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diff --git a/doc/method.dbk b/doc/method.dbk new file mode 100644 index 0000000..ea49c5b --- /dev/null +++ b/doc/method.dbk @@ -0,0 +1,732 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" + "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [ +<!ENTITY % aptent SYSTEM "apt.ent"> %aptent; +<!ENTITY % aptverbatiment SYSTEM "apt-verbatim.ent"> %aptverbatiment; +<!ENTITY % aptvendor SYSTEM "apt-vendor.ent"> %aptvendor; +]> + +<book lang="en"> + +<title>APT Method Interface</title> + +<bookinfo> + +<authorgroup> + <author> + <personname>Jason Gunthorpe</personname><email>jgg@debian.org</email> + </author> +</authorgroup> + +<releaseinfo>Version &apt-product-version;</releaseinfo> + +<abstract> +<para> +This document describes the interface that APT uses to the archive access +methods. +</para> +</abstract> + +<copyright><year>1998</year><holder>Jason Gunthorpe</holder></copyright> + +<legalnotice> +<title>License Notice</title> +<para> +"APT" and this document are free software; you can redistribute them and/or +modify them 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. +</para> +<para> +For more details, on Debian systems, see the file +/usr/share/common-licenses/GPL for the full license. +</para> +</legalnotice> + +</bookinfo> + +<chapter id="ch1"><title>Introduction</title> + +<section id="s1.1"><title>General</title> +<para> +The APT method interface allows APT to acquire archive files (.deb), index +files (Packages, Release, Mirrors) and source files (.tar.gz, .diff). It is a +general, extensible system designed to satisfy all of these requirements: +</para> +<orderedlist numeration="arabic"> +<listitem> +<para> +Remote methods that download files from a distant site +</para> +</listitem> +<listitem> +<para> +Resume of aborted downloads +</para> +</listitem> +<listitem> +<para> +Progress reporting +</para> +</listitem> +<listitem> +<para> +If-Modified-Since (IMS) checking for index files +</para> +</listitem> +<listitem> +<para> +In-Line MD5 generation +</para> +</listitem> +<listitem> +<para> +No-copy in-filesystem methods +</para> +</listitem> +<listitem> +<para> +Multi-media methods (like CD's) +</para> +</listitem> +<listitem> +<para> +Dynamic source selection for failure recovery +</para> +</listitem> +<listitem> +<para> +User interaction for user/password requests and media swaps +</para> +</listitem> +<listitem> +<para> +Global configuration +</para> +</listitem> +</orderedlist> +<para> +Initial releases of APT (0.1.x) used a completely different method interface +that only supported the first 6 items. This new interface deals with the +remainder. +</para> +</section> + +<section id="s1.2"><title>Terms</title> +<para> +Several terms are used through out the document, they have specific meanings +which may not be immediately evident. To clarify they are summarized here. +</para> +<variablelist> +<varlistentry> +<term>source</term> +<listitem> +<para> +Refers to an item in source list. More specifically it is the broken down +item, that is each source maps to exactly one index file. Archive sources map +to Package files and Source Code sources map to Source files. +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>archive file</term> +<listitem> +<para> +Refers to a binary package archive (.deb, .rpm, etc). +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>source file</term> +<listitem> +<para> +Refers to one of the files making up the source code of a package. In debian +it is one of .diff.gz, .dsc. or .tar.gz. +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>URI</term> +<listitem> +<para> +Universal Resource Identifier (URI) is a super-set of the familiar URL +syntax used by web browsers. It consists of an access specification +followed by a specific location in that access space. The form is +<access>:<location>. Network addresses are given with the form +<access>://[<user>[:<pas>]@]hostname[:port]/<location>. +Some examples: +</para> +<screen> +file:/var/mirrors/debian/ +ftp://ftp.debian.org/debian +ftp://jgg:MooCow@localhost:21/debian +nfs://bigred/var/mirrors/debian +rsync://debian.midco.net/debian +cdrom:Debian 2.0r1 Disk 1/ +</screen> +</listitem> +</varlistentry> +<varlistentry> +<term>method</term> +<listitem> +<para> +There is a one to one mapping of URI access specifiers to methods. A method is +a program that knows how to handle a URI access type and operates according to +the specifications in this file. +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>method instance</term> +<listitem> +<para> +A specific running method. There can be more than one instance of each method +as APT is capable of concurrent method handling. +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>message</term> +<listitem> +<para> +A series of lines terminated by a blank line sent down one of the communication +lines. The first line should have the form xxx TAG where xxx are digits +forming the status code and TAG is an informational string +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>acquire</term> +<listitem> +<para> +The act of bring a URI into the local pathname space. This may simply be +verifying the existence of the URI or actually downloading it from a remote +site. +</para> +</listitem> +</varlistentry> +</variablelist> +</section> + +</chapter> + +<chapter id="ch2"><title>Specification</title> + +<section id="s2.1"><title>Overview</title> +<para> +All methods operate as a sub process of a main controlling parent. 