115 lines
2.6 KiB
Go
115 lines
2.6 KiB
Go
// Package agentproxy relays a single TCP connection between a local service and
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// the control plane, so a control plane that cannot route to this host's network
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// can still open a console session.
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//
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// The dial host is hardcoded to loopback. The control plane supplies only a
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// port, and nothing in this package can be made to dial anywhere else.
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package agentproxy
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import (
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"errors"
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"fmt"
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"io"
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"net"
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"strconv"
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"time"
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"gitea.hostxtra.co.uk/vantage/vantage-shared/grpc/pb"
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)
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const (
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loopbackHost = "127.0.0.1"
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chunkSize = 32 * 1024
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dialTimeout = 10 * time.Second
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)
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// Stream is the agent's half of a ProxyStream.
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type Stream interface {
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Send(*pb.ProxyClientMsg) error
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Recv() (*pb.ProxyServerMsg, error)
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CloseSend() error
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}
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// Open dials the local port, announces itself on the stream, and relays until
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// either side ends. A refused dial is reported as an explicit close so the
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// operator sees a reason rather than a hang.
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func Open(stream Stream, serverID, agentToken, proxyID string, port uint32) error {
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conn, dialErr := net.DialTimeout("tcp",
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net.JoinHostPort(loopbackHost, strconv.Itoa(int(port))), dialTimeout)
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if err := stream.Send(&pb.ProxyClientMsg{Open: &pb.ProxyOpen{
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ServerId: serverID,
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AgentToken: agentToken,
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ProxyId: proxyID,
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}}); err != nil {
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if conn != nil {
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_ = conn.Close()
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}
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return fmt.Errorf("send open: %w", err)
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}
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if dialErr != nil {
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_ = stream.Send(&pb.ProxyClientMsg{Close: &pb.ProxyClose{
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Reason: "dial_refused: " + dialErr.Error(),
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}})
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_ = stream.CloseSend()
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return fmt.Errorf("dial 127.0.0.1:%d: %w", port, dialErr)
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}
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defer conn.Close()
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return relay(conn, stream)
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}
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func relay(conn net.Conn, stream Stream) error {
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errCh := make(chan error, 2)
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// local service -> control plane
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go func() {
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buf := make([]byte, chunkSize)
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for {
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n, err := conn.Read(buf)
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if n > 0 {
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chunk := make([]byte, n)
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copy(chunk, buf[:n])
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if sendErr := stream.Send(&pb.ProxyClientMsg{Data: chunk}); sendErr != nil {
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errCh <- sendErr
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return
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}
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}
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if err != nil {
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errCh <- err
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return
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}
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}
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}()
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// control plane -> local service
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go func() {
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for {
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msg, err := stream.Recv()
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if err != nil {
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errCh <- err
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return
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}
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if msg.Close != nil {
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errCh <- fmt.Errorf("server closed relay: %s", msg.Close.Reason)
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return
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}
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if len(msg.Data) > 0 {
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if _, err := conn.Write(msg.Data); err != nil {
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errCh <- err
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return
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}
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}
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}
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}()
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err := <-errCh
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_ = conn.Close()
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_ = stream.CloseSend()
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if errors.Is(err, io.EOF) {
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return nil
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}
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return err
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}
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