fix: use jsdelivr when npm has a truncated readme

server/utils/readme-loaders.ts

@@ -1,6 +1,10 @@
 import * as v from 'valibot'
 import { PackageRouteParamsSchema } from '#shared/schemas/package'
-import { CACHE_MAX_AGE_ONE_HOUR, NPM_MISSING_README_SENTINEL } from '#shared/utils/constants'
+import {
+  CACHE_MAX_AGE_ONE_HOUR,
+  NPM_MISSING_README_SENTINEL,
+  NPM_README_TRUNCATION_THRESHOLD,
+} from '#shared/utils/constants'
 
 /** Standard README filenames to try when fetching from jsdelivr (case-sensitive CDN) */
 const standardReadmeFilenames = [
@@ -75,11 +79,16 @@ export const resolvePackageReadmeSource = defineCachedFunction(
 
     const hasValidNpmReadme = readmeContent && readmeContent !== NPM_MISSING_README_SENTINEL
 
-    if (!hasValidNpmReadme || !isStandardReadme(readmeFilename)) {
+    if (
+      !hasValidNpmReadme ||
+      !isStandardReadme(readmeFilename) ||
+      readmeContent!.length >= NPM_README_TRUNCATION_THRESHOLD
+    ) {
+      const resolvedVersion = version ?? packageData['dist-tags']?.latest
       const jsdelivrReadme = await fetchReadmeFromJsdelivr(
         packageName,
         standardReadmeFilenames,
-        version,
+        resolvedVersion,
       )
       if (jsdelivrReadme) {
         readmeContent = jsdelivrReadme

shared/utils/constants.ts

@@ -21,6 +21,8 @@ export const ERROR_PACKAGE_REQUIREMENTS_FAILED =
 export const ERROR_FILE_LIST_FETCH_FAILED = 'Failed to fetch file list.'
 export const ERROR_CALC_INSTALL_SIZE_FAILED = 'Failed to calculate install size.'
 export const NPM_MISSING_README_SENTINEL = 'ERROR: No README data found!'
+/** The npm registry truncates the packument readme field at 65,536 characters (2^16) */
+export const NPM_README_TRUNCATION_THRESHOLD = 64_000
 export const ERROR_JSR_FETCH_FAILED = 'Failed to fetch package from JSR registry.'
 export const ERROR_NPM_FETCH_FAILED = 'Failed to fetch package from npm registry.'
 export const ERROR_PROVENANCE_FETCH_FAILED = 'Failed to fetch provenance.'

test/unit/server/utils/readme-loaders.spec.ts

@@ -214,6 +214,29 @@ describe('resolvePackageReadmeSource', () => {
     })
   })
 
+  it('fetches from jsdelivr when packument readme exceeds truncation threshold', async () => {
+    const truncatedReadme = 'x'.repeat(64_000)
+    const fullReadme = 'x'.repeat(80_000)
+    fetchNpmPackageMock.mockResolvedValue({
+      'readme': truncatedReadme,
+      'readmeFilename': 'README.md',
+      'repository': undefined,
+      'versions': {},
+      'dist-tags': { latest: '1.0.0' },
+    })
+    parseRepositoryInfoMock.mockReturnValue(undefined)
+    const fetchMock = vi.fn().mockResolvedValue({
+      ok: true,
+      text: async () => fullReadme,
+    })
+    vi.stubGlobal('fetch', fetchMock)
+
+    const result = await resolvePackageReadmeSource('pkg')
+
+    expect(result).toMatchObject({ markdown: fullReadme })
+    expect(fetchMock).toHaveBeenCalled()
+  })
+
   it('uses package repository for repoInfo when markdown is present', async () => {
     fetchNpmPackageMock.mockResolvedValue({
       readme: '# Hi',