3 FD's are +opened for use by the method allowing two way communication and emergency error +reporting. The FD's correspond to the well known unix FD's, stdin, stdout and +stderr. +</para> +<para> +Through operation of the method communication is done via http style plain +text. Specifically RFC-822 (like the Package file) fields are used to describe +items and a numeric-like header is used to indicate what is happening. Each of +these distinct communication messages should be sent quickly and without pause. +</para> +<para> +In some instances APT may pre-invoke a method to allow things like file URI's +to determine how many files are available locally. +</para> +</section> + +<section id="s2.2"><title>Message Overview</title> +<para> +The first line of each message is called the message header. The first 3 +digits (called the Status Code) have the usual meaning found in the http +protocol. 1xx is informational, 2xx is successful and 4xx is failure. The 6xx +series is used to specify things sent to the method. After the status code is +an informational string provided for visual debugging. +</para> +<itemizedlist> +<listitem> +<para> +100 Capabilities - Method capabilities +</para> +</listitem> +<listitem> +<para> +101 Log - General Logging +</para> +</listitem> +<listitem> +<para> +102 Status - Inter-URI status reporting (login progress) +</para> +</listitem> +<listitem> +<para> +200 URI Start - URI is starting acquire +</para> +</listitem> +<listitem> +<para> +201 URI Done - URI is finished acquire +</para> +</listitem> +<listitem> +<para> +351 Aux Request - Method requests an auxiliary file +</para> +</listitem> +<listitem> +<para> +400 URI Failure - URI has failed to acquire +</para> +</listitem> +<listitem> +<para> +401 General Failure - Method did not like something sent to it +</para> +</listitem> +<listitem> +<para> +402 Authorization Required - Method requires authorization to access the URI. +Authorization is User/Pass +</para> +</listitem> +<listitem> +<para> +403 Media Failure - Method requires a media change +</para> +</listitem> +<listitem> +<para> +600 URI Acquire - Request a URI be acquired +</para> +</listitem> +<listitem> +<para> +601 Configuration - Sends the configuration space +</para> +</listitem> +<listitem> +<para> +602 Authorization Credentials - Response to the 402 message +</para> +</listitem> +<listitem> +<para> +603 Media Changed - Response to the 403 message +</para> +</listitem> +</itemizedlist> +<para> +Only the 6xx series of status codes is sent TO the method. Furthermore the +method may not emit status codes in the 6xx range. The Codes 351, 402 and 403 +require that the method continue reading all other 6xx codes until the proper +600/602/603 code is received. This means the method must be capable of handling an +unlimited number of 600 messages. +</para> +<para> +The flow of messages starts with the method sending out a <emphasis>100 +Capabilities</emphasis> and APT sending out a <emphasis>601 +Configuration</emphasis>. After that APT begins sending <emphasis>600 URI +Acquire</emphasis> and the method sends out <emphasis>200 URI Start</emphasis>, +<emphasis>201 URI Done</emphasis> or <emphasis>400 URI Failure</emphasis>. No +synchronization is performed, it is expected that APT will send <emphasis>600 +URI Acquire</emphasis> messages at -any- time and that the method should queue +the messages. This allows methods like http to pipeline requests to the remote +server. It should be noted however that APT will buffer messages so it is not +necessary for the method to be constantly ready to receive them. +</para> +</section> + +<section id="s2.3"><title>Header Fields</title> +<para> +The following is a short index of the header fields that are supported +</para> +<variablelist> +<varlistentry> +<term>URI</term> +<listitem> +<para> +URI being described by the message +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>Filename</term> +<listitem> +<para> +Location in the filesystem +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>Last-Modified</term> +<listitem> +<para> +A time stamp in RFC1123 notation for use by