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    private:
  95    /** \brief FD of the Lock file we acquire in Setup (if any) */
  96    int LockFD;
  97    /** \brief dpointer placeholder (for later in case we need it) */
  98    void *d;
  99
 100    public:
 101
 102    class Item;
 103    class Queue;
 104    class Worker;
 105    struct MethodConfig;
 106    struct ItemDesc;
 107    friend class Item;
 108    friend class Queue;
 109
 110    typedef vector<Item *>::iterator ItemIterator;
 111    typedef vector<Item *>::const_iterator ItemCIterator;
 112
 113    protected:
 114
 115    /** \brief A list of items to download.
 116     *
 117     *  This is built monotonically as items are created and only
 118     *  emptied when the download shuts down.
 119     */
 120    vector<Item *> Items;
 121
 122    /** \brief The head of the list of active queues.
 123     *
 124     *  \todo why a hand-managed list of queues instead of std::list or
 125     *  std::set?
 126     */
 127    Queue *Queues;
 128
 129    /** \brief The head of the list of active workers.
 130     *
 131     *  \todo why a hand-managed list of workers instead of std::list
 132     *  or std::set?
 133     */
 134    Worker *Workers;
 135
 136    /** \brief The head of the list of acquire method configurations.
 137     *
 138     *  Each protocol (http, ftp, gzip, etc) via which files can be
 139     *  fetched can have a representation in this list.  The
 140     *  configuration data is filled in by parsing the 100 Capabilities
 141     *  string output by a method on startup (see
 142     *  pkgAcqMethod::pkgAcqMethod and pkgAcquire::GetConfig).
 143     *
 144     *  \todo why a hand-managed config dictionary instead of std::map?
 145     */
 146    MethodConfig *Configs;
 147
 148    /** \brief The progress indicator for this download. */
 149    pkgAcquireStatus *Log;
 150
 151    /** \brief The number of files which are to be fetched. */
 152    unsigned long ToFetch;
 153
 154    // Configurable parameters for the scheduler
 155
 156    /** \brief Represents the queuing strategy for remote URIs. */
 157    enum QueueStrategy {
 158      /** \brief Generate one queue for each protocol/host combination; downloads from
 159       *  multiple hosts can proceed in parallel.
 160       */
 161      QueueHost,
 162      /** \brief Generate a single queue for each protocol; serialize
 163       *  downloads from multiple hosts.
 164       */
 165      QueueAccess} QueueMode;
 166
 167    /** \brief If \b true, debugging information will be dumped to std::clog. */
 168    bool const Debug;
 169    /** \brief If \b true, a download is currently in progress. */
 170    bool Running;
 171
 172    /** \brief Add the given item to the list of items. */
 173    void Add(Item *Item);
 174
 175    /** \brief Remove the given item from the list of items. */
 176    void Remove(Item *Item);
 177
 178    /** \brief Add the given worker to the list of workers. */
 179    void Add(Worker *Work);
 180
 181    /** \brief Remove the given worker from the list of workers. */
 182    void Remove(Worker *Work);
 183
 184    /** \brief Insert the given fetch request into the appropriate queue.
 185     *
 186     *  \param Item The URI to download and the item to download it
 187     *  for.  Copied by value into the queue; no reference to Item is
 188     *  retained.
 189     */
 190    void Enqueue(ItemDesc &Item);
 191
 192    /** \brief Remove all fetch requests for this item from all queues. */
 193    void Dequeue(Item *Item);
 194
 195    /** \brief Determine the fetch method and queue of a URI.
 196     *
 197     *  \param URI The URI to fetch.
 198     *
 199     *  \param[out] Config A location in which to place the method via
 200     *  which the URI is to be fetched.
 201     *
 202     *  \return the string-name of the queue in which a fetch request
 203     *  for the given URI should be placed.
 204     */
 205    string QueueName(string URI,MethodConfig const *&Config);
 206
 207    /** \brief Build up the set of file descriptors upon which select() should
 208     *  block.
 209     *
 210     *  The default implementation inserts the file descriptors
 211     *  corresponding to active downloads.
 212     *
 213     *  \param[out] Fd The largest file descriptor in the generated sets.
 214     *
 215     *  \param[out] RSet The set of file descriptors that should be
 216     *  watched for input.
 217     *
 218     *  \param[out] WSet The set of file descriptors that should be
 219     *  watched for output.
 220     */
 221    virtual void SetFds(int &Fd,fd_set *RSet,fd_set *WSet);
 222
 223    /** Handle input from and output to file descriptors which select()
 224     *  has determined are ready.  The default implementation
 225     *  dispatches to all active downloads.
