EDK: Add mojo::util::StringPrintf() (etc.) and convert away from base's.

mojo/edk/util/string_printf.cc

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "mojo/edk/util/string_printf.h"
+
+#include <assert.h>
+#include <errno.h>
+#include <stdarg.h>
+#include <stddef.h>
+#include <stdio.h>
+
+#include <memory>
+
+namespace mojo {
+namespace util {
+namespace {
+
+void StringVAppendfHelper(std::string* dest, const char* format, va_list ap) {
+  // Size of the small stack buffer to use first. This should be kept in sync
+  // with the numbers in StringPrintfTest.StringPrintf_Boundary.
+  constexpr size_t kStackBufferSize = 1024u;
+
+  // First, try with a small buffer on the stack.
+  char stack_buf[kStackBufferSize];
+  // Copy |ap| (which can only be used once), in case we need to retry.
+  va_list ap_copy;
+  va_copy(ap_copy, ap);
+  int result = vsnprintf(stack_buf, kStackBufferSize, format, ap_copy);
+  va_end(ap_copy);
+  if (result < 0) {
+    // As far as I can tell, we'd only get |EOVERFLOW| if the result is so large
+    // that it can't be represented by an |int| (in which case retrying would be
+    // futile), so Chromium's implementation is wrong.
+    return;
+  }
+  // |result| should be the number of characters we need, not including the
+  // terminating null. However, |vsnprintf()| always null-terminates!
+  size_t output_size = static_cast<size_t>(result);
+  // Check if the output fit into our stack buffer. This is "<" not "<=", since
+  // |vsnprintf()| will null-terminate.
+  if (output_size < kStackBufferSize) {
+    // It fit.
+    dest->append(stack_buf, static_cast<size_t>(result));
+    return;
+  }
+
+  // Since we have the required output size, we can just heap allocate that.
+  // (Add 1 because |vsnprintf()| will always null-terminate.)
+  size_t heap_buf_size = output_size + 1u;
+  std::unique_ptr<char[]> heap_buf(new char[heap_buf_size]);
+  result = vsnprintf(heap_buf.get(), heap_buf_size, format, ap);
+  if (result < 0 || static_cast<size_t>(result) > output_size) {
+    assert(false);
+    return;
+  }
+  assert(static_cast<size_t>(result) == output_size);
+  dest->append(heap_buf.get(), static_cast<size_t>(result));
+}
+
+}  // namespace
+
+std::string StringPrintf(const char* format, ...) {
+  va_list ap;
+  va_start(ap, format);
+  std::string rv;
+  StringVAppendf(&rv, format, ap);
+  va_end(ap);
+  return rv;
+}
+
+std::string StringVPrintf(const char* format, va_list ap) {
+  std::string rv;
+  StringVAppendf(&rv, format, ap);
+  return rv;
+}
+
+void StringAppendf(std::string* dest, const char* format, ...) {
+  va_list ap;
+  va_start(ap, format);
+  StringVAppendf(dest, format, ap);
+  va_end(ap);
+}
+
+void StringVAppendf(std::string* dest, const char* format, va_list ap) {
+  int old_errno = errno;
+  StringVAppendfHelper(dest, format, ap);
+  errno = old_errno;
+}
+
+}  // namespace util
+}  // namespace mojo