OADP-4640: Downstream only to allow override kopia default algorithms

Introduction of downstream only option to override Kopia default:
 - hashing algorithm
 - splitting algorithm
 - encryption algorithm

With introduction of 3 environment variables it is possible to override
Kopia algorithms used by Velero:

KOPIA_HASHING_ALGORITHM
KOPIA_SPLITTER_ALGORITHM
KOPIA_ENCRYPTION_ALGORITHM

If the env algorithms are not set or they are not within
Kopia SupportedAlgorithms, the default algorithm will be used.
This behavior is consistent with current behavior without this
change.

Signed-off-by: Michal Pryc <mpryc@redhat.com>

pkg/repository/udmrepo/kopialib/backend/common.go

@@ -18,6 +18,8 @@ package backend
 
 import (
 	"context"
+	"os"
+	"slices"
 	"time"
 
 	"github.com/kopia/kopia/repo"
@@ -48,16 +50,28 @@ func setupLimits(ctx context.Context, flags map[string]string) throttling.Limits
 	}
 }
 
+// Helper function to choose between environment variable and default kopia algorithm value
+func getKopiaAlgorithm(key, envKey string, flags map[string]string, supportedAlgorithms []string, defaultValue string) string {
+	algorithm := os.Getenv(envKey)
+	if len(algorithm) > 0 {
+		if slices.Contains(supportedAlgorithms, algorithm) {
+			return algorithm
+		}
+	}
+
+	return optionalHaveStringWithDefault(key, flags, defaultValue)
+}
+
 // SetupNewRepositoryOptions setups the options when creating a new Kopia repository
 func SetupNewRepositoryOptions(ctx context.Context, flags map[string]string) repo.NewRepositoryOptions {
 	return repo.NewRepositoryOptions{
 		BlockFormat: format.ContentFormat{
-			Hash:       optionalHaveStringWithDefault(udmrepo.StoreOptionGenHashAlgo, flags, hashing.DefaultAlgorithm),
-			Encryption: optionalHaveStringWithDefault(udmrepo.StoreOptionGenEncryptAlgo, flags, encryption.DefaultAlgorithm),
+			Hash:       getKopiaAlgorithm(udmrepo.StoreOptionGenHashAlgo, "KOPIA_HASHING_ALGORITHM", flags, hashing.SupportedAlgorithms(), hashing.DefaultAlgorithm),
+			Encryption: getKopiaAlgorithm(udmrepo.StoreOptionGenEncryptAlgo, "KOPIA_ENCRYPTION_ALGORITHM", flags, encryption.SupportedAlgorithms(false), encryption.DefaultAlgorithm),
 		},
 
 		ObjectFormat: format.ObjectFormat{
-			Splitter: optionalHaveStringWithDefault(udmrepo.StoreOptionGenSplitAlgo, flags, splitter.DefaultAlgorithm),
+			Splitter: getKopiaAlgorithm(udmrepo.StoreOptionGenSplitAlgo, "KOPIA_SPLITTER_ALGORITHM", flags, splitter.SupportedAlgorithms(), splitter.DefaultAlgorithm),
 		},
 
 		RetentionMode:   blob.RetentionMode(optionalHaveString(udmrepo.StoreOptionGenRetentionMode, flags)),

