apt-pkg/acquire.h

   1 // -*- mode: cpp; mode: fold -*-
   2 // Description                                                          /*{{{*/
   3 // $Id: acquire.h,v 1.29.2.1 2003/12/24 23:09:17 mdz Exp $
   4 /* ######################################################################
   5
   6    Acquire - File Acquiration
   7
   8    This module contians the Acquire system. It is responsible for bringing
   9    files into the local pathname space. It deals with URIs for files and
  10    URI handlers responsible for downloading or finding the URIs.
  11
  12    Each file to download is represented by an Acquire::Item class subclassed
  13    into a specialization. The Item class can add itself to several URI
  14    acquire queues each prioritized by the download scheduler. When the
  15    system is run the proper URI handlers are spawned and the the acquire
  16    queues are fed into the handlers by the schedular until the queues are
  17    empty. This allows for an Item to be downloaded from an alternate source
  18    if the first try turns out to fail. It also alows concurrent downloading
  19    of multiple items from multiple sources as well as dynamic balancing
  20    of load between the sources.
  21
  22    Schedualing of downloads is done on a first ask first get basis. This
  23    preserves the order of the download as much as possible. And means the
  24    fastest source will tend to process the largest number of files.
  25
  26    Internal methods and queues for performing gzip decompression,
  27    md5sum hashing and file copying are provided to allow items to apply
  28    a number of transformations to the data files they are working with.
  29
  30    ##################################################################### */
  31                                                                         /*}}}*/
  32
  33 /** \defgroup acquire Acquire system                                    {{{
  34  *
  35  *  \brief The Acquire system is responsible for retrieving files from
  36  *  local or remote URIs and postprocessing them (for instance,
  37  *  verifying their authenticity).  The core class in this system is
  38  *  pkgAcquire, which is responsible for managing the download queues
  39  *  during the download.  There is at least one download queue for
  40  *  each supported protocol; protocols such as http may provide one
  41  *  queue per host.
  42  *
  43  *  Each file to download is represented by a subclass of
  44  *  pkgAcquire::Item.  The files add themselves to the download
  45  *  queue(s) by providing their URI information to
  46  *  pkgAcquire::Item::QueueURI, which calls pkgAcquire::Enqueue.
  47  *
  48  *  Once the system is set up, the Run method will spawn subprocesses
  49  *  to handle the enqueued URIs; the scheduler will then take items
  50  *  from the queues and feed them into the handlers until the queues
  51  *  are empty.
  52  *
  53  *  \todo Acquire supports inserting an object into several queues at
  54  *  once, but it is not clear what its behavior in this case is, and
  55  *  no subclass of pkgAcquire::Item seems to actually use this
  56  *  capability.
  57  */                                                                     /*}}}*/
  58
  59 /** \addtogroup acquire
  60  *
  61  *  @{
  62  *
  63  *  \file acquire.h
  64  */
  65
  66 #ifndef PKGLIB_ACQUIRE_H
  67 #define PKGLIB_ACQUIRE_H
  68
  69 #include <apt-pkg/macros.h>
  70 #include <apt-pkg/weakptr.h>
  71
  72 #include <vector>
  73 #include <string>
  74
  75 using std::vector;
  76 using std::string;
  77
  78
  79 #include <sys/time.h>
  80 #include <unistd.h>
  81
  82 class pkgAcquireStatus;
  83
  84 /** \brief The core download scheduler.                                 {{{
  85  *
  86  *  This class represents an ongoing download.  It manages the lists
  87  *  of active and pending downloads and handles setting up and tearing
  88  *  down download-related structures.
  89  *
  90  *  \todo Why all the protected data items and methods?
  91  */
  92 class pkgAcquire
  93 {
  94    public:
  95
  96    class Item;
  97    class Queue;
  98    class Worker;
  99    struct MethodConfig;
 100    struct ItemDesc;
 101    friend class Item;
 102    friend class Queue;
 103
 104    typedef vector<Item *>::iterator ItemIterator;
 105    typedef vector<Item *>::const_iterator ItemCIterator;
 106
 107    protected:
 108
 109    /** \brief A list of items to download.
