Source file src/time/format.go

Documentation: time

     1  // Copyright 2010 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package time
     6  
     7  import "errors"
     8  
     9  // These are predefined layouts for use in Time.Format and time.Parse.
    10  // The reference time used in the layouts is the specific time:
    11  //	Mon Jan 2 15:04:05 MST 2006
    12  // which is Unix time 1136239445. Since MST is GMT-0700,
    13  // the reference time can be thought of as
    14  //	01/02 03:04:05PM '06 -0700
    15  // To define your own format, write down what the reference time would look
    16  // like formatted your way; see the values of constants like ANSIC,
    17  // StampMicro or Kitchen for examples. The model is to demonstrate what the
    18  // reference time looks like so that the Format and Parse methods can apply
    19  // the same transformation to a general time value.
    20  //
    21  // Some valid layouts are invalid time values for time.Parse, due to formats
    22  // such as _ for space padding and Z for zone information.
    23  //
    24  // Within the format string, an underscore _ represents a space that may be
    25  // replaced by a digit if the following number (a day) has two digits; for
    26  // compatibility with fixed-width Unix time formats.
    27  //
    28  // A decimal point followed by one or more zeros represents a fractional
    29  // second, printed to the given number of decimal places. A decimal point
    30  // followed by one or more nines represents a fractional second, printed to
    31  // the given number of decimal places, with trailing zeros removed.
    32  // When parsing (only), the input may contain a fractional second
    33  // field immediately after the seconds field, even if the layout does not
    34  // signify its presence. In that case a decimal point followed by a maximal
    35  // series of digits is parsed as a fractional second.
    36  //
    37  // Numeric time zone offsets format as follows:
    38  //	-0700  ±hhmm
    39  //	-07:00 ±hh:mm
    40  //	-07    ±hh
    41  // Replacing the sign in the format with a Z triggers
    42  // the ISO 8601 behavior of printing Z instead of an
    43  // offset for the UTC zone. Thus:
    44  //	Z0700  Z or ±hhmm
    45  //	Z07:00 Z or ±hh:mm
    46  //	Z07    Z or ±hh
    47  //
    48  // The recognized day of week formats are "Mon" and "Monday".
    49  // The recognized month formats are "Jan" and "January".
    50  //
    51  // The formats 2, _2, and 02 are unpadded, space-padded, and zero-padded
    52  // day of month. The formats __2 and 002 are space-padded and zero-padded
    53  // three-character day of year; there is no unpadded day of year format.
    54  //
    55  // Text in the format string that is not recognized as part of the reference
    56  // time is echoed verbatim during Format and expected to appear verbatim
    57  // in the input to Parse.
    58  //
    59  // The executable example for Time.Format demonstrates the working
    60  // of the layout string in detail and is a good reference.
    61  //
    62  // Note that the RFC822, RFC850, and RFC1123 formats should be applied
    63  // only to local times. Applying them to UTC times will use "UTC" as the
    64  // time zone abbreviation, while strictly speaking those RFCs require the
    65  // use of "GMT" in that case.
    66  // In general RFC1123Z should be used instead of RFC1123 for servers
    67  // that insist on that format, and RFC3339 should be preferred for new protocols.
    68  // RFC3339, RFC822, RFC822Z, RFC1123, and RFC1123Z are useful for formatting;
    69  // when used with time.Parse they do not accept all the time formats
    70  // permitted by the RFCs.
    71  // The RFC3339Nano format removes trailing zeros from the seconds field
    72  // and thus may not sort correctly once formatted.
    73  const (
    74  	ANSIC       = "Mon Jan _2 15:04:05 2006"
    75  	UnixDate    = "Mon Jan _2 15:04:05 MST 2006"
    76  	RubyDate    = "Mon Jan 02 15:04:05 -0700 2006"
    77  	RFC822      = "02 Jan 06 15:04 MST"
    78  	RFC822Z     = "02 Jan 06 15:04 -0700" // RFC822 with numeric zone
    79  	RFC850      = "Monday, 02-Jan-06 15:04:05 MST"
    80  	RFC1123     = "Mon, 02 Jan 2006 15:04:05 MST"
    81  	RFC1123Z    = "Mon, 02 Jan 2006 15:04:05 -0700" // RFC1123 with numeric zone
    82  	RFC3339     = "2006-01-02T15:04:05Z07:00"
    83  	RFC3339Nano = "2006-01-02T15:04:05.999999999Z07:00"
    84  	Kitchen     = "3:04PM"
    85  	// Handy time stamps.
    86  	Stamp      = "Jan _2 15:04:05"
    87  	StampMilli = "Jan _2 15:04:05.000"
    88  	StampMicro = "Jan _2 15:04:05.000000"
    89  	StampNano  = "Jan _2 15:04:05.000000000"
    90  )
    91  
    92  const (
    93  	_                        = iota
    94  	stdLongMonth             = iota + stdNeedDate  // "January"
    95  	stdMonth                                       // "Jan"
    96  	stdNumMonth                                    // "1"
    97  	stdZeroMonth                                   // "01"
    98  	stdLongWeekDay                                 // "Monday"
    99  	stdWeekDay                                     // "Mon"
   100  	stdDay                                         // "2"
   101  	stdUnderDay                                    // "_2"
   102  	stdZeroDay                                     // "02"
   103  	stdUnderYearDay                                // "__2"
   104  	stdZeroYearDay                                 // "002"
   105  	stdHour                  = iota + stdNeedClock // "15"
   106  	stdHour12                                      // "3"
   107  	stdZeroHour12                                  // "03"
   108  	stdMinute                                      // "4"
   109  	stdZeroMinute                                  // "04"
   110  	stdSecond                                      // "5"
   111  	stdZeroSecond                                  // "05"
   112  	stdLongYear              = iota + stdNeedDate  // "2006"
   113  	stdYear                                        // "06"
   114  	stdPM                    = iota + stdNeedClock // "PM"
   115  	stdpm                                          // "pm"
   116  	stdTZ                    = iota                // "MST"
   117  	stdISO8601TZ                                   // "Z0700"  // prints Z for UTC
   118  	stdISO8601SecondsTZ                            // "Z070000"
   119  	stdISO8601ShortTZ                              // "Z07"
   120  	stdISO8601ColonTZ                              // "Z07:00" // prints Z for UTC
   121  	stdISO8601ColonSecondsTZ                       // "Z07:00:00"
   122  	stdNumTZ                                       // "-0700"  // always numeric
   123  	stdNumSecondsTz                                // "-070000"
   124  	stdNumShortTZ                                  // "-07"    // always numeric
   125  	stdNumColonTZ                                  // "-07:00" // always numeric
   126  	stdNumColonSecondsTZ                           // "-07:00:00"
   127  	stdFracSecond0                                 // ".0", ".00", ... , trailing zeros included
   128  	stdFracSecond9                                 // ".9", ".99", ..., trailing zeros omitted
   129  
   130  	stdNeedDate  = 1 << 8             // need month, day, year
   131  	stdNeedClock = 2 << 8             // need hour, minute, second
   132  	stdArgShift  = 16                 // extra argument in high bits, above low stdArgShift
   133  	stdMask      = 1<<stdArgShift - 1 // mask out argument
   134  )
   135  
   136  // std0x records the std values for "01", "02", ..., "06".
   137  var std0x = [...]int{stdZeroMonth, stdZeroDay, stdZeroHour12, stdZeroMinute, stdZeroSecond, stdYear}
   138  
   139  // startsWithLowerCase reports whether the string has a lower-case letter at the beginning.
