Source file src/time/format.go

     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 these layouts is the specific time stamp:
    11  //	01/02 03:04:05PM '06 -0700
    12  // (January 2, 15:04:05, 2006, in time zone seven hours west of GMT).
    13  // That value is recorded as the constant named Layout, listed below. As a Unix
    14  // time, this is 1136239445. Since MST is GMT-0700, the reference would be
    15  // printed by the Unix date command as:
    16  //	Mon Jan 2 15:04:05 MST 2006
    17  // It is a regrettable historic error that the date uses the American convention
    18  // of putting the numerical month before the day.
    19  //
    20  // The example for Time.Format demonstrates the working of the layout string
    21  // in detail and is a good reference.
    22  //
    23  // Note that the RFC822, RFC850, and RFC1123 formats should be applied
    24  // only to local times. Applying them to UTC times will use "UTC" as the
    25  // time zone abbreviation, while strictly speaking those RFCs require the
    26  // use of "GMT" in that case.
    27  // In general RFC1123Z should be used instead of RFC1123 for servers
    28  // that insist on that format, and RFC3339 should be preferred for new protocols.
    29  // RFC3339, RFC822, RFC822Z, RFC1123, and RFC1123Z are useful for formatting;
    30  // when used with time.Parse they do not accept all the time formats
    31  // permitted by the RFCs and they do accept time formats not formally defined.
    32  // The RFC3339Nano format removes trailing zeros from the seconds field
    33  // and thus may not sort correctly once formatted.
    34  //
    35  // Most programs can use one of the defined constants as the layout passed to
    36  // Format or Parse. The rest of this comment can be ignored unless you are
    37  // creating a custom layout string.
    38  //
    39  // To define your own format, write down what the reference time would look like
    40  // formatted your way; see the values of constants like ANSIC, StampMicro or
    41  // Kitchen for examples. The model is to demonstrate what the reference time
    42  // looks like so that the Format and Parse methods can apply the same
    43  // transformation to a general time value.
    44  //
    45  // Here is a summary of the components of a layout string. Each element shows by
    46  // example the formatting of an element of the reference time. Only these values
    47  // are recognized. Text in the layout string that is not recognized as part of
    48  // the reference time is echoed verbatim during Format and expected to appear
    49  // verbatim in the input to Parse.
    50  //
    51  //	Year: "2006" "06"
    52  //	Month: "Jan" "January"
    53  //	Textual day of the week: "Mon" "Monday"
    54  //	Numeric day of the month: "2" "_2" "02"
    55  //	Numeric day of the year: "__2" "002"
    56  //	Hour: "15" "3" "03" (PM or AM)
    57  //	Minute: "4" "04"
    58  //	Second: "5" "05"
    59  //	AM/PM mark: "PM"
    60  //
    61  // Numeric time zone offsets format as follows:
    62  //	"-0700"  ±hhmm
    63  //	"-07:00" ±hh:mm
    64  //	"-07"    ±hh
    65  // Replacing the sign in the format with a Z triggers
    66  // the ISO 8601 behavior of printing Z instead of an
    67  // offset for the UTC zone. Thus:
    68  //	"Z0700"  Z or ±hhmm
    69  //	"Z07:00" Z or ±hh:mm
    70  //	"Z07"    Z or ±hh
    71  //
    72  // Within the format string, the underscores in "_2" and "__2" represent spaces
    73  // that may be replaced by digits if the following number has multiple digits,
    74  // for compatibility with fixed-width Unix time formats. A leading zero represents
    75  // a zero-padded value.
    76  //
    77  // The formats __2 and 002 are space-padded and zero-padded
    78  // three-character day of year; there is no unpadded day of year format.
    79  //
    80  // A comma or decimal point followed by one or more zeros represents
    81  // a fractional second, printed to the given number of decimal places.
    82  // A comma or decimal point followed by one or more nines represents
    83  // a fractional second, printed to the given number of decimal places, with
    84  // trailing zeros removed.
    85  // For example "15:04:05,000" or "15:04:05.000" formats or parses with
    86  // millisecond precision.
    87  //
    88  // Some valid layouts are invalid time values for time.Parse, due to formats
    89  // such as _ for space padding and Z for zone information.
    90  //
    91  const (
    92  	Layout      = "01/02 03:04:05PM '06 -0700" // The reference time, in numerical order.
    93  	ANSIC       = "Mon Jan _2 15:04:05 2006"
    94  	UnixDate    = "Mon Jan _2 15:04:05 MST 2006"
    95  	RubyDate    = "Mon Jan 02 15:04:05 -0700 2006"
    96  	RFC822      = "02 Jan 06 15:04 MST"
    97  	RFC822Z     = "02 Jan 06 15:04 -0700" // RFC822 with numeric zone
    98  	RFC850      = "Monday, 02-Jan-06 15:04:05 MST"
    99  	RFC1123     = "Mon, 02 Jan 2006 15:04:05 MST"
   100  	RFC1123Z    = "Mon, 02 Jan 2006 15:04:05 -0700" // RFC1123 with numeric zone
   101  	RFC3339     = "2006-01-02T15:04:05Z07:00"
   102  	RFC3339Nano = "2006-01-02T15:04:05.999999999Z07:00"
   103  	Kitchen     = "3:04PM"
   104  	// Handy time stamps.
   105  	Stamp      = "Jan _2 15:04:05"
   106  	StampMilli = "Jan _2 15:04:05.000"
   107  	StampMicro = "Jan _2 15:04:05.000000"
   108  	StampNano  = "Jan _2 15:04:05.000000000"
   109  )
   110  
   111  const (
   112  	_                        = iota
   113  	stdLongMonth             = iota + stdNeedDate  // "January"
   114  	stdMonth                                       // "Jan"
   115  	stdNumMonth                                    // "1"
   116  	stdZeroMonth                                   // "01"
   117  	stdLongWeekDay                                 // "Monday"
   118  	stdWeekDay                                     // "Mon"
   119  	stdDay                                         // "2"
   120  	stdUnderDay                                    // "_2"
   121  	stdZeroDay                                     // "02"
   122  	stdUnderYearDay                                // "__2"
   123  	stdZeroYearDay                                 // "002"
   124  	stdHour                  = iota + stdNeedClock // "15"
   125  	stdHour12                                      // "3"
   126  	stdZeroHour12                                  // "03"
   127  	stdMinute                                      // "4"
   128  	stdZeroMinute                                  // "04"
   129  	stdSecond                                      // "5"
   130  	stdZeroSecond                                  // "05"
   131  	stdLongYear              = iota + stdNeedDate  // "2006"
   132  	stdYear                                        // "06"
   133  	stdPM                    = iota + stdNeedClock // "PM"
   134  	stdpm                                          // "pm"
   135  	stdTZ                    = iota                // "MST"
   136  	stdISO8601TZ                                   // "Z0700"  // prints Z for UTC
   137  	stdISO8601SecondsTZ                            // "Z070000"
   138  	stdISO8601ShortTZ                              // "Z07"
   139  	stdISO8601ColonTZ                              // "Z07:00" // prints Z for UTC
   140  	stdISO8601ColonSecondsTZ                       // "Z07:00:00"
   141  	stdNumTZ                                       // "-0700"  // always numeric
   142  	stdNumSecondsTz                                // "-070000"
   143  	stdNumShortTZ                                  // "-07"    // always numeric
   144  	stdNumColonTZ                                  // "-07:00" // always numeric
   145  	stdNumColonSecondsTZ                           // "-07:00:00"
   146  	stdFracSecond0                                 // ".0", ".00", ... , trailing zeros included
   147  	stdFracSecond9                                 // ".9", ".99", ..., trailing zeros omitted
   148  
   149  	stdNeedDate       = 1 << 8             // need month, day, year
   150  	stdNeedClock      = 2 << 8             // need hour, minute, second
   151  	stdArgShift       = 16                 // extra argument in high bits, above low stdArgShift
   152  	stdSeparatorShift = 28                 // extra argument in high 4 bits for fractional second separators
   153  	stdMask           = 1<<stdArgShift - 1 // mask out argument
   154  )
   155  
   156  // std0x records the std values for "01", "02", ..., "06".
   157  var std0x = [...]int{stdZeroMonth, stdZeroDay, stdZeroHour12, stdZeroMinute, stdZeroSecond, stdYear}
   158  
   159  // startsWithLowerCase reports whether the string has a lower-case letter at the beginning.
