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swh-merkle-dag.pdf
swh-merkle-dag.svg
MERKLE_DAG = swh-merkle-dag.pdf swh-merkle-dag.svg
BUILD_TARGETS =
BUILD_TARGETS += $(MERKLE_DAG)
all: $(BUILD_TARGETS)
%.svg: %.dia
inkscape -l $@ $<
%.pdf: %.dia
inkscape -A $@ $<
clean:
-rm -f $(BUILD_TARGETS)
File deleted
.. _swh-model:
Software Heritage - Data model
==============================
Implementation of the :ref:`data-model` to archive source code artifacts.
.. toctree::
:caption: Overview:
:titlesonly:
data-model
persistent-identifiers
cli
/apidoc/swh.model
.. _persistent-identifiers:
=================================================
SoftWare Heritage persistent IDentifiers (SWHIDs)
=================================================
**version 1.5, last modified 2020-05-14**
.. contents::
:local:
:depth: 2
Overview
========
You can point to objects present in the `Software Heritage
<https://www.softwareheritage.org/>`_ `archive
<https://archive.softwareheritage.org/>`_ by the means of **SoftWare Heritage
persistent IDentifiers**, or **SWHIDs** for short, that are guaranteed to
remain stable (persistent) over time. Their syntax, meaning, and usage is
described below. Note that they are identifiers and not URLs, even though
URL-based `resolvers`_ for SWHIDs are also available.
A SWHID consists of two separate parts, a mandatory *core identifier* that can
point to any software artifact (or "object") available in the Software Heritage
archive, and an optional list of *qualifiers* that allows to specify the
context where the object is meant to be seen and point to a subpart of the
object itself.
Objects come in different types:
* contents
* directories
* revisions
* releases
* snapshots
Each object is identified by an intrinsic, type-specific object identifier that
is embedded in its SWHID as described below. The intrinsic identifiers embedded
in SWHIDs are strong cryptographic hashes computed on the entire set of object
properties. Together, these identifiers form a `Merkle structure
<https://en.wikipedia.org/wiki/Merkle_tree>`_, specifically a Merkle `DAG
<https://en.wikipedia.org/wiki/Directed_acyclic_graph>`_.
See the :ref:`Software Heritage data model <data-model>` for an overview of
object types and how they are linked together. See
:py:mod:`swh.model.identifiers` for details on how the intrinsic identifiers
embedded in SWHIDs are computed.
The optional qualifiers are of two kinds:
* **context qualifiers:** carry information about the context where a given
object is meant to be seen. This is particularly important, as the same
object can be reached in the Merkle graph following different *paths*
starting from different nodes (or *anchors*), and it may have been retrieved
from different *origins*, that may evolve between different *visits*
* **fragment qualifiers:** allow to pinpoint specific subparts of an object
Syntax
======
Syntactically, SWHIDs are generated by the ``<identifier>`` entry point in the
following grammar:
.. code-block:: bnf
<identifier> ::= <identifier_core> [ <qualifiers> ] ;
<identifier_core> ::= "swh" ":" <scheme_version> ":" <object_type> ":" <object_id> ;
<scheme_version> ::= "1" ;
<object_type> ::=
"snp" (* snapshot *)
| "rel" (* release *)
| "rev" (* revision *)
| "dir" (* directory *)
| "cnt" (* content *)
;
<object_id> ::= 40 * <hex_digit> ; (* intrinsic object id, as hex-encoded SHA1 *)
<dec_digit> ::= "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
<hex_digit> ::= <dec_digit> | "a" | "b" | "c" | "d" | "e" | "f" ;
<qualifiers> := ";" <qualifier> [ <qualifiers> ] ;
<qualifier> ::=
<context_qualifier>
| <fragment_qualifier>
;
<context_qualifier> ::=
<origin_ctxt>
| <visit_ctxt>
| <anchor_ctxt>
| <path_ctxt>
;
<origin_ctxt> ::= "origin" "=" <url_escaped> ;
<visit_ctxt> ::= "visit" "=" <identifier_core> ;
<anchor_ctxt> ::= "anchor" "=" <identifier_core> ;
<path_ctxt> ::= "path" "=" <path_absolute_escaped> ;
<fragment_qualifier> ::= "lines" "=" <line_number> ["-" <line_number>] ;
<line_number> ::= <dec_digit> + ;
<url_escaped> ::= (* RFC 3987 IRI *)
<path_absolute_escaped> ::= (* RFC 3987 absolute path *)
Where:
- ``<path_absolute_escaped>`` is an ``<ipath-absolute>`` from `RFC 3987`_, and
- ``<url_escaped>`` is a `RFC 3987`_ IRI
in either case all occurrences of ``;`` (and ``%``, as required by the RFC)
have been percent-encoded (as ``%3B`` and ``%25`` respectively). Other
characters *can* be percent-encoded, e.g., to improve readability and/or
embeddability of SWHID in other contexts.