   140  // Its purpose is to prevent matching strings like "Month" when looking for "Mon".
   141  func startsWithLowerCase(str string) bool {
   142  	if len(str) == 0 {
   143  		return false
   144  	}
   145  	c := str[0]
   146  	return 'a' <= c && c <= 'z'
   147  }
   148  
   149  // nextStdChunk finds the first occurrence of a std string in
   150  // layout and returns the text before, the std string, and the text after.
   151  func nextStdChunk(layout string) (prefix string, std int, suffix string) {
   152  	for i := 0; i < len(layout); i++ {
   153  		switch c := int(layout[i]); c {
   154  		case 'J': // January, Jan
   155  			if len(layout) >= i+3 && layout[i:i+3] == "Jan" {
   156  				if len(layout) >= i+7 && layout[i:i+7] == "January" {
   157  					return layout[0:i], stdLongMonth, layout[i+7:]
   158  				}
   159  				if !startsWithLowerCase(layout[i+3:]) {
   160  					return layout[0:i], stdMonth, layout[i+3:]
   161  				}
   162  			}
   163  
   164  		case 'M': // Monday, Mon, MST
   165  			if len(layout) >= i+3 {
   166  				if layout[i:i+3] == "Mon" {
   167  					if len(layout) >= i+6 && layout[i:i+6] == "Monday" {
   168  						return layout[0:i], stdLongWeekDay, layout[i+6:]
   169  					}
   170  					if !startsWithLowerCase(layout[i+3:]) {
   171  						return layout[0:i], stdWeekDay, layout[i+3:]
   172  					}
   173  				}
   174  				if layout[i:i+3] == "MST" {
   175  					return layout[0:i], stdTZ, layout[i+3:]
   176  				}
   177  			}
   178  
   179  		case '0': // 01, 02, 03, 04, 05, 06, 002
   180  			if len(layout) >= i+2 && '1' <= layout[i+1] && layout[i+1] <= '6' {
   181  				return layout[0:i], std0x[layout[i+1]-'1'], layout[i+2:]
   182  			}
   183  			if len(layout) >= i+3 && layout[i+1] == '0' && layout[i+2] == '2' {
   184  				return layout[0:i], stdZeroYearDay, layout[i+3:]
   185  			}
   186  
   187  		case '1': // 15, 1
   188  			if len(layout) >= i+2 && layout[i+1] == '5' {
   189  				return layout[0:i], stdHour, layout[i+2:]
   190  			}
   191  			return layout[0:i], stdNumMonth, layout[i+1:]
   192  
   193  		case '2': // 2006, 2
   194  			if len(layout) >= i+4 && layout[i:i+4] == "2006" {
   195  				return layout[0:i], stdLongYear, layout[i+4:]
   196  			}
   197  			return layout[0:i], stdDay, layout[i+1:]
   198  
   199  		case '_': // _2, _2006, __2
   200  			if len(layout) >= i+2 && layout[i+1] == '2' {
   201  				//_2006 is really a literal _, followed by stdLongYear
   202  				if len(layout) >= i+5 && layout[i+1:i+5] == "2006" {
   203  					return layout[0 : i+1], stdLongYear, layout[i+5:]
   204  				}
   205  				return layout[0:i], stdUnderDay, layout[i+2:]
   206  			}
   207  			if len(layout) >= i+3 && layout[i+1] == '_' && layout[i+2] == '2' {
   208  				return layout[0:i], stdUnderYearDay, layout[i+3:]
   209  			}
   210  
   211  		case '3':
   212  			return layout[0:i], stdHour12, layout[i+1:]
   213  
   214  		case '4':
   215  			return layout[0:i], stdMinute, layout[i+1:]
   216  
   217  		case '5':
   218  			return layout[0:i], stdSecond, layout[i+1:]
   219  
   220  		case 'P': // PM
   221  			if len(layout) >= i+2 && layout[i+1] == 'M' {
   222  				return layout[0:i], stdPM, layout[i+2:]
   223  			}
   224  
   225  		case 'p': // pm
   226  			if len(layout) >= i+2 && layout[i+1] == 'm' {
   227  				return layout[0:i], stdpm, layout[i+2:]
   228  			}
   229  
   230  		case '-': // -070000, -07:00:00, -0700, -07:00, -07
   231  			if len(layout) >= i+7 && layout[i:i+7] == "-070000" {
   232  				return layout[0:i], stdNumSecondsTz, layout[i+7:]
   233  			}
   234  			if len(layout) >= i+9 && layout[i:i+9] == "-07:00:00" {
   235  				return layout[0:i], stdNumColonSecondsTZ, layout[i+9:]
   236  			}
   237  			if len(layout) >= i+5 && layout[i:i+5] == "-0700" {
   238  				return layout[0:i], stdNumTZ, layout[i+5:]
   239  			}
   240  			if len(layout) >= i+6 && layout[i:i+6] == "-07:00" {
   241  				return layout[0:i], stdNumColonTZ, layout[i+6:]
   242  			}
   243  			if len(layout) >= i+3 && layout[i:i+3] == "-07" {
   244  				return layout[0:i], stdNumShortTZ, layout[i+3:]
   245  			}
   246  
   247  		case 'Z': // Z070000, Z07:00:00, Z0700, Z07:00,
   248  			if len(layout) >= i+7 && layout[i:i+7] == "Z070000" {
   249  				return layout[0:i], stdISO8601SecondsTZ, layout[i+7:]
   250  			}
   251  			if len(layout) >= i+9 && layout[i:i+9] == "Z07:00:00" {
   252  				return layout[0:i], stdISO8601ColonSecondsTZ, layout[i+9:]
   253  			}
   254  			if len(layout) >= i+5 && layout[i:i+5] == "Z0700" {
   255  				return layout[0:i], stdISO8601TZ, layout[i+5:]
   256  			}
   257  			if len(layout) >= i+6 && layout[i:i+6] == "Z07:00" {
   258  				return layout[0:i], stdISO8601ColonTZ, layout[i+6:]
   259  			}
   260  			if len(layout) >= i+3 && layout[i:i+3] == "Z07" {
   261  				return layout[0:i], stdISO8601ShortTZ, layout[i+3:]
   262  			}
   263  
   264  		case '.': // .000 or .999 - repeated digits for fractional seconds.
   265  			if i+1 < len(layout) && (layout[i+1] == '0' || layout[i+1] == '9') {
   266  				ch := layout[i+1]
   267  				j := i + 1
   268  				for j < len(layout) && layout[j] == ch {
   269  					j++
   270  				}
   271  				// String of digits must end here - only fractional second is all digits.
   272  				if !isDigit(layout, j) {
   273  					std := stdFracSecond0
   274  					if layout[i+1] == '9' {
   275  						std = stdFracSecond9
   276  					}
   277  					std |= (j - (i + 1)) << stdArgShift
   278  					return layout[0:i], std, layout[j:]
   279  				}
   280  			}
   281  		}
   282  	}
   283  	return layout, 0, ""
   284  }
   285  
   286  var longDayNames = []string{
   287  	"Sunday",
   288  	"Monday",
   289  	"Tuesday",
   290  	"Wednesday",
   291  	"Thursday",
   292  	"Friday",
   293  	"Saturday",
   294  }
   295  
   296  var shortDayNames = []string{
   297  	"Sun",
   298  	"Mon",
   299  	"Tue",
   300  	"Wed",
   301  	"Thu",
   302  	"Fri",
   303  	"Sat",
   304  }
   305  
   306  var shortMonthNames = []string{
   307  	"Jan",
   308  	"Feb",
   309  	"Mar",
   310  	"Apr",
   311  	"May",
   312  	"Jun",
   313  	"Jul",
   314  	"Aug",
   315  	"Sep",
   316  	"Oct",
   317  	"Nov",
   318  	"Dec",
   319  }
   320  
   321  var longMonthNames = []string{
   322  	"January",
   323  	"February",
   324  	"March",
   325  	"April",
   326  	"May",
   327  	"June",
   328  	"July",
   329  	"August",
   330  	"September",
   331  	"October",
   332  	"November",
   333  	"December",
   334  }
   335  
   336  // match reports whether s1 and s2 match ignoring case.
