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When the content at a given bundle URI is not understood as a bundle
(based on inspecting the initial content), then Git currently gives up
and ignores that content. Independent bundle providers may want to split
up the bundle content into multiple bundles, but still make them
available from a single URI.
Teach Git to attempt parsing the bundle URI content as a Git config file
providing the key=value pairs for a bundle list. Git then looks at the
mode of the list to see if ANY single bundle is sufficient or if ALL
bundles are required. The content at the selected URIs are downloaded
and the content is inspected again, creating a recursive process.
To guard the recursion against malformed or malicious content, limit the
recursion depth to a reasonable four for now. This can be converted to a
configured value in the future if necessary. The value of four is twice
as high as expected to be useful (a bundle list is unlikely to point to
more bundle lists).
To test this scenario, create an interesting bundle topology where three
incremental bundles are built on top of a single full bundle. By using a
merge commit, the two middle bundles are "independent" in that they do
not require each other in order to unbundle themselves. They each only
need the base bundle. The bundle containing the merge commit requires
both of the middle bundles, though. This leads to some interesting
decisions when unbundling, especially when we later implement heuristics
that promote downloading bundles until the prerequisite commits are
satisfied.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When a bundle provider wants to operate independently from a Git remote,
they want to provide a single, consistent URI that users can use in
their 'git clone --bundle-uri' commands. At this point, the Git client
expects that URI to be a single bundle that can be unbundled and used to
bootstrap the rest of the clone from the Git server. This single bundle
cannot be re-used to assist with future incremental fetches.
To allow for the incremental fetch case, teach Git to understand a
bundle list that could be advertised at an independent bundle URI. Such
a bundle list is likely to be inspected by human readers, even if only
by the bundle provider creating the list. For this reason, we can take
our expected "key=value" pairs and instead format them using Git config
format.
Create bundle_uri_parse_config_format() to parse a file in config format
and convert that into a 'struct bundle_list' filled with its
understanding of the contents.
Be careful to use error_action CONFIG_ERROR_ERROR when calling
git_config_from_file_with_options() because the default action for
git_config_from_file() is to die() on a parsing error. The current
warning isn't particularly helpful if it arises to a user, but it will
be made more verbose at a higher layer later.
Update 'test-tool bundle-uri' to take this config file format as input.
It uses a filename instead of stdin because there is no existing way to
parse a FILE pointer in the config machinery. Using
git_config_from_mem() is overly complicated and more likely to introduce
bugs than this simpler version.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Create a new 'test-tool bundle-uri' test helper. This helper will assist
in testing logic deep in the bundle URI feature.
This change introduces the 'parse-key-values' subcommand, which parses
an input file as a list of lines. These are fed into
bundle_uri_parse_line() to test how we construct a 'struct bundle_list'
from that data. The list is then output to stdout as if the key-value
pairs were a Git config file.
We use an input file instead of stdin because of a future change to
parse in config-file format that works better as an input file.
Co-authored-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When advertising a bundle list over Git's protocol v2, we will use
packet lines. Each line will be of the form "key=value" representing a
bundle list. Connect the API necessary for Git's transport to the
key-value pair parsing created in the previous change.
We are not currently implementing this protocol v2 functionality, but
instead preparing to expose this parsing to be unit-testable.
Co-authored-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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It will likely be rare where a user uses a single bundle URI and expects
that URI to point to a bundle. Instead, that URI will likely be a list
of bundles provided in some format. Alternatively, the Git server could
advertise a list of bundles.
In anticipation of these two ways of advertising multiple bundles,
create a data structure that represents such a list. This will be
populated using a common API, but for now focus on what data can be
represented.
Each list contains a number of remote_bundle_info structs. These contain
an 'id' that is used to uniquely identify them in the list, and also a
'uri' that contains the location of its data. Finally, there is a strbuf
containing the filename used when Git downloads the contents to disk.
The list itself stores these remote_bundle_info structs in a hashtable
using 'id' as the key. The order of the structs in the input is
considered unimportant, but future modifications to the format and these
data structures will place ordering possibilities on the set. The list
also has a few "global" properties, including the version (used when
parsing the list) and the mode. The mode is one of these two options:
1. BUNDLE_MODE_ALL: all listed URIs are intended to be combined
together. The client should download all of the advertised data to
have a complete copy of the data.
2. BUNDLE_MODE_ANY: any one listed item is sufficient to have a complete
copy of the data. The client can choose arbitrarily from these
options. In the future, the client may use pings to find the closest
URI among geodistributed replicas, or use some other heuristic
information added to the format.
This API is currently unused, but will soon be expanded with parsing
logic and then be consumed by the bundle URI download logic.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Before implementing a way to fetch bundles into a repository, create the
basic logic. Assume that the URI is actually a file path. Future logic
will make this more careful to other protocols.
For now, we also only succeed if the content at the URI is a bundle
file, not a bundle list. Bundle lists will be implemented in a future
change.
Note that the discovery of a temporary filename is slightly racy because
the odb_mkstemp() relies on the temporary file not existing. With the
current implementation being limited to file copies, we could replace
the copy_file() with copy_fd(). The tricky part comes in future changes
that send the filename to 'git remote-https' and its 'get' capability.
At that point, we need the file descriptor closed _and_ the file
unlinked. If we were to keep the file descriptor open for the sake of
normal file copies, then we would pollute the rest of the code for
little benefit. This is especially the case because we expect that most
bundle URI use will be based on HTTPS instead of file copies.
Reviewed-by: Josh Steadmon <steadmon@google.com>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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