Add strptime(3).

libc/Makefile

@@ -258,6 +258,7 @@ time/mktime.o \
 timespec/timespec.o \
 time/strftime_l.o \
 time/strftime.o \
+time/strptime.o \
 time/timegm.o \
 ubsan/ubsan.o \
 wchar/btowc.o \

libc/time/strptime.c

@@ -0,0 +1,234 @@
+/*
+ * Copyright (c) 2023 Jonas 'Sortie' Termansen.
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ * time/strptime.c
+ * Parse date and time.
+ */
+
+#include <ctype.h>
+#include <limits.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <string.h>
+#include <time.h>
+
+static const char* wdays[] = {"Sunday", "Monday", "Tuesday", "Wednesday",
+                              "Thursday", "Friday", "Saturday", NULL};
+static const char* months[] = {"January", "February", "March", "April", "May",
+                               "June", "July", "August", "September", "October",
+                               "November", "December", NULL};
+
+static const char* strptime_str(const char* str,
+                                int* output,
+                                const char* const* list)
+{
+	for ( int i = 0; list[i]; i++ )
+	{
+		size_t len = strlen(list[i]);
+		if ( !strncasecmp(str, list[i], len) )
+			return *output = i, str + len;
+		if ( !strncasecmp(str, list[i], 3) )
+			return *output = i, str + 3;
+	}
+	return NULL;
+}
+
+static const char* strptime_num(const char* str,
+                                int* output,
+                                int minimum,
+                                int maximum,
+                                size_t min_digits,
+                                size_t max_digits,
+                                int offset)
+{
+	int value = 0;
+	size_t i = 0;
+	while ( i < max_digits )
+	{
+		if ( str[i] < '0'|| '9' < str[i] )
+		{
+			if ( min_digits <= i )
+				break;
+			return NULL;
+		}
+		if ( __builtin_mul_overflow(value, 10, &value) ||
+		     __builtin_add_overflow(value, str[i++] - '0', &value) )
+			return NULL;
+	}
+	str += i;
+	if ( value < minimum || maximum < value  )
+		return NULL;
+	if ( __builtin_add_overflow(value, offset, &value) )
+		return NULL;
+	return *output = value, str;
+}
+
+char* strptime(const char* restrict str,
+               const char* restrict format,
+               struct tm* restrict tm)
+{
+	bool pm = false;
+	bool need_mktime = false;
+	int year_high = -1, year_low = -1;
+	for ( size_t i = 0; format[i]; )
+	{
+		if ( isspace((unsigned char) format[i]) )
+		{
+			do i++;
+			while ( isspace((unsigned char) format[i]) );
+			if ( !isspace((unsigned char) *str) )
+				return NULL;
+			do str++;
+			while ( isspace((unsigned char) *str) );
+			continue;
+		}
+		else if ( format[i] != '%' )
+		{
+
+			if ( format[i++] != *str++ )
+				return NULL;
+			continue;
+		}
+		i++;
+		if ( format[i] == '0' || format[i] == '+'  )
+			i++;
+		bool has_width = '0' <= format[i] && format[i] <= '9';
+		size_t width = 0;
+		while ( '0' <= format[i] && format[i] <= '9' )
+			width = width * 10 + (format[i++] - '0');
+		// TODO: Maximum width.
+		bool modifier_E = false, modifier_O = false;
+		if ( format[i] == 'E' )
+			modifier_E = true, i++;
+		else if ( format[i] == 'O' )
+			modifier_O = true, i++;
+		(void) modifier_E, (void) modifier_O;
+		switch ( format[i] )
+		{
+		case 'a':
+		case 'A': str = strptime_str(str, &tm->tm_wday, wdays); break;
+		case 'b':
+		case 'B':
+		case 'h':
+			str = strptime_str(str, &tm->tm_mon, months);
+			need_mktime = true;
+			break;
+		case 'c': str = strptime(str, "%a %b %e %H:%M:%S %Y", tm); break;
