{"record":{"id":"fec13d547b2453fe","repo":"vercel/next.js","slug":"failed-to-read-file-contents-of-filename","errorCode":null,"errorMessage":"Failed to read file contents of ${filename}.","messagePattern":"Failed to read file contents of (.+?)\\.","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"packages/next/src/server/dev/get-source-map-from-file.ts","lineNumber":35,"sourceCode":"  if (!(match && match[1])) {\n    return null\n  }\n  return match[1].toString()\n}\n\nexport async function getSourceMapFromFile(\n  filename: string\n): Promise<RawSourceMap | undefined> {\n  filename = filename.startsWith('file://')\n    ? url.fileURLToPath(filename)\n    : filename\n\n  let fileContents: string\n\n  try {\n    fileContents = await fs.readFile(filename, 'utf-8')\n  } catch (error) {\n    throw new Error(`Failed to read file contents of ${filename}.`, {\n      cause: error,\n    })\n  }\n\n  const sourceUrl = getSourceMapUrl(fileContents)\n\n  if (!sourceUrl) {\n    return undefined\n  }\n\n  if (sourceUrl.startsWith('data:')) {\n    let buffer: dataUriToBuffer.MimeBuffer\n\n    try {\n      buffer = dataUriToBuffer(sourceUrl)\n    } catch (error) {\n      throw new Error(`Failed to parse source map URL for ${filename}.`, {\n        cause: error,","sourceCodeStart":17,"sourceCodeEnd":53,"githubUrl":"https://github.com/vercel/next.js/blob/0ae8c72462952df163f1b1e0726641bc5b40dc93/packages/next/src/server/dev/get-source-map-from-file.ts#L17-L53","documentation":"Thrown by `getSourceMapFromFile` in packages/next/src/server/dev/get-source-map-from-file.ts:35 when `fs.readFile(filename, 'utf-8')` rejects. The original error is attached via the `cause` option. This utility is used by the dev server to fetch original source for stack traces/overlays; a missing or unreadable file surfaces here.","triggerScenarios":"The `filename` points to a file that does not exist, has been deleted, lacks read permissions, or is a directory; a `file://` URL that resolves to a non-existent path (the function converts `file://` via `url.fileURLToPath` first).","commonSituations":"Source files referenced by a source map that were removed during a rebuild; stale `.next` build cache pointing at deleted modules; permission issues in containerized builds; race between file deletion and dev-server overlay reading it.","solutions":["Verify the file at the reported path exists and is readable.","Clear the `.next` build directory and restart the dev server to regenerate fresh source maps.","If the path is a `file://` URL, confirm the underlying file is present on disk.","Check container/CI filesystem permissions for the project directory."],"exampleFix":"rm -rf .next && pnpm --filter=next dev","handlingStrategy":"try-catch","validationCode":"import { access } from 'fs/promises';\nasync function fileReadable(p: string) {\n  try { await access(p); return true; } catch { return false; }\n}\nif (!(await fileReadable(filename))) { /* skip or warn */ }","typeGuard":"async function exists(p: string): Promise<boolean> {\n  try { await access(p); return true; } catch { return false; }\n}","tryCatchPattern":"try {\n  const map = await getSourceMapFromFile(filename);\n} catch (err) {\n  // err.cause holds the original fs error; degrade gracefully\n  console.warn(`source map unavailable for ${filename}:`, (err as Error).cause);\n}","preventionTips":["Clear `.next` after deleting modules to avoid stale source-map references.","Wrap `getSourceMapFromFile` calls so a missing map degrades rather than crashes.","Verify filesystem permissions in containerized builds."],"tags":["source-maps","dev-server","filesystem"],"analyzedSha":"0ae8c72462952df163f1b1e0726641bc5b40dc93","analyzedAt":"2026-08-06T19:44:29.143Z","schemaVersion":2},"datasetVersion":"2026-08-07T02:17:10.218Z"}