@helia/verified-fetch/dist/src/plugins/plugin-handle-dag-walk.js

A fetch-like API for obtaining verified & trustless IPFS content on the web

import { code as dagCborCode } from '@ipld/dag-cbor';
import { code as dagPbCode } from '@ipld/dag-pb';
import { handlePathWalking } from '../utils/walk-path.js';
import { BasePlugin } from './plugin-base.js';
/**
 * This plugin should almost always run first because it's going to handle path walking if needed, and will only say it can handle
 * the request if path walking is possible (path is not empty, terminalCid is unknown, and the path has not been walked yet).
 *
 * Once this plugin has run, the PluginContext will be updated and then this plugin will return false for canHandle, so it won't run again.
 */
export class DagWalkPlugin extends BasePlugin {
    id = 'dag-walk-plugin';
    /**
     * Return false if the path has already been walked, otherwise return true if the CID is encoded with a codec that supports pathing.
     */
    canHandle(context) {
        this.log('checking if we can handle %c with accept %s', context.cid, context.accept);
        const { pathDetails, cid } = context;
        if (pathDetails != null) {
            // path has already been walked
            return false;
        }
        return (cid.code === dagPbCode || cid.code === dagCborCode);
    }
    async handle(context) {
        const { cid, resource, options, withServerTiming = false } = context;
        const { getBlockstore, handleServerTiming } = this.pluginOptions;
        const blockstore = getBlockstore(cid, resource, options?.session ?? true, options);
        // TODO: migrate handlePathWalking into this plugin
        const pathDetails = await handleServerTiming('path-walking', '', async () => handlePathWalking({ ...context, blockstore, log: this.log }), withServerTiming);
        if (pathDetails instanceof Response) {
            this.log.trace('path walking failed');
            if (pathDetails.status === 404) {
                // invalid or incorrect path.. we walked the path but nothing is there
                // send the 404 response
                return pathDetails;
            }
            // some other error walking the path (codec doesn't support pathing, etc..), let the next plugin try to handle it
            return null;
        }
        context.modified++;
        context.pathDetails = pathDetails;
        return null;
    }
}
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