X-Git-Url: https://git.saurik.com/apt.git/blobdiff_plain/6db194289ece36e62cb8dab0aa178209b46c59f2..08fcf9628806af202e555bd02b3611e4e9a3d757:/doc/external-dependency-solver-protocol.txt diff --git a/doc/external-dependency-solver-protocol.txt b/doc/external-dependency-solver-protocol.txt index 7a124d8f9..452212602 100644 --- a/doc/external-dependency-solver-protocol.txt +++ b/doc/external-dependency-solver-protocol.txt @@ -1,10 +1,18 @@ -# APT External Dependency Solver Protocol (EDSP) - version 0.4 +# APT External Dependency Solver Protocol (EDSP) - version 0.5 This document describes the communication protocol between APT and external dependency solvers. The protocol is called APT EDSP, for "APT External Dependency Solver Protocol". +## Terminology + +In the following we use the term **architecture qualified package name** +(or *arch-qualified package names* for short) to refer to package +identifiers of the form "package:arch" where "package" is a package name +and "arch" a dpkg architecture. + + ## Components - **APT**: we know this one. @@ -50,17 +58,30 @@ configuration documentation for more, and more up to date, information. - **APT::Solver**: the name of the solver to be used for dependency solving. Defaults to `internal` +- **Dir::Bin::Solvers**: absolute path of the directory where to look for + external solvers. Defaults to `/usr/lib/apt/solvers`. + - **APT::Solver::Strict-Pinning**: whether pinning must be strictly respected (as the internal solver does) or can be slightly deviated from. Defaults to `yes`. -- **APT::Solver::NAME::Preferences** (where NAME is a solver name): - solver-specific user preference string used during dependency solving, - when the solver NAME is in use. Check solver-specific documentation - for what is supported here. Defaults to the empty string. +- **APT::Solver::Preferences**: user preference string used during + dependency solving by the requested solver. Check the documentation + of the solver you are using if and what is supported as a value here. + Defaults to the empty string. + +- **APT::Solver::RunAsUser**: if APT itself is run as root it will + change to this user before executing the solver. Defaults to the value + of APT::Sandbox::User, which itself defaults to `_apt`. Can be + disabled by set this option to `root`. + +The options **Strict-Pinning** and **Preferences** can also be set for +a specific solver only via **APT::Solver::NAME::Strict-Pinning** and +**APT::Solver::NAME::Preferences** respectively where `NAME` is the name +of the external solver this option should apply to. These options if set +override the generic options; for simplicity the documentation will +refer only to the generic options. -- **Dir::Bin::Solvers**: absolute path of the directory where to look for - external solvers. Defaults to `/usr/lib/apt/solvers`. ## Protocol @@ -110,39 +131,56 @@ Within a dependency solving scenario, a request represents the action on installed packages requested by the user. A request is a single Deb 822 stanza opened by a mandatory Request field -and followed by a mixture of action and preference fields. +and followed by a mixture of action, preference, and global +configuration fields. The value of the **Request:** field is a string describing the EDSP protocol which will be used to communicate. At present, the string must -be `EDSP 0.4`. +be `EDSP 0.5`. Request fields are mainly used to identify the beginning +of a request stanza; their actual values are otherwise not used by the +EDSP protocol. + +The following **configuration fields** are supported in request stanzas: -a unique request identifier, such as an -UUID. Request fields are mainly used to identify the beginning of a -request stanza; their actual values are otherwise not used by the EDSP -protocol. +- **Architecture:** (mandatory) The name of the *native* architecture on + the user machine (see also: `dpkg --print-architecture`) + +- **Architectures:** (optional, defaults to the native architecture) A + space separated list of *all* architectures known to APT (this is + roughly equivalent to the union of `dpkg --print-architecture` and + `dpkg --print-foreign-architectures`) The following **action fields** are supported in request stanzas: - **Install:** (optional, defaults to the empty string) A space - separated list of package names, with *no version attached*, to - install. This field denotes a list of packages that the user wants to - install, usually via an APT `install` request. + separated list of arch-qualified package names, with *no version + attached*, to install. This field denotes a list of packages that the + user wants to install, usually via an APT `install` request. - **Remove:** (optional, defaults to the empty string) Same syntax of Install. This field denotes a list of packages that the user wants to remove, usually via APT `remove` or `purge` requests. -- **Upgrade:** (optional, defaults to `no`). Allowed values: `yes`, +- **Upgrade-All:** (optional, defaults to `no`). Allowed values `yes`, `no`. When set to `yes`, an upgrade of all installed packages has been - requested, usually via an APT `upgrade` request. - -- **Dist-Upgrade:** (optional, defaults to `no`). Allowed values: `yes`, - `no`. Same as Upgrade, but for APT `dist-upgrade` requests. + requested, usually via an upgrade command like 'apt full-upgrade'. - **Autoremove:** (optional, defaults to `no`). Allowed values: `yes`, `no`. When set to `yes`, a clean up of unused automatically installed packages has been requested, usually via an APT `autoremove` request. +- **Upgrade:** (deprecated, optional, defaults to `no`). Allowed values: + `yes`, `no`. When set to `yes`, an upgrade of all installed packages + has been requested, usually via an APT `upgrade` request. A value of + `yes` is equivalent