 226     *
 227     *  \param RSet The set of file descriptors that are ready for
 228     *  input.
 229     *
 230     *  \param WSet The set of file descriptors that are ready for
 231     *  output.
 232     */
 233    virtual void RunFds(fd_set *RSet,fd_set *WSet);
 234
 235    /** \brief Check for idle queues with ready-to-fetch items.
 236     *
 237     *  Called by pkgAcquire::Queue::Done each time an item is dequeued
 238     *  but remains on some queues; i.e., another queue should start
 239     *  fetching it.
 240     */
 241    void Bump();
 242
 243    public:
 244
 245    /** \brief Retrieve information about a fetch method by name.
 246     *
 247     *  \param Access The name of the method to look up.
 248     *
 249     *  \return the method whose name is Access, or \b NULL if no such method exists.
 250     */
 251    MethodConfig *GetConfig(string Access);
 252
 253    /** \brief Provides information on how a download terminated. */
 254    enum RunResult {
 255      /** \brief All files were fetched successfully. */
 256      Continue,
 257
 258      /** \brief Some files failed to download. */
 259      Failed,
 260
 261      /** \brief The download was cancelled by the user (i.e., #Log's
 262       *  pkgAcquireStatus::Pulse() method returned \b false).
 263       */
 264      Cancelled};
 265
 266    /** \brief Download all the items that have been Add()ed to this
 267     *  download process.
 268     *
 269     *  This method will block until the download completes, invoking
 270     *  methods on #Log to report on the progress of the download.
 271     *
 272     *  \param PulseInterval The method pkgAcquireStatus::Pulse will be
 273     *  invoked on #Log at intervals of PulseInterval milliseconds.
 274     *
 275     *  \return the result of the download.
 276     */
 277    RunResult Run(int PulseInterval=500000);
 278
 279    /** \brief Remove all items from this download process, terminate
 280     *  all download workers, and empty all queues.
 281     */
 282    void Shutdown();
 283
 284    /** \brief Get the first #Worker object.
 285     *
 286     *  \return the first active worker in this download process.
 287     */
 288    inline Worker *WorkersBegin() {return Workers;};
 289
 290    /** \brief Advance to the next #Worker object.
 291     *
 292     *  \return the worker immediately following I, or \b NULL if none
 293     *  exists.
 294     */
 295    Worker *WorkerStep(Worker *I);
 296
 297    /** \brief Get the head of the list of items. */
 298    inline ItemIterator ItemsBegin() {return Items.begin();};
 299
 300    /** \brief Get the end iterator of the list of items. */
 301    inline ItemIterator ItemsEnd() {return Items.end();};
 302
 303    // Iterate over queued Item URIs
 304    class UriIterator;
 305    /** \brief Get the head of the list of enqueued item URIs.
 306     *
 307     *  This iterator will step over every element of every active
 308     *  queue.
 309     */
 310    UriIterator UriBegin();
 311    /** \brief Get the end iterator of the list of enqueued item URIs. */
 312    UriIterator UriEnd();
 313
 314    /** Deletes each entry in the given directory that is not being
 315     *  downloaded by this object.  For instance, when downloading new
 316     *  list files, calling Clean() will delete the old ones.
 317     *
 318     *  \param Dir The directory to be cleaned out.
 319     *
 320     *  \return \b true if the directory exists and is readable.
 321     */
 322    bool Clean(string Dir);
 323
 324    /** \return the total size in bytes of all the items included in
 325     *  this download.
 326     */
 327    unsigned long long TotalNeeded();
 328
 329    /** \return the size in bytes of all non-local items included in
 330     *  this download.
 331     */
 332    unsigned long long FetchNeeded();
 333
 334    /** \return the amount of data to be fetched that is already
 335     *  present on the filesystem.
 336     */
 337    unsigned long long PartialPresent();
 338
 339    /** \brief Delayed constructor
 340     *
 341     *  \param Progress indicator associated with this download or
 342     *  \b NULL for none.  This object is not owned by the
 343     *  download process and will not be deleted when the pkgAcquire
 344     *  object is destroyed.  Naturally, it should live for at least as
 345     *  long as the pkgAcquire object does.
 346     *  \param Lock defines a lock file that should be acquired to ensure
 347     *  only one Acquire class is in action at the time or an empty string
 348     *  if no lock file should be used.
 349     */
 350    bool Setup(pkgAcquireStatus *Progress = NULL, string const &Lock = "");
 351
 352    /** \brief Construct a new pkgAcquire. */
 353    pkgAcquire(pkgAcquireStatus *Log) __deprecated;
 354    pkgAcquire();
 355
 356    /** \brief Destroy this pkgAcquire object.
