view data/fileio/FileSource.h @ 1376:d9511f9e04d7 dev/refactor-piper-related

Introduce some POD structs for describing an external server application and the desired libraries to load from it, and disambiguating between empty list request and invalid list request. This allows for overriding PiperVampPluginFactory behaviour for using a PluginScan to populate the list request.

/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */

/*
    Sonic Visualiser
    An audio file viewer and annotation editor.
    Centre for Digital Music, Queen Mary, University of London.
    This file copyright 2007 QMUL.
    
    This program is free software; you can redistribute it and/or
    modify it under the terms of the GNU General Public License as
    published by the Free Software Foundation; either version 2 of the
    License, or (at your option) any later version.  See the file
    COPYING included with this distribution for more information.
*/

#ifndef _FILE_SOURCE_H_
#define _FILE_SOURCE_H_

#include <QUrl>
#include <QMutex>
#include <QString>
#include <QTimer>
#include <QNetworkReply>

#include <map>

#include "base/Debug.h"

class QFile;
class ProgressReporter;

/**
 * FileSource is a class used to refer to the contents of a file that
 * may be either local or at a remote location such as a HTTP URL.
 *
 * When a FileSource object is constructed, the file or URL passed to
 * its constructor is tested for validity, and if it refers to a
 * remote HTTP or FTP location it is retrieved asynchronously (the Qt
 * event loop must be running) and cached locally.  You can then query
 * a local path for the file and refer to that as a normal filename.
 *
 * Use isAvailable() to test whether the file or remote URL exists,
 * and isOK() to test for internal validity or transmission errors.
 * Call waitForStatus() to block until the availability and validity
 * of the URL have been established so that isAvailable may be called,
 * and waitForData() to block until the entire file has been cached.
 *
 * FileSource handles reference counting for cache files.  You can
 * construct many FileSource objects with the same URL and you will
 * receive the same cached file for each; it is also reasonable to
 * pass FileSource objects by value.  FileSource only makes sense for
 * stateless URLs that result in the same data on each request.
 *
 * Cached files share a lifetime with their "owning" FileSource
 * objects; when the last FileSource referring to a given URL is
 * deleted or goes out of scope, its cached file (if any) is also
 * removed.
 */
class FileSource : public QObject
{
    Q_OBJECT

public:
    /**
     * Construct a FileSource using the given local file path or URL.
     * The URL may be raw or encoded.
     *
     * If a ProgressReporter is provided, it will be updated with
     * progress status.  Note that the progress() signal will also be
     * emitted regularly during retrieval, even if no reporter is
     * supplied here.  Caller retains ownership of the reporter object.
     */
    FileSource(QString fileOrUrl,
               ProgressReporter *reporter = 0,
               QString preferredContentType = "");

    /**
     * Construct a FileSource using the given remote URL.
     *
     * If a ProgressReporter is provided, it will be updated with
     * progress status.  Note that the progress() signal will also be
     * emitted regularly during retrieval, even if no reporter is
     * supplied here.  Caller retains ownership of the reporter object.
     */
    FileSource(QUrl url, ProgressReporter *reporter = 0);

    FileSource(const FileSource &);

    virtual ~FileSource();

    /**
     * Block on a sub-event-loop until the availability of the file or
     * remote URL is known.
     */
    void waitForStatus();

    /**
     * Block on a sub-event-loop until the whole of the data has been
     * retrieved (if it is remote).
     */
    void waitForData();

    /**
     * Return true if the FileSource object is valid and neither error
     * nor cancellation occurred while retrieving the file or remote
     * URL.  Non-existence of the file or URL is not an error -- call
     * isAvailable() to test for that.
     */
    bool isOK() const;

    /**
     * Return true if the file or remote URL exists.  This may block
     * on a sub-event-loop (calling waitForStatus) if the status is
     * not yet available.
     */
    bool isAvailable();

