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derp, derp/derphttp: remove one RTT from DERP setup

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* advertise server's DERP public key following its ServerHello
* have client look for that DEPR public key in the response
  PeerCertificates
* let client advertise it's going into a "fast start" mode
  if it finds it
* modify server to support that fast start mode, just not
  sending the HTTP response header

Cuts down another round trip, bringing the latency of being able to
write our first DERP frame from SF to Bangalore from ~725ms
(3 RTT) to ~481ms (2 RTT: TCP and TLS).

Fixes #693

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick
2020-08-18 15:32:32 -07:00
committed by Brad Fitzpatrick
parent 9337a99dff
commit e415991256
7 changed files with 193 additions and 28 deletions
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19
derp/derp_client.go
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@@ -48,7 +48,8 @@ func (f clientOptFunc) update(o *clientOpt) { f(o) }
// clientOpt are the options passed to newClient.
type clientOpt struct {
MeshKey string
MeshKey string
ServerPub key.Public
}
// MeshKey returns a ClientOpt to pass to the DERP server during connect to get
@@ -57,6 +58,12 @@ type clientOpt struct {
// An empty key means to not use a mesh key.
func MeshKey(key string) ClientOpt { return clientOptFunc(func(o *clientOpt) { o.MeshKey = key }) }
// ServerPublicKey returns a ClientOpt to declare that the server's DERP public key is known.
// If key is the zero value, the returned ClientOpt is a no-op.
func ServerPublicKey(key key.Public) ClientOpt {
return clientOptFunc(func(o *clientOpt) { o.ServerPub = key })
}
func NewClient(privateKey key.Private, nc Conn, brw *bufio.ReadWriter, logf logger.Logf, opts ...ClientOpt) (*Client, error) {
var opt clientOpt
for _, o := range opts {
@@ -78,8 +85,12 @@ func newClient(privateKey key.Private, nc Conn, brw *bufio.ReadWriter, logf logg
bw: brw.Writer,
meshKey: opt.MeshKey,
}
if err := c.recvServerKey(); err != nil {
return nil, fmt.Errorf("derp.Client: failed to receive server key: %v", err)
if opt.ServerPub.IsZero() {
if err := c.recvServerKey(); err != nil {
return nil, fmt.Errorf("derp.Client: failed to receive server key: %v", err)
}
} else {
c.serverKey = opt.ServerPub
}
if err := c.sendClientKey(); err != nil {
return nil, fmt.Errorf("derp.Client: failed to send client key: %v", err)
@@ -144,7 +155,7 @@ func (c *Client) sendClientKey() error {
return err
}
msg, err := json.Marshal(clientInfo{
Version: protocolVersion,
Version: ProtocolVersion,
MeshKey: c.meshKey,
})
if err != nil {