 110     *
 111     *  This is built monotonically as items are created and only
 112     *  emptied when the download shuts down.
 113     */
 114    vector<Item *> Items;
 115
 116    /** \brief The head of the list of active queues.
 117     *
 118     *  \todo why a hand-managed list of queues instead of std::list or
 119     *  std::set?
 120     */
 121    Queue *Queues;
 122
 123    /** \brief The head of the list of active workers.
 124     *
 125     *  \todo why a hand-managed list of workers instead of std::list
 126     *  or std::set?
 127     */
 128    Worker *Workers;
 129
 130    /** \brief The head of the list of acquire method configurations.
 131     *
 132     *  Each protocol (http, ftp, gzip, etc) via which files can be
 133     *  fetched can have a representation in this list.  The
 134     *  configuration data is filled in by parsing the 100 Capabilities
 135     *  string output by a method on startup (see
 136     *  pkgAcqMethod::pkgAcqMethod and pkgAcquire::GetConfig).
 137     *
 138     *  \todo why a hand-managed config dictionary instead of std::map?
 139     */
 140    MethodConfig *Configs;
 141
 142    /** \brief The progress indicator for this download. */
 143    pkgAcquireStatus *Log;
 144
 145    /** \brief The total size of the files which are to be fetched.
 146     *
 147     *  This is not necessarily the total number of bytes to download
 148     *  when, e.g., download resumption and list updates via patches
 149     *  are taken into account.
 150     */
 151    unsigned long ToFetch;
 152
 153    // Configurable parameters for the scheduler
 154
 155    /** \brief Represents the queuing strategy for remote URIs. */
 156    enum QueueStrategy {
 157      /** \brief Generate one queue for each protocol/host combination; downloads from
 158       *  multiple hosts can proceed in parallel.
 159       */
 160      QueueHost,
 161      /** \brief Generate a single queue for each protocol; serialize
 162       *  downloads from multiple hosts.
 163       */
 164      QueueAccess} QueueMode;
 165
 166    /** \brief If \b true, debugging information will be dumped to std::clog. */
 167    bool const Debug;
 168    /** \brief If \b true, a download is currently in progress. */
 169    bool Running;
 170
 171    /** \brief Add the given item to the list of items. */
 172    void Add(Item *Item);
 173
 174    /** \brief Remove the given item from the list of items. */
 175    void Remove(Item *Item);
 176
 177    /** \brief Add the given worker to the list of workers. */
 178    void Add(Worker *Work);
 179
 180    /** \brief Remove the given worker from the list of workers. */
 181    void Remove(Worker *Work);
 182
 183    /** \brief Insert the given fetch request into the appropriate queue.
 184     *
 185     *  \param Item The URI to download and the item to download it
 186     *  for.  Copied by value into the queue; no reference to Item is
 187     *  retained.
 188     */
 189    void Enqueue(ItemDesc &Item);
 190
 191    /** \brief Remove all fetch requests for this item from all queues. */
 192    void Dequeue(Item *Item);
 193
 194    /** \brief Determine the fetch method and queue of a URI.
 195     *
 196     *  \param URI The URI to fetch.
 197     *
 198     *  \param[out] Config A location in which to place the method via
 199     *  which the URI is to be fetched.
 200     *
 201     *  \return the string-name of the queue in which a fetch request
 202     *  for the given URI should be placed.
 203     */
 204    string QueueName(string URI,MethodConfig const *&Config);
 205
 206    /** \brief Build up the set of file descriptors upon which select() should
 207     *  block.
 208     *
 209     *  The default implementation inserts the file descriptors
 210     *  corresponding to active downloads.
 211     *
 212     *  \param[out] Fd The largest file descriptor in the generated sets.
 213     *
 214     *  \param[out] RSet The set of file descriptors that should be
 215     *  watched for input.
 216     *
 217     *  \param[out] WSet The set of file descriptors that should be
 218     *  watched for output.