 357     *
 358     *  Destroys all queue, method, and item objects associated with
 359     *  this download.
 360     */
 361    virtual ~pkgAcquire();
 362
 363 };
 364
 365 /** \brief Represents a single download source from which an item
 366  *  should be downloaded.
 367  *
 368  *  An item may have several assocated ItemDescs over its lifetime.
 369  */
 370 struct pkgAcquire::ItemDesc : public WeakPointable
 371 {
 372    /** \brief The URI from which to download this item. */
 373    string URI;
 374    /** brief A description of this item. */
 375    string Description;
 376    /** brief A shorter description of this item. */
 377    string ShortDesc;
 378    /** brief The underlying item which is to be downloaded. */
 379    Item *Owner;
 380 };
 381                                                                         /*}}}*/
 382 /** \brief A single download queue in a pkgAcquire object.              {{{
 383  *
 384  *  \todo Why so many protected values?
 385  */
 386 class pkgAcquire::Queue
 387 {
 388    friend class pkgAcquire;
 389    friend class pkgAcquire::UriIterator;
 390    friend class pkgAcquire::Worker;
 391
 392    /** \brief dpointer placeholder (for later in case we need it) */
 393    void *d;
 394
 395    /** \brief The next queue in the pkgAcquire object's list of queues. */
 396    Queue *Next;
 397
 398    protected:
 399
 400    /** \brief A single item placed in this queue. */
 401    struct QItem : pkgAcquire::ItemDesc
 402    {
 403       /** \brief The next item in the queue. */
 404       QItem *Next;
 405       /** \brief The worker associated with this item, if any. */
 406       pkgAcquire::Worker *Worker;
 407
 408       /** \brief Assign the ItemDesc portion of this QItem from
 409        *  another ItemDesc
 410        */
 411       void operator =(pkgAcquire::ItemDesc const &I)
 412       {
 413          URI = I.URI;
 414          Description = I.Description;
 415          ShortDesc = I.ShortDesc;
 416          Owner = I.Owner;
 417       };
 418    };
 419
 420    /** \brief The name of this queue. */
 421    string Name;
 422
 423    /** \brief The head of the list of items contained in this queue.
 424     *
 425     *  \todo why a by-hand list instead of an STL structure?
 426     */
 427    QItem *Items;
 428
 429    /** \brief The head of the list of workers associated with this queue.
 430     *
 431     *  \todo This is plural because support exists in Queue for
 432     *  multiple workers.  However, it does not appear that there is
 433     *  any way to actually associate more than one worker with a
 434     *  queue.
 435     *
 436     *  \todo Why not just use a std::set?
 437     */
 438    pkgAcquire::Worker *Workers;
 439
 440    /** \brief the download scheduler with which this queue is associated. */
 441    pkgAcquire *Owner;
 442
 443    /** \brief The number of entries in this queue that are currently
 444     *  being downloaded.
 445     */
 446    signed long PipeDepth;
 447
 448    /** \brief The maximum number of entries that this queue will
 449     *  attempt to download at once.
 450     */
 451    unsigned long MaxPipeDepth;
 452
 453    public:
 454
 455    /** \brief Insert the given fetch request into this queue.
 456     *
 457     *  \return \b true if the queuing was successful. May return
 458     *  \b false if the Item is already in the queue
 459     */
 460    bool Enqueue(ItemDesc &Item);
 461
 462    /** \brief Remove all fetch requests for the given item from this queue.
 463     *
 464     *  \return \b true if at least one request was removed from the queue.
 465     */
 466    bool Dequeue(Item *Owner);
 467
 468    /** \brief Locate an item in this queue.
 469     *
 470     *  \param URI A URI to match against.
 471     *  \param Owner A pkgAcquire::Worker to match against.
 472     *
 473     *  \return the first item in the queue whose URI is #URI and that
 474     *  is being downloaded by #Owner.
 475     */
 476    QItem *FindItem(string URI,pkgAcquire::Worker *Owner);
 477
 478    /** Presumably this should start downloading an item?
 479     *
 480     *  \todo Unimplemented.  Implement it or remove?
 481     */
 482    bool ItemStart(QItem *Itm,unsigned long long Size);
 483
 484    /** \brief Remove the given item from this queue and set its state
 485     *  to pkgAcquire::Item::StatDone.
 486     *
 487     *  If this is the only queue containing the item, the item is also
 488     *  removed from the main queue by calling pkgAcquire::Dequeue.
 489     *
 490     *  \param Itm The item to remove.
