Add strftime function

docs/language/functions/strftime.md

@@ -0,0 +1,67 @@
+### Function
+
+  **strftime** — format time values
+
+### Synopsis
+```
+strftime(format: string, t: time) -> string
+```
+
+### Description
+The _strftime_ function returns a string represenation of time `t`
+as specified by the provided string `format`. `format` is a string
+containing format directives that dictate how the time string is
+formatted.
+
+These directives are supported:
+
+| Directive | Explanation | Example |
+|-----------|-------------|---------|
+| %A | Weekday as full name | Sunday, Monday, ..., Saturday |
+| %a | Weekday as abbreviated name | Sun, Mon, ..., Sat |
+| %B | Month as full name | January, February, ..., December |
+| %b | Month as abbreviated name | Jan, Feb, ..., Dec |
+| %C | Century number (year / 100) as a 2-digit integer | 20 |
+| %c | Locale's appropriate date and time representation | Tue Jul 30 14:30:15 2024 |
+| %D | Equivalent to `%m/%d/%y` | 7/30/24 |
+| %d | Day of the month as a zero-padded decimal number | 01, 02, ..., 31 |
+| %e | Day of the month as a decimal number (1-31); single digits are preceded by a blank | 1, 2, ..., 31 |
+| %F | Equivalent to `%Y-%m-%d` | 2024-07-30 |
+| %H | Hour (24-hour clock) as a zero-padded decimal number | 00, 01, ..., 23 |
+| %I | Hour (12-hour clock) as a zero-padded decimal number | 00, 01, ..., 12 |
+| %j | Day of the year as a zero-padded decimal number | 001, 002, ..., 366 |
+| %k | Hour (24-hour clock) as a decimal number; single digits are preceded by a blank | 0, 1, ..., 23 |
+| %l | Hour (12-hour clock) as a decimal number; single digits are preceded by a blank | 0, 1, ..., 12 |
+| %M | Minute as a zero-padded decimal number | 00, 01, ..., 59 |
+| %m | Month as a zero-padded decimal number | 01, 02, ..., 12 |
+| %n | Newline character | \n |
+| %p | "ante meridiem" (a.m.) or "post meridiem" (p.m.) | AM, PM |
+| %R | Equivalent to `%H:%M` | 18:49 |
+| %r | Equivalent to `%I:%M:%S %p` | 06:50:58 PM |
+| %S | Second as a zero-padded decimal number | 00, 01, ..., 59 |
+| %T | Equivalent to `%H:%M:%S` | 18:50:58 |
+| %t | Tab character | \t |
+| %U | Week number of the year (Sunday as the first day of the week) | 00, 01, ..., 53 |
+| %u | Weekday as a decimal number, range 1 to 7, with Monday being 1 | 1, 2, ..., 7 |
+| %V | Week number of the year (Monday as the first day of the week) as a decimal number (01-53) | 01, 02, ..., 53 |
+| %v | Equivalent to `%e-%b-%Y` | 31-Jul-2024 |
+| %W | Week number of the year (Monday as the first day of the week) | 00, 01, ..., 53 |
+| %w | Weekday as a decimal number, range 0 to 6, with Sunday being 0 | 0, 1, ..., 6 |
+| %X | Locale's appropriate time representation | 14:30:15 |
+| %x | Locale's appropriate date representation | 07/30/24 |
+| %Y | Year with century as a decimal number | 2024 |
+| %y | Year without century as a decimal number | 24, 23 |
+| %Z | Timezone name | UTC |
+| %z | +hhmm or -hhmm numeric timezone (that is, the hour and minute offset from UTC) | +0000 |
+| %% | A literal '%' character | % |
+
+### Examples
+
+Print the year number as a string
+```mdtest-command
+echo 2024-07-30T20:05:15.118252Z | zq -z 'strftime("%Y", this)' -
+```
+=>
+```mdtest-output
+"2024"
+```

go.mod

@@ -16,6 +16,7 @@ require (
 	github.com/gosuri/uilive v0.0.4
 	github.com/hashicorp/golang-lru/v2 v2.0.1
 	github.com/kr/text v0.2.0
+	github.com/lestrrat-go/strftime v1.0.6
 	github.com/paulbellamy/ratecounter v0.2.0
 	github.com/pbnjay/memory v0.0.0-20190104145345-974d429e7ae4
 	github.com/peterh/liner v1.1.0
@@ -61,6 +62,7 @@ require (
 	github.com/matttproud/golang_protobuf_extensions v1.0.1 // indirect
 	github.com/minio/asm2plan9s v0.0.0-20200509001527-cdd76441f9d8 // indirect
 	github.com/minio/c2goasm v0.0.0-20190812172519-36a3d3bbc4f3 // indirect
+	github.com/pkg/errors v0.9.1 // indirect
 	github.com/prometheus/common v0.37.0 // indirect
 	github.com/prometheus/procfs v0.8.0 // indirect
 	github.com/rivo/uniseg v0.1.0 // indirect

