time: Add Until helper function

Adds an Until() function that returns the duration until the given time.
This compliments the existing Since() function and makes writing
expressions that have expiration times more readable; for example:

    <-After(time.Until(connExpires)):

Fixes #14595

Change-Id: I87998a924b11d4dad5512e010b29d2da6b123456
Reviewed-on: https://go-review.googlesource.com/20118
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

diff --git a/src/time/time.go b/src/time/time.go
index c31de357d58e29ec2159fa27cf96ffa9ab6d3814..a6e100fa71702d607bd25018e9bfac8e1f3c3466 100644 (file)
--- a/src/time/time.go
+++ b/src/time/time.go
@@ -640,6 +640,12 @@ func Since(t Time) Duration {
        return Now().Sub(t)
 }
 
+// Until returns the duration until t.
+// It is shorthand for t.Sub(time.Now()).
+func Until(t Time) Duration {
+       return t.Sub(Now())
+}
+
 // AddDate returns the time corresponding to adding the
 // given number of years, months, and days to t.
 // For example, AddDate(-1, 2, 3) applied to January 1, 2011