database_mcp_postgres/tools/
list_databases.rs

1//! MCP tool: `list_databases`.
2
3use std::borrow::Cow;
4use std::sync::Arc;
5
6use database_mcp_server::AppError;
7use database_mcp_server::types::ListDatabasesResponse;
8use database_mcp_sql::timeout::execute_with_timeout;
9use rmcp::handler::server::common::schema_for_empty_input;
10use rmcp::handler::server::router::tool::{AsyncTool, ToolBase};
11use rmcp::model::{ErrorData, JsonObject, ToolAnnotations};
12
13use crate::PostgresHandler;
14
15/// Marker type for the `list_databases` MCP tool.
16pub(crate) struct ListDatabasesTool;
17
18impl ListDatabasesTool {
19    const NAME: &'static str = "list_databases";
20    const DESCRIPTION: &'static str = "List all accessible databases on the connected database server.\nCall this first to discover available database names.";
21}
22
23impl ToolBase for ListDatabasesTool {
24    type Parameter = ();
25    type Output = ListDatabasesResponse;
26    type Error = ErrorData;
27
28    fn name() -> Cow<'static, str> {
29        Self::NAME.into()
30    }
31
32    fn description() -> Option<Cow<'static, str>> {
33        Some(Self::DESCRIPTION.into())
34    }
35
36    fn input_schema() -> Option<Arc<JsonObject>> {
37        Some(schema_for_empty_input())
38    }
39
40    fn annotations() -> Option<ToolAnnotations> {
41        Some(
42            ToolAnnotations::new()
43                .read_only(true)
44                .destructive(false)
45                .idempotent(true)
46                .open_world(false),
47        )
48    }
49}
50
51impl AsyncTool<PostgresHandler> for ListDatabasesTool {
52    async fn invoke(handler: &PostgresHandler, _params: Self::Parameter) -> Result<Self::Output, Self::Error> {
53        Ok(handler.list_databases().await?)
54    }
55}
56
57impl PostgresHandler {
58    /// Lists all accessible databases.
59    ///
60    /// Uses the default pool intentionally — `pg_database` is a server-wide
61    /// catalog that returns all databases regardless of which database the
62    /// connection targets.
63    ///
64    /// # Errors
65    ///
66    /// Returns [`AppError`] if the query fails.
67    pub async fn list_databases(&self) -> Result<ListDatabasesResponse, AppError> {
68        let pool = self.get_pool(None).await?;
69        let sql = "SELECT datname FROM pg_database WHERE datistemplate = false ORDER BY datname";
70        let rows: Vec<(String,)> =
71            execute_with_timeout(self.config.query_timeout, sql, sqlx::query_as(sql).fetch_all(&pool)).await?;
72        Ok(ListDatabasesResponse {
73            databases: rows.into_iter().map(|r| r.0).collect(),
74        })
75    }
76}
database_mcp_postgres/tools/list_databases.rs

database_mcp_postgres/tools/
list_databases.rs
