@sema-agent/core/dist/core/mcp-failure.js

Stateless, task-oriented AI agent core

import { McpError, ErrorCode } from "@modelcontextprotocol/sdk/types.js";
import { StreamableHTTPError } from "@modelcontextprotocol/sdk/client/streamableHttp.js";
export const MCP_FAILURE_KINDS = Object.freeze([
    "connect_refused",
    "connection_failed",
    "connection_closed",
    "http_status",
    "not_mcp_response",
    "spawn_failed",
    "timeout",
    "protocol",
    "invalid_config",
    "unknown",
]);
export const MCP_DELIVERY_VERDICTS = Object.freeze(["yes", "no", "unknown"]);
export const DELIVERED_BY_KIND = {
    connect_refused: "no",
    connection_failed: "unknown",
    connection_closed: "unknown",
    http_status: "unknown",
    not_mcp_response: "unknown",
    spawn_failed: "no",
    timeout: "unknown",
    protocol: "yes",
    invalid_config: "no",
    unknown: "unknown",
};
export const MCP_LIVENESS_STATES = Object.freeze(["reachable", "unreachable", "unknown"]);
export const LIVENESS_BY_FAILURE_KIND = {
    connect_refused: "unreachable",
    connection_failed: "unreachable",
    connection_closed: "unreachable",
    http_status: "unknown",
    not_mcp_response: "unknown",
    spawn_failed: "unreachable",
    timeout: "unreachable",
    protocol: "reachable",
    invalid_config: undefined,
    unknown: "unknown",
};
export function livenessOf(outcome, observedAt) {
    if (outcome === "completed")
        return { state: "reachable", observedAt };
    const state = LIVENESS_BY_FAILURE_KIND[outcome];
    if (state === undefined)
        return undefined;
    return state === "unreachable" ? { state, observedAt, errorCode: outcome } : { state, observedAt };
}
const CONNECT_KEEPS_THE_TABLE_VERDICT = new Set(["protocol", "http_status"]);
const NETWORK_CODES_NEVER_DELIVERED = new Set([
    "ECONNREFUSED",
    "ENOTFOUND",
    "EAI_AGAIN",
    "EHOSTUNREACH",
    "ENETUNREACH",
    "UND_ERR_CONNECT_TIMEOUT",
]);
export function networkErrorCode(err, depth = 0) {
    if (depth > 5 || !(err instanceof Error))
        return undefined;
    const code = err.code;
    if (typeof code === "string" && /^(?:E[A-Z_]+|UND_ERR_[A-Z_]+)$/.test(code))
        return code;
    if (err instanceof AggregateError) {
        for (const inner of err.errors) {
            const found = networkErrorCode(inner, depth + 1);
            if (found !== undefined)
                return found;
        }
    }
    return networkErrorCode(err.cause, depth + 1);
}
const isNodeErrCode = (code) => code.startsWith("ERR_");
export const FAILURE_CLASSIFIER = [
    {
        name: "sdk connection closed",
        when: (err) => err instanceof McpError && err.code === ErrorCode.ConnectionClosed,
        reads: () => ({ kind: "connection_closed" }),
    },
    {
        name: "sdk request timeout",
        when: (err) => err instanceof McpError && err.code === ErrorCode.RequestTimeout,
        reads: () => ({ kind: "timeout" }),
    },
    {
        name: "server answered with a protocol error",
        when: (err) => err instanceof McpError,
        reads: () => ({ kind: "protocol" }),
    },
    {
        name: "http endpoint answered a status",
        when: (err) => err instanceof StreamableHTTPError && typeof err.code === "number" && err.code > 0,
        reads: (err) => ({ kind: "http_status", httpStatus: err.code }),
    },
    {
        name: "http endpoint answered a non-mcp payload",
        when: (err) => err instanceof StreamableHTTPError,
        reads: () => ({ kind: "not_mcp_response" }),
    },
    {
        name: "malformed declaration",
        when: (err, at) => at.phase === "connect" && err instanceof Error && err.code === "ERR_INVALID_URL",
        reads: () => ({ kind: "invalid_config" }),
    },
    {
        name: "node error code, not a network errno",
        when: (err) => {
            const code = networkErrorCode(err);
            return code !== undefined && isNodeErrCode(code);
        },
        reads: () => ({ kind: "unknown" }),
    },
    {
        name: "stdio spawn failed",
        when: (err, at) => at.phase === "connect" && at.transport === "stdio" && networkErrorCode(err) !== undefined,
        reads: () => ({ kind: "spawn_failed" }),
    },
    {
        name: "connect-phase errno",
        when: (err) => {
            const code = networkErrorCode(err);
            return code !== undefined && NETWORK_CODES_NEVER_DELIVERED.has(code);
        },
        reads: () => ({ kind: "connect_refused" }),
    },
    {
        name: "network errno past the connect phase",
        when: (err) => networkErrorCode(err) !== undefined,
        reads: () => ({ kind: "connection_failed" }),
    },
    {
        name: "no structure",
        when: () => true,
        reads: () => ({ kind: "unknown" }),
    },
];
export function classifyMcpFailure(err, at) {
    for (const rule of FAILURE_CLASSIFIER) {
        if (!rule.when(err, at))
            continue;
        const read = rule.reads(err);
        const dialled = at.phase === "connect" && !CONNECT_KEEPS_THE_TABLE_VERDICT.has(read.kind);
        return { ...read, delivered: dialled ? "no" : DELIVERED_BY_KIND[read.kind] };
    }
    return { kind: "unknown", delivered: "unknown" };
}
export function describeHttpTransportFailure(err) {
    const f = classifyMcpFailure(err, { phase: "request" });
    switch (f.kind) {
        case "http_status":
            return { condition: `its HTTP endpoint answered ${f.httpStatus} instead of an MCP response`, delivered: f.delivered, httpStatus: f.httpStatus };
        case "not_mcp_response":
            return { condition: "its HTTP endpoint answered something that is not an MCP response", delivered: f.delivered };
        case "connect_refused":
            return { condition: `its HTTP endpoint could not be reached (${networkErrorCode(err)})`, delivered: f.delivered };
        case "connection_failed":
            return { condition: `the connection to its HTTP endpoint failed (${networkErrorCode(err)})`, delivered: f.delivered };
        case "connection_closed":
        case "spawn_failed":
        case "timeout":
        case "protocol":
        case "invalid_config":
        case "unknown":
            return undefined;
    }
}