Add DisabledAssignmentStore to use when assignments are disabled

Praefect can still be configured to run without the database. To
support such a configuration, this commit adds a DisabledAssignmentStore
which can be plugged in if the database is not used. It simply returns
all storages as assigned and doesn't allow for configuring replication
factors.

1 files changed, 33 insertions, 0 deletions

diff --git a/internal/praefect/assignment.go b/internal/praefect/assignment.go
new file mode 100644
index 000000000..f0f38e5af
--- /dev/null
+++ b/internal/praefect/assignment.go
@@ -0,0 +1,33 @@
+package praefect
+
+import (
+	"context"
+	"errors"
+)
+
+// AssignmentStore is the interface which Praefect uses to operate on repository assignments.
+type AssignmentStore interface {
+	AssignmentGetter
+	// SetReplicationFactor sets a repository's replication factor to the desired value and returns the
+	// resulting assignments.
+	SetReplicationFactor(ctx context.Context, virtualStorage, relativePath string, replicationFactor int) ([]string, error)
+}
+
+type disabledAssignments map[string][]string
+
+// NewDisabledAssignmentStore returns an assignments store that can be used if no
+// database is configured. It returns every configured storage as assigned and
+// errors when trying to set assignments.
+func NewDisabledAssignmentStore(storages map[string][]string) AssignmentStore {
+	return disabledAssignments(storages)
+}
+
+// GetHostAssigments simply returns all of the storages configured for the virtual storage.
+func (storages disabledAssignments) GetHostAssignments(ctx context.Context, virtualStorage, relativePath string) ([]string, error) {
+	return storages[virtualStorage], nil
+}
+
+// SetReplicationFactor errors when attempting to set assignments.
+func (disabledAssignments) SetReplicationFactor(context.Context, string, string, int) ([]string, error) {
+	return nil, errors.New("assignments are disabled")
+}