transformMiddleware() — vite Function Reference

Source Code

packages/vite/src/node/server/middlewares/transform.ts lines 106–375

export function transformMiddleware(
  server: ViteDevServer,
): Connect.NextHandleFunction {
  // Keep the named function. The name is visible in debug logs via `DEBUG=connect:dispatcher ...`

  // check if public dir is inside root dir
  const { root, publicDir } = server.config
  const publicDirInRoot = publicDir.startsWith(withTrailingSlash(root))
  const publicPath = `${publicDir.slice(root.length)}/`

  return async function viteTransformMiddleware(req, res, next) {
    const environment = server.environments.client

    if (
      (req.method !== 'GET' && req.method !== 'HEAD') ||
      knownIgnoreList.has(req.url!) ||
      isDocumentFetchDest(req)
    ) {
      return next()
    }

    let url: string
    try {
      url = decodeURI(removeTimestampQuery(req.url!)).replace(
        NULL_BYTE_PLACEHOLDER,
        '\0',
      )
    } catch (e) {
      if (e instanceof URIError) {
        server.config.logger.warn(
          colors.yellow(
            `Malformed URI sequence in request URL: ${removeTimestampQuery(req.url!)}`,
          ),
        )
        return next()
      }
      return next(e)
    }

    const withoutQuery = cleanUrl(url)

    try {
      const isSourceMap = withoutQuery.endsWith('.map')
      // since we generate source map references, handle those requests here
      if (isSourceMap) {
        const depsOptimizer = environment.depsOptimizer
        if (depsOptimizer?.isOptimizedDepUrl(url)) {
          // If the browser is requesting a source map for an optimized dep, it
          // means that the dependency has already been pre-bundled and loaded
          const sourcemapPath = url.startsWith(FS_PREFIX)
            ? fsPathFromId(url)
            : normalizePath(path.resolve(server.config.root, url.slice(1)))
          try {
            const map = JSON.parse(
              await fsp.readFile(sourcemapPath, 'utf-8'),
            ) as ExistingRawSourceMap

            applySourcemapIgnoreList(
              map,
              sourcemapPath,
              server.config.server.sourcemapIgnoreList,
              server.config.logger,
            )

            return send(req, res, JSON.stringify(map), 'json', {
              headers: server.config.server.headers,
            })
          } catch {
            // Outdated source map request for optimized deps, this isn't an error
            // but part of the normal flow when re-optimizing after missing deps
            // Send back an empty source map so the browser doesn't issue warnings
            const dummySourceMap = {
              version: 3,
              file: sourcemapPath.replace(/\.map$/, ''),
              sources: [],
              sourcesContent: [],
              names: [],
              mappings: ';;;;;;;;;',
            }
            return send(req, res, JSON.stringify(dummySourceMap), 'json', {
              cacheControl: 'no-cache',