Acquire system {{{

The Acquire system is responsible for retrieving files from local or remote URIs and postprocessing them (for instance, verifying their authenticity). More...

Files
file	acquire-item.h
file	acquire-method.h
file	acquire-worker.h
file	acquire.h

Classes
struct	DiffInfo
	Information about an index patch (aka diff). More...
class	IndexTarget
	Information about an index file. More...
class	OptionalIndexTarget
	Information about an optional index file. More...
class	OptionalSubIndexTarget
	Information about an subindex index file. More...
class	pkgAcqArchive
	An item that is responsible for fetching a package file. More...
class	pkgAcqDiffIndex
	An item that is responsible for fetching an index file of {{{ package list diffs and starting the package list's download. More...
class	pkgAcqFile
	Retrieve an arbitrary file to the current directory. More...
class	pkgAcqIndex
	An acquire item that is responsible for fetching an index {{{ file (e.g., Packages or Sources). More...
class	pkgAcqIndexDiffs
	An item that is responsible for fetching all the patches {{{ that need to be applied to a given package index file. More...
class	pkgAcqIndexTrans
	An acquire item that is responsible for fetching a {{{ translated index file. More...
class	pkgAcqMetaClearSig
	An item repsonsible for downloading clearsigned metaindexes {{{. More...
class	pkgAcqMetaIndex
	An item that is responsible for downloading the meta-index {{{ file (i.e., Release) itself and verifying its signature. More...
class	pkgAcqMetaSig
	An acquire item that downloads the detached signature {{{ of a meta-index (Release) file, then queues up the release file itself. More...
class	pkgAcqMethod
class	pkgAcqSubIndex
	An item that is responsible for fetching a SubIndex {{{. More...
class	pkgAcquire
	The core download scheduler. More...
class	pkgAcquire::Item
	Represents the process by which a pkgAcquire object should {{{ retrieve a file or a collection of files. More...
struct	pkgAcquire::ItemDesc
	Represents a single download source from which an item should be downloaded. More...
struct	pkgAcquire::MethodConfig
	Information about the properties of a single acquire method. More...
class	pkgAcquire::Queue
	A single download queue in a pkgAcquire object. More...
class	pkgAcquire::UriIterator
	Iterates over all the URIs being fetched by a pkgAcquire object. More...
class	pkgAcquire::Worker
	A fetch subprocess. More...
class	pkgAcquireStatus
	A monitor object for downloads controlled by the pkgAcquire class. More...
class	SubIndexTarget
	Information about an subindex index file. More...

Detailed Description

The Acquire system is responsible for retrieving files from local or remote URIs and postprocessing them (for instance, verifying their authenticity).

The core class in this system is pkgAcquire, which is responsible for managing the download queues during the download. There is at least one download queue for each supported protocol; protocols such as http may provide one queue per host.

Each file to download is represented by a subclass of pkgAcquire::Item. The files add themselves to the download queue(s) by providing their URI information to pkgAcquire::Item::QueueURI, which calls pkgAcquire::Enqueue.

Once the system is set up, the Run method will spawn subprocesses to handle the enqueued URIs; the scheduler will then take items from the queues and feed them into the handlers until the queues are empty.

Todo:

Acquire supports inserting an object into several queues at once, but it is not clear what its behavior in this case is, and no subclass of pkgAcquire::Item seems to actually use this capability.