annotate mercurial/utils/storageutil.py @ 39877:f8eb71f9e3bd

storageutil: new module for storage primitives (API)

There will exist common code between storage backends. It would
be nice to have a central place to put that code.

This commit attempts to create that place by creating the
"storageutil" module.

The first thing we move is revlog.hash(), which is the function for
computing the SHA-1 hash of revision fulltext and parents.

Differential Revision: https://phab.mercurial-scm.org/D4753

# storageutil.py - Storage functionality agnostic of backend implementation.
#
# Copyright 2018 Gregory Szorc <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

import hashlib

from ..node import (
    nullid,
)

_nullhash = hashlib.sha1(nullid)

def hashrevisionsha1(text, p1, p2):
    """Compute the SHA-1 for revision data and its parents.

    This hash combines both the current file contents and its history
    in a manner that makes it easy to distinguish nodes with the same
    content in the revision graph.
    """
    # As of now, if one of the parent node is null, p2 is null
    if p2 == nullid:
        # deep copy of a hash is faster than creating one
        s = _nullhash.copy()
        s.update(p1)
    else:
        # none of the parent nodes are nullid
        if p1 < p2:
            a = p1
            b = p2
        else:
            a = p2
            b = p1
        s = hashlib.sha1(a)
        s.update(b)
    s.update(text)
    return s.digest()