   337  // It is assumed s1 and s2 are the same length.
   338  func match(s1, s2 string) bool {
   339  	for i := 0; i < len(s1); i++ {
   340  		c1 := s1[i]
   341  		c2 := s2[i]
   342  		if c1 != c2 {
   343  			// Switch to lower-case; 'a'-'A' is known to be a single bit.
   344  			c1 |= 'a' - 'A'
   345  			c2 |= 'a' - 'A'
   346  			if c1 != c2 || c1 < 'a' || c1 > 'z' {
   347  				return false
   348  			}
   349  		}
   350  	}
   351  	return true
   352  }
   353  
   354  func lookup(tab []string, val string) (int, string, error) {
   355  	for i, v := range tab {
   356  		if len(val) >= len(v) && match(val[0:len(v)], v) {
   357  			return i, val[len(v):], nil
   358  		}
   359  	}
   360  	return -1, val, errBad
   361  }
   362  
   363  // appendInt appends the decimal form of x to b and returns the result.
   364  // If the decimal form (excluding sign) is shorter than width, the result is padded with leading 0's.
   365  // Duplicates functionality in strconv, but avoids dependency.
   366  func appendInt(b []byte, x int, width int) []byte {
   367  	u := uint(x)
   368  	if x < 0 {
   369  		b = append(b, '-')
   370  		u = uint(-x)
   371  	}
   372  
   373  	// Assemble decimal in reverse order.
   374  	var buf [20]byte
   375  	i := len(buf)
   376  	for u >= 10 {
   377  		i--
   378  		q := u / 10
   379  		buf[i] = byte('0' + u - q*10)
   380  		u = q
   381  	}
   382  	i--
   383  	buf[i] = byte('0' + u)
   384  
   385  	// Add 0-padding.
   386  	for w := len(buf) - i; w < width; w++ {
   387  		b = append(b, '0')
   388  	}
   389  
   390  	return append(b, buf[i:]...)
   391  }
   392  
   393  // Never printed, just needs to be non-nil for return by atoi.
   394  var atoiError = errors.New("time: invalid number")
   395  
   396  // Duplicates functionality in strconv, but avoids dependency.
   397  func atoi(s string) (x int, err error) {
   398  	neg := false
   399  	if s != "" && (s[0] == '-' || s[0] == '+') {
   400  		neg = s[0] == '-'
   401  		s = s[1:]
   402  	}
   403  	q, rem, err := leadingInt(s)
   404  	x = int(q)
   405  	if err != nil || rem != "" {
   406  		return 0, atoiError
   407  	}
   408  	if neg {
   409  		x = -x
   410  	}
   411  	return x, nil
   412  }
   413  
   414  // formatNano appends a fractional second, as nanoseconds, to b
   415  // and returns the result.
   416  func formatNano(b []byte, nanosec uint, n int, trim bool) []byte {
   417  	u := nanosec
   418  	var buf [9]byte
   419  	for start := len(buf); start > 0; {
   420  		start--
   421  		buf[start] = byte(u%10 + '0')
   422  		u /= 10
   423  	}
   424  
   425  	if n > 9 {
   426  		n = 9
   427  	}
   428  	if trim {
   429  		for n > 0 && buf[n-1] == '0' {
   430  			n--
   431  		}
   432  		if n == 0 {
   433  			return b
   434  		}
   435  	}
   436  	b = append(b, '.')
   437  	return append(b, buf[:n]...)
   438  }
   439  
   440  // String returns the time formatted using the format string
   441  //	"2006-01-02 15:04:05.999999999 -0700 MST"
   442  //
   443  // If the time has a monotonic clock reading, the returned string
   444  // includes a final field "m=±<value>", where value is the monotonic
   445  // clock reading formatted as a decimal number of seconds.
   446  //
   447  // The returned string is meant for debugging; for a stable serialized
   448  // representation, use t.MarshalText, t.MarshalBinary, or t.Format
   449  // with an explicit format string.
   450  func (t Time) String() string {
   451  	s := t.Format("2006-01-02 15:04:05.999999999 -0700 MST")
   452  
   453  	// Format monotonic clock reading as m=±ddd.nnnnnnnnn.
   454  	if t.wall&hasMonotonic != 0 {
   455  		m2 := uint64(t.ext)
   456  		sign := byte('+')
   457  		if t.ext < 0 {
   458  			sign = '-'
   459  			m2 = -m2
   460  		}
   461  		m1, m2 := m2/1e9, m2%1e9
   462  		m0, m1 := m1/1e9, m1%1e9
   463  		var buf []byte
   464  		buf = append(buf, " m="...)
   465  		buf = append(buf, sign)
   466  		wid := 0
   467  		if m0 != 0 {
   468  			buf = appendInt(buf, int(m0), 0)
   469  			wid = 9
   470  		}
   471  		buf = appendInt(buf, int(m1), wid)
   472  		buf = append(buf, '.')
   473  		buf = appendInt(buf, int(m2), 9)
   474  		s += string(buf)
   475  	}
   476  	return s
   477  }
   478  
   479  // Format returns a textual representation of the time value formatted
   480  // according to layout, which defines the format by showing how the reference
   481  // time, defined to be
   482  //	Mon Jan 2 15:04:05 -0700 MST 2006
   483  // would be displayed if it were the value; it serves as an example of the
   484  // desired output. The same display rules will then be applied to the time
   485  // value.
   486  //
   487  // A fractional second is represented by adding a period and zeros
   488  // to the end of the seconds section of layout string, as in "15:04:05.000"
   489  // to format a time stamp with millisecond precision.
   490  //
   491  // Predefined layouts ANSIC, UnixDate, RFC3339 and others describe standard
   492  // and convenient representations of the reference time. For more information
   493  // about the formats and the definition of the reference time, see the
   494  // documentation for ANSIC and the other constants defined by this package.
   495  func (t Time) Format(layout string) string {
   496  	const bufSize = 64
   497  	var b []byte
   498  	max := len(layout) + 10
   499  	if max < bufSize {
   500  		var buf [bufSize]byte
   501  		b = buf[:0]
   502  	} else {
   503  		b = make([]byte, 0, max)
   504  	}
   505  	b = t.AppendFormat(b, layout)
   506  	return string(b)
   507  }
   508  
   509  // AppendFormat is like Format but appends the textual
   510  // representation to b and returns the extended buffer.
   511  func (t Time) AppendFormat(b []byte, layout string) []byte {
   512  	var (
   513  		name, offset, abs = t.locabs()
   514  
   515  		year  int = -1
   516  		month Month
   517  		day   int
   518  		yday  int
   519  		hour  int = -1
   520  		min   int
   521  		sec   int
   522  	)
   523  	// Each iteration generates one std value.
   524  	for layout != "" {
   525  		prefix, std, suffix := nextStdChunk(layout)
   526  		if prefix != "" {
   527  			b = append(b, prefix...)