IMS checks +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>IMS-Hit</term> +<listitem> +<para> +The already existing item is valid +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>Size</term> +<listitem> +<para> +Size of the file in bytes +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>Resume-Point</term> +<listitem> +<para> +Location that transfer was started +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>MD5-Hash</term> +<listitem> +<para> +Computed MD5 hash for the file +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>Message</term> +<listitem> +<para> +String indicating some displayable message +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>Media</term> +<listitem> +<para> +String indicating the media name required +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>Site</term> +<listitem> +<para> +String indicating the site authorization is required for +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>User</term> +<listitem> +<para> +Username for authorization +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>Password</term> +<listitem> +<para> +Password for authorization +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>Fail</term> +<listitem> +<para> +Operation failed +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>Drive</term> +<listitem> +<para> +Drive the media should be placed in +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>Config-Item</term> +<listitem> +<para> +A string of the form +<replaceable>item</replaceable>=<replaceable>value</replaceable> derived from +the APT configuration space. These may include method specific values and +general values not related to the method. It is up to the method to filter out +the ones it wants. +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>Single-Instance</term> +<listitem> +<para> +Requires that only one instance of the method be run This is a yes/no value. +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>Pipeline</term> +<listitem> +<para> +The method is capable of pipelining. +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>Local</term> +<listitem> +<para> +The method only returns Filename: fields. +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>Send-Config</term> +<listitem> +<para> +Send configuration to the method. +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>Needs-Cleanup</term> +<listitem> +<para> +The process is kept around while the files it returned are being used. This is +primarily intended for CD-ROM and File URIs that need to unmount filesystems. +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>Version</term> +<listitem> +<para> +Version string for the method +</para> +</listitem> +</varlistentry> +</variablelist> +<para> +This is a list of which headers each status code can use +</para> +<variablelist> +<varlistentry> +<term>100 Capabilities</term> +<listitem> +<para> +Displays the capabilities of the method. Methods should set the pipeline bit +if their underlying protocol supports pipelining. The only known method that +does support pipelining is http. Fields: Version, Single-Instance, Local-Only, +Pipeline, Send-Config, Needs-Cleanup, Removable, AuxRequests, Send-URI-Encoded +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>101 Log</term> +<listitem> +<para> +A log message may be printed to the screen if debugging is enabled. This is +only for debugging the method. Fields: Message +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>102 Status</term> +<listitem> +<para> +Message gives a progress indication for the method. It can be used to show +pre-transfer status for Internet type methods. Fields: Message +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>200 URI Start</term> +<listitem> +<para> +Indicates the URI is starting to be transferred. The URI is specified along +with stats about the file itself. Fields: URI, Size, Last-Modified, +Resume-Point +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>201 URI Done</term> +<listitem> +<para> +Indicates that a URI has completed being transferred. It is possible to +specify a <emphasis>201 URI Done</emphasis> without a <emphasis>URI +Start</emphasis> which would mean no data was transferred but the file is now +available. A Filename field is specified when the URI is directly available in +the local pathname space. APT will either directly use that file or copy it +into another location. It is possible to return Alt-* fields to indicate that +another possibility for the URI has been found in the local pathname space. +This is done if a decompressed version of a .gz file is found. Fields: URI, +Size, Last-Modified, Filename, MD5-Hash +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>351 Aux Request</term> +<listitem> +<para> +Indicates a request for an auxiliary file to be downloaded