fix(spanner): destroy session when client is closing

spanner/session.go

@@ -25,6 +25,7 @@ import (
 	"math"
 	"math/rand"
 	"runtime/debug"
+	"strings"
 	"sync"
 	"time"
 
@@ -1723,3 +1724,12 @@ func isSessionNotFoundError(err error) bool {
 	}
 	return false
 }
+
+// isClientClosing returns true if the given error is a
+// `Connection is closing` error.
+func isClientClosing(err error) bool {
+	if err == nil {
+		return false
+	}
+	return ErrCode(err) == codes.Canceled && strings.Contains(err.Error(), "the client connection is closing")
+}

spanner/transaction.go

@@ -779,7 +779,7 @@ func (t *ReadOnlyTransaction) release(err error) {
 	sh := t.sh
 	t.mu.Unlock()
 	if sh != nil { // sh could be nil if t.acquire() fails.
-		if isSessionNotFoundError(err) {
+		if isSessionNotFoundError(err) || isClientClosing(err) {
 			sh.destroy()
 		}
 		if t.singleUse {