   528  		}
   529  		if std == 0 {
   530  			break
   531  		}
   532  		layout = suffix
   533  
   534  		// Compute year, month, day if needed.
   535  		if year < 0 && std&stdNeedDate != 0 {
   536  			year, month, day, yday = absDate(abs, true)
   537  			yday++
   538  		}
   539  
   540  		// Compute hour, minute, second if needed.
   541  		if hour < 0 && std&stdNeedClock != 0 {
   542  			hour, min, sec = absClock(abs)
   543  		}
   544  
   545  		switch std & stdMask {
   546  		case stdYear:
   547  			y := year
   548  			if y < 0 {
   549  				y = -y
   550  			}
   551  			b = appendInt(b, y%100, 2)
   552  		case stdLongYear:
   553  			b = appendInt(b, year, 4)
   554  		case stdMonth:
   555  			b = append(b, month.String()[:3]...)
   556  		case stdLongMonth:
   557  			m := month.String()
   558  			b = append(b, m...)
   559  		case stdNumMonth:
   560  			b = appendInt(b, int(month), 0)
   561  		case stdZeroMonth:
   562  			b = appendInt(b, int(month), 2)
   563  		case stdWeekDay:
   564  			b = append(b, absWeekday(abs).String()[:3]...)
   565  		case stdLongWeekDay:
   566  			s := absWeekday(abs).String()
   567  			b = append(b, s...)
   568  		case stdDay:
   569  			b = appendInt(b, day, 0)
   570  		case stdUnderDay:
   571  			if day < 10 {
   572  				b = append(b, ' ')
   573  			}
   574  			b = appendInt(b, day, 0)
   575  		case stdZeroDay:
   576  			b = appendInt(b, day, 2)
   577  		case stdUnderYearDay:
   578  			if yday < 100 {
   579  				b = append(b, ' ')
   580  				if yday < 10 {
   581  					b = append(b, ' ')
   582  				}
   583  			}
   584  			b = appendInt(b, yday, 0)
   585  		case stdZeroYearDay:
   586  			b = appendInt(b, yday, 3)
   587  		case stdHour:
   588  			b = appendInt(b, hour, 2)
   589  		case stdHour12:
   590  			// Noon is 12PM, midnight is 12AM.
   591  			hr := hour % 12
   592  			if hr == 0 {
   593  				hr = 12
   594  			}
   595  			b = appendInt(b, hr, 0)
   596  		case stdZeroHour12:
   597  			// Noon is 12PM, midnight is 12AM.
   598  			hr := hour % 12
   599  			if hr == 0 {
   600  				hr = 12
   601  			}
   602  			b = appendInt(b, hr, 2)
   603  		case stdMinute:
   604  			b = appendInt(b, min, 0)
   605  		case stdZeroMinute:
   606  			b = appendInt(b, min, 2)
   607  		case stdSecond:
   608  			b = appendInt(b, sec, 0)
   609  		case stdZeroSecond:
   610  			b = appendInt(b, sec, 2)
   611  		case stdPM:
   612  			if hour >= 12 {
   613  				b = append(b, "PM"...)
   614  			} else {
   615  				b = append(b, "AM"...)
   616  			}
   617  		case stdpm:
   618  			if hour >= 12 {
   619  				b = append(b, "pm"...)
   620  			} else {
   621  				b = append(b, "am"...)
   622  			}
   623  		case stdISO8601TZ, stdISO8601ColonTZ, stdISO8601SecondsTZ, stdISO8601ShortTZ, stdISO8601ColonSecondsTZ, stdNumTZ, stdNumColonTZ, stdNumSecondsTz, stdNumShortTZ, stdNumColonSecondsTZ:
   624  			// Ugly special case. We cheat and take the "Z" variants
   625  			// to mean "the time zone as formatted for ISO 8601".
   626  			if offset == 0 && (std == stdISO8601TZ || std == stdISO8601ColonTZ || std == stdISO8601SecondsTZ || std == stdISO8601ShortTZ || std == stdISO8601ColonSecondsTZ) {
   627  				b = append(b, 'Z')
   628  				break
   629  			}
   630  			zone := offset / 60 // convert to minutes
   631  			absoffset := offset
   632  			if zone < 0 {
   633  				b = append(b, '-')
   634  				zone = -zone
   635  				absoffset = -absoffset
   636  			} else {
   637  				b = append(b, '+')
   638  			}
   639  			b = appendInt(b, zone/60, 2)
   640  			if std == stdISO8601ColonTZ || std == stdNumColonTZ || std == stdISO8601ColonSecondsTZ || std == stdNumColonSecondsTZ {
   641  				b = append(b, ':')
   642  			}
   643  			if std != stdNumShortTZ && std != stdISO8601ShortTZ {
   644  				b = appendInt(b, zone%60, 2)
   645  			}
   646  
   647  			// append seconds if appropriate
   648  			if std == stdISO8601SecondsTZ || std == stdNumSecondsTz || std == stdNumColonSecondsTZ || std == stdISO8601ColonSecondsTZ {
   649  				if std == stdNumColonSecondsTZ || std == stdISO8601ColonSecondsTZ {
   650  					b = append(b, ':')
   651  				}
   652  				b = appendInt(b, absoffset%60, 2)
   653  			}
   654  
   655  		case stdTZ:
   656  			if name != "" {
   657  				b = append(b, name...)
   658  				break
   659  			}
   660  			// No time zone known for this time, but we must print one.
   661  			// Use the -0700 format.
   662  			zone := offset / 60 // convert to minutes
   663  			if zone < 0 {
   664  				b = append(b, '-')
   665  				zone = -zone
   666  			} else {
   667  				b = append(b, '+')
   668  			}
   669  			b = appendInt(b, zone/60, 2)
   670  			b = appendInt(b, zone%60, 2)
   671  		case stdFracSecond0, stdFracSecond9:
   672  			b = formatNano(b, uint(t.Nanosecond()), std>>stdArgShift, std&stdMask == stdFracSecond9)
   673  		}
   674  	}
   675  	return b
   676  }
   677  
   678  var errBad = errors.New("bad value for field") // placeholder not passed to user
   679  
   680  // ParseError describes a problem parsing a time string.
   681  type ParseError struct {
   682  	Layout     string
   683  	Value      string
   684  	LayoutElem string
   685  	ValueElem  string
   686  	Message    string
   687  }
   688  
   689  func quote(s string) string {
   690  	return "\"" + s + "\""
   691  }
   692  
   693  // Error returns the string representation of a ParseError.
   694  func (e *ParseError) Error() string {
   695  	if e.Message == "" {
   696  		return "parsing time " +
   697  			quote(e.Value) + " as " +
   698  			quote(e.Layout) + ": cannot parse " +
   699  			quote(e.ValueElem) + " as " +
   700  			quote(e.LayoutElem)
   701  	}
   702  	return "parsing time " +
   703  		quote(e.Value) + e.Message
   704  }
   705  
   706  // isDigit reports whether s[i] is in range and is a decimal digit.
   707  func isDigit(s string, i int) bool {
   708  	if len(s) <= i {
   709  		return false
   710  	}
   711  	c := s[i]
   712  	return '0' <= c && c <= '9'
   713  }
   714  
   715  // getnum parses s[0:1] or s[0:2] (fixed forces s[0:2])
   716  // as a decimal integer and returns the integer and the
   717  // remainder of the string.