+		case 'C': str = strptime_num(str, &year_high, 0, 99, 1, 2, 0); break;
+		case 'd':
+		case 'e':
+			str = strptime_num(str, &tm->tm_mday, 1, 31, 1, 2, 0);
+			need_mktime = true;
+			break;
+		case 'D': str = strptime(str, "%m/%d/%y", tm); break;
+		case 'H': str = strptime_num(str, &tm->tm_hour, 0, 23, 1, 2, 0); break;
+		case 'I':
+			str = strptime_num(str, &tm->tm_hour, 1, 12, 1, 2, 0);
+			if ( tm->tm_hour == 12 )
+				tm->tm_hour = 0;
+			break;
+		case 'j': str = strptime_num(str, &tm->tm_yday, 1, 366, 3, 3, -1); break;
+		case 'm':
+			str = strptime_num(str, &tm->tm_mon, 1, 12, 1, 2, -1);
+			need_mktime = true;
+			break;
+		case 'M': str = strptime_num(str, &tm->tm_min, 0, 59, 1, 2, 0); break;
+		case 'n':
+		case 't':
+			if ( !isspace((unsigned char) *str) )
+				return NULL;
+			do str++;
+			while ( isspace((unsigned char) *str) );
+			break;
+		case 'p':
+			if ( !strncasecmp(str, "am", 2) )
+				str += 2, pm = false;
+			else if ( !strncasecmp(str, "pm", 2) )
+				str += 2, pm = true;
+			else
+				return NULL;
+			break;
+		case 'r': str = strptime(str, "%I:%M:%S %p", tm); break;
+		case 'R': str = strptime(str, "%H:%M", tm); break;
+		case 'S': str = strptime_num(str, &tm->tm_sec, 0, 60, 1, 2, 0); break;
+		case 'T': str = strptime(str, "%H:%M:%S", tm); break;
+		// TODO: %U week number
+		case 'w': str = strptime_num(str, &tm->tm_wday, 0, 6, 1, 1, 0); break;
+		// TODO: %W week number
+		case 'x': str = strptime(str, "%m/%d/%Y", tm); break;
+		case 'X': str = strptime(str, "%H:%M:%S", tm); break;
+		case 'y': str = strptime_num(str, &year_low, 0, 99, 1, 2, 0); break;
+		case 'Y':
+			// POSIX divergence: Avoid year 10k problem by allowing more than
+			// four characters by default.
+			if ( !has_width )
+				width = SIZE_MAX;
+			// TODO: Allow leading + and - per POSIX.
+			str = strptime_num(str, &tm->tm_year, INT_MIN, INT_MAX, 1, width,
+			                   -1900);
+			need_mktime = true;
+			break;
+		case 'z':
+			// TODO: More exact.
+			if ( *str != '-' || *str != '+' )
+				return NULL;
+			int hours, minutes;
+			if ( !(str = strptime_num(str, &hours, -12, 12, 2, 2, 0)) ||
+			     !(str = strptime_num(str, &minutes, 0, 59, 2, 2, 0)) )
+				return NULL;
+			tm->tm_isdst = 0;
+			// TODO: What is done with this timezone information?
+			break;
+		case 'Z':
+			// TODO: Other timezones.
+			if ( strncmp(str, "UTC", 3) != 0 )
+				return NULL;
+			str += 3;
+			tm->tm_isdst = 0;
+			// TODO: What is done with this timezone information?
+			break;
+		case '%':
+			if ( *str++ != '%' )
+				return NULL;
+			break;
+		default: NULL;
+		}
+		if ( !str )
+			return NULL;
+		i++;
+	}
+	if ( str )
+	{
+		if ( pm )
+			tm->tm_hour += 12;
+		if ( year_high != -1 || year_low != -1 )
+		{
+			if ( year_high == -1 )
+				year_high = year_low < 70 ? 20 : 19;
+			else if ( year_low == -1 )
+				year_low = 0;
+			tm->tm_year = year_high * 100 + year_low - 1900;
+			need_mktime = true;
+		}
+		if ( need_mktime )
+		{
+			struct tm copy = *tm;
+			mktime(&copy);
+			tm->tm_wday = copy.tm_wday;
+			tm->tm_yday = copy.tm_yday;
+		}
+	}
+	return (char*) str;
+}

share/man/man7/portability.7

@@ -243,9 +243,6 @@ should be use instead as the destination buffer size should always be known,
 otherwise the invocation is suspicious.
 The superior alternative is to combine allocation and initialization using
 .Xr asprintf 3 .
-.Ss strptime
-.Xr strptime 3
-is not currently implemented.
 .Ss <sys/param.h>
 .In sys/param.h
 is not implemented as there is little agreement on what it's supposed to contain