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control/controlhttp: extract the last network connection

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The same context we use for the HTTP request here might be re-used by
the dialer, which could result in `GotConn` being called multiple times.
We only care about the last one.

Fixes #13009

Signed-off-by: Anton Tolchanov <anton@tailscale.com>
This commit is contained in:
Anton Tolchanov
2024-08-03 13:37:01 +01:00
committed by Anton Tolchanov
parent b3fc345aba
commit 7bac5dffcb
2 changed files with 60 additions and 12 deletions
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25
control/controlhttp/client.go
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@@ -46,6 +46,7 @@ import (
"tailscale.com/net/sockstats"
"tailscale.com/net/tlsdial"
"tailscale.com/net/tshttpproxy"
"tailscale.com/syncs"
"tailscale.com/tailcfg"
"tailscale.com/tstime"
"tailscale.com/util/multierr"
@@ -497,11 +498,9 @@ func (a *Dialer) tryURLUpgrade(ctx context.Context, u *url.URL, addr netip.Addr,
tr.DisableCompression = true
// (mis)use httptrace to extract the underlying net.Conn from the
// transport. We make exactly 1 request using this transport, so
// there will be exactly 1 GotConn call. Additionally, the
// transport handles 101 Switching Protocols correctly, such that
// the Conn will not be reused or kept alive by the transport once
// the response has been handed back from RoundTrip.
// transport. The transport handles 101 Switching Protocols correctly,
// such that the Conn will not be reused or kept alive by the transport
// once the response has been handed back from RoundTrip.
//
// In theory, the machinery of net/http should make it such that
// the trace callback happens-before we get the response, but
@@ -517,10 +516,16 @@ func (a *Dialer) tryURLUpgrade(ctx context.Context, u *url.URL, addr netip.Addr,
// unexpected EOFs...), and we're bound to forget someday and
// introduce a protocol optimization at a higher level that starts
// eagerly transmitting from the server.
connCh := make(chan net.Conn, 1)
var lastConn syncs.AtomicValue[net.Conn]
trace := httptrace.ClientTrace{
// Even though we only make a single HTTP request which should
// require a single connection, the context (with the attached
// trace configuration) might be used by our custom dialer to
// make other HTTP requests (e.g. BootstrapDNS). We only care
// about the last connection made, which should be the one to
// the control server.
GotConn: func(info httptrace.GotConnInfo) {
connCh <- info.Conn
lastConn.Store(info.Conn)
},
}
ctx = httptrace.WithClientTrace(ctx, &trace)
@@ -548,11 +553,7 @@ func (a *Dialer) tryURLUpgrade(ctx context.Context, u *url.URL, addr netip.Addr,
// is still a read buffer attached to it within resp.Body. So, we
// must direct I/O through resp.Body, but we can still use the
// underlying net.Conn for stuff like deadlines.
var switchedConn net.Conn
select {
case switchedConn = <-connCh:
default:
}
switchedConn := lastConn.Load()
if switchedConn == nil {
resp.Body.Close()
return nil, fmt.Errorf("httptrace didn't provide a connection")