to the fields `Upgrade-All`, + `Forbid-New-Install`and `Forbid-Remove` all set to `yes`. + +- **Dist-Upgrade:** (deprecated, optional, defaults to `no`). Allowed + values: `yes`, `no`. Same as Upgrade, but for APT `dist-upgrade` + requests. A value of `yes` is equivalent to the field `Upgrade-All` + set to `yes` and the fields `Forbid-New-Install`and `Forbid-Remove` + set to `no`. + The following **preference fields** are supported in request stanzas: - **Strict-Pinning:** (optional, defaults to `yes`). Allowed values: @@ -154,8 +192,21 @@ The following **preference fields** are supported in request stanzas: field comes from the `APT::Solver::Strict-Pinning` configuration option. -- **Preferences:** a solver-specific optimization string, usually coming - from the `APT::Solver::Preferences` configuration option. +- **Forbid-New-Install:* (optional, defaults to `no`). Allowed values: + `yes`, `no`. When set to `yes` the resolver is forbidden to install + new packages in its returned solution. + +- **Forbid-Remove:* (optional, defaults to `no`). Allowed values: `yes`, + `no`. When set to `yes` the resolver is forbidden to remove currently + installed packages in its returned solution. + +- **Solver:** (optional, defaults to the empty string) a purely + informational string specifying to which solver this request was send + initially. + +- **Preferences:** (optional, defaults to the empty string) + a solver-specific optimization string, usually coming from the + `APT::Solver::Preferences` configuration option. #### Package universe @@ -193,7 +244,7 @@ field. The following fields are supported in package stanzas: - **APT-Candidate:** (optional, defaults to `no`). Allowed values: `yes`, `no`. When set to `yes`, the corresponding package is the APT candidate for installation among all available packages with the same - name. + name and architecture. - **APT-Automatic:** (optional, defaults to `no`). Allowed values: `yes`, `no`. When set to `yes`, the corresponding package is marked by @@ -201,6 +252,22 @@ field. The following fields are supported in package stanzas: should be removed by the solver only when the Autoremove action is requested (see Request section). +- **APT-Release:** (optional) The releases the package belongs to, according to + APT. The format of this field is multiline with one value per line and the + first line (the one containing the field name) empty. Each subsequent line + corresponds to one of the releases the package belongs to and looks like + this: `o=Debian,a=unstable,n=sid,l=Debian,c=main`. That is, each release line + is a comma-separated list of "key=value" pairs, each of which denotes a + Release file entry (Origin, Label, Codename, etc.) in the format of + APT_PREFERENCES(5). + +- **Source:** (optional) The name of the source package the binary + package this record is for was built from. + This field does NOT include the version of the source package unlike + the Source field in the dpkg database. The version is optionally + available in the **Source-Version:** field. + + ### Answer An answer from the external solver to APT is either a *solution* or an @@ -209,20 +276,20 @@ An answer from the external solver to APT is either a *solution* or an The following invariant on **exit codes** must hold true. When the external solver is *able to find a solution*, it will write the solution to standard output and then exit with an exit code of 0. When the -external solver is *unable to find a solution* (and s aware of that), it -will write an error to standard output and then exit with an exit code -of 0. An exit code other than 0 will be interpreted as a solver crash -with no meaningful error about dependency resolution to convey to the -user. +external solver is *unable to find a solution* (and is aware of that), +it will write an error to standard output and then exit with an exit +code of 0. An exit code other than 0 will be interpreted as a solver +crash with no meaningful error about dependency resolution to convey to +the user. #### Solution -A solution is a list of Deb 822 stanzas. Each of them could be an -install stanza (telling APT to install a specific package), a remove -stanza (telling APT to remove one), or an autoremove stanza (telling APT -about the *future* possibility of removing a package using the -Autoremove action). +A solution is a list of Deb 822 stanzas. Each of them could be an install +stanza (telling APT to install a specific new package or to upgrade or +downgrade a package to a specific version), a remove stanza (telling APT to +remove one), or an autoremove stanza (telling APT about the *future* +possibility of removing a package using the Autoremove action). An **install stanza** starts with an Install field and supports the following fields: @@ -244,6 +311,16 @@ this protocol makes no assumption on the fact that a subsequent invocation of an Autoremove action will actually remove the very same packages indicated by Autoremove stanzas in the former solution. +A package can't be installed in multiple versions at the same time, so +for each package there can at most one version be selected either for +installation or removal. This especially means that a solver is neither +allowed to represent package upgrades as a remove of the installed +version and the installation of another (the remove is implicit and must +be omitted from the solution) nor is it supported to revert previous +actions in the solution with later actions. APT is allowed to show +warnings and might even misbehave in earlier versions if a solver is +violating this assumption. + In terms of expressivity, install and remove stanzas can carry one single field each, as APT-IDs are enough to pinpoint packages to be installed/removed. Nonetheless, for protocol readability, it is