use a trait object for the server, for dynamic dispatch

sync-server/src/server/mod.rs

@@ -0,0 +1,52 @@
+use crate::types::{AddVersionResult, ClientId, GetVersionResult, HistorySegment, VersionId};
+use failure::Fallible;
+use taskchampion::Uuid;
+
+pub(crate) trait SyncServer {
+    fn get_child_version(
+        &self,
+        client_id: ClientId,
+        parent_version_id: VersionId,
+    ) -> Fallible<Option<GetVersionResult>>;
+
+    fn add_version(
+        &self,
+        client_id: ClientId,
+        parent_version_id: VersionId,
+        history_segment: &HistorySegment,
+    ) -> Fallible<AddVersionResult>;
+}
+
+// TODO: temporary
+/// A "null" sync server's implementation; HTTP API methods call through to methods on a single
+/// instance of this type.
+pub(crate) struct NullSyncServer {}
+
+impl NullSyncServer {
+    pub(crate) fn new() -> Self {
+        Self {}
+    }
+}
+
+impl SyncServer for NullSyncServer {
+    fn get_child_version(
+        &self,
+        _client_id: ClientId,
+        parent_version_id: VersionId,
+    ) -> Fallible<Option<GetVersionResult>> {
+        Ok(Some(GetVersionResult {
+            version_id: Uuid::new_v4(),
+            parent_version_id,
+            history_segment: b"abcd".to_vec(),
+        }))
+    }
+
+    fn add_version(
+        &self,
+        _client_id: ClientId,
+        _parent_version_id: VersionId,
+        _history_segment: &HistorySegment,
+    ) -> Fallible<AddVersionResult> {
+        Ok(AddVersionResult::Ok(Uuid::new_v4()))
+    }
+}