dbmcp_postgres/tools/
read_query.rs

1//! MCP tool: `readQuery`.
2
3use std::borrow::Cow;
4
5use dbmcp_server::pagination::{Cursor, Pager};
6use dbmcp_server::types::{PinnedReadQueryRequest, ReadQueryResponse, UnpinnedReadQueryRequest};
7use dbmcp_sql::Connection as _;
8use dbmcp_sql::StatementKind;
9use dbmcp_sql::pagination::with_limit_offset;
10use dbmcp_sql::validation::validate_read_only;
11use rmcp::handler::server::router::tool::{AsyncTool, ToolBase};
12use rmcp::model::{ErrorData, ToolAnnotations};
13
14use crate::PostgresHandler;
15
16const NAME: &str = "readQuery";
17const TITLE: &str = "Read Query";
18const DESCRIPTION_PINNED: &str = include_str!("../../assets/tools/read_query/pinned.md");
19const DESCRIPTION_UNPINNED: &str = include_str!("../../assets/tools/read_query/unpinned.md");
20
21fn annotations() -> ToolAnnotations {
22    ToolAnnotations::new()
23        .read_only(true)
24        .destructive(false)
25        .idempotent(true)
26        .open_world(true)
27}
28
29/// Marker type for the `readQuery` MCP tool (pinned variant — no `database` field).
30pub(crate) struct PinnedReadQueryTool;
31
32impl ToolBase for PinnedReadQueryTool {
33    type Parameter = PinnedReadQueryRequest;
34    type Output = ReadQueryResponse;
35    type Error = ErrorData;
36
37    fn name() -> Cow<'static, str> {
38        NAME.into()
39    }
40
41    fn title() -> Option<String> {
42        Some(TITLE.into())
43    }
44
45    fn description() -> Option<Cow<'static, str>> {
46        Some(DESCRIPTION_PINNED.into())
47    }
48
49    fn annotations() -> Option<ToolAnnotations> {
50        Some(annotations())
51    }
52}
53
54impl AsyncTool<PostgresHandler> for PinnedReadQueryTool {
55    async fn invoke(handler: &PostgresHandler, params: Self::Parameter) -> Result<Self::Output, Self::Error> {
56        handler.read_query(params.query, None, params.cursor).await
57    }
58}
59
60/// Marker type for the `readQuery` MCP tool (unpinned variant — carries `database`).
61pub(crate) struct UnpinnedReadQueryTool;
62
63impl ToolBase for UnpinnedReadQueryTool {
64    type Parameter = UnpinnedReadQueryRequest;
65    type Output = ReadQueryResponse;
66    type Error = ErrorData;
67
68    fn name() -> Cow<'static, str> {
69        NAME.into()
70    }
71
72    fn title() -> Option<String> {
73        Some(TITLE.into())
74    }
75
76    fn description() -> Option<Cow<'static, str>> {
77        Some(DESCRIPTION_UNPINNED.into())
78    }
79
80    fn annotations() -> Option<ToolAnnotations> {
81        Some(annotations())
82    }
83}
84
85impl AsyncTool<PostgresHandler> for UnpinnedReadQueryTool {
86    async fn invoke(handler: &PostgresHandler, params: Self::Parameter) -> Result<Self::Output, Self::Error> {
87        handler
88            .read_query(params.inner.query, params.database, params.inner.cursor)
89            .await
90    }
91}
92
93impl PostgresHandler {
94    /// Executes a read-only SQL query, paginating `SELECT` result rows.
95    ///
96    /// Validates that the query is read-only, then dispatches on the
97    /// classified [`StatementKind`]: `Select` is wrapped in a subquery with
98    /// a server-controlled `LIMIT`/`OFFSET`; `NonSelect` (`SHOW`, `EXPLAIN`
99    /// under the PG dialect) is executed as-is and returned in a single
100    /// page. A malformed `cursor` is rejected by the serde deserializer
101    /// before this method is called, producing JSON-RPC `-32602`.
102    ///
103    /// # Errors
104    ///
105    /// Returns [`SqlError::ReadOnlyViolation`] if the query is not
106    /// read-only, or [`SqlError::Query`] if the backend reports an error.
107    pub async fn read_query(
108        &self,
109        query: String,
110        database: Option<String>,
111        cursor: Option<Cursor>,
112    ) -> Result<ReadQueryResponse, ErrorData> {
113        let kind = validate_read_only(&query, &sqlparser::dialect::PostgreSqlDialect {})?;
114        let database = database.as_deref().map(str::trim).filter(|s| !s.is_empty());
115
116        match kind {
117            StatementKind::Select => {
118                let pager = Pager::new(cursor, self.config.page_size);
119                let wrapped = with_limit_offset(&query, pager.limit(), pager.offset());
120                let rows = self.connection.fetch_json(wrapped.as_str(), database).await?;
121                let (mut rows, next_cursor) = pager.paginate(rows);
122                if let Some(r) = &self.redactor {
123                    r.apply(&mut rows)?;
124                }
125                Ok(ReadQueryResponse { rows, next_cursor })
126            }
127            StatementKind::NonSelect => {
128                let mut rows = self.connection.fetch_json(query.as_str(), database).await?;
129                if let Some(r) = &self.redactor {
130                    r.apply(&mut rows)?;
131                }
132                Ok(ReadQueryResponse {
133                    rows,
134                    next_cursor: None,
135                })
136            }
137        }
138    }
139}
dbmcp_postgres/tools/read_query.rs

dbmcp_postgres/tools/
read_query.rs