.. _RFC 3987: https://tools.ietf.org/html/rfc3987
Semantics
=========
Core identifiers
----------------
``:`` is used as separator between the logical parts of core identifiers. The
``swh`` prefix makes explicit that these identifiers are related to *SoftWare
Heritage*. ``1`` (``<scheme_version>``) is the current version of this
identifier *scheme*. Future editions will use higher version numbers, possibly
breaking backward compatibility, but without breaking the resolvability of
SWHIDs that conform to previous versions of the scheme.
A SWHID points to a single object, whose type is explicitly captured by
``<object_type>``:
* ``snp`` to **snapshots**,
* ``rel`` to **releases**,
* ``rev`` to **revisions**,
* ``dir`` to **directories**,
* ``cnt`` to **contents**.
The actual object pointed to is identified by the intrinsic identifier
``<object_id>``, which is a hex-encoded (using lowercase ASCII characters) SHA1
computed on the content and metadata of the object itself, as follows:
* for **snapshots**, intrinsic identifiers are computed as per
:py:func:`swh.model.identifiers.snapshot_identifier`
* for **releases**, as per
:py:func:`swh.model.identifiers.release_identifier`
that produces the same result as a git release hash
* for **revisions**, as per
:py:func:`swh.model.identifiers.revision_identifier`
that produces the same result as a git commit hash
* for **directories**, per
:py:func:`swh.model.identifiers.directory_identifier`
that produces the same result as a git tree hash
* for **contents**, the intrinsic identifier is the ``sha1_git`` hash returned by
:py:func:`swh.model.identifiers.content_identifier`, i.e., the SHA1 of a byte
sequence obtained by juxtaposing the ASCII string ``"blob"`` (without
quotes), a space, the length of the content as decimal digits, a NULL byte,
and the actual content of the file.
Qualifiers
----------
``;`` is used as separator between the core identifier and the optional
qualifiers, as well as between qualifiers. Each qualifier is specified as a
key/value pair, using ``=`` as a separator.
The following *context qualifiers* are available:
* **origin:** the *software origin* where an object has been found or observed
in the wild, as an URI;
* **visit:** the core identifier of a *snapshot* corresponding to a specific
*visit* of a repository containing the designated object;
* **anchor:** a *designated node* in the Merkle DAG relative to which a *path
to the object* is specified, as the core identifier of a directory, a
revision, a release or a snapshot;
* **path:** the *absolute file path*, from the *root directory* associated to
the *anchor node*, to the object; when the anchor denotes a directory or a
revision, and almost always when it's a release, the root directory is
uniquely determined; when the anchor denotes a snapshot, the root directory
is the one pointed to by ``HEAD`` (possibly indirectly), and undefined if
such a reference is missing;
The following *fragment qualifier* is available:
* **lines:** *line number(s)* of interest, usually within a content object
We recommend to equip identifiers meant to be shared with as many qualifiers as
possible. While qualifiers may be listed in any order, it is good practice to
present them in the order given above, i.e., ``origin``, ``visit``, ``anchor``,
``path``, ``lines``. Redundant information should be omitted: for example, if
the *visit* is present, and the *path* is relative to the snapshot indicated
there, then the *anchor* qualifier is superfluous; similarly, if the *path* is
empty, it may be omitted.
