Adds tiny rtc::StringFormat utility

Bug: webrtc:11493
Change-Id: If11a0362dfa820e4464129d0ea58ff8bc4ce86bc
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/173323
Commit-Queue: Henrik Andreassson <henrika@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31043}

rtc_base/BUILD.gn

@@ -390,6 +390,8 @@ rtc_library("stringutils") {
     "string_utils.h",
     "strings/string_builder.cc",
     "strings/string_builder.h",
+    "strings/string_format.cc",
+    "strings/string_format.h",
   ]
   deps = [
     ":checks",
@@ -819,12 +821,12 @@ rtc_library("rtc_base") {
     "net_helpers.cc",
     "net_helpers.h",
     "network.cc",
-    "network_route.cc",
     "network.h",
     "network_constants.cc",
     "network_constants.h",
     "network_monitor.cc",
     "network_monitor.h",
+    "network_route.cc",
     "network_route.h",
     "null_socket_server.cc",
     "null_socket_server.h",
@@ -1171,6 +1173,7 @@ if (rtc_include_tests) {
       "string_utils_unittest.cc",
       "stringize_macros_unittest.cc",
       "strings/string_builder_unittest.cc",
+      "strings/string_format_unittest.cc",
       "swap_queue_unittest.cc",
       "thread_annotations_unittest.cc",
       "thread_checker_unittest.cc",
@@ -1307,8 +1310,8 @@ if (rtc_include_tests) {
       "memory_usage_unittest.cc",
       "message_digest_unittest.cc",
       "nat_unittest.cc",
-      "network_unittest.cc",
       "network_route_unittest.cc",
+      "network_unittest.cc",
       "proxy_unittest.cc",
       "rolling_accumulator_unittest.cc",
       "rtc_certificate_generator_unittest.cc",

rtc_base/strings/string_format.cc

@@ -0,0 +1,41 @@
+/*
+ *  Copyright 2020 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include <cstdarg>
+
+#include "rtc_base/strings/string_format.h"
+
+#include "rtc_base/checks.h"
+
+namespace rtc {
+
+namespace {
+
+// This is an arbitrary limitation that can be changed if necessary, or removed
+// if someone has the time and inclination to replicate the fancy logic from
+// Chromium's base::StringPrinf().
+constexpr int kMaxSize = 512;
+
+}  // namespace
+
+std::string StringFormat(const char* fmt, ...) {
+  char buffer[kMaxSize];
+  va_list args;
+  va_start(args, fmt);
+  int result = vsnprintf(buffer, kMaxSize, fmt, args);
+  va_end(args);
+  RTC_DCHECK_GE(result, 0) << "ERROR: vsnprintf() failed with error " << result;
+  RTC_DCHECK_LT(result, kMaxSize)
+      << "WARNING: string was truncated from " << result << " to "
+      << (kMaxSize - 1) << " characters";
+  return std::string(buffer);
+}
+
+}  // namespace rtc

rtc_base/strings/string_format.h

@@ -0,0 +1,31 @@
+/*
+ *  Copyright 2020 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef RTC_BASE_STRINGS_STRING_FORMAT_H_
+#define RTC_BASE_STRINGS_STRING_FORMAT_H_
+
+#include <string>
+
+namespace rtc {
+
+#if defined(__GNUC__)
+#define RTC_PRINTF_FORMAT(format_param, dots_param) \
+  __attribute__((format(printf, format_param, dots_param)))
+#else
+#define RTC_PRINTF_FORMAT(format_param, dots_param)
+#endif
+
+// Return a C++ string given printf-like input.
+// Based on base::StringPrintf() in Chrome but without its fancy dynamic memory
+// allocation for any size of the input buffer.
+std::string StringFormat(const char* fmt, ...) RTC_PRINTF_FORMAT(1, 2);
+}  // namespace rtc
+
+#endif  // RTC_BASE_STRINGS_STRING_FORMAT_H_

rtc_base/strings/string_format_unittest.cc

@@ -0,0 +1,35 @@
+/*
+ *  Copyright 2020 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "rtc_base/strings/string_format.h"
+
+#include "rtc_base/checks.h"
+#include "test/gtest.h"
+
+namespace rtc {
+
+TEST(StringFormatTest, Empty) {
+  EXPECT_EQ("", StringFormat("%s", ""));
+}
+
+TEST(StringFormatTest, Misc) {
+  EXPECT_EQ("123hello w", StringFormat("%3d%2s %1c", 123, "hello", 'w'));
+  EXPECT_EQ("3 = three", StringFormat("%d = %s", 1 + 2, "three"));
+}
+
+TEST(StringFormatTest, MaxSizeShouldWork) {
+  const int kSrcLen = 512;
+  char str[kSrcLen];
+  std::fill_n(str, kSrcLen, 'A');
+  str[kSrcLen - 1] = 0;
+  EXPECT_EQ(str, StringFormat("%s", str));
+}
+
+}  // namespace rtc