The basic 8 steps to update .git/shallow does not fully apply here
because the user may choose to accept just a few refs (while fetch
always accepts all refs). The steps are modified a bit.

1-6. same as before. After calling assign_shallow_commits_to_refs at
   step 6, each shallow commit has a bitmap that marks all refs that
   require it.

7. mark all "ours" shallow commits that are reachable from any
   refs. We will need to do the original step 7 on them later.

8. go over all shallow commit bitmaps, mark refs that require new
   shallow commits.

9. setup a strict temporary shallow file to plug all the holes, even
   if it may cut some of our history short. This file is used by all
   hooks. The hooks could use --shallow-file=$GIT_DIR/shallow to
   overcome this and reach everything in current repo.

10. go over the new refs one by one. For each ref, do the reachability
   test if it needs a shallow commit on the list from step 7. Remove
   it if it's reachable from our refs. Gather all required shallow
   commits, run check_everything_connected() with the new ref, then
   install them to .git/shallow.

This mode is disabled by default and can be turned on with
receive.shallowupdate
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

This is the preparation for adding --shallow-file to both
unpack-objects and index-pack. To sum up:

 - struct argv_array used instead of const char **

 - status/code, ip/child, unpacker/keeper are moved out to function
   top level

 - successful flow now ends at the end of the function
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

If either receive-pack or upload-pack is called on a shallow
repository, shallow commits (*) will be sent after the ref
advertisement (but before the packet flush), so that the receiver has
the full "shape" of the sender's commit graph. This will be needed for
the receiver to update its .git/shallow if necessary.

This breaks the protocol for all clients trying to push to a shallow
repo, or fetch from one. Which is basically the same end result as
today's "is_repository_shallow() && die()" in receive-pack and
upload-pack. New clients will be made aware of shallow upstream and
can make use of this information.

The sender must send all shallow commits that are sent in the
following pack. It may send more shallow commits than necessary.

upload-pack for example may choose to advertise no shallow commits if
it knows in advance that the pack it's going to send contains no
shallow commits. But upload-pack is the server, so we choose the
cheaper way, send full .git/shallow and let the client deal with it.

Smart HTTP is not affected by this patch. Shallow support on
smart-http comes later separately.

(*) A shallow commit is a commit that terminates the revision
    walker. It is usually put in .git/shallow in order to keep the
    revision walker from going out of bound because there is no
    guarantee that objects behind this commit is available.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Expose lock_ref_sha1_basic's type_p argument to callers of
lock_any_ref_for_update.  Update all call sites to ignore it by passing
NULL for now.
Signed-off-by: NBrad King <brad.king@kitware.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

- From the beginning of push.c in 755225de, 2006-04-29, "thin" option
  was enabled by default but could be turned off with --no-thin.

- Then Shawn changed the default to 0 in favor of saving server
  resources in a4503a15, 2007-09-09. --no-thin worked great.

- One day later, in 9b288516 Daniel extracted some code from push.c to
  create transport.c. He (probably accidentally) flipped the default
  value from 0 to 1 in transport_get().

From then on --no-thin is effectively no-op because git-push still
expects the default value to be false and only calls
transport_set_option() when "thin" variable in push.c is true (which
is unnecessary). Correct the code to respect --no-thin by calling
transport_set_option() in both cases.

receive-pack learns about --reject-thin-pack-for-testing option,
which only is for testing purposes, hence no document update.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The definition of "struct ref" in "cache.h", a header file so
central to the system, always confused me.  This structure is not
about the local ref used by sha1-name API to name local objects.

It is what refspecs are expanded into, after finding out what refs
the other side has, to define what refs are updated after object
transfer succeeds to what values.  It belongs to "remote.h" together
with "struct refspec".

While we are at it, also move the types and functions related to the
Git transport connection to a new header file connect.h
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since commit a22e6f85 (receive-pack: send pack-processing
stderr over sideband, 2012-09-21), receive-pack will start
an async sideband thread to copy the stderr from our
index-pack or unpack-objects child to the client. We hand
the thread's input descriptor to unpack(), which puts it in
the "err" member of the "struct child_process".

After unpack() returns, we use finish_async() to reap the
sideband thread. The thread is only ready to die when it
gets EOF on its pipe, which is connected to the err
descriptor. So we expect all of the write ends of that pipe
to be closed as part of unpack().

Normally, this works fine. After start_command forks, it
closes the parent copy of the descriptor. Then once the
child exits (whether it was successful or not), that closes
the only remaining writer.

