Infer MCP Server

Instructions

Implementation Reference

• src/tools/dbQuery.ts:34-71 (handler)

  MCP tool handler for the 'dbQuery' tool. It processes input arguments, reports progress, calls the database service to execute the query, and returns structured content in MCP format.
  async (args, extra) => { const progress = createProgressReporter(extra, "dbQuery"); const total = 1; progress?.({ progress: 0, total, message: "Dispatching database query" }); const result: DatabaseQueryResult = await executeDatabaseQuery( args.profile, args.query, args.parameters, { timeoutMs: args.timeoutMs, rowLimit: args.rowLimit, requestId: String(extra.requestId), tool: "dbQuery", signal: extra.signal, onProgress: (update) => { progress?.({ progress: update.progress, total, message: update.message }); } } ); const structuredContent: Record<string, unknown> = { rows: result.rows, rowCount: result.rowCount, truncated: result.truncated, durationMs: result.durationMs }; return { content: [], structuredContent }; }
• src/tools/dbQuery.ts:9-24 (schema)

  Zod schemas defining the input and output shapes for the dbQuery tool.
  const DbQueryInputSchema = z.object({ profile: z.string().describe("Database profile to use"), query: z.string().min(1).describe("SQL query to execute"), parameters: z.array(z.unknown()).optional().describe("Positional parameters for the query"), timeoutMs: z.number().int().positive().optional().describe("Query timeout in milliseconds"), rowLimit: z.number().int().positive().optional().describe("Override maximum number of rows to return") }); const DbQueryOutputShape = { rows: z.array(z.record(z.string(), z.unknown())), rowCount: z.number().int().nonnegative(), truncated: z.boolean(), durationMs: z.number().int().nonnegative() }; const DbQueryOutputSchema = z.object(DbQueryOutputShape);
• src/tools/dbQuery.ts:26-73 (registration)

  Registers the 'dbQuery' tool with the MCP server using registerTool, specifying name, schemas, and handler.
  export function registerDbTool(server: McpServer): void { server.registerTool( "dbQuery", { description: "Execute a SQL query on a PostgreSQL database using a configured profile", inputSchema: DbQueryInputSchema.shape, outputSchema: DbQueryOutputShape }, async (args, extra) => { const progress = createProgressReporter(extra, "dbQuery"); const total = 1; progress?.({ progress: 0, total, message: "Dispatching database query" }); const result: DatabaseQueryResult = await executeDatabaseQuery( args.profile, args.query, args.parameters, { timeoutMs: args.timeoutMs, rowLimit: args.rowLimit, requestId: String(extra.requestId), tool: "dbQuery", signal: extra.signal, onProgress: (update) => { progress?.({ progress: update.progress, total, message: update.message }); } } ); const structuredContent: Record<string, unknown> = { rows: result.rows, rowCount: result.rowCount, truncated: result.truncated, durationMs: result.durationMs }; return { content: [], structuredContent }; } ); }
• src/services/databaseService.ts:95-209 (helper)

  Core helper function that performs the actual database query execution against PostgreSQL, including safety validations, concurrency control, timeouts, row limits, abort signals, and progress updates.
  export async function executeDatabaseQuery( profileName: string, query: string, values: unknown[] | undefined, options: DatabaseQueryOptions = {} ): Promise<DatabaseQueryResult> { const config = getConfig(); const profile = config.databaseProfiles[profileName]; if (!profile) { throw new Error(`Database profile '${profileName}' not found`); } validateQuerySafety(query); ensureQueryAllowed(query, profile.allowedStatementPatterns); const timeoutMs = Math.min(options.timeoutMs ?? profile.maxExecutionMs, profile.maxExecutionMs); const rowLimit = Math.min(options.rowLimit ?? profile.maxRows, profile.maxRows); options.onProgress?.({ progress: 0, message: "Waiting for database availability" }); const release = await dbConcurrency.acquire(profileName, profile.maxConcurrent, options.signal); const client = new Client({ connectionString: profile.connectionString }); const start = Date.now(); const abortError = createAbortError("Database query cancelled"); let aborted = false; let abortListener: (() => void) | undefined; logger.info("Executing database query", { profile: profileName, requestId: options.requestId, tool: options.tool }); try { if (options.signal) { if (options.signal.aborted) { aborted = true; throw abortError; } abortListener = () => { aborted = true; options.onProgress?.({ progress: 1, message: "Database query cancelled" }); if (client.connection?.stream) { client.connection.stream.destroy(abortError); } }; options.signal.addEventListener("abort", abortListener, { once: true }); } options.onProgress?.({ progress: 0.1, message: "Connecting to database" }); await client.connect(); if (aborted) { throw abortError; } options.onProgress?.({ progress: 0.3, message: "Applying session limits" }); await applyTimeout(client, timeoutMs); options.onProgress?.({ progress: 0.6, message: "Executing query" }); const result: QueryResult = await client.query({ text: query, values }); if (aborted) { throw abortError; } const rows = result.rows.slice(0, rowLimit); const truncated = result.rows.length > rows.length; const rowCount = result.rowCount ?? rows.length; const durationMs = Date.now() - start; logger.info("Database query completed", { profile: profileName, requestId: options.requestId, tool: options.tool, rowCount, truncated, durationMs }); options.onProgress?.({ progress: 1, message: "Database query completed" }); return { rows, rowCount, truncated, durationMs }; } catch (error) { if (aborted) { throw abortError; } logger.error("Database query failed", { profile: profileName, requestId: options.requestId, tool: options.tool, error: error instanceof Error ? error.message : String(error) }); throw error; } finally { if (options.signal && abortListener) { options.signal.removeEventListener("abort", abortListener); } try { await client.end(); } catch (endError) { logger.debug("Error closing database client", { profile: profileName, error: endError instanceof Error ? endError.message : String(endError) }); } release(); } }
• src/tools/index.ts:3-8 (registration)

  Top-level tool registration entry point that calls registerDbTool to register the dbQuery tool.
  import { registerDbTool } from "./dbQuery.js"; import { registerTrainingTool } from "./trainClassifier.js"; export function registerTools(server: McpServer): void { registerSshTool(server); registerDbTool(server);