fix: clear stale end-of-wal-stream flag before pg_rewind restore

The previous commit stopped pg_rewind restores from checking the
end-of-wal-stream flag, but left an existing flag on disk untouched.
A flag set by a normal-recovery invocation before this pod was
demoted would then resurface once the rewind finished and wrongly
abort the following normal-recovery invocation.

Clear the flag unconditionally in rewind mode, before the spool
short-circuit, so a request for a WAL file already staged in the
spool cannot skip the clear.

Signed-off-by: Marco Nenciarini <marco.nenciarini@enterprisedb.com>

internal/cnpgi/common/wal.go

@@ -323,6 +323,20 @@ func (w WALServiceImplementation) restoreFromBarmanObjectStore(
 		return fmt.Errorf("while creating the restorer: %w", err)
 	}
 
+	// A flag left over from a normal-recovery invocation that ran before this pod
+	// was demoted must not survive into a pg_rewind restore: the flag machinery
+	// does not apply while restoring on behalf of pg_rewind (see
+	// shouldUseEndOfWALStreamFlag below), so it is never checked here, but left
+	// untouched it would resurface and wrongly abort the first normal-recovery
+	// invocation that runs once the rewind is done. This runs unconditionally,
+	// before the spool short-circuit in Step 1, so a request for a WAL file that
+	// happens to already be staged in the spool cannot skip the clear.
+	if rewindMode {
+		if err := clearEndOfWALStreamFlag(walRestorer); err != nil {
+			return err
+		}
+	}
+
 	// Step 1: check if this WAL file is not already in the spool
 	var wasInSpool bool
 	if wasInSpool, err = walRestorer.RestoreFromSpool(walName, destinationPath); err != nil {
@@ -526,6 +540,22 @@ func checkEndOfWALStreamFlag(walRestorer *barmanRestorer.WALRestorer) error {
 	return nil
 }
 
+// clearEndOfWALStreamFlag removes the end-of-wal-stream flag, if present, without
+// treating it as an error. It is used instead of checkEndOfWALStreamFlag when
+// restoring on behalf of pg_rewind, which must not abort on a flag it did not
+// set itself.
+func clearEndOfWALStreamFlag(walRestorer *barmanRestorer.WALRestorer) error {
+	contain, err := walRestorer.IsEndOfWALStream()
+	if err != nil {
+		return err
+	}
+
+	if contain {
+		return walRestorer.ResetEndOfWalStream()
+	}
+	return nil
+}
+
 // isEndOfWALStream returns true if one of the downloads has returned
 // a file-not-found error.
 func isEndOfWALStream(results []barmanRestorer.Result) bool {

internal/cnpgi/common/wal_test.go

@@ -20,7 +20,10 @@ SPDX-License-Identifier: Apache-2.0
 package common
 
 import (
+	"context"
+
 	barmanapi "github.com/cloudnative-pg/barman-cloud/pkg/api"
+	barmanRestorer "github.com/cloudnative-pg/barman-cloud/pkg/restorer"
 	cnpgv1 "github.com/cloudnative-pg/cloudnative-pg/api/v1"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
@@ -141,3 +144,36 @@ var _ = Describe("shouldUseEndOfWALStreamFlag", func() {
 		Entry("rewind mode wins over streaming availability", clusterWithPrimary("cluster-1"), "cluster-2", true, false),
 	)
 })
+
+var _ = Describe("clearEndOfWALStreamFlag", func() {
+	newRestorer := func() *barmanRestorer.WALRestorer {
+		restorer, err := barmanRestorer.New(context.Background(), nil, GinkgoT().TempDir())
+		Expect(err).ToNot(HaveOccurred())
+		return restorer
+	}
+
+	It("is a no-op when the flag is not set", func() {
+		restorer := newRestorer()
+
+		Expect(clearEndOfWALStreamFlag(restorer)).To(Succeed())
+
+		isEOS, err := restorer.IsEndOfWALStream()
+		Expect(err).ToNot(HaveOccurred())
+		Expect(isEOS).To(BeFalse())
+	})
+
+	// Regression guard: a flag left over from a normal-recovery invocation that
+	// ran before this pod was demoted must not survive a pg_rewind restore, or
+	// it would resurface and wrongly abort the first normal-recovery invocation
+	// that runs once the rewind is done.
+	It("removes a pre-existing flag without returning an error", func() {
+		restorer := newRestorer()
+		Expect(restorer.SetEndOfWALStream()).To(Succeed())
+
+		Expect(clearEndOfWALStreamFlag(restorer)).To(Succeed())
+
+		isEOS, err := restorer.IsEndOfWALStream()
+		Expect(err).ToNot(HaveOccurred())
+		Expect(isEOS).To(BeFalse())
+	})
+})