From 421a04f5fde2ff2923f98d7dc415571cf693d407 Mon Sep 17 00:00:00 2001 From: Aiden Cline <63023139+rekram1-node@users.noreply.github.com> Date: Fri, 2 Oct 2026 17:22:25 -0500 Subject: [PATCH] fix(core): retry transient MCP connect failures (#52614) --- packages/core/src/mcp/client.ts | 67 ++++++++++++++++++++++++--------- packages/core/test/mcp.test.ts | 2 +- 2 files changed, 50 insertions(+), 19 deletions(-) diff --git a/packages/core/src/mcp/client.ts b/packages/core/src/mcp/client.ts index bd294bbe1711..39a7085ec6b1 100644 --- a/packages/core/src/mcp/client.ts +++ b/packages/core/src/mcp/client.ts @@ -26,7 +26,7 @@ import { type Transport, type VersionNegotiationOptions, } from "@modelcontextprotocol/client" -import { Cause, Effect, Exit, Schema } from "effect" +import { Cause, Clock, Duration, Effect, Exit, Schedule, Schema } from "effect" import { ConfigMCP } from "@opencode/schema/config/mcp" import type { Session } from "@opencode/schema/session" import { McpStdio } from "./stdio.js" @@ -49,6 +49,14 @@ const describe = (error: unknown) => { return detail && !error.message.includes(detail) ? `${error.message} (${detail})` : error.message } +// Overloaded or restarting servers and dropped connections usually recover within a second. +// Fetch reports network failures as a TypeError carrying a system error code. +// 501 means the server will never support the request. +const isTransient = (error: unknown) => + error instanceof SdkHttpError + ? error.status === 408 || error.status === 429 || (error.status >= 500 && error.status !== 501) + : error instanceof TypeError && "code" in error + export type { GetPromptResult, Prompt, ReadResourceResult, Resource, Tool } export type ResourceTemplate = ResourceTemplateType @@ -159,6 +167,20 @@ export const connect = Effect.fnUntraced(function* ( ? `${describe(error)}: ${lastError}` : describe(error) + // Two more attempts, 250 ms and 1 s later, while the failure is transient and the deadline has not passed. + const retrying = (what: string, effect: Effect.Effect, deadline = Infinity) => + Effect.retry( + effect, + Schedule.max([Schedule.exponential("250 millis", 4), Schedule.recurs(2)]).pipe( + Schedule.setInputType(), + Schedule.while(({ input, now, duration }) => + !isTransient(input) || now + Duration.toMillis(duration) >= deadline + ? Effect.succeed(false) + : Effect.logWarning(`retrying ${what}`, { server, error: describe(input) }).pipe(Effect.as(true)), + ), + ), + ) + const initialize = Effect.fnUntraced(function* (transport: Transport) { const runFork = Effect.runForkWith(yield* Effect.context()) const client = new Client(clientInfo, { @@ -245,22 +267,28 @@ export const connect = Effect.fnUntraced(function* ( const url = new URL(config.url) const addedCodemode = config.codemode !== false && !url.searchParams.has("codemode") if (addedCodemode) url.searchParams.set("codemode", "false") - const open = (url: URL) => { + const open = Effect.fnUntraced(function* (url: URL) { session.transport = new StreamableHTTPClientTransport(url, { requestInit: config.headers ? { headers: config.headers } : undefined, authProvider, fetch, }) - return initialize(session.transport) - } + return yield* initialize(session.transport) + }) - return yield* open(url).pipe( - Effect.catch((error) => { - if (!addedCodemode || !(error instanceof SdkHttpError) || (error.status !== 400 && error.status !== 404)) - return Effect.fail(error) - // Servers that reject unknown query params get one retry at the configured URL. - return open(new URL(config.url)) - }), + // Every attempt opens a fresh transport; no retry starts once the startup timeout has passed. + const deadline = (yield* Clock.currentTimeMillis) + (config.timeout?.startup ?? DEFAULT_STARTUP_TIMEOUT) + return yield* retrying( + "MCP connect", + open(url).pipe( + Effect.catch((error) => { + if (!addedCodemode || !(error instanceof SdkHttpError) || (error.status !== 400 && error.status !== 404)) + return Effect.fail(error) + // Servers that reject unknown query params get one retry at the configured URL. + return open(new URL(config.url)) + }), + ), + deadline, ) }).pipe(Effect.exit) if (Exit.isSuccess(exit)) { @@ -292,20 +320,23 @@ export const connect = Effect.fnUntraced(function* ( Effect.tryPromise({ try: run, catch: failure }).pipe( Effect.tapError((error) => Effect.logWarning(`failed to ${what}`, { server, error: error.message })), ) + // Listing is read-only, so a transient failure is safe to retry. + const list = (what: string, run: () => Promise) => + retrying(what, Effect.tryPromise({ try: run, catch: (error) => error })).pipe( + Effect.mapError(failure), + Effect.tapError((error) => Effect.logWarning(`failed to ${what}`, { server, error: error.message })), + ) return { modern: client.getProtocolEra() === "modern", instructions: client.getInstructions()?.trim() || undefined, - tools: () => - request("list MCP tools", () => client.listTools(undefined, catalog)).pipe(Effect.map((r) => r.tools)), + tools: () => list("list MCP tools", () => client.listTools(undefined, catalog)).pipe(Effect.map((r) => r.tools)), prompts: () => - request("list MCP prompts", () => client.listPrompts(undefined, catalog)).pipe(Effect.map((r) => r.prompts)), + list("list MCP prompts", () => client.listPrompts(undefined, catalog)).pipe(Effect.map((r) => r.prompts)), resources: () => - request("list MCP resources", () => client.listResources(undefined, catalog)).pipe( - Effect.map((r) => r.resources), - ), + list("list MCP resources", () => client.listResources(undefined, catalog)).pipe(Effect.map((r) => r.resources)), resourceTemplates: () => - request("list MCP resource templates", () => client.listResourceTemplates(undefined, catalog)).pipe( + list("list MCP resource templates", () => client.listResourceTemplates(undefined, catalog)).pipe( Effect.map((r) => r.resourceTemplates), ), readResource: (input) => { diff --git a/packages/core/test/mcp.test.ts b/packages/core/test/mcp.test.ts index 81785d1d3698..314b81fcb8aa 100644 --- a/packages/core/test/mcp.test.ts +++ b/packages/core/test/mcp.test.ts @@ -1048,7 +1048,7 @@ for (const entry of [ { name: "second 400", status: 400, query: "", codemode: undefined, attempts: 2 }, { name: "401", status: 401, query: "", codemode: undefined, attempts: 1 }, { name: "403", status: 403, query: "", codemode: undefined, attempts: 1 }, - { name: "500", status: 500, query: "", codemode: undefined, attempts: 1 }, + { name: "501", status: 501, query: "", codemode: undefined, attempts: 1 }, { name: "user codemode=true", status: 404, query: "?codemode=true", codemode: undefined, attempts: 1 }, { name: "user codemode=false", status: 404, query: "?codemode=false", codemode: undefined, attempts: 1 }, { name: "empty user codemode", status: 404, query: "?codemode=", codemode: undefined, attempts: 1 },