   160  // Its purpose is to prevent matching strings like "Month" when looking for "Mon".
   161  func startsWithLowerCase(str string) bool {
   162  	if len(str) == 0 {
   163  		return false
   164  	}
   165  	c := str[0]
   166  	return 'a' <= c && c <= 'z'
   167  }
   168  
   169  // nextStdChunk finds the first occurrence of a std string in
   170  // layout and returns the text before, the std string, and the text after.
   171  func nextStdChunk(layout string) (prefix string, std int, suffix string) {
   172  	for i := 0; i < len(layout); i++ {
   173  		switch c := int(layout[i]); c {
   174  		case 'J': // January, Jan
   175  			if len(layout) >= i+3 && layout[i:i+3] == "Jan" {
   176  				if len(layout) >= i+7 && layout[i:i+7] == "January" {
   177  					return layout[0:i], stdLongMonth, layout[i+7:]
   178  				}
   179  				if !startsWithLowerCase(layout[i+3:]) {
   180  					return layout[0:i], stdMonth, layout[i+3:]
   181  				}
   182  			}
   183  
   184  		case 'M': // Monday, Mon, MST
   185  			if len(layout) >= i+3 {
   186  				if layout[i:i+3] == "Mon" {
   187  					if len(layout) >= i+6 && layout[i:i+6] == "Monday" {
   188  						return layout[0:i], stdLongWeekDay, layout[i+6:]
   189  					}
   190  					if !startsWithLowerCase(layout[i+3:]) {
   191  						return layout[0:i], stdWeekDay, layout[i+3:]
   192  					}
   193  				}
   194  				if layout[i:i+3] == "MST" {
   195  					return layout[0:i], stdTZ, layout[i+3:]
   196  				}
   197  			}
   198  
   199  		case '0': // 01, 02, 03, 04, 05, 06, 002
   200  			if len(layout) >= i+2 && '1' <= layout[i+1] && layout[i+1] <= '6' {
   201  				return layout[0:i], std0x[layout[i+1]-'1'], layout[i+2:]
   202  			}
   203  			if len(layout) >= i+3 && layout[i+1] == '0' && layout[i+2] == '2' {
   204  				return layout[0:i], stdZeroYearDay, layout[i+3:]
   205  			}
   206  
   207  		case '1': // 15, 1
   208  			if len(layout) >= i+2 && layout[i+1] == '5' {
   209  				return layout[0:i], stdHour, layout[i+2:]
   210  			}
   211  			return layout[0:i], stdNumMonth, layout[i+1:]
   212  
   213  		case '2': // 2006, 2
   214  			if len(layout) >= i+4 && layout[i:i+4] == "2006" {
   215  				return layout[0:i], stdLongYear, layout[i+4:]
   216  			}
   217  			return layout[0:i], stdDay, layout[i+1:]
   218  
   219  		case '_': // _2, _2006, __2
   220  			if len(layout) >= i+2 && layout[i+1] == '2' {
   221  				//_2006 is really a literal _, followed by stdLongYear
   222  				if len(layout) >= i+5 && layout[i+1:i+5] == "2006" {
   223  					return layout[0 : i+1], stdLongYear, layout[i+5:]
   224  				}
   225  				return layout[0:i], stdUnderDay, layout[i+2:]
   226  			}
   227  			if len(layout) >= i+3 && layout[i+1] == '_' && layout[i+2] == '2' {
   228  				return layout[0:i], stdUnderYearDay, layout[i+3:]
   229  			}
   230  
   231  		case '3':
   232  			return layout[0:i], stdHour12, layout[i+1:]
   233  
   234  		case '4':
   235  			return layout[0:i], stdMinute, layout[i+1:]
   236  
   237  		case '5':
   238  			return layout[0:i], stdSecond, layout[i+1:]
   239  
   240  		case 'P': // PM
   241  			if len(layout) >= i+2 && layout[i+1] == 'M' {
   242  				return layout[0:i], stdPM, layout[i+2:]
   243  			}
   244  
   245  		case 'p': // pm
   246  			if len(layout) >= i+2 && layout[i+1] == 'm' {
   247  				return layout[0:i], stdpm, layout[i+2:]
   248  			}
   249  
   250  		case '-': // -070000, -07:00:00, -0700, -07:00, -07
   251  			if len(layout) >= i+7 && layout[i:i+7] == "-070000" {
   252  				return layout[0:i], stdNumSecondsTz, layout[i+7:]
   253  			}
   254  			if len(layout) >= i+9 && layout[i:i+9] == "-07:00:00" {
   255  				return layout[0:i], stdNumColonSecondsTZ, layout[i+9:]
   256  			}
   257  			if len(layout) >= i+5 && layout[i:i+5] == "-0700" {
   258  				return layout[0:i], stdNumTZ, layout[i+5:]
   259  			}
   260  			if len(layout) >= i+6 && layout[i:i+6] == "-07:00" {
   261  				return layout[0:i], stdNumColonTZ, layout[i+6:]
   262  			}
   263  			if len(layout) >= i+3 && layout[i:i+3] == "-07" {
   264  				return layout[0:i], stdNumShortTZ, layout[i+3:]
   265  			}
   266  
   267  		case 'Z': // Z070000, Z07:00:00, Z0700, Z07:00,
   268  			if len(layout) >= i+7 && layout[i:i+7] == "Z070000" {
   269  				return layout[0:i], stdISO8601SecondsTZ, layout[i+7:]
   270  			}
   271  			if len(layout) >= i+9 && layout[i:i+9] == "Z07:00:00" {
   272  				return layout[0:i], stdISO8601ColonSecondsTZ, layout[i+9:]
   273  			}
   274  			if len(layout) >= i+5 && layout[i:i+5] == "Z0700" {
   275  				return layout[0:i], stdISO8601TZ, layout[i+5:]
   276  			}
   277  			if len(layout) >= i+6 && layout[i:i+6] == "Z07:00" {
   278  				return layout[0:i], stdISO8601ColonTZ, layout[i+6:]
   279  			}
   280  			if len(layout) >= i+3 && layout[i:i+3] == "Z07" {
   281  				return layout[0:i], stdISO8601ShortTZ, layout[i+3:]
   282  			}
   283  
   284  		case '.', ',': // ,000, or .000, or ,999, or .999 - repeated digits for fractional seconds.
   285  			if i+1 < len(layout) && (layout[i+1] == '0' || layout[i+1] == '9') {
   286  				ch := layout[i+1]
   287  				j := i + 1
   288  				for j < len(layout) && layout[j] == ch {
   289  					j++
   290  				}
   291  				// String of digits must end here - only fractional second is all digits.
   292  				if !isDigit(layout, j) {
   293  					code := stdFracSecond0
   294  					if layout[i+1] == '9' {
   295  						code = stdFracSecond9
   296  					}
   297  					std := stdFracSecond(code, j-(i+1), c)
   298  					return layout[0:i], std, layout[j:]
   299  				}
   300  			}
   301  		}
   302  	}
   303  	return layout, 0, ""
   304  }
   305  
   306  var longDayNames = []string{
   307  	"Sunday",
   308  	"Monday",
   309  	"Tuesday",
   310  	"Wednesday",
   311  	"Thursday",
   312  	"Friday",
   313  	"Saturday",
   314  }
   315  
   316  var shortDayNames = []string{
   317  	"Sun",
   318  	"Mon",
   319  	"Tue",
   320  	"Wed",
   321  	"Thu",
   322  	"Fri",
   323  	"Sat",
   324  }
   325  
   326  var shortMonthNames = []string{
   327  	"Jan",
   328  	"Feb",
   329  	"Mar",
   330  	"Apr",
   331  	"May",
   332  	"Jun",
   333  	"Jul",
   334  	"Aug",
   335  	"Sep",
   336  	"Oct",
   337  	"Nov",
   338  	"Dec",
   339  }
   340  
   341  var longMonthNames = []string{
   342  	"January",
   343  	"February",
   344  	"March",
   345  	"April",
   346  	"May",
   347  	"June",
   348  	"July",
   349  	"August",
   350  	"September",
   351  	"October",
   352  	"November",
   353  	"December",
   354  }
   355  
   356  // match reports whether s1 and s2 match ignoring case.
