import type { ReadResourceRequest, ReadResourceResult } from '@modelcontextprotocol/sdk/types.js';
import type { AppResource } from '../types/types.js';
import { ErrorCode, McpError } from '@modelcontextprotocol/sdk/types.js';
const APP_CSP_RESOURCE_DOMAINS = [
'https://images.metmuseum.org',
'data:',
];
const MISSING_UI_BUNDLE_ERROR_PREFIX = 'UI bundle is missing.';
const MISSING_UI_BUNDLE_USER_MESSAGE = 'This interactive view is temporarily unavailable because required UI files are missing on the server. Please contact your server administrator.';
const READ_RESOURCE_ERROR_MESSAGE = 'Unable to load this interactive view right now. Please try again later.';
export class ReadResourceHandler {
private readonly appResources: AppResource[];
constructor(appResources: AppResource[]) {
this.appResources = appResources;
}
public async handleReadResource(request: ReadResourceRequest): Promise<ReadResourceResult> {
const uri = request.params.uri;
const resource = this.appResources.find(candidate => candidate.uri === uri);
if (!resource) {
throw new McpError(ErrorCode.InvalidRequest, `Resource not found: ${uri}`);
}
let html: string;
try {
html = await resource.getHtml();
}
catch (error) {
if (error instanceof Error && error.message.startsWith(MISSING_UI_BUNDLE_ERROR_PREFIX)) {
console.error('[ReadResourceHandler] Missing UI bundle while reading resource:', {
uri,
cause: error.message,
});
throw new McpError(ErrorCode.InternalError, MISSING_UI_BUNDLE_USER_MESSAGE);
}
console.error('[ReadResourceHandler] Failed to read resource:', { uri, error });
throw new McpError(ErrorCode.InternalError, READ_RESOURCE_ERROR_MESSAGE);
}
return {
contents: [{
uri,
mimeType: resource.mimeType,
text: html,
_meta: {
ui: {
csp: {
resourceDomains: APP_CSP_RESOURCE_DOMAINS,
},
},
},
}],
};
}
}
