unix: add function for converting time.Time to Timespec

Add function TimeToTimespec for converting time.Time to Timespec.

Fixes golang/go#23078.

Change-Id: I685a4871d49131191f330b56b15bfd4f3131a9a5
Reviewed-on: https://go-review.googlesource.com/82919
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

unix/timestruct.go

@@ -6,6 +6,8 @@
 
 package unix
 
+import "time"
+
 // TimespecToNsec converts a Timespec value into a number of
 // nanoseconds since the Unix epoch.
 func TimespecToNsec(ts Timespec) int64 { return int64(ts.Sec)*1e9 + int64(ts.Nsec) }
@@ -22,6 +24,24 @@ func NsecToTimespec(nsec int64) Timespec {
 	return setTimespec(sec, nsec)
 }
 
+// TimeToTimespec converts t into a Timespec.
+// On some 32-bit systems the range of valid Timespec values are smaller
+// than that of time.Time values.  So if t is out of the valid range of
+// Timespec, it returns a zero Timespec and ERANGE.
+func TimeToTimespec(t time.Time) (Timespec, error) {
+	sec := t.Unix()
+	nsec := int64(t.Nanosecond())
+	ts := setTimespec(sec, nsec)
+
+	// Currently all targets have either int32 or int64 for Timespec.Sec.
+	// If there were a new target with floating point type for it, we have
+	// to consider the rounding error.
+	if int64(ts.Sec) != sec {
+		return Timespec{}, ERANGE
+	}
+	return ts, nil
+}
+
 // TimevalToNsec converts a Timeval value into a number of nanoseconds
 // since the Unix epoch.
 func TimevalToNsec(tv Timeval) int64 { return int64(tv.Sec)*1e9 + int64(tv.Usec)*1e3 }

unix/timestruct_test.go

@@ -0,0 +1,54 @@
+// Copyright 2017 The Go Authors. All right reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build darwin dragonfly freebsd linux netbsd openbsd solaris
+
+package unix_test
+
+import (
+	"testing"
+	"time"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+func TestTimeToTimespec(t *testing.T) {
+	timeTests := []struct {
+		time  time.Time
+		valid bool
+	}{
+		{time.Unix(0, 0), true},
+		{time.Date(2009, time.November, 10, 23, 0, 0, 0, time.UTC), true},
+		{time.Date(2262, time.December, 31, 23, 0, 0, 0, time.UTC), false},
+		{time.Unix(0x7FFFFFFF, 0), true},
+		{time.Unix(0x80000000, 0), false},
+		{time.Unix(0x7FFFFFFF, 1000000000), false},
+		{time.Unix(0x7FFFFFFF, 999999999), true},
+		{time.Unix(-0x80000000, 0), true},
+		{time.Unix(-0x80000001, 0), false},
+		{time.Date(2038, time.January, 19, 3, 14, 7, 0, time.UTC), true},
+		{time.Date(2038, time.January, 19, 3, 14, 8, 0, time.UTC), false},
+		{time.Date(1901, time.December, 13, 20, 45, 52, 0, time.UTC), true},
+		{time.Date(1901, time.December, 13, 20, 45, 51, 0, time.UTC), false},
+	}
+
+	// Currently all targets have either int32 or int64 for Timespec.Sec.
+	// If there were a new target with unsigned or floating point type for
+	// it, this test must be adjusted.
+	have64BitTime := (unsafe.Sizeof(unix.Timespec{}.Sec) == 8)
+	for _, tt := range timeTests {
+		ts, err := unix.TimeToTimespec(tt.time)
+		tt.valid = tt.valid || have64BitTime
+		if tt.valid && err != nil {
+			t.Errorf("TimeToTimespec(%v): %v", tt.time, err)
+		}
+		if err == nil {
+			tstime := time.Unix(int64(ts.Sec), int64(ts.Nsec))
+			if !tstime.Equal(tt.time) {
+				t.Errorf("TimeToTimespec(%v) is the time %v", tt.time, tstime)
+			}
+		}
+	}
+}