Interoperability
================
URI scheme
----------
The ``swh`` URI scheme is registered at IANA for SWHIDs. The present documents
constitutes the scheme specification for such URI scheme.
Git compatibility
-----------------
SWHIDs for contents, directories, revisions, and releases are, at present,
compatible with the `Git <https://git-scm.com/>`_ way of `computing identifiers
<https://git-scm.com/book/en/v2/Git-Internals-Git-Objects>`_ for its objects.
The ``<object_id>`` part of a SWHID for a content object is the Git blob
identifier of any file with the same content; for a revision it is the Git
commit identifier for the same revision, etc. This is not the case for
snapshot identifiers, as Git does not have a corresponding object type.
Note that Git compatibility is incidental and is not guaranteed to be
maintained in future versions of this scheme (or Git).
Examples
========
Core identifiers
----------------
* ``swh:1:cnt:94a9ed024d3859793618152ea559a168bbcbb5e2`` points to the content
of a file containing the full text of the GPL3 license
* ``swh:1:dir:d198bc9d7a6bcf6db04f476d29314f157507d505`` points to a directory
containing the source code of the Darktable photography application as it was
at some point on 4 May 2017
* ``swh:1:rev:309cf2674ee7a0749978cf8265ab91a60aea0f7d`` points to a commit in
the development history of Darktable, dated 16 January 2017, that added
undo/redo supports for masks
* ``swh:1:rel:22ece559cc7cc2364edc5e5593d63ae8bd229f9f`` points to Darktable
release 2.3.0, dated 24 December 2016
* ``swh:1:snp:c7c108084bc0bf3d81436bf980b46e98bd338453`` points to a snapshot
of the entire Darktable Git repository taken on 4 May 2017 from GitHub
Identifiers with qualifiers
---------------------------
* The following `SWHID
<https://archive.softwareheritage.org/swh:1:cnt:4d99d2d18326621ccdd70f5ea66c2e2ac236ad8b;origin=https://gitorious.org/ocamlp3l/ocamlp3l_cvs.git;visit=swh:1:snp:d7f1b9eb7ccb596c2622c4780febaa02549830f9;anchor=swh:1:rev:2db189928c94d62a3b4757b3eec68f0a4d4113f0;path=/Examples/SimpleFarm/simplefarm.ml;lines=9-15>`_
denotes the lines 9 to 15 of a file content that can be found at absolute
path ``/Examples/SimpleFarm/simplefarm.ml`` from the root directory of the
revision ``swh:1:rev:2db189928c94d62a3b4757b3eec68f0a4d4113f0`` that is
contained in the snapshot
``swh:1:snp:d7f1b9eb7ccb596c2622c4780febaa02549830f9`` taken from the origin
``https://gitorious.org/ocamlp3l/ocamlp3l_cvs.git``:
.. code-block:: url
swh:1:cnt:4d99d2d18326621ccdd70f5ea66c2e2ac236ad8b;
origin=https://gitorious.org/ocamlp3l/ocamlp3l_cvs.git;
visit=swh:1:snp:d7f1b9eb7ccb596c2622c4780febaa02549830f9;
anchor=swh:1:rev:2db189928c94d62a3b4757b3eec68f0a4d4113f0;
path=/Examples/SimpleFarm/simplefarm.ml;
lines=9-15
* Here is an example of a `SWHID
<https://archive.softwareheritage.org/swh:1:cnt:f10371aa7b8ccabca8479196d6cd640676fd4a04;origin=https://github.com/web-platform-tests/wpt;visit=swh:1:snp:b37d435721bbd450624165f334724e3585346499;anchor=swh:1:rev:259d0612af038d14f2cd889a14a3adb6c9e96d96;path=/html/semantics/document-metadata/the-meta-element/pragma-directives/attr-meta-http-equiv-refresh/support/x%3Burl=foo/>`_
with a file path that requires percent-escaping:
.. code-block:: url
swh:1:cnt:f10371aa7b8ccabca8479196d6cd640676fd4a04;
origin=https://github.com/web-platform-tests/wpt;
visit=swh:1:snp:b37d435721bbd450624165f334724e3585346499;
anchor=swh:1:rev:259d0612af038d14f2cd889a14a3adb6c9e96d96;
path=/html/semantics/document-metadata/the-meta-element/pragma-directives/attr-meta-http-equiv-refresh/support/x%3Burl=foo/
Implementation
==============
Computing
---------
An important property of any SWHID is that its core identifier is *intrinsic*:
it can be *computed from the object itself*, without having to rely on any
third party. An implementation of SWHID that allows to do so locally is the
`swh identify <https://docs.softwareheritage.org/devel/swh-model/cli.html>`_
tool, available from the `swh.model <https://pypi.org/project/swh.model/>`_
Python package under the GPL license.
