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fast-import: let importers retrieve blobs

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New objects written by fast-import are not available immediately.
Until a checkpoint has been started and finishes writing the pack
index, any new blobs will not be accessible using standard git tools.

So introduce a new way to access them: a "cat-blob" command in the
command stream requests for fast-import to print a blob to stdout or a
file descriptor specified by the argument to --cat-blob-fd.  The value
for cat-blob-fd cannot be specified in the stream because that would
be a layering violation: the decision of where to direct a stream has
to be made when fast-import is started anyway, so we might as well
make the stream format is independent of that detail.

Output uses the same format as "git cat-file --batch".

Thanks to Sverre Rabbelier and Sam Vilain for guidance in designing
the protocol.

Based-on-patch-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: David Barr <david.barr@cordelta.com>
Acked-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
David Barr
2010-11-28 13:45:01 -06:00
committed by Junio C Hamano
parent 4980fffb2c
commit 85c62395b1
3 changed files with 329 additions and 2 deletions
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41
Documentation/git-fast-import.txt
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@ -92,6 +92,11 @@ OPTIONS
--(no-)-relative-marks= with the --(import|export)-marks=
options.
--cat-blob-fd=<fd>::
Specify the file descriptor that will be written to
when the `cat-blob` command is encountered in the stream.
The default behaviour is to write to `stdout`.
--export-pack-edges=<file>::
After creating a packfile, print a line of data to
<file> listing the filename of the packfile and the last
@ -320,6 +325,11 @@ and control the current import process. More detailed discussion
standard output. This command is optional and is not needed
to perform an import.
`cat-blob`::
Causes fast-import to print a blob in 'cat-file --batch'
format to the file descriptor set with `--cat-blob-fd` or
`stdout` if unspecified.
`feature`::
Require that fast-import supports the specified feature, or
abort if it does not.
@ -879,6 +889,29 @@ Placing a `progress` command immediately after a `checkpoint` will
inform the reader when the `checkpoint` has been completed and it
can safely access the refs that fast-import updated.
`cat-blob`
~~~~~~~~~~
Causes fast-import to print a blob to a file descriptor previously
arranged with the `--cat-blob-fd` argument. The command otherwise
has no impact on the current import; its main purpose is to
retrieve blobs that may be in fast-import's memory but not
accessible from the target repository.
....
'cat-blob' SP <dataref> LF
....
The `<dataref>` can be either a mark reference (`:<idnum>`)
set previously or a full 40-byte SHA-1 of a Git blob, preexisting or
ready to be written.
output uses the same format as `git cat-file --batch`:
====
<sha1> SP 'blob' SP <size> LF
<contents> LF
====
`feature`
~~~~~~~~~
Require that fast-import supports the specified feature, or abort if
@ -905,6 +938,13 @@ import-marks::
second, an --import-marks= command-line option overrides
any "feature import-marks" command in the stream.
cat-blob::
Ignored. Versions of fast-import not supporting the
"cat-blob" command will exit with a message indicating so.
This lets the import error out early with a clear message,
rather than wasting time on the early part of an import
before the unsupported command is detected.
`option`
~~~~~~~~
Processes the specified option so that git fast-import behaves in a
@ -930,6 +970,7 @@ not be passed as option:
* date-format
* import-marks
* export-marks
* cat-blob-fd
* force
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