   357  // It is assumed s1 and s2 are the same length.
   358  func match(s1, s2 string) bool {
   359  	for i := 0; i < len(s1); i++ {
   360  		c1 := s1[i]
   361  		c2 := s2[i]
   362  		if c1 != c2 {
   363  			// Switch to lower-case; 'a'-'A' is known to be a single bit.
   364  			c1 |= 'a' - 'A'
   365  			c2 |= 'a' - 'A'
   366  			if c1 != c2 || c1 < 'a' || c1 > 'z' {
   367  				return false
   368  			}
   369  		}
   370  	}
   371  	return true
   372  }
   373  
   374  func lookup(tab []string, val string) (int, string, error) {
   375  	for i, v := range tab {
   376  		if len(val) >= len(v) && match(val[0:len(v)], v) {
   377  			return i, val[len(v):], nil
   378  		}
   379  	}
   380  	return -1, val, errBad
   381  }
   382  
   383  // appendInt appends the decimal form of x to b and returns the result.
   384  // If the decimal form (excluding sign) is shorter than width, the result is padded with leading 0's.
   385  // Duplicates functionality in strconv, but avoids dependency.
   386  func appendInt(b []byte, x int, width int) []byte {
   387  	u := uint(x)
   388  	if x < 0 {
   389  		b = append(b, '-')
   390  		u = uint(-x)
   391  	}
   392  
   393  	// Assemble decimal in reverse order.
   394  	var buf [20]byte
   395  	i := len(buf)
   396  	for u >= 10 {
   397  		i--
   398  		q := u / 10
   399  		buf[i] = byte('0' + u - q*10)
   400  		u = q
   401  	}
   402  	i--
   403  	buf[i] = byte('0' + u)
   404  
   405  	// Add 0-padding.
   406  	for w := len(buf) - i; w < width; w++ {
   407  		b = append(b, '0')
   408  	}
   409  
   410  	return append(b, buf[i:]...)
   411  }
   412  
   413  // Never printed, just needs to be non-nil for return by atoi.
   414  var atoiError = errors.New("time: invalid number")
   415  
   416  // Duplicates functionality in strconv, but avoids dependency.
   417  func atoi(s string) (x int, err error) {
   418  	neg := false
   419  	if s != "" && (s[0] == '-' || s[0] == '+') {
   420  		neg = s[0] == '-'
   421  		s = s[1:]
   422  	}
   423  	q, rem, err := leadingInt(s)
   424  	x = int(q)
   425  	if err != nil || rem != "" {
   426  		return 0, atoiError
   427  	}
   428  	if neg {
   429  		x = -x
   430  	}
   431  	return x, nil
   432  }
   433  
   434  // The "std" value passed to formatNano contains two packed fields: the number of
   435  // digits after the decimal and the separator character (period or comma).
   436  // These functions pack and unpack that variable.
   437  func stdFracSecond(code, n, c int) int {
   438  	// Use 0xfff to make the failure case even more absurd.
   439  	if c == '.' {
   440  		return code | ((n & 0xfff) << stdArgShift)
   441  	}
   442  	return code | ((n & 0xfff) << stdArgShift) | 1<<stdSeparatorShift
   443  }
   444  
   445  func digitsLen(std int) int {
   446  	return (std >> stdArgShift) & 0xfff
   447  }
   448  
   449  func separator(std int) byte {
   450  	if (std >> stdSeparatorShift) == 0 {
   451  		return '.'
   452  	}
   453  	return ','
   454  }
   455  
   456  // formatNano appends a fractional second, as nanoseconds, to b
   457  // and returns the result.
   458  func formatNano(b []byte, nanosec uint, std int) []byte {
   459  	var (
   460  		n         = digitsLen(std)
   461  		separator = separator(std)
   462  		trim      = std&stdMask == stdFracSecond9
   463  	)
   464  	u := nanosec
   465  	var buf [9]byte
   466  	for start := len(buf); start > 0; {
   467  		start--
   468  		buf[start] = byte(u%10 + '0')
   469  		u /= 10
   470  	}
   471  
   472  	if n > 9 {
   473  		n = 9
   474  	}
   475  	if trim {
   476  		for n > 0 && buf[n-1] == '0' {
   477  			n--
   478  		}
   479  		if n == 0 {
   480  			return b
   481  		}
   482  	}
   483  	b = append(b, separator)
   484  	return append(b, buf[:n]...)
   485  }
   486  
   487  // String returns the time formatted using the format string
   488  //	"2006-01-02 15:04:05.999999999 -0700 MST"
   489  //
   490  // If the time has a monotonic clock reading, the returned string
   491  // includes a final field "m=±<value>", where value is the monotonic
   492  // clock reading formatted as a decimal number of seconds.
   493  //
   494  // The returned string is meant for debugging; for a stable serialized
   495  // representation, use t.MarshalText, t.MarshalBinary, or t.Format
   496  // with an explicit format string.
   497  func (t Time) String() string {
   498  	s := t.Format("2006-01-02 15:04:05.999999999 -0700 MST")
   499  
   500  	// Format monotonic clock reading as m=±ddd.nnnnnnnnn.
   501  	if t.wall&hasMonotonic != 0 {
   502  		m2 := uint64(t.ext)
   503  		sign := byte('+')
   504  		if t.ext < 0 {
   505  			sign = '-'
   506  			m2 = -m2
   507  		}
   508  		m1, m2 := m2/1e9, m2%1e9
   509  		m0, m1 := m1/1e9, m1%1e9
   510  		buf := make([]byte, 0, 24)
   511  		buf = append(buf, " m="...)
   512  		buf = append(buf, sign)
   513  		wid := 0
   514  		if m0 != 0 {
   515  			buf = appendInt(buf, int(m0), 0)
   516  			wid = 9
   517  		}
   518  		buf = appendInt(buf, int(m1), wid)
   519  		buf = append(buf, '.')
   520  		buf = appendInt(buf, int(m2), 9)
   521  		s += string(buf)
   522  	}
   523  	return s
   524  }
   525  
   526  // GoString implements fmt.GoStringer and formats t to be printed in Go source
   527  // code.
   528  func (t Time) GoString() string {
   529  	buf := make([]byte, 0, 70)
   530  	buf = append(buf, "time.Date("...)
   531  	buf = appendInt(buf, t.Year(), 0)
   532  	month := t.Month()
   533  	if January <= month && month <= December {
   534  		buf = append(buf, ", time."...)
   535  		buf = append(buf, t.Month().String()...)
   536  	} else {
   537  		// It's difficult to construct a time.Time with a date outside the
   538  		// standard range but we might as well try to handle the case.
   539  		buf = appendInt(buf, int(month), 0)
   540  	}
   541  	buf = append(buf, ", "...)
   542  	buf = appendInt(buf, t.Day(), 0)
   543  	buf = append(buf, ", "...)
   544  	buf = appendInt(buf, t.Hour(), 0)
   545  	buf = append(buf, ", "...)
   546  	buf = appendInt(buf, t.Minute(), 0)
   547  	buf = append(buf, ", "...)
   548  	buf = appendInt(buf, t.Second(), 0)
   549  	buf = append(buf, ", "...)
   550  	buf = appendInt(buf, t.Nanosecond(), 0)
   551  	buf = append(buf, ", "...)
   552  	switch loc := t.Location(); loc {
   553  	case UTC, nil:
   554  		buf = append(buf, "time.UTC"...)
   555  	case Local:
   556  		buf = append(buf, "time.Local"...)
   557  	default:
   558  		// there are several options for how we could display this, none of
   559  		// which are great:
   560  		//
   561  		// - use Location(loc.name), which is not technically valid syntax
   562  		// - use LoadLocation(loc.name), which will cause a syntax error when
   563  		// embedded and also would require us to escape the string without
   564  		// importing fmt or strconv
   565  		// - try to use FixedZone, which would also require escaping the name
   566  		// and would represent e.g. "America/Los_Angeles" daylight saving time
   567  		// shifts inaccurately
   568  		// - use the pointer format, which is no worse than you'd get with the
   569  		// old fmt.Sprintf("%#v", t) format.
   570  		//
   571  		// Of these, Location(loc.name) is the least disruptive. This is an edge
   572  		// case we hope not to hit too often.
