dbmcp_postgres/tools/
list_databases.rs

1//! MCP tool: `listDatabases`.
2
3use std::borrow::Cow;
4
5use dbmcp_server::pagination::Pager;
6use dbmcp_server::types::{ListDatabasesRequest, ListDatabasesResponse};
7use dbmcp_sql::Connection as _;
8use rmcp::handler::server::router::tool::{AsyncTool, ToolBase};
9use rmcp::model::{ErrorData, ToolAnnotations};
10
11use crate::PostgresHandler;
12
13const NAME: &str = "listDatabases";
14const TITLE: &str = "List Databases";
15const DESCRIPTION: &str = include_str!("../../assets/tools/list_databases/default.md");
16
17/// Marker type for the `listDatabases` MCP tool.
18pub(crate) struct ListDatabasesTool;
19
20impl ToolBase for ListDatabasesTool {
21    type Parameter = ListDatabasesRequest;
22    type Output = ListDatabasesResponse;
23    type Error = ErrorData;
24
25    fn name() -> Cow<'static, str> {
26        NAME.into()
27    }
28
29    fn title() -> Option<String> {
30        Some(TITLE.into())
31    }
32
33    fn description() -> Option<Cow<'static, str>> {
34        Some(DESCRIPTION.into())
35    }
36
37    fn annotations() -> Option<ToolAnnotations> {
38        Some(
39            ToolAnnotations::new()
40                .read_only(true)
41                .destructive(false)
42                .idempotent(true)
43                .open_world(false),
44        )
45    }
46}
47
48impl AsyncTool<PostgresHandler> for ListDatabasesTool {
49    async fn invoke(handler: &PostgresHandler, params: Self::Parameter) -> Result<Self::Output, Self::Error> {
50        handler.list_databases(params).await
51    }
52}
53
54impl PostgresHandler {
55    /// Lists one page of accessible databases.
56    ///
57    /// Uses the default pool intentionally — `pg_database` is a server-wide
58    /// catalog that returns all databases regardless of which database the
59    /// connection targets.
60    ///
61    /// # Errors
62    ///
63    /// Returns [`ErrorData`] with code `-32602` if `cursor` is malformed,
64    /// or an internal-error [`ErrorData`] if the underlying query fails.
65    pub async fn list_databases(
66        &self,
67        ListDatabasesRequest { cursor }: ListDatabasesRequest,
68    ) -> Result<ListDatabasesResponse, ErrorData> {
69        let pager = Pager::new(cursor, self.config.page_size);
70        let query = format!(
71            r"
72            SELECT datname
73            FROM pg_database
74            WHERE datistemplate = false
75            ORDER BY datname
76            LIMIT {} OFFSET {}",
77            pager.limit(),
78            pager.offset(),
79        );
80
81        let rows: Vec<String> = self.connection.fetch_scalar(query.as_str(), None).await?;
82        let (databases, next_cursor) = pager.paginate(rows);
83
84        Ok(ListDatabasesResponse { databases, next_cursor })
85    }
86}
dbmcp_postgres/tools/list_databases.rs

dbmcp_postgres/tools/
list_databases.rs