   718  func getnum(s string, fixed bool) (int, string, error) {
   719  	if !isDigit(s, 0) {
   720  		return 0, s, errBad
   721  	}
   722  	if !isDigit(s, 1) {
   723  		if fixed {
   724  			return 0, s, errBad
   725  		}
   726  		return int(s[0] - '0'), s[1:], nil
   727  	}
   728  	return int(s[0]-'0')*10 + int(s[1]-'0'), s[2:], nil
   729  }
   730  
   731  // getnum3 parses s[0:1], s[0:2], or s[0:3] (fixed forces s[0:3])
   732  // as a decimal integer and returns the integer and the remainder
   733  // of the string.
   734  func getnum3(s string, fixed bool) (int, string, error) {
   735  	var n, i int
   736  	for i = 0; i < 3 && isDigit(s, i); i++ {
   737  		n = n*10 + int(s[i]-'0')
   738  	}
   739  	if i == 0 || fixed && i != 3 {
   740  		return 0, s, errBad
   741  	}
   742  	return n, s[i:], nil
   743  }
   744  
   745  func cutspace(s string) string {
   746  	for len(s) > 0 && s[0] == ' ' {
   747  		s = s[1:]
   748  	}
   749  	return s
   750  }
   751  
   752  // skip removes the given prefix from value,
   753  // treating runs of space characters as equivalent.
   754  func skip(value, prefix string) (string, error) {
   755  	for len(prefix) > 0 {
   756  		if prefix[0] == ' ' {
   757  			if len(value) > 0 && value[0] != ' ' {
   758  				return value, errBad
   759  			}
   760  			prefix = cutspace(prefix)
   761  			value = cutspace(value)
   762  			continue
   763  		}
   764  		if len(value) == 0 || value[0] != prefix[0] {
   765  			return value, errBad
   766  		}
   767  		prefix = prefix[1:]
   768  		value = value[1:]
   769  	}
   770  	return value, nil
   771  }
   772  
   773  // Parse parses a formatted string and returns the time value it represents.
   774  // The layout defines the format by showing how the reference time,
   775  // defined to be
   776  //	Mon Jan 2 15:04:05 -0700 MST 2006
   777  // would be interpreted if it were the value; it serves as an example of
   778  // the input format. The same interpretation will then be made to the
   779  // input string.
   780  //
   781  // Predefined layouts ANSIC, UnixDate, RFC3339 and others describe standard
   782  // and convenient representations of the reference time. For more information
   783  // about the formats and the definition of the reference time, see the
   784  // documentation for ANSIC and the other constants defined by this package.
   785  // Also, the executable example for Time.Format demonstrates the working
   786  // of the layout string in detail and is a good reference.
   787  //
   788  // Elements omitted from the value are assumed to be zero or, when
   789  // zero is impossible, one, so parsing "3:04pm" returns the time
   790  // corresponding to Jan 1, year 0, 15:04:00 UTC (note that because the year is
   791  // 0, this time is before the zero Time).
   792  // Years must be in the range 0000..9999. The day of the week is checked
   793  // for syntax but it is otherwise ignored.
   794  //
   795  // In the absence of a time zone indicator, Parse returns a time in UTC.
   796  //
   797  // When parsing a time with a zone offset like -0700, if the offset corresponds
   798  // to a time zone used by the current location (Local), then Parse uses that
   799  // location and zone in the returned time. Otherwise it records the time as
   800  // being in a fabricated location with time fixed at the given zone offset.
   801  //
   802  // When parsing a time with a zone abbreviation like MST, if the zone abbreviation
   803  // has a defined offset in the current location, then that offset is used.
   804  // The zone abbreviation "UTC" is recognized as UTC regardless of location.
   805  // If the zone abbreviation is unknown, Parse records the time as being
   806  // in a fabricated location with the given zone abbreviation and a zero offset.
   807  // This choice means that such a time can be parsed and reformatted with the
   808  // same layout losslessly, but the exact instant used in the representation will
   809  // differ by the actual zone offset. To avoid such problems, prefer time layouts
   810  // that use a numeric zone offset, or use ParseInLocation.
   811  func Parse(layout, value string) (Time, error) {
   812  	return parse(layout, value, UTC, Local)
   813  }
   814  
   815  // ParseInLocation is like Parse but differs in two important ways.
   816  // First, in the absence of time zone information, Parse interprets a time as UTC;
   817  // ParseInLocation interprets the time as in the given location.
   818  // Second, when given a zone offset or abbreviation, Parse tries to match it
   819  // against the Local location; ParseInLocation uses the given location.
   820  func ParseInLocation(layout, value string, loc *Location) (Time, error) {
   821  	return parse(layout, value, loc, loc)
   822  }
   823  
   824  func parse(layout, value string, defaultLocation, local *Location) (Time, error) {
   825  	alayout, avalue := layout, value
   826  	rangeErrString := "" // set if a value is out of range
   827  	amSet := false       // do we need to subtract 12 from the hour for midnight?
   828  	pmSet := false       // do we need to add 12 to the hour?
   829  
   830  	// Time being constructed.
   831  	var (
   832  		year       int
   833  		month      int = -1
   834  		day        int = -1
   835  		yday       int = -1
   836  		hour       int
   837  		min        int
   838  		sec        int
   839  		nsec       int
   840  		z          *Location
   841  		zoneOffset int = -1
   842  		zoneName   string
   843  	)
   844  
   845  	// Each iteration processes one std value.
   846  	for {
   847  		var err error
   848  		prefix, std, suffix := nextStdChunk(layout)
   849  		stdstr := layout[len(prefix) : len(layout)-len(suffix)]
   850  		value, err = skip(value, prefix)
   851  		if err != nil {
   852  			return Time{}, &ParseError{alayout, avalue, prefix, value, ""}
   853  		}
   854  		if std == 0 {
   855  			if len(value) != 0 {
   856  				return Time{}, &ParseError{alayout, avalue, "", value, ": extra text: " + value}
   857  			}
   858  			break
   859  		}
   860  		layout = suffix
   861  		var p string
   862  		switch std & stdMask {
   863  		case stdYear:
   864  			if len(value) < 2 {
   865  				err = errBad
   866  				break
   867  			}
   868  			hold := value
   869  			p, value = value[0:2], value[2:]
   870  			year, err = atoi(p)
   871  			if err != nil {
   872  				value = hold
   873  			} else if year >= 69 { // Unix time starts Dec 31 1969 in some time zones
   874  				year += 1900
   875  			} else {
   876  				year += 2000
   877  			}
   878  		case stdLongYear:
   879  			if len(value) < 4 || !isDigit(value, 0) {
   880  				err = errBad
   881  				break
   882  			}
   883  			p, value = value[0:4], value[4:]
   884  			year, err = atoi(p)
   885  		case stdMonth:
   886  			month, value, err = lookup(shortMonthNames, value)
   887  			month++
   888  		case stdLongMonth:
   889  			month, value, err = lookup(longMonthNames, value)
   890  			month++
   891  		case stdNumMonth, stdZeroMonth:
   892  			month, value, err = getnum(value, std == stdZeroMonth)
   893  			if err == nil && (month <= 0 || 12 < month) {
   894  				rangeErrString = "month"
   895  			}
   896  		case stdWeekDay:
   897  			// Ignore weekday except for error checking.
   898  			_, value, err = lookup(shortDayNames, value)
   899  		case stdLongWeekDay:
   900  			_, value, err = lookup(longDayNames, value)
   901  		case stdDay, stdUnderDay, stdZeroDay:
   902  			if std == stdUnderDay && len(value) > 0 && value[0] == ' ' {
   903  				value = value[1:]
   904  			}
   905  			day, value, err = getnum(value, std == stdZeroDay)
   906  			// Note that we allow any one- or two-digit day here.
