include/mesos/uri/fetcher.hpp

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#ifndef __MESOS_URI_FETCHER_HPP__
#define __MESOS_URI_FETCHER_HPP__

#include <set>
#include <string>
#include <vector>

#include <mesos/mesos.hpp>

#include <process/future.hpp>
#include <process/owned.hpp>
#include <process/shared.hpp>

#include <stout/hashmap.hpp>
#include <stout/nothing.hpp>

#include <mesos/uri/uri.hpp>

namespace mesos {
namespace uri {


/**
 * Provides an abstraction for fetching URIs. It is pluggable through
 * plugins. Each plugin is responsible for one or more URI schemes,
 * but there should be only one plugin associated with each URI
 * scheme. The fetching request will be dispatched to the relevant
 * plugin based on the scheme in the URI.
 */
class Fetcher
{
public:
  /**
   * Represents a fetcher plugin that handles one or more URI schemes.
   */
  class Plugin
  {
  public:
    virtual ~Plugin() {}

    /**
     * Returns the URI schemes that this plugin handles.
     */
    virtual std::set<std::string> schemes() const = 0;

    /**
     * Returns the name that this plugin registered with.
     */
    virtual std::string name() const = 0;

    /**
     * Fetches a URI to the given directory. To avoid blocking or
     * crashing the current thread, this method might choose to fork
     * subprocesses for third party commands.
     *
     * @param uri the URI to fetch
     * @param directory the directory the URI will be downloaded to
     * @param data the optional user defined data
     */
    // TODO(gilbert): Change the parameter 'data' as a hashmap
    // of <string, Secret::Value>, and update the comment.
    virtual process::Future<Nothing> fetch(
        const URI& uri,
        const std::string& directory,
        const Option<std::string>& data = None()) const = 0;
  };

  /**
   * Create the Fetcher instance with the given plugins.
   *
   * @param plugins a list of plugins to register.
   */
  Fetcher(const std::vector<process::Owned<Plugin>>& plugins);

  /**
   * Fetches a URI to the given directory. This method will dispatch
   * the call to the corresponding plugin based on uri.scheme.
   *
   * @param uri the URI to fetch
   * @param directory the directory the URI will be downloaded to
   * @param data the optional user defined data
   */
  // TODO(jieyu): Consider using 'Path' for 'directory' here.
  process::Future<Nothing> fetch(
      const URI& uri,
      const std::string& directory,
      const Option<std::string>& data = None()) const;

  /**
   * Fetches a URI to the given directory. This method will dispatch
   * the call to the plugin chosen by using its name.
   *
   * @param uri the URI to fetch
   * @param directory the directory the URI will be downloaded to
   * @param name of the plugin that is used to download
   * @param data the optional user defined data
   */
  process::Future<Nothing> fetch(
      const URI& uri,
      const std::string& directory,
      const std::string& name,
      const Option<std::string>& data = None()) const;

private:
  Fetcher(const Fetcher&) = delete; // Not copyable.
  Fetcher& operator=(const Fetcher&) = delete; // Not assignable.

  hashmap<std::string, process::Shared<Plugin>> pluginsByName;
  hashmap<std::string, process::Shared<Plugin>> pluginsByScheme;
};

} // namespace uri {
} // namespace mesos {

#endif // __MESOS_URI_FETCHER_HPP__