However, there is one code-path in unpack() that does not
handle this. Before we decide which of unpack-objects or
index-pack to use, we read the pack header ourselves to see
how many objects it contains. If there is an error here, we
exit without running either sub-command, the pipe descriptor
remains open, and we are in a deadlock, waiting for the
sideband thread to die (which is in turn waiting for us to
close the pipe).

We can fix this by making sure that unpack() always closes
the pipe before returning.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Most of the callers of packet_read_line just read into a
static 1000-byte buffer (callers which handle arbitrary
binary data already use LARGE_PACKET_MAX). This works fine
in practice, because:

  1. The only variable-sized data in these lines is a ref
     name, and refs tend to be a lot shorter than 1000
     characters.

  2. When sending ref lines, git-core always limits itself
     to 1000 byte packets.

However, the only limit given in the protocol specification
in Documentation/technical/protocol-common.txt is
LARGE_PACKET_MAX; the 1000 byte limit is mentioned only in
pack-protocol.txt, and then only describing what we write,
not as a specific limit for readers.

This patch lets us bump the 1000-byte limit to
LARGE_PACKET_MAX. Even though git-core will never write a
packet where this makes a difference, there are two good
reasons to do this:

  1. Other git implementations may have followed
     protocol-common.txt and used a larger maximum size. We
     don't bump into it in practice because it would involve
     very long ref names.

  2. We may want to increase the 1000-byte limit one day.
     Since packets are transferred before any capabilities,
     it's difficult to do this in a backwards-compatible
     way. But if we bump the size of buffer the readers can
     handle, eventually older versions of git will be
     obsolete enough that we can justify bumping the
     writers, as well. We don't have plans to do this
     anytime soon, but there is no reason not to start the
     clock ticking now.

Just bumping all of the reading bufs to LARGE_PACKET_MAX
would waste memory. Instead, since most readers just read
into a temporary buffer anyway, let's provide a single
static buffer that all callers can use. We can further wrap
this detail away by having the packet_read_line wrapper just
use the buffer transparently and return a pointer to the
static storage.  That covers most of the cases, and the
remaining ones already read into their own LARGE_PACKET_MAX
buffers.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The packets sent during ref negotiation are all terminated
by newline; even though the code to chomp these newlines is
short, we end up doing it in a lot of places.

This patch teaches packet_read_line to auto-chomp the
trailing newline; this lets us get rid of a lot of inline
chomping code.

As a result, some call-sites which are not reading
line-oriented data (e.g., when reading chunks of packfiles
alongside sideband) transition away from packet_read_line to
the generic packet_read interface. This patch converts all
of the existing callsites.

Since the function signature of packet_read_line does not
change (but its behavior does), there is a possibility of
new callsites being introduced in later commits, silently
introducing an incompatibility.  However, since a later
patch in this series will change the signature, such a
commit would have to be merged directly into this commit,
not to the tip of the series; we can therefore ignore the
issue.

This is an internal cleanup and should produce no change of
behavior in the normal case. However, there is one corner
case to note. Callers of packet_read_line have never been
able to tell the difference between a flush packet ("0000")
and an empty packet ("0004"), as both cause packet_read_line
to return a length of 0. Readers treat them identically,
even though Documentation/technical/protocol-common.txt says
we must not; it also says that implementations should not
send an empty pkt-line.

By stripping out the newline before the result gets to the
caller, we will now treat the newline-only packet ("0005\n")
the same as an empty packet, which in turn gets treated like
a flush packet. In practice this doesn't matter, as neither
empty nor newline-only packets are part of git's protocols
(at least not for the line-oriented bits, and readers who
are not expecting line-oriented packets will be calling
packet_read directly, anyway). But even if we do decide to
care about the distinction later, it is orthogonal to this
patch.  The right place to tighten would be to stop treating
empty packets as flush packets, and this change does not
make doing so any harder.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

This is just write_or_die by another name. The one
distinction is that write_or_die will treat EPIPE specially
by suppressing error messages. That's fine, as we die by
SIGPIPE anyway (and in the off chance that it is disabled,
write_or_die will simulate it).
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

A repository may have refs that are only used for its internal
bookkeeping purposes that should not be exposed to the others that
come over the network.

Teach upload-pack to omit some refs from its initial advertisement
by paying attention to the uploadpack.hiderefs multi-valued
configuration variable.  Do the same to receive-pack via the
receive.hiderefs variable.  As a convenient short-hand, allow using
transfer.hiderefs to set the value to both of these variables.

Any ref that is under the hierarchies listed on the value of these
variable is excluded from responses to requests made by "ls-remote",
"fetch", etc. (for upload-pack) and "push" (for receive-pack).

