2);
+  va_end(ap2);
+
+  if (actual_size != desired_size) return false;
+
+  out->assign(buffer.get(), actual_size);
+  return true;
+}
+
+}  // namespace wvutil

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