The bundle-URI subsystem adds support for creation-token heuristics
to help incremental fetches.
* ds/bundle-uri-5:
bundle-uri: test missing bundles with heuristic
bundle-uri: store fetch.bundleCreationToken
fetch: fetch from an external bundle URI
bundle-uri: drop bundle.flag from design doc
clone: set fetch.bundleURI if appropriate
bundle-uri: download in creationToken order
bundle-uri: parse bundle.<id>.creationToken values
bundle-uri: parse bundle.heuristic=creationToken
t5558: add tests for creationToken heuristic
bundle: verify using check_connected()
bundle: test unbundling with incomplete history
When a bundle list specifies the "creationToken" heuristic, the Git
client downloads the list and then starts downloading bundles in
descending creationToken order. This process stops as soon as all
downloaded bundles can be applied to the repository (because all
required commits are present in the repository or in the downloaded
bundles).
When checking the same bundle list twice, this strategy requires
downloading the bundle with the maximum creationToken again, which is
wasteful. The creationToken heuristic promises that the client will not
have a use for that bundle if its creationToken value is at most the
previous creationToken value.
To prevent these wasteful downloads, create a fetch.bundleCreationToken
config setting that the Git client sets after downloading bundles. This
value allows skipping that maximum bundle download when this config
value is the same value (or larger).
To test that this works correctly, we can insert some "duplicate"
fetches into existing tests and demonstrate that only the bundle list is
downloaded.
The previous logic for downloading bundles by creationToken worked even
if the bundle list was empty, but now we have logic that depends on the
first entry of the list. Terminate early in the (non-sensical) case of
an empty bundle list.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Bundle providers may organize their bundle lists in a way that is
intended to improve incremental fetches, not just initial clones.
However, they do need to state that they have organized with that in
mind, or else the client will not expect to save time by downloading
bundles after the initial clone. This is done by specifying a
bundle.heuristic value.
There are two types of bundle lists: those at a static URI and those
that are advertised from a Git remote over protocol v2.
The new fetch.bundleURI config value applies for static bundle URIs that
are not advertised over protocol v2. If the user specifies a static URI
via 'git clone --bundle-uri', then Git can set this config as a reminder
for future 'git fetch' operations to check the bundle list before
connecting to the remote(s).
For lists provided over protocol v2, we will want to take a different
approach and create a property of the remote itself by creating a
remote.<id>.* type config key. That is not implemented in this change.
Later changes will update 'git fetch' to consume this option.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The creationToken heuristic provides an ordering on the bundles
advertised by a bundle list. Teach the Git client to download bundles
differently when this heuristic is advertised.
The bundles in the list are sorted by their advertised creationToken
values, then downloaded in decreasing order. This avoids the previous
strategy of downloading bundles in an arbitrary order and attempting
to apply them (likely failing in the case of required commits) until
discovering the order through attempted unbundling.
During a fresh 'git clone', it may make sense to download the bundles in
increasing order, since that would prevent the need to attempt
unbundling a bundle with required commits that do not exist in our empty
object store. The cost of testing an unbundle is quite low, and instead
the chosen order is optimizing for a future bundle download during a
'git fetch' operation with a non-empty object store.
Since the Git client continues fetching from the Git remote after
downloading and unbundling bundles, the client's object store can be
ahead of the bundle provider's object store. The next time it attempts
to download from the bundle list, it makes most sense to download only
the most-recent bundles until all tips successfully unbundle. The
strategy implemented here provides that short-circuit where the client
downloads a minimal set of bundles.
However, we are not satisfied by the naive approach of downloading
bundles until one successfully unbundles, expecting the earlier bundles
to successfully unbundle now. The example repository in t5558
demonstrates this well:
---------------- bundle-4
4
/ \
----|---|------- bundle-3
| |
| 3
| |
----|---|------- bundle-2
| |
2 |
| |
----|---|------- bundle-1
\ /
1
|
(previous commits)
In this repository, if we already have the objects for bundle-1 and then
try to fetch from this list, the naive approach will fail. bundle-4
requires both bundle-3 and bundle-2, though bundle-3 will successfully
unbundle without bundle-2. Thus, the algorithm needs to keep this in
mind.
A later implementation detail will store the maximum creationToken seen
during such a bundle download, and the client will avoid downloading a
bundle unless its creationToken is strictly greater than that stored
value. For now, if the client seeks to download from an identical
bundle list since its previous download, it will download the
most-recent bundle then stop since its required commits are already in
the object store.
Add tests that exercise this behavior, but we will expand upon these
tests when incremental downloads during 'git fetch' make use of
creationToken values.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The previous change taught Git to parse the bundle.heuristic value,
especially when its value is "creationToken". Now, teach Git to parse
the bundle.<id>.creationToken values on each bundle in a bundle list.
