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* Minimal Zeroheight MCP client: JSON-RPC `tools/call` over plain HTTP.
*
* The server needs no session or OAuth handshake; the URL itself is the
* credential, so it must never appear in logs or error messages.
*/
import { HttpError, createRateLimiter, retryAfterMs, withRetry } from './http.js';
export class McpToolError extends Error {}
/**
* Pull the JSON-RPC message out of a response body. The server answers with
* SSE (`data: {...}` lines) or plain JSON.
* @param {string} raw
* @returns {any}
*/
export function parseRpcBody(raw) {
const data = raw
.split('\n')
.filter((line) => line.startsWith('data:'))
.map((line) => line.slice(5).trim());
return JSON.parse(data.length ? data[data.length - 1] : raw);
}
/**
* Join the text items of a tool result, throwing on tool or RPC errors.
* @param {any} message
* @param {string} name
* @returns {string}
*/
export function toolText(message, name) {
Iif (message.error) throw new McpToolError(`${name}: ${message.error.message ?? 'RPC error'}`);
const result = message.result ?? {};
const text = (result.content ?? [])
.filter((/** @type {any} */ c) => c.type === 'text')
.map((/** @type {any} */ c) => c.text)
.join('');
if (result.isError) throw new McpToolError(`${name}: ${text}`);
return text;
}
/**
* @typedef {{ uri: string, mimeType: string, data: Buffer } | { uri: string, error: string }} AssetResult
*/
/**
* Match `get-page-asset` content items back to the requested URIs. Each
* failed URI comes back as a `<uri>: <message>` text item; the image items
* follow the order of the URIs that succeeded.
* @param {any} message
* @param {string[]} uris
* @returns {AssetResult[]}
*/
export function toolAssets(message, uris) {
Iif (message.error) throw new McpToolError(`get-page-asset: ${message.error.message ?? 'RPC error'}`);
const content = message.result?.content ?? [];
/** @type {Map<string, string>} */
const errors = new Map();
for (const c of content) {
if (c.type !== 'text') continue;
const m = String(c.text).match(/^(zeroheight:\/\/\S+?): (.*)$/s);
Eif (m) errors.set(m[1], m[2]);
}
const blobs = content.filter((/** @type {any} */ c) => c.type === 'image');
const ok = uris.filter((u) => !errors.has(u));
if (blobs.length !== ok.length) {
throw new McpToolError(`get-page-asset: got ${blobs.length} asset(s) for ${ok.length} URI(s)`);
}
let i = 0;
return uris.map((uri) => {
const error = errors.get(uri);
if (error !== undefined) return { uri, error };
const blob = blobs[i++];
return { uri, mimeType: blob.mimeType, data: Buffer.from(blob.data, 'base64') };
});
}
/**
* @param {{ url: string, fetchImpl?: typeof fetch, limiter?: { acquire(): Promise<void> } }} opts
*/
export function createMcpClient({
url,
fetchImpl = fetch,
limiter = createRateLimiter({ limit: 28, windowMs: 30_000 }),
}) {
let id = 0;
/**
* @param {string} name
* @param {Record<string, unknown>} args
* @returns {Promise<any>} the JSON-RPC message
*/
async function rpc(name, args) {
return withRetry(async () => {
await limiter.acquire();
const res = await fetchImpl(url, {
method: 'POST',
headers: { 'Content-Type': 'application/json', Accept: 'application/json, text/event-stream' },
body: JSON.stringify({
jsonrpc: '2.0',
id: ++id,
method: 'tools/call',
params: { name, arguments: args },
}),
});
Eif (!res.ok) throw new HttpError(`MCP ${name}: HTTP ${res.status}`, res.status, retryAfterMs(res));
return parseRpcBody(await res.text());
});
}
/**
* @param {string} name
* @param {Record<string, unknown>} args
* @returns {Promise<string>}
*/
async function callTool(name, args) {
return toolText(await rpc(name, args), name);
}
return {
callTool,
/** @returns {Promise<any>} parsed `list-pages` payload */
listPages: async () => JSON.parse(await callTool('list-pages', {})),
/** @param {number} pageId */
getPage: (pageId) => callTool('get-page', { pageId }),
/**
* @param {string[]} assetUris `zeroheight://image/<pageId>/<hash>` URIs from `get-page`
* @returns {Promise<AssetResult[]>}
*/
getPageAssets: async (assetUris) => toolAssets(await rpc('get-page-asset', { assetUris }), assetUris),
};
}
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