Function download

src/launcher/fetcher.cpp:216–260

static Try<string> download(
    const string& _sourceUri,
    const string& destinationPath,
    const Option<string>& frameworksHome,
    const Option<Duration>& stallTimeout)
{
  // Trim leading whitespace for 'sourceUri'.
  const string sourceUri = strings::trim(_sourceUri, strings::PREFIX);

  Try<Nothing> validation = Fetcher::validateUri(sourceUri);
  if (validation.isError()) {
    return Error(validation.error());
  }

  // 1. Try to fetch using a local copy.
  // We regard as local: "file://" or the absence of any URI scheme.
  Result<string> sourcePath =
    Fetcher::uriToLocalPath(sourceUri, frameworksHome);

  if (sourcePath.isError()) {
    return Error(sourcePath.error());
  } else if (sourcePath.isSome()) {
    return copyFile(sourcePath.get(), destinationPath);
  }

  // 2. Try to fetch URI using os::net / libcurl implementation.
  // We consider http, https, ftp, ftps compatible with libcurl.
  if (Fetcher::isNetUri(sourceUri)) {
    return downloadWithNet(sourceUri, destinationPath, stallTimeout);
  }

  // 3. Try to fetch the URI using hadoop client.
  // We use the hadoop client to fetch any URIs that are not
  // handled by other fetchers(local / os::net). These URIs may be
  // `hdfs://` URIs or any other URI that has been configured (and
  // hence handled) in the hadoop client. This allows mesos to
  // externalize the handling of previously unknown resource
  // endpoints without the need to support them natively.
  // Note: Hadoop Client is not a hard dependency for running mesos.
  // This allows users to get mesos up and running without a
  // hadoop_home or the hadoop client setup but in case we reach
  // this part and don't have one configured, the fetch would fail
  // and log an appropriate error.
  return downloadWithHadoopClient(sourceUri, destinationPath);
}


// TODO(bernd-mesos): Refactor this into stout so that we can more easily