   573  		buf = append(buf, `time.Location(`...)
   574  		buf = append(buf, []byte(quote(loc.name))...)
   575  		buf = append(buf, `)`...)
   576  	}
   577  	buf = append(buf, ')')
   578  	return string(buf)
   579  }
   580  
   581  // Format returns a textual representation of the time value formatted according
   582  // to the layout defined by the argument. See the documentation for the
   583  // constant called Layout to see how to represent the layout format.
   584  //
   585  // The executable example for Time.Format demonstrates the working
   586  // of the layout string in detail and is a good reference.
   587  func (t Time) Format(layout string) string {
   588  	const bufSize = 64
   589  	var b []byte
   590  	max := len(layout) + 10
   591  	if max < bufSize {
   592  		var buf [bufSize]byte
   593  		b = buf[:0]
   594  	} else {
   595  		b = make([]byte, 0, max)
   596  	}
   597  	b = t.AppendFormat(b, layout)
   598  	return string(b)
   599  }
   600  
   601  // AppendFormat is like Format but appends the textual
   602  // representation to b and returns the extended buffer.
   603  func (t Time) AppendFormat(b []byte, layout string) []byte {
   604  	var (
   605  		name, offset, abs = t.locabs()
   606  
   607  		year  int = -1
   608  		month Month
   609  		day   int
   610  		yday  int
   611  		hour  int = -1
   612  		min   int
   613  		sec   int
   614  	)
   615  	// Each iteration generates one std value.
   616  	for layout != "" {
   617  		prefix, std, suffix := nextStdChunk(layout)
   618  		if prefix != "" {
   619  			b = append(b, prefix...)
   620  		}
   621  		if std == 0 {
   622  			break
   623  		}
   624  		layout = suffix
   625  
   626  		// Compute year, month, day if needed.
   627  		if year < 0 && std&stdNeedDate != 0 {
   628  			year, month, day, yday = absDate(abs, true)
   629  			yday++
   630  		}
   631  
   632  		// Compute hour, minute, second if needed.
   633  		if hour < 0 && std&stdNeedClock != 0 {
   634  			hour, min, sec = absClock(abs)
   635  		}
   636  
   637  		switch std & stdMask {
   638  		case stdYear:
   639  			y := year
   640  			if y < 0 {
   641  				y = -y
   642  			}
   643  			b = appendInt(b, y%100, 2)
   644  		case stdLongYear:
   645  			b = appendInt(b, year, 4)
   646  		case stdMonth:
   647  			b = append(b, month.String()[:3]...)
   648  		case stdLongMonth:
   649  			m := month.String()
   650  			b = append(b, m...)
   651  		case stdNumMonth:
   652  			b = appendInt(b, int(month), 0)
   653  		case stdZeroMonth:
   654  			b = appendInt(b, int(month), 2)
   655  		case stdWeekDay:
   656  			b = append(b, absWeekday(abs).String()[:3]...)
   657  		case stdLongWeekDay:
   658  			s := absWeekday(abs).String()
   659  			b = append(b, s...)
   660  		case stdDay:
   661  			b = appendInt(b, day, 0)
   662  		case stdUnderDay:
   663  			if day < 10 {
   664  				b = append(b, ' ')
   665  			}
   666  			b = appendInt(b, day, 0)
   667  		case stdZeroDay:
   668  			b = appendInt(b, day, 2)
   669  		case stdUnderYearDay:
   670  			if yday < 100 {
   671  				b = append(b, ' ')
   672  				if yday < 10 {
   673  					b = append(b, ' ')
   674  				}
   675  			}
   676  			b = appendInt(b, yday, 0)
   677  		case stdZeroYearDay:
   678  			b = appendInt(b, yday, 3)
   679  		case stdHour:
   680  			b = appendInt(b, hour, 2)
   681  		case stdHour12:
   682  			// Noon is 12PM, midnight is 12AM.
   683  			hr := hour % 12
   684  			if hr == 0 {
   685  				hr = 12
   686  			}
   687  			b = appendInt(b, hr, 0)
   688  		case stdZeroHour12:
   689  			// Noon is 12PM, midnight is 12AM.
   690  			hr := hour % 12
   691  			if hr == 0 {
   692  				hr = 12
   693  			}
   694  			b = appendInt(b, hr, 2)
   695  		case stdMinute:
   696  			b = appendInt(b, min, 0)
   697  		case stdZeroMinute:
   698  			b = appendInt(b, min, 2)
   699  		case stdSecond:
   700  			b = appendInt(b, sec, 0)
   701  		case stdZeroSecond:
   702  			b = appendInt(b, sec, 2)
   703  		case stdPM:
   704  			if hour >= 12 {
   705  				b = append(b, "PM"...)
   706  			} else {
   707  				b = append(b, "AM"...)
   708  			}
   709  		case stdpm:
   710  			if hour >= 12 {
   711  				b = append(b, "pm"...)
   712  			} else {
   713  				b = append(b, "am"...)
   714  			}
   715  		case stdISO8601TZ, stdISO8601ColonTZ, stdISO8601SecondsTZ, stdISO8601ShortTZ, stdISO8601ColonSecondsTZ, stdNumTZ, stdNumColonTZ, stdNumSecondsTz, stdNumShortTZ, stdNumColonSecondsTZ:
   716  			// Ugly special case. We cheat and take the "Z" variants
   717  			// to mean "the time zone as formatted for ISO 8601".
   718  			if offset == 0 && (std == stdISO8601TZ || std == stdISO8601ColonTZ || std == stdISO8601SecondsTZ || std == stdISO8601ShortTZ || std == stdISO8601ColonSecondsTZ) {
   719  				b = append(b, 'Z')
   720  				break
   721  			}
   722  			zone := offset / 60 // convert to minutes
   723  			absoffset := offset
   724  			if zone < 0 {
   725  				b = append(b, '-')
   726  				zone = -zone
   727  				absoffset = -absoffset
   728  			} else {
   729  				b = append(b, '+')
   730  			}
   731  			b = appendInt(b, zone/60, 2)
   732  			if std == stdISO8601ColonTZ || std == stdNumColonTZ || std == stdISO8601ColonSecondsTZ || std == stdNumColonSecondsTZ {
   733  				b = append(b, ':')
   734  			}
   735  			if std != stdNumShortTZ && std != stdISO8601ShortTZ {
   736  				b = appendInt(b, zone%60, 2)
   737  			}
   738  
   739  			// append seconds if appropriate
   740  			if std == stdISO8601SecondsTZ || std == stdNumSecondsTz || std == stdNumColonSecondsTZ || std == stdISO8601ColonSecondsTZ {
   741  				if std == stdNumColonSecondsTZ || std == stdISO8601ColonSecondsTZ {
   742  					b = append(b, ':')
   743  				}
   744  				b = appendInt(b, absoffset%60, 2)
   745  			}
   746  
   747  		case stdTZ:
   748  			if name != "" {
   749  				b = append(b, name...)
   750  				break
   751  			}
   752  			// No time zone known for this time, but we must print one.
   753  			// Use the -0700 format.
   754  			zone := offset / 60 // convert to minutes
   755  			if zone < 0 {
   756  				b = append(b, '-')
   757  				zone = -zone
   758  			} else {
   759  				b = append(b, '+')
   760  			}
   761  			b = appendInt(b, zone/60, 2)
   762  			b = appendInt(b, zone%60, 2)
   763  		case stdFracSecond0, stdFracSecond9:
   764  			b = formatNano(b, uint(t.Nanosecond()), std)
   765  		}
   766  	}
   767  	return b
   768  }
   769  
   770  var errBad = errors.New("bad value for field") // placeholder not passed to user
   771  
   772  // ParseError describes a problem parsing a time string.
   773  type ParseError struct {
   774  	Layout     string
   775  	Value      string
   776  	LayoutElem string
   777  	ValueElem  string
   778  	Message    string
   779  }
   780  
   781  // These are borrowed from unicode/utf8 and strconv and replicate behavior in
   782  // that package, since we can't take a dependency on either.
   783  const (
   784  	lowerhex  = "0123456789abcdef"
   785  	runeSelf  = 0x80
   786  	runeError = '\uFFFD'
   787  )
   788  
   789  func quote(s string) string {
   790  	buf := make([]byte, 1, len(s)+2) // slice will be at least len(s) + quotes
   791  	buf[0] = '"'
   792  	for i, c := range s {
   793  		if c >= runeSelf || c < ' ' {
   794  			// This means you are asking us to parse a time.Duration or
   795  			// time.Location with unprintable or non-ASCII characters in it.