 491     *
 492     *  \return \b true if no errors are encountered.
 493     */
 494    bool ItemDone(QItem *Itm);
 495
 496    /** \brief Start the worker process associated with this queue.
 497     *
 498     *  If a worker process is already associated with this queue,
 499     *  this is equivalent to calling Cycle().
 500     *
 501     *  \return \b true if the startup was successful.
 502     */
 503    bool Startup();
 504
 505    /** \brief Shut down the worker process associated with this queue.
 506     *
 507     *  \param Final If \b true, then the process is stopped unconditionally.
 508     *               Otherwise, it is only stopped if it does not need cleanup
 509     *               as indicated by the pkgAcqMethod::NeedsCleanup member of
 510     *               its configuration.
 511     *
 512     *  \return \b true.
 513     */
 514    bool Shutdown(bool Final);
 515
 516    /** \brief Send idle items to the worker process.
 517     *
 518     *  Fills up the pipeline by inserting idle items into the worker's queue.
 519     */
 520    bool Cycle();
 521
 522    /** \brief Check for items that could be enqueued.
 523     *
 524     *  Call this after an item placed in multiple queues has gone from
 525     *  the pkgAcquire::Item::StatFetching state to the
 526     *  pkgAcquire::Item::StatIdle state, to possibly refill an empty queue.
 527     *  This is an alias for Cycle().
 528     *
 529     *  \todo Why both this and Cycle()?  Are they expected to be
 530     *  different someday?
 531     */
 532    void Bump();
 533
 534    /** \brief Create a new Queue.
 535     *
 536     *  \param Name The name of the new queue.
 537     *  \param Owner The download process that owns the new queue.
 538     */
 539    Queue(string Name,pkgAcquire *Owner);
 540
 541    /** Shut down all the worker processes associated with this queue
 542     *  and empty the queue.
 543     */
 544    virtual ~Queue();
 545 };
 546                                                                         /*}}}*/
 547 /** \brief Iterates over all the URIs being fetched by a pkgAcquire object.     {{{*/
 548 class pkgAcquire::UriIterator
 549 {
 550    /** \brief dpointer placeholder (for later in case we need it) */
 551    void *d;
 552
 553    /** The next queue to iterate over. */
 554    pkgAcquire::Queue *CurQ;
 555    /** The item that we currently point at. */
 556    pkgAcquire::Queue::QItem *CurItem;
 557
 558    public:
 559
 560    inline void operator ++() {operator ++(0);};
 561
 562    void operator ++(int)
 563    {
 564       CurItem = CurItem->Next;
 565       while (CurItem == 0 && CurQ != 0)
 566       {
 567          CurItem = CurQ->Items;
 568          CurQ = CurQ->Next;
 569       }
 570    };
 571
 572    inline pkgAcquire::ItemDesc const *operator ->() const {return CurItem;};
 573    inline bool operator !=(UriIterator const &rhs) const {return rhs.CurQ != CurQ || rhs.CurItem != CurItem;};
 574    inline bool operator ==(UriIterator const &rhs) const {return rhs.CurQ == CurQ && rhs.CurItem == CurItem;};
 575
 576    /** \brief Create a new UriIterator.
 577     *
 578     *  \param Q The queue over which this UriIterator should iterate.
 579     */
 580    UriIterator(pkgAcquire::Queue *Q) : CurQ(Q), CurItem(0)
 581    {
 582       while (CurItem == 0 && CurQ != 0)
 583       {
 584          CurItem = CurQ->Items;
 585          CurQ = CurQ->Next;
 586       }
 587    }
 588    virtual ~UriIterator() {};
 589 };
 590                                                                         /*}}}*/
 591 /** \brief Information about the properties of a single acquire method. {{{*/
 592 struct pkgAcquire::MethodConfig
 593 {
 594    /** \brief dpointer placeholder (for later in case we need it) */
 595    void *d;
 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    /* \brief Destructor, empty currently */
 647    virtual ~MethodConfig() {};
 648 };
 649                                                                         /*}}}*/
 650 /** \brief A monitor object for downloads controlled by the pkgAcquire class.   {{{
 651  *
 652  *  \todo Why protected members?
 653  *
 654  *  \todo Should the double members be uint64_t?
 655  */
 656 class pkgAcquireStatus
 657 {
 658    /** \brief dpointer placeholder (for later in case we need it) */
 659    void *d;
 660
 661    protected:
 662
 663    /** \brief The last time at which this monitor object was updated. */
 664    struct timeval Time;
 665
 666    /** \brief The time at which the download started. */
 667    struct timeval StartTime;
 668
 669    /** \brief The number of bytes fetched as of the previous call to
 670     *  pkgAcquireStatus::Pulse, including local items.
