Close proxy listener if session is no longer active (#4850)

* Close proxy listener if session is no longer active

api/proxy/proxy.go

@@ -15,6 +15,8 @@ import (
 	"sync/atomic"
 	"time"
 
+	"github.com/hashicorp/boundary/api"
+	"github.com/hashicorp/boundary/api/sessions"
 	"github.com/hashicorp/boundary/api/targets"
 	cleanhttp "github.com/hashicorp/go-cleanhttp"
 	"github.com/hashicorp/go-secure-stdlib/base62"
@@ -37,6 +39,7 @@ type ClientProxy struct {
 	connectionsLeft         *atomic.Int32
 	connsLeftCh             chan int32
 	callerConnectionsLeftCh chan int32
+	apiClient               *api.Client
 	sessionAuthzData        *targets.SessionAuthorizationData
 	createTime              time.Time
 	expiration              time.Time
@@ -97,6 +100,7 @@ func New(ctx context.Context, authzToken string, opt ...Option) (*ClientProxy, e
 		callerConnectionsLeftCh: opts.WithConnectionsLeftCh,
 		started:                 new(atomic.Bool),
 		skipSessionTeardown:     opts.WithSkipSessionTeardown,
+		apiClient:               opts.withApiClient,
 	}
 
 	if opts.WithListener != nil {
@@ -260,6 +264,27 @@ func (p *ClientProxy) Start(opt ...Option) (retErr error) {
 					p.cancel()
 					return
 				}
+
+				// TODO: Determine if this is useful or if there is a better approach
+				// that we may use in the long term.
+				if p.apiClient != nil {
+					// If we can tell that the session for the connection we just
+					// closed is terminated, we can close the listener, otherwise
+					// might as well leave it open so the next connection can be
+					// tried.
+					sess, err := sessions.NewClient(p.apiClient).Read(p.ctx, p.sessionAuthzData.SessionId)
+					if err != nil || sess == nil || sess.Item == nil || sess.Item.TerminationReason == "" {
+						return
+					}
+
+					// We got a valid session response for the session we just
+					// closed a connection for. Since there is a termination reason
+					// we can treat the session as being terminated so no more
+					// connections will be able to be established.
+					fin <- fmt.Errorf("session no longer active")
+					listenerCloseFunc()
+					p.cancel()
+				}
 			}()
 		}
 	}()