   796  			// We don't expect to hit this case very often. We could try to
   797  			// reproduce strconv.Quote's behavior with full fidelity but
   798  			// given how rarely we expect to hit these edge cases, speed and
   799  			// conciseness are better.
   800  			var width int
   801  			if c == runeError {
   802  				width = 1
   803  				if i+2 < len(s) && s[i:i+3] == string(runeError) {
   804  					width = 3
   805  				}
   806  			} else {
   807  				width = len(string(c))
   808  			}
   809  			for j := 0; j < width; j++ {
   810  				buf = append(buf, `\x`...)
   811  				buf = append(buf, lowerhex[s[i+j]>>4])
   812  				buf = append(buf, lowerhex[s[i+j]&0xF])
   813  			}
   814  		} else {
   815  			if c == '"' || c == '\\' {
   816  				buf = append(buf, '\\')
   817  			}
   818  			buf = append(buf, string(c)...)
   819  		}
   820  	}
   821  	buf = append(buf, '"')
   822  	return string(buf)
   823  }
   824  
   825  // Error returns the string representation of a ParseError.
   826  func (e *ParseError) Error() string {
   827  	if e.Message == "" {
   828  		return "parsing time " +
   829  			quote(e.Value) + " as " +
   830  			quote(e.Layout) + ": cannot parse " +
   831  			quote(e.ValueElem) + " as " +
   832  			quote(e.LayoutElem)
   833  	}
   834  	return "parsing time " +
   835  		quote(e.Value) + e.Message
   836  }
   837  
   838  // isDigit reports whether s[i] is in range and is a decimal digit.
   839  func isDigit(s string, i int) bool {
   840  	if len(s) <= i {
   841  		return false
   842  	}
   843  	c := s[i]
   844  	return '0' <= c && c <= '9'
   845  }
   846  
   847  // getnum parses s[0:1] or s[0:2] (fixed forces s[0:2])
   848  // as a decimal integer and returns the integer and the
   849  // remainder of the string.
   850  func getnum(s string, fixed bool) (int, string, error) {
   851  	if !isDigit(s, 0) {
   852  		return 0, s, errBad
   853  	}
   854  	if !isDigit(s, 1) {
   855  		if fixed {
   856  			return 0, s, errBad
   857  		}
   858  		return int(s[0] - '0'), s[1:], nil
   859  	}
   860  	return int(s[0]-'0')*10 + int(s[1]-'0'), s[2:], nil
   861  }
   862  
   863  // getnum3 parses s[0:1], s[0:2], or s[0:3] (fixed forces s[0:3])
   864  // as a decimal integer and returns the integer and the remainder
   865  // of the string.
   866  func getnum3(s string, fixed bool) (int, string, error) {
   867  	var n, i int
   868  	for i = 0; i < 3 && isDigit(s, i); i++ {
   869  		n = n*10 + int(s[i]-'0')
   870  	}
   871  	if i == 0 || fixed && i != 3 {
   872  		return 0, s, errBad
   873  	}
   874  	return n, s[i:], nil
   875  }
   876  
   877  func cutspace(s string) string {
   878  	for len(s) > 0 && s[0] == ' ' {
   879  		s = s[1:]
   880  	}
   881  	return s
   882  }
   883  
   884  // skip removes the given prefix from value,
   885  // treating runs of space characters as equivalent.
   886  func skip(value, prefix string) (string, error) {
   887  	for len(prefix) > 0 {
   888  		if prefix[0] == ' ' {
   889  			if len(value) > 0 && value[0] != ' ' {
   890  				return value, errBad
   891  			}
   892  			prefix = cutspace(prefix)
   893  			value = cutspace(value)
   894  			continue
   895  		}
   896  		if len(value) == 0 || value[0] != prefix[0] {
   897  			return value, errBad
   898  		}
   899  		prefix = prefix[1:]
   900  		value = value[1:]
   901  	}
   902  	return value, nil
   903  }
   904  
   905  // Parse parses a formatted string and returns the time value it represents.
   906  // See the documentation for the constant called Layout to see how to
   907  // represent the format. The second argument must be parseable using
   908  // the format string (layout) provided as the first argument.
   909  //
   910  // The example for Time.Format demonstrates the working of the layout string
   911  // in detail and is a good reference.
   912  //
   913  // When parsing (only), the input may contain a fractional second
   914  // field immediately after the seconds field, even if the layout does not
   915  // signify its presence. In that case either a comma or a decimal point
   916  // followed by a maximal series of digits is parsed as a fractional second.
   917  // Fractional seconds are truncated to nanosecond precision.
   918  //
   919  // Elements omitted from the layout are assumed to be zero or, when
   920  // zero is impossible, one, so parsing "3:04pm" returns the time
   921  // corresponding to Jan 1, year 0, 15:04:00 UTC (note that because the year is
   922  // 0, this time is before the zero Time).
   923  // Years must be in the range 0000..9999. The day of the week is checked
   924  // for syntax but it is otherwise ignored.
   925  //
   926  // For layouts specifying the two-digit year 06, a value NN >= 69 will be treated
   927  // as 19NN and a value NN < 69 will be treated as 20NN.
   928  //
   929  // The remainder of this comment describes the handling of time zones.
   930  //
   931  // In the absence of a time zone indicator, Parse returns a time in UTC.
   932  //
   933  // When parsing a time with a zone offset like -0700, if the offset corresponds
   934  // to a time zone used by the current location (Local), then Parse uses that
   935  // location and zone in the returned time. Otherwise it records the time as
   936  // being in a fabricated location with time fixed at the given zone offset.
   937  //
   938  // When parsing a time with a zone abbreviation like MST, if the zone abbreviation
   939  // has a defined offset in the current location, then that offset is used.
   940  // The zone abbreviation "UTC" is recognized as UTC regardless of location.
   941  // If the zone abbreviation is unknown, Parse records the time as being
   942  // in a fabricated location with the given zone abbreviation and a zero offset.
   943  // This choice means that such a time can be parsed and reformatted with the
   944  // same layout losslessly, but the exact instant used in the representation will
   945  // differ by the actual zone offset. To avoid such problems, prefer time layouts
   946  // that use a numeric zone offset, or use ParseInLocation.
   947  func Parse(layout, value string) (Time, error) {
   948  	return parse(layout, value, UTC, Local)
   949  }
   950  
   951  // ParseInLocation is like Parse but differs in two important ways.
   952  // First, in the absence of time zone information, Parse interprets a time as UTC;
   953  // ParseInLocation interprets the time as in the given location.
   954  // Second, when given a zone offset or abbreviation, Parse tries to match it
   955  // against the Local location; ParseInLocation uses the given location.
   956  func ParseInLocation(layout, value string, loc *Location) (Time, error) {
   957  	return parse(layout, value, loc, loc)
   958  }
   959  
   960  func parse(layout, value string, defaultLocation, local *Location) (Time, error) {
   961  	alayout, avalue := layout, value
   962  	rangeErrString := "" // set if a value is out of range
   963  	amSet := false       // do we need to subtract 12 from the hour for midnight?
   964  	pmSet := false       // do we need to add 12 to the hour?
   965  
   966  	// Time being constructed.
   967  	var (
   968  		year       int
   969  		month      int = -1
   970  		day        int = -1
   971  		yday       int = -1
   972  		hour       int
   973  		min        int
   974  		sec        int
   975  		nsec       int
   976  		z          *Location
   977  		zoneOffset int = -1
   978  		zoneName   string
   979  	)
   980  
   981  	// Each iteration processes one std value.