SWHIDs are also automatically computed by Software Heritage for all archived
objects as part of its archival activity, and can be looked up via the project
`Web interface <https://archive.softwareheritage.org>`_.
This has various practical implications:
* when a software artifact is obtained from Software Heritage by resolving a
SWHID, it is straightforward to verify that it is exactly the intended one:
just compute the core identifier from the artefact itself, and check that it
is the same as the core identifier part of the SHWID
* the core identifier of a software artifact can be computed *before* its
archival on Software Heritage
Resolvers
---------
Software Heritage resolver
~~~~~~~~~~~~~~~~~~~~~~~~~~
SWHIDs can be resolved using the Software Heritage `Web interface
<https://archive.softwareheritage.org>`_. In particular, the **root endpoint**
``/`` can be given a SWHID and will lead to the browsing page of the
corresponding object, like this:
``https://archive.softwareheritage.org/<identifier>``.
A **dedicated** ``/resolve`` **endpoint** of the Software Heritage `Web API
<https://archive.softwareheritage.org/api/>`_ is also available to
programmatically resolve SWHIDs; see: :http:get:`/api/1/resolve/(swh_id)/`.
Examples:
* `<https://archive.softwareheritage.org/swh:1:cnt:94a9ed024d3859793618152ea559a168bbcbb5e2>`_
* `<https://archive.softwareheritage.org/swh:1:dir:d198bc9d7a6bcf6db04f476d29314f157507d505>`_
* `<https://archive.softwareheritage.org/api/1/resolve/swh:1:rev:309cf2674ee7a0749978cf8265ab91a60aea0f7d>`_
* `<https://archive.softwareheritage.org/api/1/resolve/swh:1:rel:22ece559cc7cc2364edc5e5593d63ae8bd229f9f>`_
* `<https://archive.softwareheritage.org/api/1/resolve/swh:1:snp:c7c108084bc0bf3d81436bf980b46e98bd338453>`_
* `<https://archive.softwareheritage.org/swh:1:cnt:4d99d2d18326621ccdd70f5ea66c2e2ac236ad8b;origin=https://gitorious.org/ocamlp3l/ocamlp3l_cvs.git;visit=swh:1:snp:d7f1b9eb7ccb596c2622c4780febaa02549830f9;anchor=swh:1:rev:2db189928c94d62a3b4757b3eec68f0a4d4113f0;path=/Examples/SimpleFarm/simplefarm.ml;lines=9-15>`_
* `<https://archive.softwareheritage.org/swh:1:cnt:f10371aa7b8ccabca8479196d6cd640676fd4a04;origin=https://github.com/web-platform-tests/wpt;visit=swh:1:snp:b37d435721bbd450624165f334724e3585346499;anchor=swh:1:rev:259d0612af038d14f2cd889a14a3adb6c9e96d96;path=/html/semantics/document-metadata/the-meta-element/pragma-directives/attr-meta-http-equiv-refresh/support/x%3Burl=foo/>`_
Third-party resolvers
~~~~~~~~~~~~~~~~~~~~~
The following **third party resolvers** support SWHID resolution:
* `Identifiers.org <https://identifiers.org>`_; see:
`<http://identifiers.org/swh/>`_ (registry identifier `MIR:00000655
<https://www.ebi.ac.uk/miriam/main/datatypes/MIR:00000655>`_).
