libcxx/src/tz.cpp

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 // For information see https://libcxx.llvm.org/DesignDocs/TimeZone.html
  10
  11 #include <chrono>
  12 #include <filesystem>
  13 #include <fstream>
  14 #include <stdexcept>
  15 #include <string>
  16
  17 // Contains a parser for the IANA time zone data files.
  18 //
  19 // These files can be found at https://data.iana.org/time-zones/ and are in the
  20 // public domain. Information regarding the input can be found at
  21 // https://data.iana.org/time-zones/tz-how-to.html and
  22 // https://man7.org/linux/man-pages/man8/zic.8.html.
  23 //
  24 // As indicated at https://howardhinnant.github.io/date/tz.html#Installation
  25 // For Windows another file seems to be required
  26 // https://raw.githubusercontent.com/unicode-org/cldr/master/common/supplemental/windowsZones.xml
  27 // This file seems to contain the mapping of Windows time zone name to IANA
  28 // time zone names.
  29 //
  30 // However this article mentions another way to do the mapping on Windows
  31 // https://devblogs.microsoft.com/oldnewthing/20210527-00/?p=105255
  32 // This requires Windows 10 Version 1903, which was released in May of 2019
  33 // and considered end of life in December 2020
  34 // https://learn.microsoft.com/en-us/lifecycle/announcements/windows-10-1903-end-of-servicing
  35 //
  36 // TODO TZDB Implement the Windows mapping in tzdb::current_zone
  37
  38 _LIBCPP_BEGIN_NAMESPACE_STD
  39
  40 namespace chrono {
  41
  42 // This function is weak so it can be overriden in the tests. The
  43 // declaration is in the test header test/support/test_tzdb.h
  44 _LIBCPP_WEAK string_view __libcpp_tzdb_directory() {
  45 #if defined(__linux__)
  46   return "/usr/share/zoneinfo/";
  47 #else
  48 #  error "unknown path to the IANA Time Zone Database"
  49 #endif
  50 }
  51
  52 [[nodiscard]] static bool __is_whitespace(int __c) { return __c == ' ' || __c == '\t'; }
  53
  54 static void __skip_optional_whitespace(istream& __input) {
  55   while (chrono::__is_whitespace(__input.peek()))
  56     __input.get();
  57 }
  58
  59 static void __skip_mandatory_whitespace(istream& __input) {
  60   if (!chrono::__is_whitespace(__input.get()))
  61     std::__throw_runtime_error("corrupt tzdb: expected whitespace");
  62
  63   chrono::__skip_optional_whitespace(__input);
  64 }
  65
  66 static void __matches(istream& __input, char __expected) {
  67   if (std::tolower(__input.get()) != __expected)
  68     std::__throw_runtime_error((string("corrupt tzdb: expected character '") + __expected + '\'').c_str());
  69 }
  70
  71 static void __matches(istream& __input, string_view __expected) {
  72   for (auto __c : __expected)
  73     if (std::tolower(__input.get()) != __c)
  74       std::__throw_runtime_error((string("corrupt tzdb: expected string '") + string(__expected) + '\'').c_str());
  75 }
  76
  77 [[nodiscard]] static string __parse_string(istream& __input) {
  78   string __result;
  79   while (true) {
  80     int __c = __input.get();
  81     switch (__c) {
  82     case ' ':
  83     case '\t':
  84     case '\n':
  85       __input.unget();
  86       [[fallthrough]];
  87     case istream::traits_type::eof():
  88       if (__result.empty())
  89         std::__throw_runtime_error("corrupt tzdb: expected a string");
  90
  91       return __result;
  92
  93     default:
  94       __result.push_back(__c);
  95     }
  96   }
  97 }
  98
  99 static string __parse_version(istream& __input) {
 100   // The first line in tzdata.zi contains
 101   //    # version YYYYw
 102   // The parser expects this pattern
 103   // #\s*version\s*\(.*)
 104   // This part is not documented.
 105   chrono::__matches(__input, '#');
 106   chrono::__skip_optional_whitespace(__input);
 107   chrono::__matches(__input, "version");
 108   chrono::__skip_mandatory_whitespace(__input);
 109   return chrono::__parse_string(__input);
 110 }
 111
 112 static tzdb __make_tzdb() {
 113   tzdb __result;
 114
 115   filesystem::path __root = chrono::__libcpp_tzdb_directory();
 116   ifstream __tzdata{__root / "tzdata.zi"};
 117
 118   __result.version = chrono::__parse_version(__tzdata);
 119   return __result;
 120 }
 121
 122 //===----------------------------------------------------------------------===//
 123 //                           Public API
 124 //===----------------------------------------------------------------------===//
 125
 126 _LIBCPP_NODISCARD_EXT _LIBCPP_AVAILABILITY_TZDB _LIBCPP_EXPORTED_FROM_ABI tzdb_list& get_tzdb_list() {
 127   static tzdb_list __result{chrono::__make_tzdb()};
 128   return __result;
 129 }
 130
 131 _LIBCPP_AVAILABILITY_TZDB _LIBCPP_EXPORTED_FROM_ABI const tzdb& reload_tzdb() {
 132   if (chrono::remote_version() == chrono::get_tzdb().version)
 133     return chrono::get_tzdb();
 134
 135   return chrono::get_tzdb_list().__emplace_front(chrono::__make_tzdb());
 136 }
 137
 138 _LIBCPP_NODISCARD_EXT _LIBCPP_AVAILABILITY_TZDB _LIBCPP_EXPORTED_FROM_ABI string remote_version() {
 139   filesystem::path __root = chrono::__libcpp_tzdb_directory();
 140   ifstream __tzdata{__root / "tzdata.zi"};
 141   return chrono::__parse_version(__tzdata);
 142 }
 143
 144 } // namespace chrono
 145
 146 _LIBCPP_END_NAMESPACE_STD