   982  	for {
   983  		var err error
   984  		prefix, std, suffix := nextStdChunk(layout)
   985  		stdstr := layout[len(prefix) : len(layout)-len(suffix)]
   986  		value, err = skip(value, prefix)
   987  		if err != nil {
   988  			return Time{}, &ParseError{alayout, avalue, prefix, value, ""}
   989  		}
   990  		if std == 0 {
   991  			if len(value) != 0 {
   992  				return Time{}, &ParseError{alayout, avalue, "", value, ": extra text: " + quote(value)}
   993  			}
   994  			break
   995  		}
   996  		layout = suffix
   997  		var p string
   998  		switch std & stdMask {
   999  		case stdYear:
  1000  			if len(value) < 2 {
  1001  				err = errBad
  1002  				break
  1003  			}
  1004  			hold := value
  1005  			p, value = value[0:2], value[2:]
  1006  			year, err = atoi(p)
  1007  			if err != nil {
  1008  				value = hold
  1009  			} else if year >= 69 { // Unix time starts Dec 31 1969 in some time zones
  1010  				year += 1900
  1011  			} else {
  1012  				year += 2000
  1013  			}
  1014  		case stdLongYear:
  1015  			if len(value) < 4 || !isDigit(value, 0) {
  1016  				err = errBad
  1017  				break
  1018  			}
  1019  			p, value = value[0:4], value[4:]
  1020  			year, err = atoi(p)
  1021  		case stdMonth:
  1022  			month, value, err = lookup(shortMonthNames, value)
  1023  			month++
  1024  		case stdLongMonth:
  1025  			month, value, err = lookup(longMonthNames, value)
  1026  			month++
  1027  		case stdNumMonth, stdZeroMonth:
  1028  			month, value, err = getnum(value, std == stdZeroMonth)
  1029  			if err == nil && (month <= 0 || 12 < month) {
  1030  				rangeErrString = "month"
  1031  			}
  1032  		case stdWeekDay:
  1033  			// Ignore weekday except for error checking.
  1034  			_, value, err = lookup(shortDayNames, value)
  1035  		case stdLongWeekDay:
  1036  			_, value, err = lookup(longDayNames, value)
  1037  		case stdDay, stdUnderDay, stdZeroDay:
  1038  			if std == stdUnderDay && len(value) > 0 && value[0] == ' ' {
  1039  				value = value[1:]
  1040  			}
  1041  			day, value, err = getnum(value, std == stdZeroDay)
  1042  			// Note that we allow any one- or two-digit day here.
  1043  			// The month, day, year combination is validated after we've completed parsing.
  1044  		case stdUnderYearDay, stdZeroYearDay:
  1045  			for i := 0; i < 2; i++ {
  1046  				if std == stdUnderYearDay && len(value) > 0 && value[0] == ' ' {
  1047  					value = value[1:]
  1048  				}
  1049  			}
  1050  			yday, value, err = getnum3(value, std == stdZeroYearDay)
  1051  			// Note that we allow any one-, two-, or three-digit year-day here.
  1052  			// The year-day, year combination is validated after we've completed parsing.
  1053  		case stdHour:
  1054  			hour, value, err = getnum(value, false)
  1055  			if hour < 0 || 24 <= hour {
  1056  				rangeErrString = "hour"
  1057  			}
  1058  		case stdHour12, stdZeroHour12:
  1059  			hour, value, err = getnum(value, std == stdZeroHour12)
  1060  			if hour < 0 || 12 < hour {
  1061  				rangeErrString = "hour"
  1062  			}
  1063  		case stdMinute, stdZeroMinute:
  1064  			min, value, err = getnum(value, std == stdZeroMinute)
  1065  			if min < 0 || 60 <= min {
  1066  				rangeErrString = "minute"
  1067  			}
  1068  		case stdSecond, stdZeroSecond:
  1069  			sec, value, err = getnum(value, std == stdZeroSecond)
  1070  			if sec < 0 || 60 <= sec {
  1071  				rangeErrString = "second"
  1072  				break
  1073  			}
  1074  			// Special case: do we have a fractional second but no
  1075  			// fractional second in the format?
  1076  			if len(value) >= 2 && commaOrPeriod(value[0]) && isDigit(value, 1) {
  1077  				_, std, _ = nextStdChunk(layout)
  1078  				std &= stdMask
  1079  				if std == stdFracSecond0 || std == stdFracSecond9 {
  1080  					// Fractional second in the layout; proceed normally
  1081  					break
  1082  				}
  1083  				// No fractional second in the layout but we have one in the input.
  1084  				n := 2
  1085  				for ; n < len(value) && isDigit(value, n); n++ {
  1086  				}
  1087  				nsec, rangeErrString, err = parseNanoseconds(value, n)
  1088  				value = value[n:]
  1089  			}
  1090  		case stdPM:
  1091  			if len(value) < 2 {
  1092  				err = errBad
  1093  				break
  1094  			}
  1095  			p, value = value[0:2], value[2:]
  1096  			switch p {
  1097  			case "PM":
  1098  				pmSet = true
  1099  			case "AM":
  1100  				amSet = true
  1101  			default:
  1102  				err = errBad
  1103  			}
  1104  		case stdpm:
  1105  			if len(value) < 2 {
  1106  				err = errBad
  1107  				break
  1108  			}
  1109  			p, value = value[0:2], value[2:]
  1110  			switch p {
  1111  			case "pm":
  1112  				pmSet = true
  1113  			case "am":
  1114  				amSet = true
  1115  			default:
  1116  				err = errBad
  1117  			}
  1118  		case stdISO8601TZ, stdISO8601ColonTZ, stdISO8601SecondsTZ, stdISO8601ShortTZ, stdISO8601ColonSecondsTZ, stdNumTZ, stdNumShortTZ, stdNumColonTZ, stdNumSecondsTz, stdNumColonSecondsTZ:
  1119  			if (std == stdISO8601TZ || std == stdISO8601ShortTZ || std == stdISO8601ColonTZ) && len(value) >= 1 && value[0] == 'Z' {
  1120  				value = value[1:]
  1121  				z = UTC
  1122  				break
  1123  			}
  1124  			var sign, hour, min, seconds string
  1125  			if std == stdISO8601ColonTZ || std == stdNumColonTZ {
  1126  				if len(value) < 6 {
  1127  					err = errBad
  1128  					break
  1129  				}
  1130  				if value[3] != ':' {
  1131  					err = errBad
  1132  					break
  1133  				}
  1134  				sign, hour, min, seconds, value = value[0:1], value[1:3], value[4:6], "00", value[6:]
  1135  			} else if std == stdNumShortTZ || std == stdISO8601ShortTZ {
  1136  				if len(value) < 3 {
  1137  					err = errBad
  1138  					break
  1139  				}
  1140  				sign, hour, min, seconds, value = value[0:1], value[1:3], "00", "00", value[3:]
  1141  			} else if std == stdISO8601ColonSecondsTZ || std == stdNumColonSecondsTZ {
  1142  				if len(value) < 9 {
  1143  					err = errBad
  1144  					break
  1145  				}
  1146  				if value[3] != ':' || value[6] != ':' {
  1147  					err = errBad
  1148  					break
  1149  				}
  1150  				sign, hour, min, seconds, value = value[0:1], value[1:3], value[4:6], value[7:9], value[9:]
  1151  			} else if std == stdISO8601SecondsTZ || std == stdNumSecondsTz {
  1152  				if len(value) < 7 {
  1153  					err = errBad
  1154  					break
  1155  				}
  1156  				sign, hour, min, seconds, value = value[0:1], value[1:3], value[3:5], value[5:7], value[7:]
  1157  			} else {
  1158  				if len(value) < 5 {
  1159  					err = errBad
  1160  					break
  1161  				}
  1162  				sign, hour, min, seconds, value = value[0:1], value[1:3], value[3:5], "00", value[5:]
  1163  			}
  1164  			var hr, mm, ss int
  1165  			hr, err = atoi(hour)
  1166  			if err == nil {
  1167  				mm, err = atoi(min)
  1168  			}
  1169  			if err == nil {
  1170  				ss, err = atoi(seconds)
  1171  			}
  1172  			zoneOffset = (hr*60+mm)*60 + ss // offset is in seconds
  1173  			switch sign[0] {
  1174  			case '+':
  1175  			case '-':
  1176  				zoneOffset = -zoneOffset
  1177  			default:
  1178  				err = errBad
  1179  			}
  1180  		case stdTZ:
  1181  			// Does it look like a time zone?
  1182  			if len(value) >= 3 && value[0:3] == "UTC" {
  1183  				z = UTC
  1184  				value = value[3:]
  1185  				break
  1186  			}
  1187  			n, ok := parseTimeZone(value)
  1188  			if !ok {
  1189  				err = errBad
  1190  				break
  1191  			}
  1192  			zoneName, value = value[:n], value[n:]
  1193  
  1194  		case stdFracSecond0:
  1195  			// stdFracSecond0 requires the exact number of digits as specified in
  1196  			// the layout.
