implementation of tantivy datastore + updated RPC calls to deal with tantivy + docs

src/admin_meta.rs

@@ -48,6 +48,9 @@ fn init_admin_storage(
     let storage: Arc<dyn StorageBackend> = match backend {
         options::BackendType::Redb => Arc::new(Storage::new(&db_file, true, Some(admin_secret))?),
         options::BackendType::Sled => Arc::new(SledStorage::new(&db_file, true, Some(admin_secret))?),
+        options::BackendType::Tantivy => {
+            return Err(DBError("Admin DB 0 cannot use Tantivy backend".to_string()))
+        }
     };
     Ok(storage)
 }
@@ -199,6 +202,9 @@ pub fn open_data_storage(
     let storage: Arc<dyn StorageBackend> = match effective_backend {
         options::BackendType::Redb => Arc::new(Storage::new(&db_file, should_encrypt, enc.as_deref())?),
         options::BackendType::Sled => Arc::new(SledStorage::new(&db_file, should_encrypt, enc.as_deref())?),
+        options::BackendType::Tantivy => {
+            return Err(DBError("Tantivy backend has no KV storage; use FT.* commands only".to_string()))
+        }
     };
 
     // Publish to registry
@@ -291,6 +297,7 @@ pub fn set_database_backend(
     let val = match db_backend {
         options::BackendType::Redb => "Redb",
         options::BackendType::Sled => "Sled",
+        options::BackendType::Tantivy => "Tantivy",
     };
     let _ = admin.hset(&mk, vec![("backend".to_string(), val.to_string())])?;
     Ok(())
@@ -307,6 +314,7 @@ pub fn get_database_backend(
     match admin.hget(&mk, "backend")? {
         Some(s) if s == "Redb" => Ok(Some(options::BackendType::Redb)),
         Some(s) if s == "Sled" => Ok(Some(options::BackendType::Sled)),
+        Some(s) if s == "Tantivy" => Ok(Some(options::BackendType::Tantivy)),
         _ => Ok(None),
     }
 }