[#488] middleware/policy: Add frostfs-to-s3 error transformation

Signed-off-by: Nikita Zinkevich <n.zinkevich@yadro.com>

api/errors/errors.go

@@ -1,10 +1,13 @@
 package errors
 
 import (
+	"errors"
 	"fmt"
 	"net/http"
 
-	frosterrors "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/frostfs/errors"
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/frostfs"
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/tree"
+	frosterr "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/frostfs/errors"
 )
 
 type (
@@ -1765,7 +1768,7 @@ var errorCodes = errorCodeMap{
 
 // IsS3Error checks if the provided error is a specific s3 error.
 func IsS3Error(err error, code ErrorCode) bool {
-	err = frosterrors.UnwrapErr(err)
+	err = frosterr.UnwrapErr(err)
 	e, ok := err.(Error)
 	return ok && e.ErrCode == code
 }
@@ -1802,6 +1805,26 @@ func GetAPIErrorWithError(code ErrorCode, err error) Error {
 	return errorCodes.toAPIErrWithErr(code, err)
 }
 
+// TransformToS3Error converts FrostFS error to the corresponding S3 error type.
+func TransformToS3Error(err error) error {
+	err = frosterr.UnwrapErr(err) // this wouldn't work with errors.Join
+	var s3err Error
+	if errors.As(err, &s3err) {
+		return err
+	}
+
+	if errors.Is(err, frostfs.ErrAccessDenied) ||
+		errors.Is(err, tree.ErrNodeAccessDenied) {
+		return GetAPIError(ErrAccessDenied)
+	}
+
+	if errors.Is(err, frostfs.ErrGatewayTimeout) {
+		return GetAPIError(ErrGatewayTimeout)
+	}
+
+	return GetAPIError(ErrInternalError)
+}
+
 // ObjectError -- error that is linked to a specific object.
 type ObjectError struct {
 	Err     error

api/errors/errors_test.go

@@ -2,7 +2,12 @@ package errors
 
 import (
 	"errors"
+	"fmt"
 	"testing"
+
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/frostfs"
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/tree"
+	"github.com/stretchr/testify/require"
 )
 
 func BenchmarkErrCode(b *testing.B) {
@@ -24,3 +29,56 @@ func BenchmarkErrorsIs(b *testing.B) {
 		}
 	}
 }
+
+func TestTransformS3Errors(t *testing.T) {
+	for _, tc := range []struct {
+		name     string
+		err      error
+		expected ErrorCode
+	}{
+		{
+			name:     "simple std error to internal error",
+			err:      errors.New("some error"),
+			expected: ErrInternalError,
+		},
+		{
+			name:     "layer access denied error to s3 access denied error",
+			err:      frostfs.ErrAccessDenied,
+			expected: ErrAccessDenied,
+		},
+		{
+			name:     "wrapped layer access denied error to s3 access denied error",
+			err:      fmt.Errorf("wrap: %w", frostfs.ErrAccessDenied),
+			expected: ErrAccessDenied,
+		},
+		{
+			name:     "layer node access denied error to s3 access denied error",
+			err:      tree.ErrNodeAccessDenied,
+			expected: ErrAccessDenied,
+		},
+		{
+			name:     "layer gateway timeout error to s3 gateway timeout error",
+			err:      frostfs.ErrGatewayTimeout,
+			expected: ErrGatewayTimeout,
+		},
+		{
+			name:     "s3 error to s3 error",
+			err:      GetAPIError(ErrInvalidPart),
+			expected: ErrInvalidPart,
+		},
+		{
+			name:     "wrapped s3 error to s3 error",
+			err:      fmt.Errorf("wrap: %w", GetAPIError(ErrInvalidPart)),
+			expected: ErrInvalidPart,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			err := TransformToS3Error(tc.err)
+			s3err, ok := err.(Error)
+			require.True(t, ok, "error must be s3 error")
+			require.Equalf(t, tc.expected, s3err.ErrCode,
+				"expected: '%s', got: '%s'",
+				GetAPIError(tc.expected).Code, GetAPIError(s3err.ErrCode).Code)
+		})
+	}
+}