  1197  			ndigit := 1 + digitsLen(std)
  1198  			if len(value) < ndigit {
  1199  				err = errBad
  1200  				break
  1201  			}
  1202  			nsec, rangeErrString, err = parseNanoseconds(value, ndigit)
  1203  			value = value[ndigit:]
  1204  
  1205  		case stdFracSecond9:
  1206  			if len(value) < 2 || !commaOrPeriod(value[0]) || value[1] < '0' || '9' < value[1] {
  1207  				// Fractional second omitted.
  1208  				break
  1209  			}
  1210  			// Take any number of digits, even more than asked for,
  1211  			// because it is what the stdSecond case would do.
  1212  			i := 0
  1213  			for i < 9 && i+1 < len(value) && '0' <= value[i+1] && value[i+1] <= '9' {
  1214  				i++
  1215  			}
  1216  			nsec, rangeErrString, err = parseNanoseconds(value, 1+i)
  1217  			value = value[1+i:]
  1218  		}
  1219  		if rangeErrString != "" {
  1220  			return Time{}, &ParseError{alayout, avalue, stdstr, value, ": " + rangeErrString + " out of range"}
  1221  		}
  1222  		if err != nil {
  1223  			return Time{}, &ParseError{alayout, avalue, stdstr, value, ""}
  1224  		}
  1225  	}
  1226  	if pmSet && hour < 12 {
  1227  		hour += 12
  1228  	} else if amSet && hour == 12 {
  1229  		hour = 0
  1230  	}
  1231  
  1232  	// Convert yday to day, month.
  1233  	if yday >= 0 {
  1234  		var d int
  1235  		var m int
  1236  		if isLeap(year) {
  1237  			if yday == 31+29 {
  1238  				m = int(February)
  1239  				d = 29
  1240  			} else if yday > 31+29 {
  1241  				yday--
  1242  			}
  1243  		}
  1244  		if yday < 1 || yday > 365 {
  1245  			return Time{}, &ParseError{alayout, avalue, "", value, ": day-of-year out of range"}
  1246  		}
  1247  		if m == 0 {
  1248  			m = (yday-1)/31 + 1
  1249  			if int(daysBefore[m]) < yday {
  1250  				m++
  1251  			}
  1252  			d = yday - int(daysBefore[m-1])
  1253  		}
  1254  		// If month, day already seen, yday's m, d must match.
  1255  		// Otherwise, set them from m, d.
  1256  		if month >= 0 && month != m {
  1257  			return Time{}, &ParseError{alayout, avalue, "", value, ": day-of-year does not match month"}
  1258  		}
  1259  		month = m
  1260  		if day >= 0 && day != d {
  1261  			return Time{}, &ParseError{alayout, avalue, "", value, ": day-of-year does not match day"}
  1262  		}
  1263  		day = d
  1264  	} else {
  1265  		if month < 0 {
  1266  			month = int(January)
  1267  		}
  1268  		if day < 0 {
  1269  			day = 1
  1270  		}
  1271  	}
  1272  
  1273  	// Validate the day of the month.
  1274  	if day < 1 || day > daysIn(Month(month), year) {
  1275  		return Time{}, &ParseError{alayout, avalue, "", value, ": day out of range"}
  1276  	}
  1277  
  1278  	if z != nil {
  1279  		return Date(year, Month(month), day, hour, min, sec, nsec, z), nil
  1280  	}
  1281  
  1282  	if zoneOffset != -1 {
  1283  		t := Date(year, Month(month), day, hour, min, sec, nsec, UTC)
  1284  		t.addSec(-int64(zoneOffset))
  1285  
  1286  		// Look for local zone with the given offset.
  1287  		// If that zone was in effect at the given time, use it.
  1288  		name, offset, _, _, _ := local.lookup(t.unixSec())
  1289  		if offset == zoneOffset && (zoneName == "" || name == zoneName) {
  1290  			t.setLoc(local)
  1291  			return t, nil
  1292  		}
  1293  
  1294  		// Otherwise create fake zone to record offset.
  1295  		t.setLoc(FixedZone(zoneName, zoneOffset))
  1296  		return t, nil
  1297  	}
  1298  
  1299  	if zoneName != "" {
  1300  		t := Date(year, Month(month), day, hour, min, sec, nsec, UTC)
  1301  		// Look for local zone with the given offset.
  1302  		// If that zone was in effect at the given time, use it.
  1303  		offset, ok := local.lookupName(zoneName, t.unixSec())
  1304  		if ok {
  1305  			t.addSec(-int64(offset))
  1306  			t.setLoc(local)
  1307  			return t, nil
  1308  		}
  1309  
  1310  		// Otherwise, create fake zone with unknown offset.
  1311  		if len(zoneName) > 3 && zoneName[:3] == "GMT" {
  1312  			offset, _ = atoi(zoneName[3:]) // Guaranteed OK by parseGMT.
  1313  			offset *= 3600
  1314  		}
  1315  		t.setLoc(FixedZone(zoneName, offset))
  1316  		return t, nil
  1317  	}
  1318  
  1319  	// Otherwise, fall back to default.
  1320  	return Date(year, Month(month), day, hour, min, sec, nsec, defaultLocation), nil
  1321  }
  1322  
  1323  // parseTimeZone parses a time zone string and returns its length. Time zones
  1324  // are human-generated and unpredictable. We can't do precise error checking.
  1325  // On the other hand, for a correct parse there must be a time zone at the
  1326  // beginning of the string, so it's almost always true that there's one
  1327  // there. We look at the beginning of the string for a run of upper-case letters.
  1328  // If there are more than 5, it's an error.
  1329  // If there are 4 or 5 and the last is a T, it's a time zone.
  1330  // If there are 3, it's a time zone.
  1331  // Otherwise, other than special cases, it's not a time zone.
  1332  // GMT is special because it can have an hour offset.
  1333  func parseTimeZone(value string) (length int, ok bool) {
  1334  	if len(value) < 3 {
  1335  		return 0, false
  1336  	}
  1337  	// Special case 1: ChST and MeST are the only zones with a lower-case letter.
  1338  	if len(value) >= 4 && (value[:4] == "ChST" || value[:4] == "MeST") {
  1339  		return 4, true
  1340  	}
  1341  	// Special case 2: GMT may have an hour offset; treat it specially.
  1342  	if value[:3] == "GMT" {
  1343  		length = parseGMT(value)
  1344  		return length, true
  1345  	}
  1346  	// Special Case 3: Some time zones are not named, but have +/-00 format
  1347  	if value[0] == '+' || value[0] == '-' {
  1348  		length = parseSignedOffset(value)
  1349  		ok := length > 0 // parseSignedOffset returns 0 in case of bad input
  1350  		return length, ok
  1351  	}
  1352  	// How many upper-case letters are there? Need at least three, at most five.
  1353  	var nUpper int
  1354  	for nUpper = 0; nUpper < 6; nUpper++ {
  1355  		if nUpper >= len(value) {
  1356  			break
  1357  		}
  1358  		if c := value[nUpper]; c < 'A' || 'Z' < c {
  1359  			break
  1360  		}
  1361  	}
  1362  	switch nUpper {
  1363  	case 0, 1, 2, 6:
  1364  		return 0, false
  1365  	case 5: // Must end in T to match.
  1366  		if value[4] == 'T' {
  1367  			return 5, true
  1368  		}
  1369  	case 4:
  1370  		// Must end in T, except one special case.
  1371  		if value[3] == 'T' || value[:4] == "WITA" {
  1372  			return 4, true
  1373  		}
  1374  	case 3:
  1375  		return 3, true
  1376  	}
  1377  	return 0, false
  1378  }
  1379  
  1380  // parseGMT parses a GMT time zone. The input string is known to start "GMT".
  1381  // The function checks whether that is followed by a sign and a number in the
  1382  // range -23 through +23 excluding zero.
  1383  func parseGMT(value string) int {
  1384  	value = value[3:]
  1385  	if len(value) == 0 {
  1386  		return 3
  1387  	}
  1388  
  1389  	return 3 + parseSignedOffset(value)
  1390  }
  1391  
  1392  // parseSignedOffset parses a signed timezone offset (e.g. "+03" or "-04").
