swh.model.identifiers module

swh.model.identifiers.identifier_to_bytes(identifier)[source]

Convert a text identifier to bytes.

Parameters

identifier – an identifier, either a 40-char hexadecimal string or a bytes object of length 20

Returns

The length 20 bytestring corresponding to the given identifier

Raises

ValueError – if the identifier is of an unexpected type or length.

swh.model.identifiers.identifier_to_str(identifier)[source]

Convert an identifier to an hexadecimal string.

Parameters

identifier – an identifier, either a 40-char hexadecimal string or a bytes object of length 20

Returns

The length 40 string corresponding to the given identifier, hex encoded

Raises

ValueError – if the identifier is of an unexpected type or length.

swh.model.identifiers.content_identifier(content)[source]

Return the intrinsic identifier for a content.

A content’s identifier is the sha1, sha1_git and sha256 checksums of its data.

Parameters

content – a content conforming to the Software Heritage schema

Returns

A dictionary with all the hashes for the data

Raises

KeyError – if the content doesn’t have a data member.

swh.model.identifiers.directory_entry_sort_key(entry)[source]

The sorting key for tree entries

swh.model.identifiers.escape_newlines(snippet)[source]

Escape the newlines present in snippet according to git rules.

New lines in git manifests are escaped by indenting the next line by one space.

swh.model.identifiers.directory_identifier(directory)[source]

Return the intrinsic identifier for a directory.

A directory’s identifier is the tree sha1 à la git of a directory listing, using the following algorithm, which is equivalent to the git algorithm for trees:

  1. Entries of the directory are sorted using the name (or the name with ‘/’ appended for directory entries) as key, in bytes order.

  2. For each entry of the directory, the following bytes are output:

  • the octal representation of the permissions for the entry (stored in the ‘perms’ member), which is a representation of the entry type:

    • b’100644’ (int 33188) for files

    • b’100755’ (int 33261) for executable files

    • b’120000’ (int 40960) for symbolic links

    • b’40000’ (int 16384) for directories

    • b’160000’ (int 57344) for references to revisions

  • an ascii space (b’ ‘)

  • the entry’s name (as raw bytes), stored in the ‘name’ member

  • a null byte (b’')

  • the 20 byte long identifier of the object pointed at by the entry, stored in the ‘target’ member:

    • for files or executable files: their blob sha1_git

    • for symbolic links: the blob sha1_git of a file containing the link destination

    • for directories: their intrinsic identifier

    • for revisions: their intrinsic identifier

(Note that there is no separator between entries)

swh.model.identifiers.format_date(date)[source]

Convert a date object into an UTC timestamp encoded as ascii bytes.

Git stores timestamps as an integer number of seconds since the UNIX epoch.

However, Software Heritage stores timestamps as an integer number of microseconds (postgres type “datetime with timezone”).

Therefore, we print timestamps with no microseconds as integers, and timestamps with microseconds as floating point values. We elide the trailing zeroes from microsecond values, to “future-proof” our representation if we ever need more precision in timestamps.

swh.model.identifiers.format_offset(offset, negative_utc=None)[source]

Convert an integer number of minutes into an offset representation.

The offset representation is [+-]hhmm where:

  • hh is the number of hours;

  • mm is the number of minutes.

A null offset is represented as +0000.

swh.model.identifiers.normalize_timestamp(time_representation)[source]

Normalize a time representation for processing by Software Heritage

This function supports a numeric timestamp (representing a number of seconds since the UNIX epoch, 1970-01-01 at 00:00 UTC), a datetime.datetime object (with timezone information), or a normalized Software Heritage time representation (idempotency).

Parameters

time_representation – the representation of a timestamp

Returns

a normalized dictionary with three keys:

  • timestamp: a dict with two optional keys:

    • seconds: the integral number of seconds since the UNIX epoch

    • microseconds: the integral number of microseconds

  • offset: the timezone offset as a number of minutes relative to UTC

  • negative_utc: a boolean representing whether the offset is -0000 when offset = 0.

Return type

dict

swh.model.identifiers.format_author(author)[source]

Format the specification of an author.

An author is either a byte string (passed unchanged), or a dict with three keys, fullname, name and email.