   907  			// The month, day, year combination is validated after we've completed parsing.
   908  		case stdUnderYearDay, stdZeroYearDay:
   909  			for i := 0; i < 2; i++ {
   910  				if std == stdUnderYearDay && len(value) > 0 && value[0] == ' ' {
   911  					value = value[1:]
   912  				}
   913  			}
   914  			yday, value, err = getnum3(value, std == stdZeroYearDay)
   915  			// Note that we allow any one-, two-, or three-digit year-day here.
   916  			// The year-day, year combination is validated after we've completed parsing.
   917  		case stdHour:
   918  			hour, value, err = getnum(value, false)
   919  			if hour < 0 || 24 <= hour {
   920  				rangeErrString = "hour"
   921  			}
   922  		case stdHour12, stdZeroHour12:
   923  			hour, value, err = getnum(value, std == stdZeroHour12)
   924  			if hour < 0 || 12 < hour {
   925  				rangeErrString = "hour"
   926  			}
   927  		case stdMinute, stdZeroMinute:
   928  			min, value, err = getnum(value, std == stdZeroMinute)
   929  			if min < 0 || 60 <= min {
   930  				rangeErrString = "minute"
   931  			}
   932  		case stdSecond, stdZeroSecond:
   933  			sec, value, err = getnum(value, std == stdZeroSecond)
   934  			if sec < 0 || 60 <= sec {
   935  				rangeErrString = "second"
   936  				break
   937  			}
   938  			// Special case: do we have a fractional second but no
   939  			// fractional second in the format?
   940  			if len(value) >= 2 && value[0] == '.' && isDigit(value, 1) {
   941  				_, std, _ = nextStdChunk(layout)
   942  				std &= stdMask
   943  				if std == stdFracSecond0 || std == stdFracSecond9 {
   944  					// Fractional second in the layout; proceed normally
   945  					break
   946  				}
   947  				// No fractional second in the layout but we have one in the input.
   948  				n := 2
   949  				for ; n < len(value) && isDigit(value, n); n++ {
   950  				}
   951  				nsec, rangeErrString, err = parseNanoseconds(value, n)
   952  				value = value[n:]
   953  			}
   954  		case stdPM:
   955  			if len(value) < 2 {
   956  				err = errBad
   957  				break
   958  			}
   959  			p, value = value[0:2], value[2:]
   960  			switch p {
   961  			case "PM":
   962  				pmSet = true
   963  			case "AM":
   964  				amSet = true
   965  			default:
   966  				err = errBad
   967  			}
   968  		case stdpm:
   969  			if len(value) < 2 {
   970  				err = errBad
   971  				break
   972  			}
   973  			p, value = value[0:2], value[2:]
   974  			switch p {
   975  			case "pm":
   976  				pmSet = true
   977  			case "am":
   978  				amSet = true
   979  			default:
   980  				err = errBad
   981  			}
   982  		case stdISO8601TZ, stdISO8601ColonTZ, stdISO8601SecondsTZ, stdISO8601ShortTZ, stdISO8601ColonSecondsTZ, stdNumTZ, stdNumShortTZ, stdNumColonTZ, stdNumSecondsTz, stdNumColonSecondsTZ:
   983  			if (std == stdISO8601TZ || std == stdISO8601ShortTZ || std == stdISO8601ColonTZ) && len(value) >= 1 && value[0] == 'Z' {
   984  				value = value[1:]
   985  				z = UTC
   986  				break
   987  			}
   988  			var sign, hour, min, seconds string
   989  			if std == stdISO8601ColonTZ || std == stdNumColonTZ {
   990  				if len(value) < 6 {
   991  					err = errBad
   992  					break
   993  				}
   994  				if value[3] != ':' {
   995  					err = errBad
   996  					break
   997  				}
   998  				sign, hour, min, seconds, value = value[0:1], value[1:3], value[4:6], "00", value[6:]
   999  			} else if std == stdNumShortTZ || std == stdISO8601ShortTZ {
  1000  				if len(value) < 3 {
  1001  					err = errBad
  1002  					break
  1003  				}
  1004  				sign, hour, min, seconds, value = value[0:1], value[1:3], "00", "00", value[3:]
  1005  			} else if std == stdISO8601ColonSecondsTZ || std == stdNumColonSecondsTZ {
  1006  				if len(value) < 9 {
  1007  					err = errBad
  1008  					break
  1009  				}
  1010  				if value[3] != ':' || value[6] != ':' {
  1011  					err = errBad
  1012  					break
  1013  				}
  1014  				sign, hour, min, seconds, value = value[0:1], value[1:3], value[4:6], value[7:9], value[9:]
  1015  			} else if std == stdISO8601SecondsTZ || std == stdNumSecondsTz {
  1016  				if len(value) < 7 {
  1017  					err = errBad
  1018  					break
  1019  				}
  1020  				sign, hour, min, seconds, value = value[0:1], value[1:3], value[3:5], value[5:7], value[7:]
  1021  			} else {
  1022  				if len(value) < 5 {
  1023  					err = errBad
  1024  					break
  1025  				}
  1026  				sign, hour, min, seconds, value = value[0:1], value[1:3], value[3:5], "00", value[5:]
  1027  			}
  1028  			var hr, mm, ss int
  1029  			hr, err = atoi(hour)
  1030  			if err == nil {
  1031  				mm, err = atoi(min)
  1032  			}
  1033  			if err == nil {
  1034  				ss, err = atoi(seconds)
  1035  			}
  1036  			zoneOffset = (hr*60+mm)*60 + ss // offset is in seconds
  1037  			switch sign[0] {
  1038  			case '+':
  1039  			case '-':
  1040  				zoneOffset = -zoneOffset
  1041  			default:
  1042  				err = errBad
  1043  			}
  1044  		case stdTZ:
  1045  			// Does it look like a time zone?
  1046  			if len(value) >= 3 && value[0:3] == "UTC" {
  1047  				z = UTC
  1048  				value = value[3:]
  1049  				break
  1050  			}
  1051  			n, ok := parseTimeZone(value)
  1052  			if !ok {
  1053  				err = errBad
  1054  				break
  1055  			}
  1056  			zoneName, value = value[:n], value[n:]
  1057  
  1058  		case stdFracSecond0:
  1059  			// stdFracSecond0 requires the exact number of digits as specified in
  1060  			// the layout.
  1061  			ndigit := 1 + (std >> stdArgShift)
  1062  			if len(value) < ndigit {
  1063  				err = errBad
  1064  				break
  1065  			}
  1066  			nsec, rangeErrString, err = parseNanoseconds(value, ndigit)
  1067  			value = value[ndigit:]
  1068  
  1069  		case stdFracSecond9:
  1070  			if len(value) < 2 || value[0] != '.' || value[1] < '0' || '9' < value[1] {
  1071  				// Fractional second omitted.
  1072  				break
  1073  			}
  1074  			// Take any number of digits, even more than asked for,
  1075  			// because it is what the stdSecond case would do.
