As mentioned in the hash function transition plan commit mergetag
lines need to be handled. The commit mergetag lines embed an entire
tag object in a commit object.
Keep the implementation sane if not fast by unembedding the tag
object, converting the tag object, and embedding the new tag object,
in the new commit object.
In the long run I don't expect any other approach is maintainable, as
tag objects may be extended in ways that require additional
translation.
To keep the implementation of convert_commit_object maintainable I
have modified convert_commit_object to process the lines in any order,
and to fail on unknown lines. We can't know ahead of time if a new
line might embed something that needs translation or not so it is
better to fail and require the code to be updated instead of silently
mistranslating objects.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When writing a commit object in a repository with both SHA-1 and
SHA-256, we'll need to convert our commit objects so that we can write
the hash values for both into the repository. To do so, let's add a
function to convert commit objects.
Read the commit object and map the tree value and any of the parent
values, and copy the rest of the commit through unmodified. Note that
we don't need to modify the signature headers, because they are the
same under both algorithms.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Upon close examination I discovered that while brian's code to convert
tag objects was functionally correct, it leaked memory.
Rearrange the code so that all error checking happens before any
memory is allocated.
Add code to release the temporary strbufs the code uses.
The code pretty much assumes the tag object ends with a newline,
so add an explict test to verify that is the case.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When writing a tag object in a repository with both SHA-1 and SHA-256,
we'll need to convert our commit objects so that we can write the hash
values for both into the repository. To do so, let's add a function to
convert tag objects.
Note that signatures for tag objects in the current algorithm trail the
message, and those for the alternate algorithm are in headers.
Therefore, we parse the tag object for both a trailing signature and a
header and then, when writing the other format, swap the two around.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In the future, we're going to want to provide SHA-256 repositories that
have compatibility support for SHA-1 as well. In order to do so, we'll
need to be able to convert tree objects from SHA-256 to SHA-1 by writing
a tree with each SHA-256 object ID mapped to a SHA-1 object ID.
We implement a function, convert_tree_object, that takes an existing
tree buffer and writes it to a new strbuf, converting between
algorithms. Let's make this function generic, because while we only
need it to convert from the main algorithm to the compatibility
algorithm now, we may need to do the other way around in the future,
such as for transport.
We avoid reusing the code in decode_tree_entry because that code
normalizes data, and we don't want that here. We want to produce a
complete round trip of data, so if, for example, the old entry had a
wrongly zero-padded mode, we'd want to preserve that when converting to
ensure a stable hash value.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
As part of the transition plan, we'd like to add a file in the .git
directory that maps loose objects between SHA-1 and SHA-256. Let's
implement the specification in the transition plan and store this data
on a per-repository basis in struct repository.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Two basic functions are provided:
- convert_object_file Takes an object file it's type and hash algorithm
and converts it into the equivalent object file that would
have been generated with hash algorithm "to".
For blob objects there is no conversation to be done and it is an
error to use this function on them.
For commit, tree, and tag objects embedded oids are replaced by the
oids of the objects they refer to with those objects and their
object ids reencoded in with the hash algorithm "to". Signatures
are rearranged so that they remain valid after the object has
been reencoded.
- repo_oid_to_algop which takes an oid that refers to an object file
and returns the oid of the equivalent object file generated
with the target hash algorithm.
The pair of files object-file-convert.c and object-file-convert.h are
introduced to hold as much of this logic as possible to keep this
conversion logic cleanly separated from everything else and in the
hopes that someday the code will be clean enough git can support
compiling out support for sha1 and the various conversion functions.
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