 219     */
 220    virtual void SetFds(int &Fd,fd_set *RSet,fd_set *WSet);
 221
 222    /** Handle input from and output to file descriptors which select()
 223     *  has determined are ready.  The default implementation
 224     *  dispatches to all active downloads.
 225     *
 226     *  \param RSet The set of file descriptors that are ready for
 227     *  input.
 228     *
 229     *  \param WSet The set of file descriptors that are ready for
 230     *  output.
 231     */
 232    virtual void RunFds(fd_set *RSet,fd_set *WSet);
 233
 234    /** \brief Check for idle queues with ready-to-fetch items.
 235     *
 236     *  Called by pkgAcquire::Queue::Done each time an item is dequeued
 237     *  but remains on some queues; i.e., another queue should start
 238     *  fetching it.
 239     */
 240    void Bump();
 241
 242    public:
 243
 244    /** \brief Retrieve information about a fetch method by name.
 245     *
 246     *  \param Access The name of the method to look up.
 247     *
 248     *  \return the method whose name is Access, or \b NULL if no such method exists.
 249     */
 250    MethodConfig *GetConfig(string Access);
 251
 252    /** \brief Provides information on how a download terminated. */
 253    enum RunResult {
 254      /** \brief All files were fetched successfully. */
 255      Continue,
 256
 257      /** \brief Some files failed to download. */
 258      Failed,
 259
 260      /** \brief The download was cancelled by the user (i.e., #Log's
 261       *  pkgAcquireStatus::Pulse() method returned \b false).
 262       */
 263      Cancelled};
 264
 265    /** \brief Download all the items that have been Add()ed to this
 266     *  download process.
 267     *
 268     *  This method will block until the download completes, invoking
 269     *  methods on #Log to report on the progress of the download.
 270     *
 271     *  \param PulseInterval The method pkgAcquireStatus::Pulse will be
 272     *  invoked on #Log at intervals of PulseInterval milliseconds.
 273     *
 274     *  \return the result of the download.
 275     */
 276    RunResult Run(int PulseInterval=500000);
 277
 278    /** \brief Remove all items from this download process, terminate
 279     *  all download workers, and empty all queues.
 280     */
 281    void Shutdown();
 282
 283    /** \brief Get the first #Worker object.
 284     *
 285     *  \return the first active worker in this download process.
 286     */
 287    inline Worker *WorkersBegin() {return Workers;};
 288
 289    /** \brief Advance to the next #Worker object.
 290     *
 291     *  \return the worker immediately following I, or \b NULL if none
 292     *  exists.
 293     */
 294    Worker *WorkerStep(Worker *I);
 295
 296    /** \brief Get the head of the list of items. */
 297    inline ItemIterator ItemsBegin() {return Items.begin();};
 298
 299    /** \brief Get the end iterator of the list of items. */
 300    inline ItemIterator ItemsEnd() {return Items.end();};
 301
 302    // Iterate over queued Item URIs
 303    class UriIterator;
 304    /** \brief Get the head of the list of enqueued item URIs.
 305     *
 306     *  This iterator will step over every element of every active
 307     *  queue.
 308     */
 309    UriIterator UriBegin();
 310    /** \brief Get the end iterator of the list of enqueued item URIs. */
 311    UriIterator UriEnd();
 312
 313    /** Deletes each entry in the given directory that is not being
 314     *  downloaded by this object.  For instance, when downloading new
 315     *  list files, calling Clean() will delete the old ones.
 316     *
 317     *  \param Dir The directory to be cleaned out.
 318     *
 319     *  \return \b true if the directory exists and is readable.
 320     */
 321    bool Clean(string Dir);
 322
 323    /** \return the total size in bytes of all the items included in
 324     *  this download.
 325     */
 326    double TotalNeeded();
 327
 328    /** \return the size in bytes of all non-local items included in
 329     *  this download.
 330     */
 331    double FetchNeeded();
 332
 333    /** \return the amount of data to be fetched that is already
 334     *  present on the filesystem.