    /**
     * Return true if the entire file has been retrieved and is
     * available.
     */
    bool isDone() const;

    /**
     * Return true if the operation was cancelled by the user through
     * the ProgressReporter interface. Note that the cancelled()
     * signal will have been emitted, and isOK() will also return
     * false in this case.
     */
    bool wasCancelled() const;

    /**
     * Return true if this FileSource is referring to a QRC resource.
     */
    bool isResource() const;

    /**
     * Return true if this FileSource is referring to a remote URL.
     */
    bool isRemote() const;

    /**
     * Return the location filename or URL as passed to the
     * constructor.
     */
    QString getLocation() const;

    /**
     * Return the name of the local file this FileSource refers to.
     * This is the filename that should be used when reading normally
     * from the FileSource.  If the filename passed to the constructor
     * was a local file, this will return the same filename; otherwise
     * this will be the name of the temporary cache file owned by the
     * FileSource.
     */
    QString getLocalFilename() const;

    /**
     * Return the base name, i.e. the final path element (including
     * extension, if any) of the location.
     */
    QString getBasename() const;

    /**
     * Return the MIME content type of this file, if known.
     */
    QString getContentType() const;

    /**
     * Return the file extension for this file, if any. The returned
     * extension is always lower-case.
     */
    QString getExtension() const;

    /**
     * Return an error message, if isOK() is false.
     */
    QString getErrorString() const;

    /**
     * Specify whether any local, cached file should remain on disc
     * after this FileSource has been destroyed.  The default is false
     * (cached files share their FileSource owners' lifespans).
     */
    void setLeaveLocalFile(bool leave);

    /**
     * Return true if the given filename or URL refers to a remote
     * URL.
     */
    static bool isRemote(QString fileOrUrl);

    /**
     * Return true if FileSource can handle the retrieval scheme for
     * the given URL (or if the URL is for a local file).
     */
    static bool canHandleScheme(QUrl url);

    /**
     * Print some stats, if FileSource was compiled with debugging.
     * It's safe to leave a call to this function in release code, as
     * long as FileSource itself is compiled with release flags.
     */
    static void debugReport();
    
signals:
    /**
     * Emitted during URL retrieval, when the retrieval progress
     * notches up to a new percentage.
     */
    void progress(int percent);

    /**
     * Emitted when the file's existence has been tested and/or
     * response header received.  Calls to isAvailable() after this
     * has been emitted will not block.
     */
    void statusAvailable();

    /**
     * Emitted when the entire file data has been retrieved and the
     * local file is complete (if no error has occurred).
     */
    void ready();

protected slots:
    void metaDataChanged();
    void readyRead();
    void replyFailed(QNetworkReply::NetworkError);
    void replyFinished();
    void downloadProgress(qint64 done, qint64 total);
    void cancelled();

protected:
    FileSource &operator=(const FileSource &); // not provided

    QString m_rawFileOrUrl;
    QUrl m_url;
    QFile *m_localFile;
    QNetworkReply *m_reply;
    QString m_localFilename;
    QString m_errorString;
    QString m_contentType;
    QString m_preferredContentType;
    bool m_ok;
    bool m_cancelled;
    int m_lastStatus;
    bool m_resource;
    bool m_remote;
    bool m_done;
    bool m_leaveLocalFile;
    ProgressReporter *m_reporter;

    typedef std::map<QUrl, int> RemoteRefCountMap;
    typedef std::map<QUrl, QString> RemoteLocalMap;
    static RemoteRefCountMap m_refCountMap;
    static RemoteLocalMap m_remoteLocalMap;
    static QMutex m_mapMutex;
    bool m_refCounted;

    void init();
    void initRemote();

    void cleanup();

    // Create a local file for m_url.  If it already existed, return true.
    // The local filename is stored in m_localFilename.
    bool createCacheFile();
    void deleteCacheFile();

    static QMutex m_fileCreationMutex;
    static int m_count;
};

#endif