Before implementing any logic based on creationToken values for the
creationToken heuristic, parse and print these values for testing
purposes.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The bundle.heuristic value communicates that the bundle list is
organized to make use of the bundle.<id>.creationToken values that may
be provided in the bundle list. Those values will create a total order
on the bundles, allowing the Git client to download them in a specific
order and even remember previously-downloaded bundles by storing the
maximum creation token value.
Before implementing any logic that parses or uses the
bundle.<id>.creationToken values, teach Git to parse the
bundle.heuristic value from a bundle list. We can use 'test-tool
bundle-uri' to print the heuristic value and verify that the parsing
works correctly.
As an extra precaution, create the internal 'heuristics' array to be a
list of (enum, string) pairs so we can iterate through the array entries
carefully, regardless of the enum values.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
It's more readable to use starts_with() instead of strncmp() to match a
prefix, as the latter requires a manually-computed length, and has the
funny "matching is zero" return value common to cmp functions. This
patch converts several cases which were found with:
git grep 'strncmp(.*, [0-9]*)'
But note that it doesn't convert all such cases. There are several where
the magic length number is repeated elsewhere in the code, like:
/* handle "buf" which isn't NUL-terminated and might be too small */
if (len >= 3 && !strncmp(buf, "foo", 3))
or:
/* exact match for "foo", but within a larger string */
if (end - buf == 3 && !strncmp(buf, "foo", 3))
While it would not produce the wrong outcome to use starts_with() in
these cases, we'd still be left with one instance of "3". We're better
to leave them for now, as the repeated "3" makes it clear that the two
are linked (there may be other refactorings that handle both, but
they're out of scope for this patch).
A few things to note while reading the patch:
- all cases but one are trying to match, and so lose the extra "!".
The case in the first hunk of urlmatch.c is not-matching, and hence
gains a "!".
- the case in remote-fd.c is matching the beginning of "connect foo",
but we never look at str+8 to parse the "foo" part (which would make
this a candidate for skip_prefix(), not starts_with()). This seems
at first glance like a bug, but is a limitation of how remote-fd
works.
- the second hunk in urlmatch.c shows some cases adjacent to other
strncmp() calls that are left. These are of the "exact match within
a larger string" type, as described above.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The logic in fetch_bundle_uri() is useful for the --bundle-uri option of
'git clone', but is not helpful when the clone operation discovers a
list of URIs from the bundle-uri protocol v2 command. To actually
download and unbundle the advertised bundles, we need a different
mechanism.
Create the new fetch_bundle_list() method which is very similar to
fetch_bundle_uri() except that it relies on download_bundle_list()
instead of fetch_bundle_uri_internal(). The download_bundle_list()
method will recursively call fetch_bundle_uri_internal() if any of the
advertised URIs serve a bundle list instead of a bundle. This will also
follow the bundle.list.mode setting from the input list: "any" will
download only one such URI while "all" will download data from all of
the URIs.
In an identical way to fetch_bundle_uri(), the bundles are unbundled
after all of the bundle lists have been expanded and all necessary URIs.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Bundle providers may want to distribute that data across multiple CDNs.
This might require a change in the base URI, all the way to the domain
name. If all bundles require an absolute URI in their 'uri' value, then
every push to a CDN would require altering the table of contents to
match the expected domain and exact location within it.
Allow a bundle list to specify a relative URI for the bundles. This URI
is based on where the client received the bundle list. For a list
provided in the 'bundle-uri' protocol v2 command, the Git remote URI is
the base URI. Otherwise, the bundle list was provided from an HTTP URI
not using the Git protocol, and that URI is the base URI. This allows
easier distribution of bundle data.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Implement the "bundle-uri" protocol v2 capability by populating the
key=value packet lines from the local Git config. The list of bundles is
provided from the keys beginning with "bundle.".
In the future, we may want to filter this list to be more specific to
the exact known keys that the server intends to share, but for
flexibility at the moment we will assume that the config values are
well-formed.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a skeleton server-side implementation of a new "bundle-uri" command
to protocol v2. This will allow conforming clients to optionally seed
their initial clones or incremental fetches from URLs containing
"*.bundle" files created with "git bundle create".
This change only performs the basic boilerplate of advertising a new
protocol v2 capability. The new 'bundle-uri' capability allows a client
to request a list of bundles. Right now, the server only returns a flush
packet, which corresponds to an empty advertisement. The bundle.* config
namespace describes which key-value pairs will be communicated across
this interface in future updates.
The critical bit right now is that the new boolean
uploadPack.adverstiseBundleURIs config value signals whether or not this
capability should be advertised at all.
An earlier version of this patch [1] used a different transfer format
than the "key=value" pairs in the current implementation. The change was
made to unify the protocol v2 command with the bundle lists provided by
independent bundle servers. Further, the standard allows for the server
to advertise a URI that contains a bundle list. This allows users
automatically discovering bundle providers that are loosely associated
with the origin server, but without the origin server knowing exactly
which bundles are currently available.
