dbmcp_postgres/tools/
read_query.rs

1//! MCP tool: `readQuery`.
2
3use std::borrow::Cow;
4
5use dbmcp_pii::MaybeRedact as _;
6use dbmcp_server::pagination::{Cursor, Pager};
7use dbmcp_server::types::{PinnedReadQueryRequest, ReadQueryResponse, UnpinnedReadQueryRequest};
8use dbmcp_sql::Connection as _;
9use dbmcp_sql::StatementKind;
10use dbmcp_sql::pagination::with_limit_offset;
11use dbmcp_sql::validation::validate_read_only;
12use rmcp::handler::server::router::tool::{AsyncTool, ToolBase};
13use rmcp::model::{ErrorData, ToolAnnotations};
14
15use crate::PostgresHandler;
16
17const NAME: &str = "readQuery";
18const TITLE: &str = "Read Query";
19const DESCRIPTION_PINNED: &str = include_str!("../../assets/tools/read_query/pinned.md");
20const DESCRIPTION_UNPINNED: &str = include_str!("../../assets/tools/read_query/unpinned.md");
21
22fn annotations() -> ToolAnnotations {
23    ToolAnnotations::new()
24        .read_only(true)
25        .destructive(false)
26        .idempotent(true)
27        .open_world(true)
28}
29
30/// Marker type for the `readQuery` MCP tool (pinned variant — no `database` field).
31pub(crate) struct PinnedReadQueryTool;
32
33impl ToolBase for PinnedReadQueryTool {
34    type Parameter = PinnedReadQueryRequest;
35    type Output = ReadQueryResponse;
36    type Error = ErrorData;
37
38    fn name() -> Cow<'static, str> {
39        NAME.into()
40    }
41
42    fn title() -> Option<String> {
43        Some(TITLE.into())
44    }
45
46    fn description() -> Option<Cow<'static, str>> {
47        Some(DESCRIPTION_PINNED.into())
48    }
49
50    fn annotations() -> Option<ToolAnnotations> {
51        Some(annotations())
52    }
53}
54
55impl AsyncTool<PostgresHandler> for PinnedReadQueryTool {
56    async fn invoke(handler: &PostgresHandler, params: Self::Parameter) -> Result<Self::Output, Self::Error> {
57        handler.read_query(params.query, None, params.cursor).await
58    }
59}
60
61/// Marker type for the `readQuery` MCP tool (unpinned variant — carries `database`).
62pub(crate) struct UnpinnedReadQueryTool;
63
64impl ToolBase for UnpinnedReadQueryTool {
65    type Parameter = UnpinnedReadQueryRequest;
66    type Output = ReadQueryResponse;
67    type Error = ErrorData;
68
69    fn name() -> Cow<'static, str> {
70        NAME.into()
71    }
72
73    fn title() -> Option<String> {
74        Some(TITLE.into())
75    }
76
77    fn description() -> Option<Cow<'static, str>> {
78        Some(DESCRIPTION_UNPINNED.into())
79    }
80
81    fn annotations() -> Option<ToolAnnotations> {
82        Some(annotations())
83    }
84}
85
86impl AsyncTool<PostgresHandler> for UnpinnedReadQueryTool {
87    async fn invoke(handler: &PostgresHandler, params: Self::Parameter) -> Result<Self::Output, Self::Error> {
88        handler
89            .read_query(params.inner.query, params.database, params.inner.cursor)
90            .await
91    }
92}
93
94impl PostgresHandler {
95    /// Executes a read-only SQL query, paginating `SELECT` result rows.
96    ///
97    /// Validates that the query is read-only, then dispatches on the
98    /// classified [`StatementKind`]: `Select` is wrapped in a subquery with
99    /// a server-controlled `LIMIT`/`OFFSET`; `NonSelect` (`SHOW`, `EXPLAIN`
100    /// under the PG dialect) is executed as-is and returned in a single
101    /// page. A malformed `cursor` is rejected by the serde deserializer
102    /// before this method is called, producing JSON-RPC `-32602`.
103    ///
104    /// # Errors
105    ///
106    /// Returns [`SqlError::ReadOnlyViolation`] if the query is not
107    /// read-only, or [`SqlError::Query`] if the backend reports an error.
108    pub async fn read_query(
109        &self,
110        query: String,
111        database: Option<String>,
112        cursor: Option<Cursor>,
113    ) -> Result<ReadQueryResponse, ErrorData> {
114        let kind = validate_read_only(&query, &sqlparser::dialect::PostgreSqlDialect {})?;
115        let database = database.as_deref().map(str::trim).filter(|s| !s.is_empty());
116
117        let (rows, next_cursor) = match kind {
118            StatementKind::Select => {
119                let pager = Pager::new(cursor, self.config.page_size);
120                let wrapped = with_limit_offset(&query, pager.limit(), pager.offset());
121                let rows = self.connection.fetch_json(wrapped.as_str(), database).await?;
122                pager.paginate(rows)
123            }
124            StatementKind::NonSelect => {
125                let rows = self.connection.fetch_json(query.as_str(), database).await?;
126                (rows, None)
127            }
128        };
129        let rows = self.redactor.redact_rows(rows).await?;
130        Ok(ReadQueryResponse { rows, next_cursor })
131    }
132}
dbmcp_postgres/tools/read_query.rs

dbmcp_postgres/tools/
read_query.rs
