Function createWebFetch

src/tools/fetch/web-fetch.ts:42–125

(model: string)

 * to derive the fast variant that processes fetched content.
 */
export function createWebFetch(model: string): DynamicStructuredTool {
  return new DynamicStructuredTool({
    name: WEB_FETCH_TOOL_NAME,
    description:
      'Fetch content from a URL, convert it to markdown, and answer a prompt about it using a fast model.',
    schema: WebFetchInputSchema,
    func: async (input, _runManager, config?: RunnableConfig) => {
      const start = Date.now();
      const { url, prompt } = input;

      // Link the tool's abort controller to any signal provided by the runtime.
      const abortController = new AbortController();
      const externalSignal = config?.signal;
      if (externalSignal) {
        if (externalSignal.aborted) {
          abortController.abort();
        } else {
          externalSignal.addEventListener('abort', () => abortController.abort(), { once: true });
        }
      }

      try {
        const response = await getURLMarkdownContent(url, abortController);

        // Cross-host redirect: tell the model to re-fetch the redirect target.
        if ('type' in response && response.type === 'redirect') {
          const statusText =
            response.statusCode === 301
              ? 'Moved Permanently'
              : response.statusCode === 308
                ? 'Permanent Redirect'
                : response.statusCode === 307
                  ? 'Temporary Redirect'
                  : 'Found';

          const message = `REDIRECT DETECTED: The URL redirects to a different host.

Original URL: ${response.originalUrl}
Redirect URL: ${response.redirectUrl}
Status: ${response.statusCode} ${statusText}

To complete your request, make a new web_fetch request with these parameters:
- url: "${response.redirectUrl}"
- prompt: "${prompt}"`;

          const output: WebFetchOutput = {
            bytes: Buffer.byteLength(message),
            code: response.statusCode,
            codeText: statusText,
            result: message,
            durationMs: Date.now() - start,
            url,
          };
          return formatToolResult(output, [url]);
        }

        const { content, bytes, code, codeText, contentType, persistedPath, persistedSize } =
          response as FetchedContent;