 335     */
 336    double PartialPresent();
 337
 338    /** \brief Delayed constructor
 339     *
 340     *  \param Progress indicator associated with this download or
 341     *  \b NULL for none.  This object is not owned by the
 342     *  download process and will not be deleted when the pkgAcquire
 343     *  object is destroyed.  Naturally, it should live for at least as
 344     *  long as the pkgAcquire object does.
 345     *  \param Lock defines a lock file that should be acquired to ensure
 346     *  only one Acquire class is in action at the time or an empty string
 347     *  if no lock file should be used.
 348     */
 349    bool Setup(pkgAcquireStatus *Progress = NULL, string const &Lock = "");
 350
 351    /** \brief Construct a new pkgAcquire. */
 352    pkgAcquire(pkgAcquireStatus *Log) __deprecated;
 353    pkgAcquire();
 354
 355    /** \brief Destroy this pkgAcquire object.
 356     *
 357     *  Destroys all queue, method, and item objects associated with
 358     *  this download.
 359     */
 360    virtual ~pkgAcquire();
 361
 362    private:
 363    /** \brief FD of the Lock file we acquire in Setup (if any) */
 364    int LockFD;
 365
 366    /** \brief Ensure the existence of the given Path
 367     *
 368     *  \param Parent directory of the Path directory - a trailing
 369     *  /apt/ will be removed before CreateDirectory call.
 370     *  \param Path which should exist after (successful) call
 371     */
 372    bool CheckDirectory(string const &Parent, string const &Path) const;
 373 };
 374
 375 /** \brief Represents a single download source from which an item
 376  *  should be downloaded.
 377  *
 378  *  An item may have several assocated ItemDescs over its lifetime.
 379  */
 380 struct pkgAcquire::ItemDesc : public WeakPointable
 381 {
 382    /** \brief The URI from which to download this item. */
 383    string URI;
 384    /** brief A description of this item. */
 385    string Description;
 386    /** brief A shorter description of this item. */
 387    string ShortDesc;
 388    /** brief The underlying item which is to be downloaded. */
 389    Item *Owner;
 390 };
 391                                                                         /*}}}*/
 392 /** \brief A single download queue in a pkgAcquire object.              {{{
 393  *
 394  *  \todo Why so many protected values?
 395  */
 396 class pkgAcquire::Queue
 397 {
 398    friend class pkgAcquire;
 399    friend class pkgAcquire::UriIterator;
 400    friend class pkgAcquire::Worker;
 401
 402    /** \brief The next queue in the pkgAcquire object's list of queues. */
 403    Queue *Next;
 404
 405    protected:
 406
 407    /** \brief A single item placed in this queue. */
 408    struct QItem : pkgAcquire::ItemDesc
 409    {
 410       /** \brief The next item in the queue. */
 411       QItem *Next;
 412       /** \brief The worker associated with this item, if any. */
 413       pkgAcquire::Worker *Worker;
 414
 415       /** \brief Assign the ItemDesc portion of this QItem from
 416        *  another ItemDesc
 417        */
 418       void operator =(pkgAcquire::ItemDesc const &I)
 419       {
 420          URI = I.URI;
 421          Description = I.Description;
 422          ShortDesc = I.ShortDesc;
 423          Owner = I.Owner;
 424       };
 425    };
 426
 427    /** \brief The name of this queue. */
 428    string Name;
 429
 430    /** \brief The head of the list of items contained in this queue.
 431     *
 432     *  \todo why a by-hand list instead of an STL structure?
 433     */
 434    QItem *Items;
 435
 436    /** \brief The head of the list of workers associated with this queue.
 437     *
 438     *  \todo This is plural because support exists in Queue for
 439     *  multiple workers.  However, it does not appear that there is
 440     *  any way to actually associate more than one worker with a
 441     *  queue.
 442     *
 443     *  \todo Why not just use a std::set?
 444     */
 445    pkgAcquire::Worker *Workers;
 446
 447    /** \brief the download scheduler with which this queue is associated. */
 448    pkgAcquire *Owner;
 449
 450    /** \brief The number of entries in this queue that are currently
 451     *  being downloaded.
