Unable to parse webpack source URLs, how to work around around?

It looks like it's failing right here:

https://github.com/mozilla/source-map/blob/60adcb064bf033702d954d6d3f9bc3635dcb744b/lib/util.js#L181

I have this code for parsing the string sourcemap from a JS file, but it's not working:

const CACHE: Record<string, SourceMapConsumer> = {}

async function loadFile(
  line: string,
): Promise<SourceMapConsumer | void> {
  const link = CACHE[`${line}`]
  if (link) {
    return link
  }

  const res = await fetch(line)
  const text = await res.text()
  const last = text.trim().split('\n').pop() ?? ''
  console.log(text)
  console.log(last)
  if (
    last.match(
      /(\/\/# sourceMappingURL=data:application\/json;charset=utf-8;base64,)/,
    )
  ) {
    console.log(last.slice(RegExp.$1.length))
    const json = JSON.parse(
      atob(last.slice(RegExp.$1.length)),
    ) as RawSourceMap
    json.sources.forEach((source, i) => {
      json.sources[i] = source.replace(/^webpack:\/\//g, 'http://')
    })
    console.log(json)

    const sm = await new SourceMapConsumer(json)
    CACHE[`${line}`] = sm
    return sm
  }
}

async function readFileLocation(
  file: string,
  line: number,
  rise: number,
): Promise<[string, number | undefined, number | undefined]> {
  const link = await loadFile(file)

  const trace = {
    column: rise,
    filename: file,
    line: line,
  }

  if (link) {
    const token = link.originalPositionFor(trace)
    if (token.source) {
      return [
        token.source,
        token.line == null ? undefined : token.line,
        token.column == null ? undefined : token.column,
      ]
    } else {
      return [file, line, rise]
    }
  } else {
    return [file, line, rise]
  }
}

export async function testSourceMaps(error: Error): Promise<string> {
  const stack = getFileLineColumn(error.stack?.split('\n') ?? [])
  const list: Array<string> = []

  for (const data of stack) {
    const [file, line, column] = await readFileLocation(
      data.file,
      data.line ?? 0,
      data.column ?? 0,
    )

    console.log(file, line, column)
  }
}

As you can see in the example, I tried to replace webpack:// with http:// but it didn't seem to help:

json.sources[i] = source.replace(/^webpack:\/\//g, 'http://')

How do I get this working, any suggestions? The error I'm getting is:

Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'decode')
    at new URLStateMachine (url-state-machine.js:546:1)
    at module.exports.basicURLParse (url-state-machine.js:1264:1)
    at new URLImpl (URL-impl.js:13:1)
    at Object.setup (URL.js:317:1)
    at new URL (URL.js:26:1)
    at util.js:179:1
    at Object.computeSourceURL (util.js:431:1)
    at source-map-consumer.js:207:1
    at Array.map (<anonymous>)
    at source-map-consumer.js:206:1

The JSON looks liek this when I parse the sourcemap in this fashion:

Any help would be greatly appreciated. Thank you.

Start with the failing path in lib/util.js around line 181, then follow its callers in source-map-consumer.js around lines 206-207 and the provided webpack source-map example. Reproduce the URL parsing error with the supplied TypeScript code and inspect how the parsed sources are passed into computeSourceURL. Done means the webpack source URLs no longer trigger the reported decode error.