If the fullname exists, return it; if it doesn’t, we construct a fullname using the following heuristics: if the name value is None, we return the email in angle brackets, else, we return the name, a space, and the email in angle brackets.

swh.model.identifiers.format_manifest(headers: Iterable[Tuple[bytes, bytes]], message: Optional[bytes] = None) → bytes[source]

Format a manifest comprised of a sequence of headers and an optional message.

The manifest format, compatible with the git format for tag and commit objects, is as follows:

  • for each key, value in headers, emit:

    • the key, literally

    • an ascii space (\x20)

    • the value, with newlines escaped using escape_newlines(),

    • an ascii newline (\x0a)

  • if the message is not None, emit:

    • an ascii newline (\x0a)

    • the message, literally

Parameters

  • headers – a sequence of key/value headers stored in the manifest;

  • message – an optional message used to trail the manifest.

Returns

the formatted manifest as bytes

swh.model.identifiers.hash_manifest(type: str, headers: Iterable[Tuple[bytes, bytes]], message: Optional[bytes] = None)[source]

Hash the manifest of an object of type type, comprised of a sequence of headers and an optional message.

Before hashing, the manifest is serialized with the format_manifest() function.

We then use the git “salted sha1” (swh.model.hashutil.hash_git_data()) with the given type to hash the manifest.

Parameters

  • type – the type of object for which we’re computing a manifest (e.g. “tag”, “commit”, …)

  • headers – a sequence of key/value headers stored in the manifest;

  • message – an optional message used to trail the manifest.

swh.model.identifiers.format_author_data(author, date_offset) → bytes[source]

Format authorship data according to git standards.

Git authorship data has two components:

  • an author specification, usually a name and email, but in practice an arbitrary bytestring

  • optionally, a timestamp with a UTC offset specification

The authorship data is formatted thus:

`name and email`[ `timestamp` `utc_offset`]

The timestamp is encoded as a (decimal) number of seconds since the UNIX epoch (1970-01-01 at 00:00 UTC). As an extension to the git format, we support fractional timestamps, using a dot as the separator for the decimal part.

The utc offset is a number of minutes encoded as ‘[+-]HHMM’. Note that some tools can pass a negative offset corresponding to the UTC timezone (‘-0000’), which is valid and is encoded as such.

Parameters

  • author – an author specification (dict with two bytes values: name and email, or byte value)

  • date_offset – a normalized date/time representation as returned by normalize_timestamp().

Returns

the byte string containing the authorship data

swh.model.identifiers.revision_identifier(revision)[source]

Return the intrinsic identifier for a revision.

The fields used for the revision identifier computation are:

  • directory

  • parents

  • author

  • author_date

  • committer

  • committer_date

  • extra_headers or metadata -> extra_headers

  • message

A revision’s identifier is the ‘git’-checksum of a commit manifest constructed as follows (newlines are a single ASCII newline character):

tree <directory identifier>
[for each parent in parents]
parent <parent identifier>
[end for each parents]
author <author> <author_date>
committer <committer> <committer_date>
[for each key, value in extra_headers]
<key> <encoded value>
[end for each extra_headers]

<message>

The directory identifier is the ascii representation of its hexadecimal encoding.

Author and committer are formatted with the format_author() function. Dates are formatted with the format_offset() function.

Extra headers are an ordered list of [key, value] pairs. Keys are strings and get encoded to utf-8 for identifier computation. Values are either byte strings, unicode strings (that get encoded to utf-8), or integers (that get encoded to their utf-8 decimal representation).

Multiline extra header values are escaped by indenting the continuation lines with one ascii space.

If the message is None, the manifest ends with the last header. Else, the message is appended to the headers after an empty line.

The checksum of the full manifest is computed using the ‘commit’ git object type.

swh.model.identifiers.target_type_to_git(target_type)[source]

Convert a software heritage target type to a git object type

swh.model.identifiers.release_identifier(release)[source]

Return the intrinsic identifier for a release.

swh.model.identifiers.snapshot_identifier(snapshot, *, ignore_unresolved=False)[source]

Return the intrinsic identifier for a snapshot.

Snapshots are a set of named branches, which are pointers to objects at any level of the Software Heritage DAG.

As well as pointing to other objects in the Software Heritage DAG, branches can also be alias*es, in which case their target is the name of another branch in the same snapshot, or *dangling, in which case the target is unknown (and represented by the None value).