* `Name-to-Thing (N2T) <https://n2t.net/>`_
Note that resolution via Identifiers.org currently only supports *core
identifiers* due to `syntactic incompatibilities with qualifiers
<http://identifiers.org/documentation#custom_requests>`_.
Examples:
* `<https://identifiers.org/swh:1:cnt:94a9ed024d3859793618152ea559a168bbcbb5e2>`_
* `<https://identifiers.org/swh:1:dir:d198bc9d7a6bcf6db04f476d29314f157507d505>`_
* `<https://identifiers.org/swh:1:rev:309cf2674ee7a0749978cf8265ab91a60aea0f7d>`_
* `<https://n2t.net/swh:1:rel:22ece559cc7cc2364edc5e5593d63ae8bd229f9f>`_
* `<https://n2t.net/swh:1:snp:c7c108084bc0bf3d81436bf980b46e98bd338453>`_
* `<https://n2t.net/swh:1:cnt:4d99d2d18326621ccdd70f5ea66c2e2ac236ad8b;origin=https://gitorious.org/ocamlp3l/ocamlp3l_cvs.git;visit=swh:1:snp:d7f1b9eb7ccb596c2622c4780febaa02549830f9;anchor=swh:1:rev:2db189928c94d62a3b4757b3eec68f0a4d4113f0;path=/Examples/SimpleFarm/simplefarm.ml;lines=9-15>`_
* `<https://n2t.net/swh:1:cnt:f10371aa7b8ccabca8479196d6cd640676fd4a04;origin=https://github.com/web-platform-tests/wpt;visit=swh:1:snp:b37d435721bbd450624165f334724e3585346499;anchor=swh:1:rev:259d0612af038d14f2cd889a14a3adb6c9e96d96;path=/html/semantics/document-metadata/the-meta-element/pragma-directives/attr-meta-http-equiv-refresh/support/x%3Burl=foo/>`_
References
==========
* Roberto Di Cosmo, Morane Gruenpeter, Stefano Zacchiroli. `Identifiers for
Digital Objects: the Case of Software Source Code Preservation
<https://hal.archives-ouvertes.fr/hal-01865790v4>`_. In Proceedings of `iPRES
2018 <https://ipres2018.org/>`_: 15th International Conference on Digital
Preservation, Boston, MA, USA, September 2018, 9 pages.
* Roberto Di Cosmo, Morane Gruenpeter, Stefano Zacchiroli. `Referencing Source
Code Artifacts: a Separate Concern in Software Citation
<https://arxiv.org/abs/2001.08647>`_. In Computing in Science and
Engineering, volume 22, issue 2, pages 33-43. ISSN 1521-9615,
IEEE. March 2020.
[mypy]
namespace_packages = True
warn_unused_ignores = True
# 3rd party libraries without stubs (yet)
[mypy-attrs_strict.*] # a bit sad, but...
ignore_missing_imports = True
[mypy-django.*] # false positive, only used my hypotesis' extras
ignore_missing_imports = True
[mypy-dulwich.*]
ignore_missing_imports = True
[mypy-iso8601.*]
ignore_missing_imports = True
[mypy-pkg_resources.*]
ignore_missing_imports = True
[mypy-pyblake2.*]
ignore_missing_imports = True
[mypy-pytest.*]
ignore_missing_imports = True
[pytest]
addopts = --doctest-modules
norecursedirs = docs
[flake8]
# E203: whitespaces before ':' <https://github.com/psf/black/issues/315>
# E231: missing whitespace after ','
# W503: line break before binary operator <https://github.com/psf/black/issues/52>
ignore = E203,E231,W503
max-line-length = 88
[egg_info]
tag_build =
tag_date = 0
Metadata-Version: 2.1
Name: swh.model
Version: 0.3.0
Summary: Software Heritage data model
Home-page: https://forge.softwareheritage.org/diffusion/DMOD/
Author: Software Heritage developers
Author-email: swh-devel@inria.fr
License: UNKNOWN
Project-URL: Bug Reports, https://forge.softwareheritage.org/maniphest
Project-URL: Funding, https://www.softwareheritage.org/donate
Project-URL: Source, https://forge.softwareheritage.org/source/swh-model
Project-URL: Documentation, https://docs.softwareheritage.org/devel/swh-model/
Description: swh-model
=========
Implementation of the Data model of the Software Heritage project, used to
archive source code artifacts.
