... and add an option to explicitly not follow them, if needed.

Closes T1135

with explicit option to hide it

Closes T1133

This commit changes the swh pids representation returned by the
parse_persistent_identifier function from a dict to a named tuple.
Also, the 'object_type' attribute of that named tuple now contains
a full name instead of an abbreviated one.

Closes T1112
Closes T1125

Close T1104
Close D346

Related T1104

As the client of this api might not be aware of what's the right id
key for a given object.

Related T1104

Related T1104

Related T1104

Related T1104

Summary:
We used to depend on the 'blake2s256' and 'blake2b512' names to be available in
hashlib.algorithms_available. It turns out that that's specific to OpenSSL 1.1.

We now try, in order:
 - blake2s256/blake2b512 as shipped by libssl1.1 (Python 3.5+ on Debian stretch
 and up)
 - blake2s/blake2b as built into Python 3.6+
 - pyblake2 if all else fails

While we're here, let's also avoid doing not-so-subtle hacks with hashlib
builtins.

Thanks to Alexios Zavras for the report.

Test Plan:
New unit tests added to check for behavior in all cases. Manually running the
tests on Python 3.4 + pyblake2, Python 3.5 and Python 3.6 as shipped by Debian
exercises all three cases.

Reviewers: zack, #reviewers!

Differential Revision: https://forge.softwareheritage.org/D347

Currently only content and directory object types are supported, but more can
be added in the future.

Closes T1039

This commits adds support for parsing optional parts in persistent
identifiers. Optional parts are defined the following way:

	<swh_id>[;key1=val1][;key2=val2]

Related T1040

Related T335

Related T335
Related T933

Summary:
Add support for snapshot identifiers

Close T566.
Related to D268.

Test Plan: Unit tests included

Reviewers: zack, #reviewers!

Maniphest Tasks: T566

Differential Revision: https://forge.softwareheritage.org/D277

Close T709

This allows loaders to lazily load data: you can read from disk and transfer
only the contents that are really missing.

Summary:
This module is a reimplementation of swh.model.git, with the underlying goal of
replacing it and fixing T709 in the process.

Reviewers: #reviewers!

Differential Revision: https://forge.softwareheritage.org/D248

Related T703

- Add module docstring
- Add blake2s256 and blake2b512 in supported algorithms
- Spawn a new variable DEFAULT_ALGORITHMS as default computed
  algorithms for the main functions

Related T692

Remove the limit on the python3 version, this should be transparent.
If the hash requested is not available, this will raise with an
explanation on the error.

Related T692

The same caveat applies, will only be supported from python3.6 onward.

Related T692

The caveat is that it will only be supported when we will be using
python3 >= 3.5.

Related T692

Related T700

Closes T255
Ref. D179

Found by investigating T75

The subversion loader (T680) has shown that throwing floating point values
around for timestamps is a mess waiting to happen.

We now coerce all clients to send us timestamps as integer numbers of seconds
and microseconds, avoiding data losses everywhere.

- default
- ignoring empty folders
- ignore folder based on pattern in names