Because these hidden refs do not count as OUR_REF, an attempt to
fetch objects at the tip of them will be rejected, and because these
refs do not get advertised, "git push :" will not see local branches
that have the same name as them as "matching" ones to be sent.

An attempt to update/delete these hidden refs with an explicit
refspec, e.g. "git push origin :refs/hidden/22", is rejected.  This
is not a new restriction.  To the pusher, it would appear that there
is no such ref, so its push request will conclude with "Now that I
sent you all the data, it is time for you to update the refs.  I saw
that the ref did not exist when I started pushing, and I want the
result to point at this commit".  The receiving end will apply the
compare-and-swap rule to this request and rejects the push with
"Well, your update request conflicts with somebody else; I see there
is such a ref.", which is the right thing to do. Otherwise a push to
a hidden ref will always be "the last one wins", which is not a good
default.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Create find_hook() function to determine if a given hook exists and is
executable.  If it is, the path to the script will be returned,
otherwise NULL is returned.

This encapsulates the tests that are used to check for the existence of
a hook in one place, making it easier to modify those checks if that is
found to be necessary.  This also makes it simple for places that can
use a hook to check if a hook exists before doing, possibly lengthy,
setup work which would be pointless if no such hook is present.

The returned value is left as a static value from get_pathname() rather
than a duplicate because it is anticipated that the return value will
either be used as a boolean, immediately added to an argv_array list
which would result in it being duplicated at that point, or used to
actually run the command without much intervening work.  Callers which
need to hold onto the returned value for a longer time are expected to
duplicate the return value themselves.
Signed-off-by: NAaron Schrab <aaron@schrab.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The output from git push currently looks like this:

  $ git push dest HEAD
  fatal: [some message from index-pack]
  error: unpack failed: index-pack abnormal exit
  To dest
   ! [remote rejected] HEAD -> master (n/a (unpacker error))

That n/a is meant to be "the per-ref status is not
available" but the nested parentheses just make it look
ugly. Let's turn the final line into just:

   ! [remote rejected] HEAD -> master (unpacker error)
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Receive-pack invokes either unpack-objects or index-pack to
handle the incoming pack. However, we do not redirect the
stderr of the sub-processes at all, so it is never seen by
the client. From the initial thread adding sideband support,
which is here:

  http://thread.gmane.org/gmane.comp.version-control.git/139471

it is clear that some messages are specifically kept off the
sideband (with the assumption that they are of interest only
to an administrator, not the client). The stderr of the
subprocesses is mentioned in the thread, but it's unclear if
they are included in that group, or were simply forgotten.

However, there are a few good reasons to show them to the
client:

  1. In many cases, they are directly about the incoming
     packfile (e.g., fsck warnings with --strict, corruption
     in the packfile, etc). Without these messages, the
     client just gets "unpacker error" with no extra useful
     diagnosis.

  2. No matter what the cause, we are probably better off
     showing the errors to the client. If the client and the
     server admin are not the same entity, it is probably
     much easier for the client to cut-and-paste the errors
     they see than for the admin to try to dig them out of a
     log and correlate them with a particular session.

  3. Users of the ssh transport typically already see these
     stderr messages, as the remote's stderr is copied
     literally by ssh. This brings other transports (http,
     and push-over-git if you are crazy enough to enable it)
     more in line with ssh. As a bonus for ssh users,
     because the messages are now fed through the sideband
     and printed by the local git, they will have "remote:"
     prepended and be properly interleaved with any local
     output to stderr.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The unpack-objects command should not generally produce any
output on stdout. However, if it's given extra input after
the packfile, it will spew the remainder to stdout. When
called by receive-pack, this means we will break protocol,
since our stdout is connected to the remote send-pack.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The original computed merge-base between the old commit and the new
commit and checked if the old commit was a merge base between them,
in order to make sure we are fast-forwarding.

Instead, call in_merge_bases(old, new) which does the same.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The standard output channel of receive-pack is a structured protocol
channel, and subprocesses must never be allowed to leak anything
into it by writing to their standard output.

Use RUN_COMMAND_STDOUT_TO_STDERR option to run_command_v_opt() just
like we do when running hooks to prevent output from "gc" leaking to
the standard output.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Instead of having the client advertise a particular version
number in the git protocol, we have managed extensions and
backwards compatibility by having clients and servers
advertise capabilities that they support. This is far more
robust than having each side consult a table of
known versions, and provides sufficient information for the
protocol interaction to complete.

However, it does not allow servers to keep statistics on
which client versions are being used. This information is
not necessary to complete the network request (the
capabilities provide enough information for that), but it
may be helpful to conduct a general survey of client
versions in use.

