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time: Add is_datetime() for RFC 3339 Internet Date/Time Format
Implements sourcemeta::core::is_datetime() in src/core/time following the same pattern as is_ipv4() and is_ipv6() in src/core/ip. - Pure string_view state machine, no heap allocations - Validates full date-time production from RFC 3339 §5.6 - Leap year per RFC 3339 Appendix C formula - Accepts leap seconds (second=60) for any date per §5.7 - Case-insensitive T/Z separators per §5.6 NOTE - Rejects colonless offsets, space separators, missing timezone - 40 unit tests covering valid and invalid inputs Relates to format-assertion support for Draft 4 and Draft 6. Signed-off-by: Tushar Verma <tusharmyself06@gmail.com>
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‎src/core/time/CMakeLists.txt‎

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@@ -1,4 +1,5 @@
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sourcemeta_library(NAMESPACE sourcemeta PROJECT core NAME time SOURCES gmt.cc)
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sourcemeta_library(NAMESPACE sourcemeta PROJECT core NAME time
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SOURCES gmt.cc datetime.cc)
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if(SOURCEMETA_CORE_INSTALL)
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sourcemeta_library_install(NAMESPACE sourcemeta PROJECT core NAME time)

‎src/core/time/datetime.cc‎

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#include <sourcemeta/core/time.h>
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#include <array> // std::array
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namespace sourcemeta::core {
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static constexpr auto is_digit(const char character) -> bool {
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return character >= '0' && character <= '9';
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}
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static constexpr auto is_leap_year(const unsigned int year) -> bool {
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return (year % 4 == 0) && (year % 100 != 0 || year % 400 == 0);
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}
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static constexpr auto max_day_in_month(const unsigned int month,
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const unsigned int year)
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-> unsigned int {
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constexpr std::array<unsigned int, 13> days{0, 31, 28, 31, 30, 31, 30,
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31, 31, 30, 31, 30, 31};
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if (month == 2 && is_leap_year(year)) {
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return 29;
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}
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return days[month];
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}
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auto is_datetime(const std::string_view value) -> bool {
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const auto size{value.size()};
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// Minimum valid date-time: "YYYY-MM-DDTHH:MM:SSZ" = 20 characters
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if (size < 20) {
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return false;
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}
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std::string_view::size_type position{0};
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// --- full-date: date-fullyear "-" date-month "-" date-mday ---
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// date-fullyear = 4DIGIT
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if (!is_digit(value[0]) || !is_digit(value[1]) || !is_digit(value[2]) ||
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!is_digit(value[3])) {
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return false;
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}
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const auto year{static_cast<unsigned int>(value[0] - '0') * 1000 +
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static_cast<unsigned int>(value[1] - '0') * 100 +
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static_cast<unsigned int>(value[2] - '0') * 10 +
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static_cast<unsigned int>(value[3] - '0')};
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position = 4;
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// "-"
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if (value[position] != '-') {
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return false;
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}
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position += 1;
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// date-month = 2DIGIT ; 01-12
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if (!is_digit(value[position]) || !is_digit(value[position + 1])) {
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return false;
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}
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const auto month{static_cast<unsigned int>(value[position] - '0') * 10 +
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static_cast<unsigned int>(value[position + 1] - '0')};
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if (month < 1 || month > 12) {
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return false;
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}
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position += 2;
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// "-"
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if (value[position] != '-') {
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return false;
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}
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position += 1;
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// date-mday = 2DIGIT ; 01-28/29/30/31 based on month/year
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if (!is_digit(value[position]) || !is_digit(value[position + 1])) {
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return false;
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}
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const auto day{static_cast<unsigned int>(value[position] - '0') * 10 +
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static_cast<unsigned int>(value[position + 1] - '0')};
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position += 2;
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// --- "T" or "t" separator ---
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if (value[position] != 'T' && value[position] != 't') {
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return false;
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}
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position += 1;
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// --- partial-time: time-hour ":" time-minute ":" time-second ---
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// time-hour = 2DIGIT ; 00-23
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if (!is_digit(value[position]) || !is_digit(value[position + 1])) {
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return false;
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}
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const auto hour{static_cast<unsigned int>(value[position] - '0') * 10 +
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static_cast<unsigned int>(value[position + 1] - '0')};
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if (hour > 23) {
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return false;
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}
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position += 2;
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// ":"
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if (value[position] != ':') {
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return false;
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}
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position += 1;
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// time-minute = 2DIGIT ; 00-59
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if (!is_digit(value[position]) || !is_digit(value[position + 1])) {
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return false;
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}
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const auto minute{static_cast<unsigned int>(value[position] - '0') * 10 +
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static_cast<unsigned int>(value[position + 1] - '0')};
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if (minute > 59) {
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return false;
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}
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position += 2;
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// ":"
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if (value[position] != ':') {
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return false;
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}
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position += 1;
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// time-second = 2DIGIT ; 00-60 (60 = leap second per §5.7)
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if (!is_digit(value[position]) || !is_digit(value[position + 1])) {
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return false;
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}
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const auto second{static_cast<unsigned int>(value[position] - '0') * 10 +
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static_cast<unsigned int>(value[position + 1] - '0')};
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if (second > 60) {
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return false;
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}
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position += 2;
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// --- [time-secfrac] = "." 1*DIGIT ---
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if (position < size && value[position] == '.') {
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position += 1;
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if (position >= size || !is_digit(value[position])) {
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// "." must be followed by at least 1 digit
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return false;
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}
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while (position < size && is_digit(value[position])) {
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position += 1;
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}
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}
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// --- time-offset = "Z" / time-numoffset ---
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if (position >= size) {
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// No time offset present — invalid
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return false;
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}
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if (value[position] == 'Z' || value[position] == 'z') {
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position += 1;
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} else if (value[position] == '+' || value[position] == '-') {
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position += 1;
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// time-numoffset = ("+" / "-") time-hour ":" time-minute
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if (position + 5 > size) {
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return false;
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}
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// Offset time-hour = 2DIGIT ; 00-23
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if (!is_digit(value[position]) || !is_digit(value[position + 1])) {
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return false;
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}
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const auto offset_hour{
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static_cast<unsigned int>(value[position] - '0') * 10 +
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static_cast<unsigned int>(value[position + 1] - '0')};
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if (offset_hour > 23) {
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return false;
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}
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position += 2;
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// ":" — REQUIRED (colonless offsets like +0530 are invalid per §5.6)
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if (value[position] != ':') {
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return false;
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}
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position += 1;
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// Offset time-minute = 2DIGIT ; 00-59
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if (!is_digit(value[position]) || !is_digit(value[position + 1])) {
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return false;
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}
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const auto offset_minute{
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static_cast<unsigned int>(value[position] - '0') * 10 +
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static_cast<unsigned int>(value[position + 1] - '0')};
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if (offset_minute > 59) {
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return false;
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}
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position += 2;
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} else {
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// Not Z, not +/-, invalid character for time-offset
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return false;
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}
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// String must be fully consumed — no trailing characters
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if (position != size) {
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return false;
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}
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// --- Validate date-mday against month/year (§5.7) ---
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if (day < 1 || day > max_day_in_month(month, year)) {
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return false;
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}
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return true;
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}
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} // namespace sourcemeta::core