  1076  			i := 0
  1077  			for i < 9 && i+1 < len(value) && '0' <= value[i+1] && value[i+1] <= '9' {
  1078  				i++
  1079  			}
  1080  			nsec, rangeErrString, err = parseNanoseconds(value, 1+i)
  1081  			value = value[1+i:]
  1082  		}
  1083  		if rangeErrString != "" {
  1084  			return Time{}, &ParseError{alayout, avalue, stdstr, value, ": " + rangeErrString + " out of range"}
  1085  		}
  1086  		if err != nil {
  1087  			return Time{}, &ParseError{alayout, avalue, stdstr, value, ""}
  1088  		}
  1089  	}
  1090  	if pmSet && hour < 12 {
  1091  		hour += 12
  1092  	} else if amSet && hour == 12 {
  1093  		hour = 0
  1094  	}
  1095  
  1096  	// Convert yday to day, month.
  1097  	if yday >= 0 {
  1098  		var d int
  1099  		var m int
  1100  		if isLeap(year) {
  1101  			if yday == 31+29 {
  1102  				m = int(February)
  1103  				d = 29
  1104  			} else if yday > 31+29 {
  1105  				yday--
  1106  			}
  1107  		}
  1108  		if yday < 1 || yday > 365 {
  1109  			return Time{}, &ParseError{alayout, avalue, "", value, ": day-of-year out of range"}
  1110  		}
  1111  		if m == 0 {
  1112  			m = yday/31 + 1
  1113  			if int(daysBefore[m]) < yday {
  1114  				m++
  1115  			}
  1116  			d = yday - int(daysBefore[m-1])
  1117  		}
  1118  		// If month, day already seen, yday's m, d must match.
  1119  		// Otherwise, set them from m, d.
  1120  		if month >= 0 && month != m {
  1121  			return Time{}, &ParseError{alayout, avalue, "", value, ": day-of-year does not match month"}
  1122  		}
  1123  		month = m
  1124  		if day >= 0 && day != d {
  1125  			return Time{}, &ParseError{alayout, avalue, "", value, ": day-of-year does not match day"}
  1126  		}
  1127  		day = d
  1128  	} else {
  1129  		if month < 0 {
  1130  			month = int(January)
  1131  		}
  1132  		if day < 0 {
  1133  			day = 1
  1134  		}
  1135  	}
  1136  
  1137  	// Validate the day of the month.
  1138  	if day < 1 || day > daysIn(Month(month), year) {
  1139  		return Time{}, &ParseError{alayout, avalue, "", value, ": day out of range"}
  1140  	}
  1141  
  1142  	if z != nil {
  1143  		return Date(year, Month(month), day, hour, min, sec, nsec, z), nil
  1144  	}
  1145  
  1146  	if zoneOffset != -1 {
  1147  		t := Date(year, Month(month), day, hour, min, sec, nsec, UTC)
  1148  		t.addSec(-int64(zoneOffset))
  1149  
  1150  		// Look for local zone with the given offset.
  1151  		// If that zone was in effect at the given time, use it.
  1152  		name, offset, _, _ := local.lookup(t.unixSec())
  1153  		if offset == zoneOffset && (zoneName == "" || name == zoneName) {
  1154  			t.setLoc(local)
  1155  			return t, nil
  1156  		}
  1157  
  1158  		// Otherwise create fake zone to record offset.
  1159  		t.setLoc(FixedZone(zoneName, zoneOffset))
  1160  		return t, nil
  1161  	}
  1162  
  1163  	if zoneName != "" {
  1164  		t := Date(year, Month(month), day, hour, min, sec, nsec, UTC)
  1165  		// Look for local zone with the given offset.
  1166  		// If that zone was in effect at the given time, use it.
  1167  		offset, ok := local.lookupName(zoneName, t.unixSec())
  1168  		if ok {
  1169  			t.addSec(-int64(offset))
  1170  			t.setLoc(local)
  1171  			return t, nil
  1172  		}
  1173  
  1174  		// Otherwise, create fake zone with unknown offset.
  1175  		if len(zoneName) > 3 && zoneName[:3] == "GMT" {
  1176  			offset, _ = atoi(zoneName[3:]) // Guaranteed OK by parseGMT.
  1177  			offset *= 3600
  1178  		}
  1179  		t.setLoc(FixedZone(zoneName, offset))
  1180  		return t, nil
  1181  	}
  1182  
  1183  	// Otherwise, fall back to default.
  1184  	return Date(year, Month(month), day, hour, min, sec, nsec, defaultLocation), nil
  1185  }
  1186  
  1187  // parseTimeZone parses a time zone string and returns its length. Time zones
  1188  // are human-generated and unpredictable. We can't do precise error checking.
  1189  // On the other hand, for a correct parse there must be a time zone at the
  1190  // beginning of the string, so it's almost always true that there's one
  1191  // there. We look at the beginning of the string for a run of upper-case letters.
  1192  // If there are more than 5, it's an error.
  1193  // If there are 4 or 5 and the last is a T, it's a time zone.
  1194  // If there are 3, it's a time zone.
  1195  // Otherwise, other than special cases, it's not a time zone.
  1196  // GMT is special because it can have an hour offset.
  1197  func parseTimeZone(value string) (length int, ok bool) {
  1198  	if len(value) < 3 {
  1199  		return 0, false
  1200  	}
  1201  	// Special case 1: ChST and MeST are the only zones with a lower-case letter.
  1202  	if len(value) >= 4 && (value[:4] == "ChST" || value[:4] == "MeST") {
  1203  		return 4, true
  1204  	}
  1205  	// Special case 2: GMT may have an hour offset; treat it specially.
  1206  	if value[:3] == "GMT" {
  1207  		length = parseGMT(value)
  1208  		return length, true
  1209  	}
  1210  	// Special Case 3: Some time zones are not named, but have +/-00 format
  1211  	if value[0] == '+' || value[0] == '-' {
  1212  		length = parseSignedOffset(value)
  1213  		ok := length > 0 // parseSignedOffset returns 0 in case of bad input
  1214  		return length, ok
  1215  	}
  1216  	// How many upper-case letters are there? Need at least three, at most five.
  1217  	var nUpper int
  1218  	for nUpper = 0; nUpper < 6; nUpper++ {
  1219  		if nUpper >= len(value) {
  1220  			break
  1221  		}
  1222  		if c := value[nUpper]; c < 'A' || 'Z' < c {
  1223  			break
  1224  		}
  1225  	}
  1226  	switch nUpper {
  1227  	case 0, 1, 2, 6:
  1228  		return 0, false
  1229  	case 5: // Must end in T to match.
  1230  		if value[4] == 'T' {
  1231  			return 5, true
  1232  		}
  1233  	case 4:
  1234  		// Must end in T, except one special case.
  1235  		if value[3] == 'T' || value[:4] == "WITA" {
  1236  			return 4, true
  1237  		}
  1238  	case 3:
  1239  		return 3, true
  1240  	}
  1241  	return 0, false
  1242  }
  1243  
  1244  // parseGMT parses a GMT time zone. The input string is known to start "GMT".
  1245  // The function checks whether that is followed by a sign and a number in the
  1246  // range -23 through +23 excluding zero.
  1247  func parseGMT(value string) int {
  1248  	value = value[3:]
  1249  	if len(value) == 0 {
  1250  		return 3
  1251  	}
  1252  
  1253  	return 3 + parseSignedOffset(value)
  1254  }
  1255  
  1256  // parseSignedOffset parses a signed timezone offset (e.g. "+03" or "-04").
  1257  // The function checks for a signed number in the range -23 through +23 excluding zero.