 452     */
 453    signed long PipeDepth;
 454
 455    /** \brief The maximum number of entries that this queue will
 456     *  attempt to download at once.
 457     */
 458    unsigned long MaxPipeDepth;
 459
 460    public:
 461
 462    /** \brief Insert the given fetch request into this queue.
 463     *
 464     *  \return \b true if the queuing was successful. May return
 465     *  \b false if the Item is already in the queue
 466     */
 467    bool Enqueue(ItemDesc &Item);
 468
 469    /** \brief Remove all fetch requests for the given item from this queue.
 470     *
 471     *  \return \b true if at least one request was removed from the queue.
 472     */
 473    bool Dequeue(Item *Owner);
 474
 475    /** \brief Locate an item in this queue.
 476     *
 477     *  \param URI A URI to match against.
 478     *  \param Owner A pkgAcquire::Worker to match against.
 479     *
 480     *  \return the first item in the queue whose URI is #URI and that
 481     *  is being downloaded by #Owner.
 482     */
 483    QItem *FindItem(string URI,pkgAcquire::Worker *Owner);
 484
 485    /** Presumably this should start downloading an item?
 486     *
 487     *  \todo Unimplemented.  Implement it or remove?
 488     */
 489    bool ItemStart(QItem *Itm,unsigned long Size);
 490
 491    /** \brief Remove the given item from this queue and set its state
 492     *  to pkgAcquire::Item::StatDone.
 493     *
 494     *  If this is the only queue containing the item, the item is also
 495     *  removed from the main queue by calling pkgAcquire::Dequeue.
 496     *
 497     *  \param Itm The item to remove.
 498     *
 499     *  \return \b true if no errors are encountered.
 500     */
 501    bool ItemDone(QItem *Itm);
 502
 503    /** \brief Start the worker process associated with this queue.
 504     *
 505     *  If a worker process is already associated with this queue,
 506     *  this is equivalent to calling Cycle().
 507     *
 508     *  \return \b true if the startup was successful.
 509     */
 510    bool Startup();
 511
 512    /** \brief Shut down the worker process associated with this queue.
 513     *
 514     *  \param Final If \b true, then the process is stopped unconditionally.
 515     *               Otherwise, it is only stopped if it does not need cleanup
 516     *               as indicated by the pkgAcqMethod::NeedsCleanup member of
 517     *               its configuration.
 518     *
 519     *  \return \b true.
 520     */
 521    bool Shutdown(bool Final);
 522
 523    /** \brief Send idle items to the worker process.
 524     *
 525     *  Fills up the pipeline by inserting idle items into the worker's queue.
 526     */
 527    bool Cycle();
 528
 529    /** \brief Check for items that could be enqueued.
 530     *
 531     *  Call this after an item placed in multiple queues has gone from
 532     *  the pkgAcquire::Item::StatFetching state to the
 533     *  pkgAcquire::Item::StatIdle state, to possibly refill an empty queue.
 534     *  This is an alias for Cycle().
 535     *
 536     *  \todo Why both this and Cycle()?  Are they expected to be
 537     *  different someday?
 538     */
 539    void Bump();
 540
 541    /** \brief Create a new Queue.
 542     *
 543     *  \param Name The name of the new queue.
 544     *  \param Owner The download process that owns the new queue.
 545     */
 546    Queue(string Name,pkgAcquire *Owner);
 547
 548    /** Shut down all the worker processes associated with this queue
 549     *  and empty the queue.
