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net: enable RFC 6555 Fast Fallback by default

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The Dialer.DualStack field is now meaningless and documented as
deprecated.

To disable fallback, set FallbackDelay to a negative value.

Fixes #22225

Change-Id: Icc212fe07bb69d7651ab81e539b8b3e3d3372fa9
Reviewed-on: https://go-review.googlesource.com/c/146659
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Brad Fitzpatrick 2018-11-01 16:29:42 +00:00
parent 0ff6e5f1b4
commit efc185029b
1 changed files with 16 additions and 7 deletions
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23
src/net/dial.go
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@ -44,16 +44,23 @@ type Dialer struct {
// If nil, a local address is automatically chosen.
LocalAddr Addr
// DualStack enables RFC 6555-compliant "Happy Eyeballs"
// dialing when the network is "tcp" and the host in the
// address parameter resolves to both IPv4 and IPv6 addresses.
// This allows a client to tolerate networks where one address
// family is silently broken.
// DualStack previously enabled RFC 6555 Fast Fallback
// support, also known as "Happy Eyeballs", in which IPv4 is
// tried soon if IPv6 appears to be misconfigured and
// hanging.
//
// Deprecated: Fast Fallback is enabled by default. To
// disable, set FallbackDelay to a negative value.
DualStack bool
// FallbackDelay specifies the length of time to wait before
// spawning a fallback connection, when DualStack is enabled.
// spawning a RFC 6555 Fast Fallback connection. That is, this
// is the amount of time to wait for IPv6 to succeed before
// assuming that IPv6 is misconfigured and falling back to
// IPv4.
//
// If zero, a default delay of 300ms is used.
// A negative value disables Fast Fallback support.
FallbackDelay time.Duration
// KeepAlive specifies the keep-alive period for an active
@ -81,6 +88,8 @@ type Dialer struct {
Control func(network, address string, c syscall.RawConn) error
}
func (d *Dialer) dualStack() bool { return d.FallbackDelay >= 0 }
func minNonzeroTime(a, b time.Time) time.Time {
if a.IsZero() {
return b
@ -393,7 +402,7 @@ func (d *Dialer) DialContext(ctx context.Context, network, address string) (Conn
}
var primaries, fallbacks addrList
if d.DualStack && network == "tcp" {
if d.dualStack() && network == "tcp" {
primaries, fallbacks = addrs.partition(isIPv4)
} else {
primaries = addrs