We already send the client version in the user-agent header
for http requests; adding it here allows us to gather
similar statistics for non-http requests.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Receive runs rev-list --verify-objects in order to detect missing
objects. However, such errors are ignored and overridden later.
Instead, consequently ignore all update commands for which an error has
already been detected.

Some tests in t5504 are obsoleted by this change, because invalid
objects are detected even if fsck is not enabled. Instead, they now test
for different error messages depending on whether or not fsck is turned
on. A better fix would be to force a corruption that will be detected by
fsck but not by rev-list.
Signed-off-by: NClemens Buchacher <drizzd@aon.at>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Currently, git push --quiet produces some non-error output, e.g.:

 $ git push --quiet
 Unpacking objects: 100% (3/3), done.

This fixes a bug reported for the fedora git package:

 https://bugzilla.redhat.com/show_bug.cgi?id=725593Reported-by: NJesse Keating <jkeating@redhat.com>
Cc: Todd Zullinger <tmz@pobox.com>

Commit 90a6c7d4 (propagate --quiet to send-pack/receive-pack)
introduced the --quiet option to receive-pack and made send-pack
pass that option. Older versions of receive-pack do not recognize
the option, however, and terminate immediately. The commit was
therefore reverted.

This change instead adds a 'quiet' capability to receive-pack,
which is a backwards compatible.

In addition, this fixes push --quiet via http: A verbosity of 0
means quiet for remote helpers.
Reported-by: NTobias Ulmer <tobiasu@tmux.org>
Signed-off-by: NClemens Buchacher <drizzd@aon.at>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

We have been carefully choosing feature names used in the protocol
extensions so that the vocabulary does not contain a word that is a
substring of another word, so it is not a real problem, but we have
recently added "quiet" feature word, which would mean we cannot later
add some other word with "quiet" (e.g. "quiet-push"), which is awkward.

Let's make sure that we can eventually be able to do so by teaching the
clients and servers that feature words consist of non whitespace
letters. This parser also allows us to later add features with parameters
e.g. "feature=1.5" (parameter values need to be quoted for whitespaces,
but we will worry about the detauls when we do introduce them).
Signed-off-by: NJunio C Hamano <gitster@pobox.com>
Signed-off-by: NClemens Buchacher <drizzd@aon.at>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The old code basically did:

     generate array of SHA1s for alternate refs
     for each unique SHA1 in array:
         add_extra_ref(".have", sha1)
     for each ref (including real refs and extra refs):
         show_ref(refname, sha1)

But there is no need to stuff the alternate refs in extra_refs; we can
call show_ref() directly when iterating over the array, then handle
real refs separately.  So change the code to:

     generate array of SHA1s for alternate refs
     for each unique SHA1 in array:
         show_ref(".have", sha1)
     for each ref (this now only includes real refs):
         show_ref(refname, sha1)
Signed-off-by: NMichael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The function is not used as a callback, so it doesn't need these
arguments.  Also change its return type to void.
Signed-off-by: NMichael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Move some more code from the calling site into write_head_info(), and
inline add_alternate_refs() there.  (Some more simplification is
coming, and it is easier if all this code is in the same place.)

Move some helper functions to avoid the need for forward declarations.
Signed-off-by: NMichael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

resolve_ref() may return a pointer to a shared buffer and can be
overwritten by the next resolve_ref() calls. Callers need to
pay attention, not to keep the pointer when the next call happens.

Rename with "_unsafe" suffix to warn developers (or reviewers) before
introducing new call sites.

This patch is generated using the following command

git grep -l 'resolve_ref(' -- '*.[ch]'|xargs sed -i 's/resolve_ref(/resolve_ref_unsafe(/g'
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

resolve_ref() may return a pointer to a static buffer. Callers that
use this value longer than a couple of statements should copy the
value to avoid some hidden resolve_ref() call that may change the
static buffer's value.

The bug found by Tony Wang <wwwjfy@gmail.com> in builtin/merge.c
demonstrates this. The first call is in cmd_merge()

branch = resolve_ref("HEAD", head_sha1, 0, &flag);

Then deep in lookup_commit_or_die() a few lines after, resolve_ref()
may be called again and destroy "branch".

lookup_commit_or_die
 lookup_commit_reference
  lookup_commit_reference_gently
   parse_object
    lookup_replace_object
     do_lookup_replace_object
      prepare_replace_object
       for_each_replace_ref
        do_for_each_ref
         get_loose_refs
          get_ref_dir
           get_ref_dir
            resolve_ref

All call sites are checked and made sure that xstrdup() is called if
the value should be saved.
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

When pushing to delete a ref, it uses 0{40} as an object name to signal
that the request is a deletion. We shouldn't trigger "deletion of a
corrupt ref" warning in such a case, which was designed to notice that a
ref points at an object that is truly missing from the repository.

