more specific error handling

pkg/recipe/recipe.go

@@ -2,6 +2,7 @@ package recipe
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -665,13 +666,21 @@ func CheckoutDefaultBranch(repo *git.Repository, recipeName string) (plumbing.Re
 	return branch, nil
 }
 
+type CatalogueOfflineError struct {
+	msg string
+}
+
+func (e *CatalogueOfflineError) Error() string {
+	return fmt.Sprintf("catalogue offline: %s", e.msg)
+}
+
 // recipeCatalogueFSIsLatest checks whether the recipe catalogue stored locally
 // is up to date.
 func recipeCatalogueFSIsLatest() (bool, error) {
 	httpClient := web.NewHTTPRetryClient()
 	res, err := httpClient.Head(RecipeCatalogueURL)
 	if err != nil {
-		return false, err
+		return false, &CatalogueOfflineError{err.Error()}
 	}
 
 	lastModified := res.Header["Last-Modified"][0]
@@ -712,17 +721,21 @@ func ReadRecipeCatalogue() (RecipeCatalogue, error) {
 
 	recipeFSIsLatest, err := recipeCatalogueFSIsLatest()
 	if err != nil {
-		logrus.Error(err)
+		var offlineErr *CatalogueOfflineError
-		logrus.Error("failed to access last recipe catalogue")
+		if errors.As(err, &offlineErr) {
+			logrus.Error(err)
+			logrus.Error("unable to retrieve catalogue from internet, using local copy.")
+			recipeFSIsLatest = true
+		} else {
+			return nil, err
+		}
 	}
 
 	if !recipeFSIsLatest {
 		if err := readRecipeCatalogueWeb(&recipes); err != nil {
-			logrus.Error(err)
+			return nil, err
-			logrus.Error("failed to access web recipe catalogue")
-		} else {
-			return recipes, nil
 		}
+		return recipes, nil
 	}
 
 	if err := readRecipeCatalogueFS(&recipes); err != nil {