go.sum

@@ -221,6 +221,10 @@ github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
 github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
 github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
 github.com/leodido/go-urn v1.1.0/go.mod h1:+cyI34gQWZcE1eQU7NVgKkkzdXDQHr1dBMtdAPozLkw=
+github.com/lestrrat-go/envload v0.0.0-20180220234015-a3eb8ddeffcc h1:RKf14vYWi2ttpEmkA4aQ3j4u9dStX2t4M8UM6qqNsG8=
+github.com/lestrrat-go/envload v0.0.0-20180220234015-a3eb8ddeffcc/go.mod h1:kopuH9ugFRkIXf3YoqHKyrJ9YfUFsckUU9S7B+XP+is=
+github.com/lestrrat-go/strftime v1.0.6 h1:CFGsDEt1pOpFNU+TJB0nhz9jl+K0hZSLE205AhTIGQQ=
+github.com/lestrrat-go/strftime v1.0.6/go.mod h1:f7jQKgV5nnJpYgdEasS+/y7EsTb8ykN2z68n3TtcTaw=
 github.com/mattn/go-isatty v0.0.9/go.mod h1:YNRxwqDuOph6SZLI9vUUz6OYw3QyUt7WiY2yME+cCiQ=
 github.com/mattn/go-isatty v0.0.19 h1:JITubQf0MOLdlGRuRq+jtsDlekdYPia9ZFsB8h/APPA=
 github.com/mattn/go-isatty v0.0.19/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=

runtime/sam/expr/function/function.go

@@ -161,6 +161,9 @@ func New(zctx *zed.Context, name string, narg int) (expr.Function, field.Path, e
 	case "regexp_replace":
 		argmin, argmax = 3, 3
 		f = &RegexpReplace{zctx: zctx}
+	case "strftime":
+		argmin, argmax = 2, 2
+		f = &Strftime{zctx: zctx}
 	case "under":
 		f = &Under{zctx: zctx}
 	case "unflatten":

runtime/sam/expr/function/time.go

@@ -1,10 +1,13 @@
 package function
 
 import (
+	"fmt"
+
 	"github.com/brimdata/zed"
 	"github.com/brimdata/zed/pkg/nano"
 	"github.com/brimdata/zed/runtime/sam/expr"
 	"github.com/brimdata/zed/runtime/sam/expr/coerce"
+	"github.com/lestrrat-go/strftime"
 )
 
 // https://github.com/brimdata/zed/blob/main/docs/language/functions.md#now
@@ -46,3 +49,34 @@ func (b *Bucket) Call(ectx expr.Context, args []zed.Value) zed.Value {
 	}
 	return zed.NewTime(nano.Ts(v).Trunc(bin))
 }
+
+// https://github.com/brimdata/zed/blob/main/docs/language/functions.md#strftime
+type Strftime struct {
+	zctx      *zed.Context
+	format    string
+	formatter *strftime.Strftime
+}
+
+func (s *Strftime) Call(ectx expr.Context, args []zed.Value) zed.Value {
+	formatArg, timeArg := args[0], args[1]
+	if !formatArg.IsString() {
+		return s.zctx.WrapError(ectx.Arena(), "strftime: string value required for format arg", formatArg)
+	}
+	if formatArg.IsNull() {
+		return zed.NullString
+	}
+	format := formatArg.AsString()
+	if zed.TypeUnder(timeArg.Type()) != zed.TypeTime {
+		return s.zctx.WrapError(ectx.Arena(), "strftime: time value required for time arg", args[1])
+	}
+	t := timeArg.AsTime()
+	if s.format != format {
+		var err error
+		if s.formatter, err = strftime.New(format); err != nil {
+			return s.zctx.WrapError(ectx.Arena(), fmt.Sprintf("strftime: %s", err), formatArg)
+		}
+		s.format = format
+	}
+	out := s.formatter.FormatString(t.Time())
+	return ectx.Arena().NewString(out)
+}

runtime/sam/expr/function/ztests/strftime.yaml

@@ -0,0 +1,11 @@
+zed: 'strftime(f, v)'
+
+input: |
+  {f:"%Y-%a",v:2024-07-30T06:15:01.062681Z}
+  {f:1,v:2024-07-30T06:15:01.062681Z}
+  {f:"%H",v:"foo"}
+
+output: |
+  "2024-Tue"
+  error({message:"strftime: string value required for format arg",on:1})
+  error({message:"strftime: time value required for time arg",on:"foo"})