[1] https://lore.kernel.org/git/RFC-patch-v2-01.13-2fc87ce092b-20220311T155841Z-avarab@gmail.com/
The very-deep headings needed to be modified to stop at level 4 due to
documentation build issues. These were not recognized in earlier builds
since the file was previously in the Documentation/technical/ directory
and was built in a different way. With its current location, the
heavily-nested details were causing build issues and they are now
replaced with a bulletted list of details.
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>
When downloading bundles from a git-remote-https subprocess, the bundle
URI logic wants to be opportunistic and download as much as possible and
work with what did succeed. This is particularly important in the "any"
mode, where any single bundle success will work.
If the URI is not available, the git-remote-https process will die()
with a "fatal:" error message, even though that error is not actually
fatal to the super process. Since stderr is passed through, it looks
like a fatal error to the user.
Suppress stderr to avoid these errors from bubbling to the surface. The
bundle URI API adds its own warning() messages on these failures.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When downloading a list of bundles in "all" mode, Git has no
understanding of the dependencies between the bundles. Git attempts to
unbundle the bundles in some order, but some may not pass the
verify_bundle() step because of missing prerequisites. This is passed as
error messages to the user, even when they eventually succeed in later
attempts after their dependent bundles are unbundled.
Add a new VERIFY_BUNDLE_QUIET flag to verify_bundle() that avoids the
error messages from the missing prerequisite commits. The method still
returns the number of missing prerequisit commits, allowing callers to
unbundle() to notice that the bundle failed to apply.
Use this flag in bundle-uri.c and test that the messages go away for
'git clone --bundle-uri' commands.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The verify_bundle() method has a 'verbose' option, but we will want to
extend this method to have more granular control over its output. First,
replace this 'verbose' option with a new 'flags' option with a single
possible value: VERIFY_BUNDLE_VERBOSE.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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>
The next change will start allowing us to parse bundle lists that are
downloaded from a provided bundle URI. Those lists might point to other
lists, which could proceed to an arbitrary depth (and even create
cycles). Restructure fetch_bundle_uri() to have an internal version that
has a recursion depth. Compare that to a new max_bundle_uri_depth
constant that is twice as high as we expect this depth to be for any
legitimate use of bundle list linking.
We can consider making max_bundle_uri_depth a configurable value if
there is demonstrated value in the future.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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>
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>
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>
There will be two primary ways to advertise a bundle list: as a list of
packet lines in Git's protocol v2 and as a config file served from a
bundle URI. Both of these fundamentally use a list of key-value pairs.
We will use the same set of key-value pairs across these formats.
Create a new bundle_list_update() method that is currently unusued, but
will be used in the next change. It inspects each key to see if it is
understood and then applies it to the given bundle_list. Here are the
keys that we teach Git to understand:
* bundle.version: This value should be an integer. Git currently
understands only version 1 and will ignore the list if the version is
any other value. This version can be increased in the future if we
need to add new keys that Git should not ignore. We can add new
"heuristic" keys without incrementing the version.
* bundle.mode: This value should be one of "all" or "any". If this
mode is not understood, then Git will ignore the list. This mode
indicates whether Git needs all of the bundle list items to make a
complete view of the content or if any single item is sufficient.
The rest of the keys use a bundle identifier "<id>" as part of the key
name. Keys using the same "<id>" describe a single bundle list item.
* bundle.<id>.uri: This stores the URI of the bundle item. This
currently is expected to be an absolute URI, but will be relaxed to be
a relative URI in the future.
While parsing, return an error if a URI key is repeated, since we can
make that restriction with bundle lists.
Make the git_parse_int() method global so we can parse the integer
version value carefully.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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>
The find_temp_filename() method was created in 53a50892be (bundle-uri:
create basic file-copy logic, 2022-08-09) and uses odb_mkstemp() to
create a temporary filename. The odb_mkstemp() method uses a strbuf in
its interface, but we do not need to continue carrying a strbuf
throughout the bundle URI code.
Convert the find_temp_filename() method to use a 'char *' and modify its
only caller. This makes sense that we don't actually need to modify this
filename directly later, so using a strbuf is overkill.
This change will simplify the data structure for tracking a bundle list
to use plain strings instead of strbufs.
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The previous change created the 'git clone --bundle-uri=<uri>' option.
Currently, <uri> must be a filename.
Update copy_uri_to_file() to first inspect the URI for an HTTP(S) prefix
and use git-remote-https as the way to download the data at that URI.
Otherwise, check to see if file:// is present and modify the prefix
accordingly.
Reviewed-by: Josh Steadmon <steadmon@google.com>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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>