 671     */
 672    double LastBytes;
 673
 674    /** \brief The current rate of download as of the most recent call
 675     *  to pkgAcquireStatus::Pulse, in bytes per second.
 676     */
 677    double CurrentCPS;
 678
 679    /** \brief The number of bytes fetched as of the most recent call
 680     *  to pkgAcquireStatus::Pulse, including local items.
 681     */
 682    double CurrentBytes;
 683
 684    /** \brief The total number of bytes that need to be fetched.
 685     *
 686     *  \warning This member is inaccurate, as new items might be
 687     *  enqueued while the download is in progress!
 688     */
 689    double TotalBytes;
 690
 691    /** \brief The total number of bytes accounted for by items that
 692     *  were successfully fetched.
 693     */
 694    double FetchedBytes;
 695
 696    /** \brief The amount of time that has elapsed since the download
 697     *   started.
 698     */
 699    unsigned long ElapsedTime;
 700
 701    /** \brief The total number of items that need to be fetched.
 702     *
 703     *  \warning This member is inaccurate, as new items might be
 704     *  enqueued while the download is in progress!
 705     */
 706    unsigned long TotalItems;
 707
 708    /** \brief The number of items that have been successfully downloaded. */
 709    unsigned long CurrentItems;
 710
 711    public:
 712
 713    /** \brief If \b true, the download scheduler should call Pulse()
 714     *  at the next available opportunity.
 715     */
 716    bool Update;
 717
 718    /** \brief If \b true, extra Pulse() invocations will be performed.
 719     *
 720     *  With this option set, Pulse() will be called every time that a
 721     *  download item starts downloading, finishes downloading, or
 722     *  terminates with an error.
 723     */
 724    bool MorePulses;
 725
 726    /** \brief Invoked when a local or remote file has been completely fetched.
 727     *
 728     *  \param Size The size of the file fetched.
 729     *
 730     *  \param ResumePoint How much of the file was already fetched.
 731     */
 732    virtual void Fetched(unsigned long long Size,unsigned long long ResumePoint);
 733
 734    /** \brief Invoked when the user should be prompted to change the
 735     *         inserted removable media.
 736     *
 737     *  This method should not return until the user has confirmed to
 738     *  the user interface that the media change is complete.
 739     *
 740     *  \param Media The name of the media type that should be changed.
 741     *
 742     *  \param Drive The identifying name of the drive whose media
 743     *               should be changed.
 744     *
 745     *  \return \b true if the user confirms the media change, \b
 746     *  false if it is cancelled.
 747     *
 748     *  \todo This is a horrible blocking monster; it should be CPSed
 749     *  with prejudice.
 750     */
 751    virtual bool MediaChange(string Media,string Drive) = 0;
 752
 753    /** \brief Invoked when an item is confirmed to be up-to-date.
 754
 755     * For instance, when an HTTP download is informed that the file on
 756     * the server was not modified.
 757     */
 758    virtual void IMSHit(pkgAcquire::ItemDesc &/*Itm*/) {};
 759
 760    /** \brief Invoked when some of an item's data is fetched. */
 761    virtual void Fetch(pkgAcquire::ItemDesc &/*Itm*/) {};
 762
 763    /** \brief Invoked when an item is successfully and completely fetched. */
 764    virtual void Done(pkgAcquire::ItemDesc &/*Itm*/) {};
 765
 766    /** \brief Invoked when the process of fetching an item encounters
 767     *  a fatal error.
 768     */
 769    virtual void Fail(pkgAcquire::ItemDesc &/*Itm*/) {};
 770
 771    /** \brief Periodically invoked while the Acquire process is underway.
 772     *
 773     *  Subclasses should first call pkgAcquireStatus::Pulse(), then
 774     *  update their status output.  The download process is blocked
 775     *  while Pulse() is being called.
 776     *
 777     *  \return \b false if the user asked to cancel the whole Acquire process.
 778     *
 779     *  \see pkgAcquire::Run
 780     */
 781    virtual bool Pulse(pkgAcquire *Owner);
 782
 783    /** \brief Invoked when the Acquire process starts running. */
 784    virtual void Start();
 785
 786    /** \brief Invoked when the Acquire process stops running. */
 787    virtual void Stop();
 788
 789    /** \brief Initialize all counters to 0 and the time to the current time. */
 790    pkgAcquireStatus();
 791    virtual ~pkgAcquireStatus() {};
 792 };
 793                                                                         /*}}}*/
 794 /** @} */
 795
 796 #endif