This module defines the notion of Persistent Identifier (PID) and provides
tools to compute them:
```sh
$ swh-identify fork.c kmod.c sched/deadline.c
swh:1:cnt:2e391c754ae730bd2d8520c2ab497c403220c6e3 fork.c
swh:1:cnt:0277d1216f80ae1adeed84a686ed34c9b2931fc2 kmod.c
swh:1:cnt:57b939c81bce5d06fa587df8915f05affbe22b82 sched/deadline.c
$ swh-identify --no-filename /usr/src/linux/kernel/
swh:1:dir:f9f858a48d663b3809c9e2f336412717496202ab
```
Platform: UNKNOWN
Classifier: Programming Language :: Python :: 3
Classifier: Intended Audience :: Developers
Classifier: License :: OSI Approved :: GNU General Public License v3 (GPLv3)
Classifier: Operating System :: OS Independent
Classifier: Development Status :: 5 - Production/Stable
Requires-Python: >=3.7
Description-Content-Type: text/markdown
Provides-Extra: cli
Provides-Extra: testing
MANIFEST.in
Makefile
README.md
pyproject.toml
requirements-cli.txt
requirements-test.txt
requirements.txt
setup.cfg
setup.py
version.txt
swh/__init__.py
swh.model.egg-info/PKG-INFO
swh.model.egg-info/SOURCES.txt
swh.model.egg-info/dependency_links.txt
swh.model.egg-info/entry_points.txt
swh.model.egg-info/requires.txt
swh.model.egg-info/top_level.txt
swh/model/__init__.py
swh/model/cli.py
swh/model/exceptions.py
swh/model/from_disk.py
swh/model/hashutil.py
swh/model/hypothesis_strategies.py
swh/model/identifiers.py
swh/model/merkle.py
swh/model/model.py
swh/model/py.typed
swh/model/toposort.py
swh/model/validators.py
swh/model/fields/__init__.py
swh/model/fields/compound.py
swh/model/fields/hashes.py
swh/model/fields/simple.py
swh/model/tests/__init__.py
swh/model/tests/generate_testdata.py
swh/model/tests/generate_testdata_from_disk.py
swh/model/tests/test_cli.py
swh/model/tests/test_from_disk.py
swh/model/tests/test_generate_testdata.py
swh/model/tests/test_hashutil.py
swh/model/tests/test_hypothesis_strategies.py
swh/model/tests/test_identifiers.py
swh/model/tests/test_merkle.py
swh/model/tests/test_model.py
swh/model/tests/test_toposort.py
swh/model/tests/test_validators.py
swh/model/tests/data/dir-folders/sample-folder.tgz
swh/model/tests/data/repos/sample-repo.tgz
swh/model/tests/fields/__init__.py
swh/model/tests/fields/test_compound.py
swh/model/tests/fields/test_hashes.py
swh/model/tests/fields/test_simple.py
\ No newline at end of file
[console_scripts]
swh-identify=swh.model.cli:identify
[swh.cli.subcommands]
identify=swh.model.cli:identify
\ No newline at end of file
vcversioner
attrs
attrs_strict>=0.0.7
hypothesis
python-dateutil
iso8601
[:python_version < "3.6"]
pyblake2
[cli]
swh.core
Click
dulwich
[testing]
Click
dulwich
pytest
pytz
swh
[tox]
envlist=black,flake8,mypy,py3
[testenv]
extras =
testing
deps =
pytest-cov
commands =
pytest --cov={envsitepackagesdir}/swh/model \
{envsitepackagesdir}/swh/model \
--cov-branch {posargs}
[testenv:black]
skip_install = true
deps =
black
commands =
{envpython} -m black --check swh
[testenv:flake8]
skip_install = true
deps =
flake8
commands =
{envpython} -m flake8
[testenv:mypy]
extras =
testing
deps =
mypy
commands =
mypy swh
v0.3.0-0-g3d9f694
\ No newline at end of file