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os, net: define and use os.ErrDeadlineExceeded

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If an I/O operation fails because a deadline was exceeded,
return os.ErrDeadlineExceeded. We used to return poll.ErrTimeout,
an internal error, and told users to check the Timeout method.
However, there are other errors with a Timeout method that returns true,
notably syscall.ETIMEDOUT which is returned for a keep-alive timeout.
Checking errors.Is(err, os.ErrDeadlineExceeded) should permit code
to reliably tell why it failed.

This change does not affect the handling of net.Dialer.Deadline,
nor does it change the handling of net.DialContext when the context
deadline is exceeded. Those cases continue to return an error
reported as "i/o timeout" for which Timeout is true, but that error
is not os.ErrDeadlineExceeded.

Fixes #31449

Change-Id: I0323f42e944324c6f2578f00c3ac90c24fe81177
Reviewed-on: https://go-review.googlesource.com/c/go/+/228645
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
This commit is contained in:
Ian Lance Taylor 2020-04-17 15:42:12 -07:00
parent 396833caef
commit d422f54619
20 changed files with 196 additions and 108 deletions
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20
src/os/error.go
View file

@ -18,11 +18,12 @@ var (
// Methods on File will return this error when the receiver is nil.
ErrInvalid = errInvalid() // "invalid argument"
ErrPermission = errPermission() // "permission denied"
ErrExist = errExist() // "file already exists"
ErrNotExist = errNotExist() // "file does not exist"
ErrClosed = errClosed() // "file already closed"
ErrNoDeadline = errNoDeadline() // "file type does not support deadline"
ErrPermission = errPermission() // "permission denied"
ErrExist = errExist() // "file already exists"
ErrNotExist = errNotExist() // "file does not exist"
ErrClosed = errClosed() // "file already closed"
ErrNoDeadline = errNoDeadline() // "file type does not support deadline"
ErrDeadlineExceeded = errDeadlineExceeded() // "i/o timeout"
)
func errInvalid() error { return oserror.ErrInvalid }
@ -32,6 +33,15 @@ func errNotExist() error { return oserror.ErrNotExist }
func errClosed() error { return oserror.ErrClosed }
func errNoDeadline() error { return poll.ErrNoDeadline }
// errDeadlineExceeded returns the value for os.ErrDeadlineExceeded.
// This error comes from the internal/poll package, which is also
// used by package net. Doing this this way ensures that the net
// package will return os.ErrDeadlineExceeded for an exceeded deadline,
// as documented by net.Conn.SetDeadline, without requiring any extra
// work in the net package and without requiring the internal/poll
// package to import os (which it can't, because that would be circular).
func errDeadlineExceeded() error { return poll.ErrDeadlineExceeded }
type timeout interface {
Timeout() bool
}