mkdtemp.hpp

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//
//     http://www.apache.org/licenses/LICENSE-2.0
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#ifndef __STOUT_OS_WINDOWS_MKDTEMP_HPP__
#define __STOUT_OS_WINDOWS_MKDTEMP_HPP__

#include <random>
#include <string>

#include <stout/error.hpp>
#include <stout/nothing.hpp>
#include <stout/path.hpp>
#include <stout/strings.hpp>
#include <stout/try.hpp>

#include <stout/os/mkdir.hpp>
#include <stout/os/temp.hpp>


namespace os {

// Creates a temporary directory using the specified path
// template. The template may be any path with _6_ `Xs' appended to
// it, for example /tmp/temp.XXXXXX. The trailing `Xs' are replaced
// with a unique alphanumeric combination.
inline Try<std::string> mkdtemp(
    const std::string& path = path::join(os::temp(), "XXXXXX"))
{
  // NOTE: We'd like to avoid reallocating `postfixTemplate` and `alphabet`,
  // and to avoid  recomputing their sizes on each call to `mkdtemp`, so we
  // make them `static const` and use the slightly awkward `sizeof` trick to
  // compute their sizes once instead of calling `strlen` for each call.
  static const char postfixTemplate[] = "XXXXXX";
  static const size_t postfixSize = sizeof(postfixTemplate) - 1;

  if (!strings::endsWith(path, postfixTemplate)) {
    return Error(
        "Invalid template passed to `os::mkdtemp`: template '" + path +
        "' should end with 6 'X' characters");
  }

  static const char alphabet[] =
    "0123456789"
    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    "abcdefghijklmnopqrstuvwxyz";

  // NOTE: The maximum addressable index in a string is the total length of the
  // string minus 1; but C strings have an extra null character at the end, so
  // the size of the array is actually one more than the length of the string,
  // which is why we're subtracting 2 here.
  static const size_t maxAlphabetIndex = sizeof(alphabet) - 2;

  std::string postfix(postfixTemplate);
  static thread_local std::mt19937 generator((std::random_device())());

  for (int i = 0; i < postfixSize; ++i) {
    int index = generator() % maxAlphabetIndex;
    postfix[i] = alphabet[index];
  }

  // Replace template, make directory.
  std::string tempPath = path
    .substr(0, path.length() - postfixSize)
    .append(postfix);

  Try<Nothing> mkdir = os::mkdir(tempPath, false);

  if (mkdir.isError()) {
    return Error(mkdir.error());
  }

  return tempPath;
}

} // namespace os {


#endif // __STOUT_OS_WINDOWS_MKDTEMP_HPP__