‎src/core/time/include/sourcemeta/core/time.h‎

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#include <sourcemeta/core/time_export.h>
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#endif
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#include <chrono> // std::chrono::system_clock::time_point
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#include <string> // std::string
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#include <chrono> // std::chrono::system_clock::time_point
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#include <string> // std::string
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#include <string_view> // std::string_view
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/// @defgroup time Time
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/// @brief A growing implementation of time-related utilities for standard such
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/// as RFC 7231 (GMT).
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/// @brief A growing implementation of time-related utilities for standards
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/// such as RFC 7231 (GMT) and RFC 3339 (Internet Date/Time Format).
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///
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/// This functionality is included as follows:
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///
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SOURCEMETA_CORE_TIME_EXPORT
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auto from_gmt(const std::string &time) -> std::chrono::system_clock::time_point;
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/// @ingroup time
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/// Check whether the given string is a valid date-time value per RFC 3339
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/// Section 5.6 (Internet Date/Time Format). This implements the full
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/// `date-time` production rule:
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///
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/// ```
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/// date-time = full-date "T" full-time
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/// ```
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///
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/// where "T" may also be lowercase "t" (per RFC 3339 §5.6 NOTE). For example:
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///
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/// ```cpp
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/// #include <sourcemeta/core/time.h>
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///
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/// #include <cassert>
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///
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/// assert(sourcemeta::core::is_datetime("1985-04-12T23:20:50.52Z"));
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/// assert(sourcemeta::core::is_datetime("1996-12-19T16:39:57-08:00"));
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/// assert(sourcemeta::core::is_datetime("1990-12-31T23:59:60Z"));
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/// assert(!sourcemeta::core::is_datetime("2024-01-15T14:30:00"));
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/// assert(!sourcemeta::core::is_datetime("2024-01-15 14:30:00Z"));
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/// ```
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SOURCEMETA_CORE_TIME_EXPORT
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auto is_datetime(std::string_view value) -> bool;
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} // namespace sourcemeta::core
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#endif

‎test/time/CMakeLists.txt‎

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sourcemeta_googletest(NAMESPACE sourcemeta PROJECT core NAME time
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SOURCES gmt_test.cc)
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SOURCES gmt_test.cc datetime_test.cc)
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target_link_libraries(sourcemeta_core_time_unit
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PRIVATE sourcemeta::core::time)

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