vercel/next.js · error · Error

Failed to read file contents of

Error message

Failed to read file contents of ${filename}.

What it means

I/O wrapper in getSourceMapFromFile: reading the file at filename (after file:// normalization) failed, and the original fs error is attached as cause. Missing files or permission problems on the compiled artifact are the usual triggers when the dev overlay tries to symbolicate a stack.

Solutions

1. Ensure the file exists and is readable; check permissions and that the path is correct.

When it happens

Trigger: Reading a file's contents to extract its source map fails.

Common situations: A deleted or unreadable file during dev error overlay source map resolution.

AI-assisted analysis of vercel/next.js@0eb3775416 (2026-08-19). Data as JSON: /api/errors/fec13d547b2453fe. Report an issue: GitHub.

Appendix: source

Thrown at packages/next/src/server/dev/get-source-map-from-file.ts:35

  if (!(match && match[1])) {
    return null
  }
  return match[1].toString()
}

export async function getSourceMapFromFile(
  filename: string
): Promise<RawSourceMap | undefined> {
  filename = filename.startsWith('file://')
    ? url.fileURLToPath(filename)
    : filename

  let fileContents: string

  try {
    fileContents = await fs.readFile(filename, 'utf-8')
  } catch (error) {
    throw new Error(`Failed to read file contents of ${filename}.`, {
      cause: error,
    })
  }

  const sourceUrl = getSourceMapUrl(fileContents)

  if (!sourceUrl) {
    return undefined
  }

  if (sourceUrl.startsWith('data:')) {
    let buffer: dataUriToBuffer.MimeBuffer

    try {
      buffer = dataUriToBuffer(sourceUrl)
    } catch (error) {
      throw new Error(`Failed to parse source map URL for ${filename}.`, {
        cause: error,

View on GitHub (pinned to 0eb3775416)