 550     */
 551    ~Queue();
 552 };
 553                                                                         /*}}}*/
 554 /** \brief Iterates over all the URIs being fetched by a pkgAcquire object.     {{{*/
 555 class pkgAcquire::UriIterator
 556 {
 557    /** The next queue to iterate over. */
 558    pkgAcquire::Queue *CurQ;
 559    /** The item that we currently point at. */
 560    pkgAcquire::Queue::QItem *CurItem;
 561
 562    public:
 563
 564    inline void operator ++() {operator ++(0);};
 565
 566    void operator ++(int)
 567    {
 568       CurItem = CurItem->Next;
 569       while (CurItem == 0 && CurQ != 0)
 570       {
 571          CurItem = CurQ->Items;
 572          CurQ = CurQ->Next;
 573       }
 574    };
 575
 576    inline pkgAcquire::ItemDesc const *operator ->() const {return CurItem;};
 577    inline bool operator !=(UriIterator const &rhs) const {return rhs.CurQ != CurQ || rhs.CurItem != CurItem;};
 578    inline bool operator ==(UriIterator const &rhs) const {return rhs.CurQ == CurQ && rhs.CurItem == CurItem;};
 579
 580    /** \brief Create a new UriIterator.
 581     *
 582     *  \param Q The queue over which this UriIterator should iterate.
 583     */
 584    UriIterator(pkgAcquire::Queue *Q) : CurQ(Q), CurItem(0)
 585    {
 586       while (CurItem == 0 && CurQ != 0)
 587       {
 588          CurItem = CurQ->Items;
 589          CurQ = CurQ->Next;
 590       }
 591    }
 592 };
 593                                                                         /*}}}*/
 594 /** \brief Information about the properties of a single acquire method. {{{*/
 595 struct pkgAcquire::MethodConfig
 596 {
 597    /** \brief The next link on the acquire method list.
 598     *
 599     *  \todo Why not an STL container?
 600     */
 601    MethodConfig *Next;
 602
 603    /** \brief The name of this acquire method (e.g., http). */
 604    string Access;
 605
 606    /** \brief The implementation version of this acquire method. */
 607    string Version;
 608
 609    /** \brief If \b true, only one download queue should be created for this
 610     *  method.
 611     */
 612    bool SingleInstance;
 613
 614    /** \brief If \b true, this method supports pipelined downloading. */
 615    bool Pipeline;
 616
 617    /** \brief If \b true, the worker process should send the entire
 618     *  APT configuration tree to the fetch subprocess when it starts
 619     *  up.
 620     */
 621    bool SendConfig;
 622
 623    /** \brief If \b true, this fetch method does not require network access;
 624     *  all files are to be acquired from the local disk.
 625     */
 626    bool LocalOnly;
 627
 628    /** \brief If \b true, the subprocess has to carry out some cleanup
 629     *  actions before shutting down.
 630     *
 631     *  For instance, the cdrom method needs to unmount the CD after it
 632     *  finishes.
 633     */
 634    bool NeedsCleanup;
 635
 636    /** \brief If \b true, this fetch method acquires files from removable media. */
 637    bool Removable;
 638
 639    /** \brief Set up the default method parameters.
 640     *
 641     *  All fields are initialized to NULL, "", or \b false as
 642     *  appropriate.
 643     */
 644    MethodConfig();
 645 };
 646                                                                         /*}}}*/
 647 /** \brief A monitor object for downloads controlled by the pkgAcquire class.   {{{
 648  *
 649  *  \todo Why protected members?
 650  *
 651  *  \todo Should the double members be uint64_t?
 652  */
 653 class pkgAcquireStatus
 654 {
 655    protected:
 656
 657    /** \brief The last time at which this monitor object was updated. */
 658    struct timeval Time;
 659
 660    /** \brief The time at which the download started. */
 661    struct timeval StartTime;
 662
 663    /** \brief The number of bytes fetched as of the previous call to
 664     *  pkgAcquireStatus::Pulse, including local items.
 665     */
 666    double LastBytes;
 667
 668    /** \brief The current rate of download as of the most recent call
 669     *  to pkgAcquireStatus::Pulse, in bytes per second.
 670     */
 671    double CurrentCPS;
 672
 673    /** \brief The number of bytes fetched as of the most recent call
 674     *  to pkgAcquireStatus::Pulse, including local items.
 675     */
 676    double CurrentBytes;
 677
 678    /** \brief The total number of bytes that need to be fetched.