  1258  // Returns length of the found offset string or 0 otherwise
  1259  func parseSignedOffset(value string) int {
  1260  	sign := value[0]
  1261  	if sign != '-' && sign != '+' {
  1262  		return 0
  1263  	}
  1264  	x, rem, err := leadingInt(value[1:])
  1265  
  1266  	// fail if nothing consumed by leadingInt
  1267  	if err != nil || value[1:] == rem {
  1268  		return 0
  1269  	}
  1270  	if sign == '-' {
  1271  		x = -x
  1272  	}
  1273  	if x < -23 || 23 < x {
  1274  		return 0
  1275  	}
  1276  	return len(value) - len(rem)
  1277  }
  1278  
  1279  func parseNanoseconds(value string, nbytes int) (ns int, rangeErrString string, err error) {
  1280  	if value[0] != '.' {
  1281  		err = errBad
  1282  		return
  1283  	}
  1284  	if ns, err = atoi(value[1:nbytes]); err != nil {
  1285  		return
  1286  	}
  1287  	if ns < 0 || 1e9 <= ns {
  1288  		rangeErrString = "fractional second"
  1289  		return
  1290  	}
  1291  	// We need nanoseconds, which means scaling by the number
  1292  	// of missing digits in the format, maximum length 10. If it's
  1293  	// longer than 10, we won't scale.
  1294  	scaleDigits := 10 - nbytes
  1295  	for i := 0; i < scaleDigits; i++ {
  1296  		ns *= 10
  1297  	}
  1298  	return
  1299  }
  1300  
  1301  var errLeadingInt = errors.New("time: bad [0-9]*") // never printed
  1302  
  1303  // leadingInt consumes the leading [0-9]* from s.
  1304  func leadingInt(s string) (x int64, rem string, err error) {
  1305  	i := 0
  1306  	for ; i < len(s); i++ {
  1307  		c := s[i]
  1308  		if c < '0' || c > '9' {
  1309  			break
  1310  		}
  1311  		if x > (1<<63-1)/10 {
  1312  			// overflow
  1313  			return 0, "", errLeadingInt
  1314  		}
  1315  		x = x*10 + int64(c) - '0'
  1316  		if x < 0 {
  1317  			// overflow
  1318  			return 0, "", errLeadingInt
  1319  		}
  1320  	}
  1321  	return x, s[i:], nil
  1322  }
  1323  
  1324  // leadingFraction consumes the leading [0-9]* from s.
  1325  // It is used only for fractions, so does not return an error on overflow,
  1326  // it just stops accumulating precision.
  1327  func leadingFraction(s string) (x int64, scale float64, rem string) {
  1328  	i := 0
  1329  	scale = 1
  1330  	overflow := false
  1331  	for ; i < len(s); i++ {
  1332  		c := s[i]
  1333  		if c < '0' || c > '9' {
  1334  			break
  1335  		}
  1336  		if overflow {
  1337  			continue
  1338  		}
  1339  		if x > (1<<63-1)/10 {
  1340  			// It's possible for overflow to give a positive number, so take care.
  1341  			overflow = true
  1342  			continue
  1343  		}
  1344  		y := x*10 + int64(c) - '0'
  1345  		if y < 0 {
  1346  			overflow = true
  1347  			continue
  1348  		}
  1349  		x = y
  1350  		scale *= 10
  1351  	}
  1352  	return x, scale, s[i:]
  1353  }
  1354  
  1355  var unitMap = map[string]int64{
  1356  	"ns": int64(Nanosecond),
  1357  	"us": int64(Microsecond),
  1358  	"µs": int64(Microsecond), // U+00B5 = micro symbol
  1359  	"μs": int64(Microsecond), // U+03BC = Greek letter mu
  1360  	"ms": int64(Millisecond),
  1361  	"s":  int64(Second),
  1362  	"m":  int64(Minute),
  1363  	"h":  int64(Hour),
  1364  }
  1365  
  1366  // ParseDuration parses a duration string.
  1367  // A duration string is a possibly signed sequence of
  1368  // decimal numbers, each with optional fraction and a unit suffix,
  1369  // such as "300ms", "-1.5h" or "2h45m".
  1370  // Valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h".
  1371  func ParseDuration(s string) (Duration, error) {
  1372  	// [-+]?([0-9]*(\.[0-9]*)?[a-z]+)+
  1373  	orig := s
  1374  	var d int64
  1375  	neg := false
  1376  
  1377  	// Consume [-+]?
  1378  	if s != "" {
  1379  		c := s[0]
  1380  		if c == '-' || c == '+' {
  1381  			neg = c == '-'
  1382  			s = s[1:]
  1383  		}
  1384  	}
  1385  	// Special case: if all that is left is "0", this is zero.
  1386  	if s == "0" {
  1387  		return 0, nil
  1388  	}
  1389  	if s == "" {
  1390  		return 0, errors.New("time: invalid duration " + orig)
  1391  	}
  1392  	for s != "" {
  1393  		var (
  1394  			v, f  int64       // integers before, after decimal point
  1395  			scale float64 = 1 // value = v + f/scale
  1396  		)
  1397  
  1398  		var err error
  1399  
  1400  		// The next character must be [0-9.]
  1401  		if !(s[0] == '.' || '0' <= s[0] && s[0] <= '9') {
  1402  			return 0, errors.New("time: invalid duration " + orig)
  1403  		}
  1404  		// Consume [0-9]*
  1405  		pl := len(s)
  1406  		v, s, err = leadingInt(s)
  1407  		if err != nil {
  1408  			return 0, errors.New("time: invalid duration " + orig)
  1409  		}
  1410  		pre := pl != len(s) // whether we consumed anything before a period
  1411  
  1412  		// Consume (\.[0-9]*)?
  1413  		post := false
  1414  		if s != "" && s[0] == '.' {
  1415  			s = s[1:]
  1416  			pl := len(s)
  1417  			f, scale, s = leadingFraction(s)
  1418  			post = pl != len(s)
  1419  		}
  1420  		if !pre && !post {
  1421  			// no digits (e.g. ".s" or "-.s")
  1422  			return 0, errors.New("time: invalid duration " + orig)
  1423  		}
  1424  
  1425  		// Consume unit.
  1426  		i := 0
  1427  		for ; i < len(s); i++ {
  1428  			c := s[i]
  1429  			if c == '.' || '0' <= c && c <= '9' {
  1430  				break
  1431  			}
  1432  		}
  1433  		if i == 0 {
  1434  			return 0, errors.New("time: missing unit in duration " + orig)
  1435  		}
  1436  		u := s[:i]
  1437  		s = s[i:]
  1438  		unit, ok := unitMap[u]
  1439  		if !ok {
  1440  			return 0, errors.New("time: unknown unit " + u + " in duration " + orig)
  1441  		}
  1442  		if v > (1<<63-1)/unit {
  1443  			// overflow
  1444  			return 0, errors.New("time: invalid duration " + orig)
  1445  		}
  1446  		v *= unit
  1447  		if f > 0 {
  1448  			// float64 is needed to be nanosecond accurate for fractions of hours.
  1449  			// v >= 0 && (f*unit/scale) <= 3.6e+12 (ns/h, h is the largest unit)
  1450  			v += int64(float64(f) * (float64(unit) / scale))
  1451  			if v < 0 {
  1452  				// overflow
  1453  				return 0, errors.New("time: invalid duration " + orig)
  1454  			}
  1455  		}
  1456  		d += v
  1457  		if d < 0 {
  1458  			// overflow
  1459  			return 0, errors.New("time: invalid duration " + orig)
  1460  		}
  1461  	}
  1462  
  1463  	if neg {
  1464  		d = -d
  1465  	}
  1466  	return Duration(d), nil
  1467  }
  1468  

View as plain text