A snapshot identifier is a salted sha1 (using the git hashing algorithm with the snapshot object type) of a manifest following the algorithm:

  1. Branches are sorted using the name as key, in bytes order.

  2. For each branch, the following bytes are output:

  • the type of the branch target:

    • content, directory, revision, release or snapshot for the corresponding entries in the DAG;

    • alias for branches referencing another branch;

    • dangling for dangling branches

  • an ascii space (\x20)

  • the branch name (as raw bytes)

  • a null byte (\x00)

  • the length of the target identifier, as an ascii-encoded decimal number (20 for current intrinsic identifiers, 0 for dangling branches, the length of the target branch name for branch aliases)

  • a colon (:)

  • the identifier of the target object pointed at by the branch, stored in the ‘target’ member:

    • for contents: their sha1_git

    • for directories, revisions, releases or snapshots: their intrinsic identifier

    • for branch aliases, the name of the target branch (as raw bytes)

    • for dangling branches, the empty string

Note that, akin to directory manifests, there is no separator between entries. Because of symbolic branches, identifiers are of arbitrary length but are length-encoded to avoid ambiguity.

Parameters

  • snapshot (dict) – the snapshot of which to compute the identifier. A single entry is needed, 'branches', which is itself a dict mapping each branch to its target

  • ignore_unresolved (bool) – if True, ignore unresolved branch aliases.

Returns

the intrinsic identifier for snapshot

Return type

str

swh.model.identifiers.origin_identifier(origin)[source]

Return the intrinsic identifier for an origin.

An origin’s identifier is the sha1 checksum of the entire origin URL

class swh.model.identifiers.SWHID(namespace: str = 'swh', scheme_version: int = 1, object_type: str = '', object_id='', metadata=ImmutableDict({}))[source]

Bases: object

Named tuple holding the relevant info associated to a SoftWare Heritage persistent IDentifier (SWHID)

Parameters

  • namespace (str) – the namespace of the identifier, defaults to swh

  • scheme_version (int) – the scheme version of the identifier, defaults to 1

  • object_type (str) – the type of object the identifier points to, either content, directory, release, revision or snapshot

  • object_id (str) – object’s identifier

  • metadata (dict) – optional dict filled with metadata related to pointed object

Raises

swh.model.exceptions.ValidationError – In case of invalid object type or id

Once created, it contains the following attributes:

namespace

the namespace of the identifier

Type

str

scheme_version

the scheme version of the identifier

Type

int

object_type

the type of object the identifier points to

Type

str

object_id

hexadecimal representation of the object hash

Type

str

metadata

metadata related to the pointed object

Type

dict

To get the raw SWHID string from an instance of this named tuple, use the str() function:

swhid = SWHID(
    object_type='content',
    object_id='8ff44f081d43176474b267de5451f2c2e88089d0'
)
swhid_str = str(swhid)
# 'swh:1:cnt:8ff44f081d43176474b267de5451f2c2e88089d0'
check_namespace(attribute, value)[source]
check_scheme_version(attribute, value)[source]
check_object_type(attribute, value)[source]
check_object_id(attribute, value)[source]
to_dict() → Dict[str, Any][source]
swh.model.identifiers.swhid(object_type: str, object_id: Union[str, Dict[str, Any]], scheme_version: int = 1, metadata: Union[swh.model.collections.ImmutableDict[str, Any], Dict[str, Any]] = ImmutableDict({})) → str[source]

Compute SoftWare Heritage persistent IDentifiers (SWHIDs)

Parameters

  • object_type – object’s type, either content, directory, release, revision or snapshot

  • object_id – object’s identifier

  • scheme_version – SWHID scheme version, defaults to 1

  • metadata – metadata related to the pointed object

Raises

swh.model.exceptions.ValidationError – In case of invalid object type or id

Returns

the SWHID of the object

swh.model.identifiers.parse_swhid(swhid: str) → swh.model.identifiers.SWHID[source]

Parse SoftWare Heritage persistent IDentifiers (SWHIDs).

Parameters

swhid (str) – A persistent identifier

Raises

swh.model.exceptions.ValidationError – in case of: * missing mandatory values (4) * invalid namespace supplied * invalid version supplied * invalid type supplied * missing hash * invalid hash identifier supplied

Returns

a named tuple holding the parsing result