pkg/repository/udmrepo/kopialib/backend/common_kopia_algorithms_test.go

@@ -0,0 +1,144 @@
+/*
+Copyright the Velero contributors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package backend
+
+import (
+	"context"
+	"testing"
+
+	"github.com/kopia/kopia/repo"
+	"github.com/kopia/kopia/repo/encryption"
+	"github.com/kopia/kopia/repo/format"
+	"github.com/kopia/kopia/repo/hashing"
+	"github.com/kopia/kopia/repo/splitter"
+	"github.com/stretchr/testify/assert"
+
+	"github.com/vmware-tanzu/velero/pkg/repository/udmrepo"
+)
+
+func TestSetupNewRepoAlgorithms(t *testing.T) {
+
+	testCases := []struct {
+		name     string
+		envVars  map[string]string
+		flags    map[string]string
+		expected repo.NewRepositoryOptions
+	}{
+		{
+			name: "with valid non-default hash algo from env",
+			envVars: map[string]string{
+				"KOPIA_HASHING_ALGORITHM": "HMAC-SHA3-224",
+			},
+			flags: map[string]string{},
+			expected: repo.NewRepositoryOptions{
+				BlockFormat: format.ContentFormat{
+					Hash:       "HMAC-SHA3-224",
+					Encryption: encryption.DefaultAlgorithm,
+				},
+				ObjectFormat: format.ObjectFormat{
+					Splitter: splitter.DefaultAlgorithm,
+				},
+			},
+		},
+		{
+			name: "with valid non-default encryption algo from env",
+			envVars: map[string]string{
+				"KOPIA_HASHING_ALGORITHM":    "",
+				"KOPIA_SPLITTER_ALGORITHM":   "",
+				"KOPIA_ENCRYPTION_ALGORITHM": "CHACHA20-POLY1305-HMAC-SHA256",
+			},
+			flags: map[string]string{},
+			expected: repo.NewRepositoryOptions{
+				BlockFormat: format.ContentFormat{
+					Hash:       hashing.DefaultAlgorithm,
+					Encryption: "CHACHA20-POLY1305-HMAC-SHA256",
+				},
+				ObjectFormat: format.ObjectFormat{
+					Splitter: splitter.DefaultAlgorithm,
+				},
+			},
+		},
+		{
+			name:    "with valid non-default splitter algo from env",
+			envVars: map[string]string{"KOPIA_SPLITTER_ALGORITHM": "FIXED-512K"},
+			flags:   map[string]string{},
+			expected: repo.NewRepositoryOptions{
+				BlockFormat: format.ContentFormat{
+					Hash:       hashing.DefaultAlgorithm,
+					Encryption: encryption.DefaultAlgorithm,
+				},
+				ObjectFormat: format.ObjectFormat{
+					Splitter: "FIXED-512K",
+				},
+			},
+		},
+		{
+			name:    "with valid non-default splitter and hashing algo from env, invalid encryption from env",
+			envVars: map[string]string{"KOPIA_SPLITTER_ALGORITHM": "FIXED-512K", "KOPIA_HASHING_ALGORITHM": "HMAC-SHA3-224", "KOPIA_ENCRYPTION_ALGORITHM": "NON-EXISTING-SHA256"},
+			flags:   map[string]string{},
+			expected: repo.NewRepositoryOptions{
+				BlockFormat: format.ContentFormat{
+					Hash:       "HMAC-SHA3-224",
+					Encryption: encryption.DefaultAlgorithm,
+				},
+				ObjectFormat: format.ObjectFormat{
+					Splitter: "FIXED-512K",
+				},
+			},
+		},
+		{
+			name:    "with unsupported hash algo in env, fallback to default",
+			envVars: map[string]string{"KOPIA_HASHING_ALGORITHM": "unsupported-hash"},
+			flags:   map[string]string{},
+			expected: repo.NewRepositoryOptions{
+				BlockFormat: format.ContentFormat{
+					Hash:       hashing.DefaultAlgorithm,
+					Encryption: encryption.DefaultAlgorithm,
+				},
+				ObjectFormat: format.ObjectFormat{
+					Splitter: splitter.DefaultAlgorithm,
+				},
+			},
+		},
+		{
+			name:    "hash in StoreOptionGenHashAlgo and env, env wins",
+			envVars: map[string]string{"KOPIA_HASHING_ALGORITHM": "HMAC-SHA3-224"},
+			flags: map[string]string{
+				udmrepo.StoreOptionGenHashAlgo: "HMAC-SHA3-256",
+			},
+			expected: repo.NewRepositoryOptions{
+				BlockFormat: format.ContentFormat{
+					Hash:       "HMAC-SHA3-224",
+					Encryption: encryption.DefaultAlgorithm,
+				},
+				ObjectFormat: format.ObjectFormat{
+					Splitter: splitter.DefaultAlgorithm,
+				},
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			for key, value := range tc.envVars {
+				t.Setenv(key, value)
+			}
+			ret := SetupNewRepositoryOptions(context.Background(), tc.flags)
+			assert.Equal(t, tc.expected, ret)
+		})
+	}
+}