  1393  // The function checks for a signed number in the range -23 through +23 excluding zero.
  1394  // Returns length of the found offset string or 0 otherwise
  1395  func parseSignedOffset(value string) int {
  1396  	sign := value[0]
  1397  	if sign != '-' && sign != '+' {
  1398  		return 0
  1399  	}
  1400  	x, rem, err := leadingInt(value[1:])
  1401  
  1402  	// fail if nothing consumed by leadingInt
  1403  	if err != nil || value[1:] == rem {
  1404  		return 0
  1405  	}
  1406  	if x > 23 {
  1407  		return 0
  1408  	}
  1409  	return len(value) - len(rem)
  1410  }
  1411  
  1412  func commaOrPeriod(b byte) bool {
  1413  	return b == '.' || b == ','
  1414  }
  1415  
  1416  func parseNanoseconds(value string, nbytes int) (ns int, rangeErrString string, err error) {
  1417  	if !commaOrPeriod(value[0]) {
  1418  		err = errBad
  1419  		return
  1420  	}
  1421  	if nbytes > 10 {
  1422  		value = value[:10]
  1423  		nbytes = 10
  1424  	}
  1425  	if ns, err = atoi(value[1:nbytes]); err != nil {
  1426  		return
  1427  	}
  1428  	if ns < 0 {
  1429  		rangeErrString = "fractional second"
  1430  		return
  1431  	}
  1432  	// We need nanoseconds, which means scaling by the number
  1433  	// of missing digits in the format, maximum length 10.
  1434  	scaleDigits := 10 - nbytes
  1435  	for i := 0; i < scaleDigits; i++ {
  1436  		ns *= 10
  1437  	}
  1438  	return
  1439  }
  1440  
  1441  var errLeadingInt = errors.New("time: bad [0-9]*") // never printed
  1442  
  1443  // leadingInt consumes the leading [0-9]* from s.
  1444  func leadingInt(s string) (x uint64, rem string, err error) {
  1445  	i := 0
  1446  	for ; i < len(s); i++ {
  1447  		c := s[i]
  1448  		if c < '0' || c > '9' {
  1449  			break
  1450  		}
  1451  		if x > 1<<63/10 {
  1452  			// overflow
  1453  			return 0, "", errLeadingInt
  1454  		}
  1455  		x = x*10 + uint64(c) - '0'
  1456  		if x > 1<<63 {
  1457  			// overflow
  1458  			return 0, "", errLeadingInt
  1459  		}
  1460  	}
  1461  	return x, s[i:], nil
  1462  }
  1463  
  1464  // leadingFraction consumes the leading [0-9]* from s.
  1465  // It is used only for fractions, so does not return an error on overflow,
  1466  // it just stops accumulating precision.
  1467  func leadingFraction(s string) (x uint64, scale float64, rem string) {
  1468  	i := 0
  1469  	scale = 1
  1470  	overflow := false
  1471  	for ; i < len(s); i++ {
  1472  		c := s[i]
  1473  		if c < '0' || c > '9' {
  1474  			break
  1475  		}
  1476  		if overflow {
  1477  			continue
  1478  		}
  1479  		if x > (1<<63-1)/10 {
  1480  			// It's possible for overflow to give a positive number, so take care.
  1481  			overflow = true
  1482  			continue
  1483  		}
  1484  		y := x*10 + uint64(c) - '0'
  1485  		if y > 1<<63 {
  1486  			overflow = true
  1487  			continue
  1488  		}
  1489  		x = y
  1490  		scale *= 10
  1491  	}
  1492  	return x, scale, s[i:]
  1493  }
  1494  
  1495  var unitMap = map[string]uint64{
  1496  	"ns": uint64(Nanosecond),
  1497  	"us": uint64(Microsecond),
  1498  	"µs": uint64(Microsecond), // U+00B5 = micro symbol
  1499  	"μs": uint64(Microsecond), // U+03BC = Greek letter mu
  1500  	"ms": uint64(Millisecond),
  1501  	"s":  uint64(Second),
  1502  	"m":  uint64(Minute),
  1503  	"h":  uint64(Hour),
  1504  }
  1505  
  1506  // ParseDuration parses a duration string.
  1507  // A duration string is a possibly signed sequence of
  1508  // decimal numbers, each with optional fraction and a unit suffix,
  1509  // such as "300ms", "-1.5h" or "2h45m".
  1510  // Valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h".
  1511  func ParseDuration(s string) (Duration, error) {
  1512  	// [-+]?([0-9]*(\.[0-9]*)?[a-z]+)+
  1513  	orig := s
  1514  	var d uint64
  1515  	neg := false
  1516  
  1517  	// Consume [-+]?
  1518  	if s != "" {
  1519  		c := s[0]
  1520  		if c == '-' || c == '+' {
  1521  			neg = c == '-'
  1522  			s = s[1:]
  1523  		}
  1524  	}
  1525  	// Special case: if all that is left is "0", this is zero.
  1526  	if s == "0" {
  1527  		return 0, nil
  1528  	}
  1529  	if s == "" {
  1530  		return 0, errors.New("time: invalid duration " + quote(orig))
  1531  	}
  1532  	for s != "" {
  1533  		var (
  1534  			v, f  uint64      // integers before, after decimal point
  1535  			scale float64 = 1 // value = v + f/scale
  1536  		)
  1537  
  1538  		var err error
  1539  
  1540  		// The next character must be [0-9.]
  1541  		if !(s[0] == '.' || '0' <= s[0] && s[0] <= '9') {
  1542  			return 0, errors.New("time: invalid duration " + quote(orig))
  1543  		}
  1544  		// Consume [0-9]*
  1545  		pl := len(s)
  1546  		v, s, err = leadingInt(s)
  1547  		if err != nil {
  1548  			return 0, errors.New("time: invalid duration " + quote(orig))
  1549  		}
  1550  		pre := pl != len(s) // whether we consumed anything before a period
  1551  
  1552  		// Consume (\.[0-9]*)?
  1553  		post := false
  1554  		if s != "" && s[0] == '.' {
  1555  			s = s[1:]
  1556  			pl := len(s)
  1557  			f, scale, s = leadingFraction(s)
  1558  			post = pl != len(s)
  1559  		}
  1560  		if !pre && !post {
  1561  			// no digits (e.g. ".s" or "-.s")
  1562  			return 0, errors.New("time: invalid duration " + quote(orig))
  1563  		}
  1564  
  1565  		// Consume unit.
  1566  		i := 0
  1567  		for ; i < len(s); i++ {
  1568  			c := s[i]
  1569  			if c == '.' || '0' <= c && c <= '9' {
  1570  				break
  1571  			}
  1572  		}
  1573  		if i == 0 {
  1574  			return 0, errors.New("time: missing unit in duration " + quote(orig))
  1575  		}
  1576  		u := s[:i]
  1577  		s = s[i:]
  1578  		unit, ok := unitMap[u]
  1579  		if !ok {
  1580  			return 0, errors.New("time: unknown unit " + quote(u) + " in duration " + quote(orig))
  1581  		}
  1582  		if v > 1<<63/unit {
  1583  			// overflow
  1584  			return 0, errors.New("time: invalid duration " + quote(orig))
  1585  		}
  1586  		v *= unit
  1587  		if f > 0 {
  1588  			// float64 is needed to be nanosecond accurate for fractions of hours.
  1589  			// v >= 0 && (f*unit/scale) <= 3.6e+12 (ns/h, h is the largest unit)
  1590  			v += uint64(float64(f) * (float64(unit) / scale))
  1591  			if v > 1<<63 {
  1592  				// overflow
  1593  				return 0, errors.New("time: invalid duration " + quote(orig))
  1594  			}
  1595  		}
  1596  		d += v
  1597  		if d > 1<<63 {
  1598  			return 0, errors.New("time: invalid duration " + quote(orig))
  1599  		}
  1600  	}
  1601  	if neg {
  1602  		return -Duration(d), nil
  1603  	}
  1604  	if d > 1<<63-1 {
  1605  		return 0, errors.New("time: invalid duration " + quote(orig))
  1606  	}
  1607  	return Duration(d), nil
  1608  }
  1609  

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