open-consul/connect/proxy/conn.go

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package proxy
import (
"io"
"net"
"sync/atomic"
)
// Conn represents a single proxied TCP connection.
type Conn struct {
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src, dst net.Conn
// TODO(banks): benchmark and consider adding _ [8]uint64 padding between
// these to prevent false sharing between the rx and tx goroutines when
// running on separate cores.
srcW, dstW countWriter
stopping int32
}
// NewConn returns a conn joining the two given net.Conn
func NewConn(src, dst net.Conn) *Conn {
return &Conn{
src: src,
dst: dst,
srcW: countWriter{w: src},
dstW: countWriter{w: dst},
stopping: 0,
}
}
// Close closes both connections.
func (c *Conn) Close() error {
// Note that net.Conn.Close can be called multiple times and atomic store is
// idempotent so no need to ensure we only do this once.
//
// Also note that we don't wait for CopyBytes to return here since we are
// closing the conns which is the only externally visible sideeffect of that
// goroutine running and there should be no way for it to hang or leak once
// the conns are closed so we can save the extra coordination.
atomic.StoreInt32(&c.stopping, 1)
c.src.Close()
c.dst.Close()
return nil
}
// CopyBytes will continuously copy bytes in both directions between src and dst
// until either connection is closed.
func (c *Conn) CopyBytes() error {
defer c.Close()
go func() {
// Need this since Copy is only guaranteed to stop when it's source reader
// (second arg) hits EOF or error but either conn might close first possibly
// causing this goroutine to exit but not the outer one. See
// TestConnSrcClosing which will fail if you comment the defer below.
defer c.Close()
io.Copy(&c.dstW, c.src)
}()
_, err := io.Copy(&c.srcW, c.dst)
// Note that we don't wait for the other goroutine to finish because it either
// already has due to it's src conn closing, or it will once our defer fires
// and closes the source conn. No need for the extra coordination.
if atomic.LoadInt32(&c.stopping) == 1 {
return nil
}
return err
}
// Stats returns number of bytes transmitted and received. Transmit means bytes
// written to dst, receive means bytes written to src.
func (c *Conn) Stats() (txBytes, rxBytes uint64) {
return c.srcW.Written(), c.dstW.Written()
}
// countWriter is an io.Writer that counts the number of bytes being written
// before passing them through. We use it to gather metrics for bytes
// sent/received. Note that since we are always copying between a net.TCPConn
// and a tls.Conn, none of the optimisations using syscalls like splice and
// ReaderTo/WriterFrom can be used anyway and io.Copy falls back to a generic
// buffered read/write loop.
//
// We use atomic updates to synchronize reads and writes here. It's the cheapest
// uncontended option based on
// https://gist.github.com/banks/e76b40c0cc4b01503f0a0e4e0af231d5. Further
// optimization can be made when if/when identified as a real overhead.
type countWriter struct {
written uint64
w io.Writer
}
// Write implements io.Writer
func (cw *countWriter) Write(p []byte) (n int, err error) {
n, err = cw.w.Write(p)
atomic.AddUint64(&cw.written, uint64(n))
return
}
// Written returns how many bytes have been written to w.
func (cw *countWriter) Written() uint64 {
return atomic.LoadUint64(&cw.written)
}