by the acquire system +(via another method) and made available for the requesting method. The requestor +will get a <emphasis>600 URI Acquire</emphasis> with the URI it requested and the +filename will either be an existing file if the request was success or if the +acquire failed for some reason the file will not exist. +Fields: URI (of the file causing the need for the auxiliary file), MaximumSize, +Aux-ShortDesc, Aux-Description, Aux-URI +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>400 URI Failure</term> +<listitem> +<para> +Indicates a fatal URI failure. The URI is not retrievable from this source. As +with <emphasis>201 URI Done</emphasis> <emphasis>200 URI Start</emphasis> is +not required to precede this message Fields: URI, Message +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>401 General Failure</term> +<listitem> +<para> +Indicates that some unspecific failure has occurred and the method is unable +to continue. The method should terminate after sending this message. It +is intended to check for invalid configuration options or other severe +conditions. Fields: Message +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>402 Authorization Required</term> +<listitem> +<para> +The method requires a Username and Password pair to continue. After sending +this message the method will expect APT to send a <emphasis>602 Authorization +Credentials</emphasis> message with the required information. It is possible +for a method to send this multiple times. Fields: Site +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>403 Media Failure</term> +<listitem> +<para> +A method that deals with multiple media requires that a new media be +inserted. The Media field contains the name of the media to be +inserted. Fields: Media, Drive +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>600 URI Acquire</term> +<listitem> +<para> +APT is requesting that a new URI be added to the acquire list. Last-Modified +has the time stamp of the currently cache file if applicable. Filename is the +name of the file that the acquired URI should be written to. Fields: URI, +Filename Last-Modified +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>601 Configuration</term> +<listitem> +<para> +APT is sending the configuration space to the method. A series of Config-Item +fields will be part of this message, each containing an entry from the +configuration space. Fields: Config-Item. +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>602 Authorization Credentials</term> +<listitem> +<para> +This is sent in response to a <emphasis>402 Authorization Required</emphasis> +message. It contains the entered username and password. Fields: Site, User, +Password +</para> +</listitem> +</varlistentry> +<varlistentry> +<term>603 Media Changed</term> +<listitem> +<para> +This is sent in response to a <emphasis>403 Media Failure</emphasis> +message. It indicates that the user has changed media and it is safe +to proceed. Fields: Media, Fail +</para> +</listitem> +</varlistentry> +</variablelist> +</section> + +<section id="s2.4"><title>Notes</title> +<para> +The methods supplied by the stock apt are: +</para> +<orderedlist numeration="arabic"> +<listitem> +<para> +cdrom - For Multi-Disc CD-ROMs +</para> +</listitem> +<listitem> +<para> +copy - (internal) For copying files around the filesystem +</para> +</listitem> +<listitem> +<para> +file - For local files +</para> +</listitem> +<listitem> +<para> +gzip - (internal) For decompression +</para> +</listitem> +<listitem> +<para> +http - For HTTP servers +</para> +</listitem> +</orderedlist> +<para> +The two internal methods, copy and gzip, are used by the acquire code to +parallelize and simplify the automatic decompression of package files as well as +copying package files around the file system. Both methods can be seen to act +the same except that one decompresses on the fly. APT uses them by generating +a copy URI that is formed identically to a file URI. The destination file is +send as normal. The method then takes the file specified by the URI and writes +it to the destination file. A typical set of operations may be: +</para> +<screen> +http://foo.com/Packages.gz -> /bar/Packages.gz +gzip:/bar/Packages.gz -> /bar/Packages.decomp +rename Packages.decomp to /final/Packages +</screen> +<para> +The http method implements a fully featured HTTP/1.1 client that supports +deep pipelining and reget. It works best when coupled with an apache 1.3 +server. The file method simply generates failures or success responses +with the filename field set to the proper location. The cdrom method acts +the same except that it checks that the mount point has a valid cdrom in +it. It does this by (effectively) computing a md5 hash of 'ls -l' on the +mountpoint. +</para> +</section> + +</chapter> + +</book> |