 679     *
 680     *  \warning This member is inaccurate, as new items might be
 681     *  enqueued while the download is in progress!
 682     */
 683    double TotalBytes;
 684
 685    /** \brief The total number of bytes accounted for by items that
 686     *  were successfully fetched.
 687     */
 688    double FetchedBytes;
 689
 690    /** \brief The amount of time that has elapsed since the download
 691     *   started.
 692     */
 693    unsigned long ElapsedTime;
 694
 695    /** \brief The total number of items that need to be fetched.
 696     *
 697     *  \warning This member is inaccurate, as new items might be
 698     *  enqueued while the download is in progress!
 699     */
 700    unsigned long TotalItems;
 701
 702    /** \brief The number of items that have been successfully downloaded. */
 703    unsigned long CurrentItems;
 704
 705    public:
 706
 707    /** \brief If \b true, the download scheduler should call Pulse()
 708     *  at the next available opportunity.
 709     */
 710    bool Update;
 711
 712    /** \brief If \b true, extra Pulse() invocations will be performed.
 713     *
 714     *  With this option set, Pulse() will be called every time that a
 715     *  download item starts downloading, finishes downloading, or
 716     *  terminates with an error.
 717     */
 718    bool MorePulses;
 719
 720    /** \brief Invoked when a local or remote file has been completely fetched.
 721     *
 722     *  \param Size The size of the file fetched.
 723     *
 724     *  \param ResumePoint How much of the file was already fetched.
 725     */
 726    virtual void Fetched(unsigned long Size,unsigned long ResumePoint);
 727
 728    /** \brief Invoked when the user should be prompted to change the
 729     *         inserted removable media.
 730     *
 731     *  This method should not return until the user has confirmed to
 732     *  the user interface that the media change is complete.
 733     *
 734     *  \param Media The name of the media type that should be changed.
 735     *
 736     *  \param Drive The identifying name of the drive whose media
 737     *               should be changed.
 738     *
 739     *  \return \b true if the user confirms the media change, \b
 740     *  false if it is cancelled.
 741     *
 742     *  \todo This is a horrible blocking monster; it should be CPSed
 743     *  with prejudice.
 744     */
 745    virtual bool MediaChange(string Media,string Drive) = 0;
 746
 747    /** \brief Invoked when an item is confirmed to be up-to-date.
 748
 749     * For instance, when an HTTP download is informed that the file on
 750     * the server was not modified.
 751     */
 752    virtual void IMSHit(pkgAcquire::ItemDesc &/*Itm*/) {};
 753
 754    /** \brief Invoked when some of an item's data is fetched. */
 755    virtual void Fetch(pkgAcquire::ItemDesc &/*Itm*/) {};
 756
 757    /** \brief Invoked when an item is successfully and completely fetched. */
 758    virtual void Done(pkgAcquire::ItemDesc &/*Itm*/) {};
 759
 760    /** \brief Invoked when the process of fetching an item encounters
 761     *  a fatal error.
 762     */
 763    virtual void Fail(pkgAcquire::ItemDesc &/*Itm*/) {};
 764
 765    /** \brief Periodically invoked while the Acquire process is underway.
 766     *
 767     *  Subclasses should first call pkgAcquireStatus::Pulse(), then
 768     *  update their status output.  The download process is blocked
 769     *  while Pulse() is being called.
 770     *
 771     *  \return \b false if the user asked to cancel the whole Acquire process.
 772     *
 773     *  \see pkgAcquire::Run
 774     */
 775    virtual bool Pulse(pkgAcquire *Owner);
 776
 777    /** \brief Invoked when the Acquire process starts running. */
 778    virtual void Start();
 779
 780    /** \brief Invoked when the Acquire process stops running. */
 781    virtual void Stop();
 782
 783    /** \brief Initialize all counters to 0 and the time to the current time. */
 784    pkgAcquireStatus();
 785    virtual ~pkgAcquireStatus() {};
 786 };
 787                                                                         /*}}}*/
 788 /** @} */
 789
 790 #endif