feat: support unpkg alias path access entry file #674 (#675)

closes #674

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
- Implemented a feature to handle compatibility with unpkg by searching
for and redirecting to possible file entries if the requested file is
not found.

- **Tests**
- Added a new test case to ensure the redirection to possible file
entries functions correctly.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

app/port/controller/PackageVersionFileController.ts

@@ -145,10 +145,22 @@ export class PackageVersionFileController extends AbstractController {
     }
 
     const file = await this.packageVersionFileService.showPackageVersionFile(packageVersion, path);
+    const hasMeta = typeof meta === 'string';
+
     if (!file) {
+      const possibleFile = await this.#searchPossibleEntries(packageVersion, path);
+
+      if (possibleFile) {
+        const route = `/${fullname}/${versionSpec}/files${possibleFile.path}${hasMeta ? '?meta' : ''}`;
+
+        ctx.redirect(route);
+
+        return;
+      }
+
       throw new NotFoundError(`File ${fullname}@${versionSpec}${path} not found`);
     }
-    const hasMeta = typeof meta === 'string';
+
     if (hasMeta) {
       ctx.set('cache-control', META_CACHE_CONTROL);
       return formatFileItem(file);
@@ -161,6 +173,26 @@ export class PackageVersionFileController extends AbstractController {
     return await this.distRepository.getDistStream(file.dist);
   }
 
+  /**
+   * compatibility with unpkg
+   * 1. try to match alias entry. e.g. accessing `index.js` or `index.json` using /index
+   * 2. if given path is directory and has `index.js` file, redirect to it. e.g. using `lib` alias to access `lib/index.js` or `lib/index.json`
+   * @param {PackageVersion} packageVersion packageVersion
+   * @param {String} path  filepath
+   * @return {Promise<PackageVersionFile | undefined>} return packageVersionFile or null
+   */
+  async #searchPossibleEntries(packageVersion: PackageVersion, path: string) {
+    const possiblePath = [ `${path}.js`, `${path}.json`, `${path}/index.js`, `${path}/index.json` ];
+
+    for (const pathItem of possiblePath) {
+      const file = await this.packageVersionFileService.showPackageVersionFile(packageVersion, pathItem);
+
+      if (file) {
+        return file;
+      }
+    }
+  }
+
   async #getPackageVersion(ctx: EggContext, fullname: string, scope: string, name: string, versionSpec: string) {
     const { blockReason, packageVersion } = await this.packageManagerService.showPackageVersionByVersionOrTag(
       scope, name, versionSpec);

test/port/controller/PackageVersionFileController/listFiles.test.ts

@@ -3,6 +3,8 @@ import { setTimeout } from 'node:timers/promises';
 import { app, mock } from 'egg-mock/bootstrap';
 import { TestUtil } from '../../../../test/TestUtil';
 import { PackageVersionFileService } from '../../../../app/core/service/PackageVersionFileService';
+import { calculateIntegrity } from '../../../../app/common/PackageUtil';
+
 
 describe('test/port/controller/PackageVersionFileController/listFiles.test.ts', () => {
   let publisher;
@@ -352,5 +354,50 @@ describe('test/port/controller/PackageVersionFileController/listFiles.test.ts',
       assert.equal(called, 1);
       assert.equal(resList.filter(res => res.status === 409 && res.body.error === '[CONFLICT] Package version file sync is currently in progress. Please try again later.').length, 1);
     });
+    it('should redirect to possible entry', async () => {
+      const tarball = await TestUtil.readFixturesFile('@cnpm/cnpm-test-find-entry-1.0.0.tgz');
+      const { integrity } = await calculateIntegrity(tarball);
+      const pkg = await TestUtil.getFullPackage({
+        name: '@cnpm/test-find-entry',
+        version: '1.0.0',
+        versionObject: {
+          description: 'test find entry description',
+        },
+        attachment: {
+          data: tarball.toString('base64'),
+          length: tarball.length,
+        },
+        dist: {
+          integrity,
+        },
+      });
+
+      await app.httpRequest()
+        .put(`/${pkg.name}`)
+        .set('authorization', publisher.authorization)
+        .set('user-agent', publisher.ua)
+        .send(pkg)
+        .expect(201);
+
+      await app.httpRequest()
+        .get(`/${pkg.name}/1.0.0/files/es/array/at`)
+        .expect(302)
+        .expect('location', `/${pkg.name}/1.0.0/files/es/array/at.js`);
+
+      await app.httpRequest()
+        .get(`/${pkg.name}/1.0.0/files/es/array`)
+        .expect(302)
+        .expect('location', `/${pkg.name}/1.0.0/files/es/array/index.js`);
+
+      await app.httpRequest()
+        .get(`/${pkg.name}/1.0.0/files/es/json/test`)
+        .expect(302)
+        .expect('location', `/${pkg.name}/1.0.0/files/es/json/test.json`);
+
+      await app.httpRequest()
+        .get(`/${pkg.name}/1.0.0/files/es/json`)
+        .expect(302)
+        .expect('location', `/${pkg.name}/1.0.0/files/es/json/index.json`);
+    });
   });
 });