Reported-by: Stefan Näwe
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Change check_ref_format() to take a flags argument that indicates what
is acceptable in the reference name (analogous to "git
check-ref-format"'s "--allow-onelevel" and "--refspec-pattern").  This
is more convenient for callers and also fixes a failure in the test
suite (and likely elsewhere in the code) by enabling "onelevel" and
"refspec-pattern" to be allowed independently of each other.

Also rename check_ref_format() to check_refname_format() to make it
obvious that it deals with refnames rather than references themselves.
Signed-off-by: NMichael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

When a push specifies deletion of non-existent refs, the post post-receive and
post-update hooks receive them as input/arguments.

For instance, for the following push, where refs/heads/nonexistent is a ref
which does not exist on the remote side:

	git push origin :refs/heads/nonexistent

the post-receive hook receives from standard input:

	<null-sha1> SP <null-sha1> SP refs/heads/nonexistent

and the post-update hook receives as arguments:

	refs/heads/nonexistent

which does not make sense since it is a no-op.

Teach receive-pack not to pass non-existent refs to the post-receive and
post-update hooks. If the push only attempts to delete non-existent refs,
these hooks are not even called.

The update and pre-receive hooks are still notified about attempted
deletion of non-existent refs to give them a chance to inspect the
situation and act on it.

[jc: mild fix-ups to avoid introducing an extra list; also added fixes to
some tests]
Signed-off-by: NPang Yan Han <pangyanhan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Running a hook has to make complex set-up to establish web of
communication between child process and multiplexer, which is common
regardless of what kind of data is fed to the hook. Refactor the parts
that is specific to the data fed to the particular set of hooks from the
part that runs the hook, so that the code can be reused to drive hooks
that take different kind of data.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Signed-off-by: NJunio C Hamano <gitster@pobox.com>

This reverts commit ffa69e61, reversing
changes made to 4a13c4d1.

Adding a new command line option to receive-pack and feed it from
send-pack is not an acceptable way to add features, as there is no
guarantee that your updated send-pack will be talking to updated
receive-pack. New features need to be added via the capability mechanism
negotiated over the protocol.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

This single variable can be used to set instead of setting fsckobjects
variable for fetch & receive independently.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Previous commit added one element to the command line, without
making sure the result fits there.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Currently, git push --quiet produces some non-error output, e.g.:

 $ git push --quiet
 Unpacking objects: 100% (3/3), done.

Add the --quiet option to send-pack/receive-pack and pass it to
unpack-objects in the receive-pack codepath and to receive-pack in
the push codepath.

This fixes a bug reported for the fedora git package:

 https://bugzilla.redhat.com/show_bug.cgi?id=725593Reported-by: NJesse Keating <jkeating@redhat.com>
Cc: Todd Zullinger <tmz@pobox.com>
Signed-off-by: NClemens Buchacher <drizzd@aon.at>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Change upload-pack and receive-pack to use the namespace-prefixed refs
when working with the repository, and use the unprefixed refs when
talking to the client, maintaining the masquerade.  This allows
clone, pull, fetch, and push to work with a suitably configured
GIT_NAMESPACE.

receive-pack advertises refs outside the current namespace as .have refs
(as it currently does for refs in alternates), so that the client can
use them to minimize data transfer but will otherwise ignore them.

With appropriate configuration, this also allows http-backend to expose
namespaces as multiple repositories with different paths.  This only
requires setting GIT_NAMESPACE, which http-backend passes through to
upload-pack and receive-pack.
Signed-off-by: NJosh Triplett <josh@joshtriplett.org>
Signed-off-by: NJamey Sharp <jamey@minilop.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

When receiving a push, we advertise ref tips from any
alternate repositories, in case that helps the client send a
smaller pack. Since these refs don't actually exist in the
destination repository, we don't transmit the real ref
names, but instead use the pseudo-ref ".have".

If your alternate has a large number of duplicate refs (for
example, because it is aggregating objects from many related
repositories, some of which will have the same tags and
branch tips), then we will send each ".have $sha1" line
multiple times. This is a pointless waste of bandwidth, as
we are simply repeating the same fact to the client over and
over.

This patch eliminates duplicate .have refs early on. It does
so efficiently by sorting the complete list and skipping
duplicates. This has the side effect of re-ordering the
.have lines by ascending sha1; this isn't a problem, though,
as the original order was meaningless.

There is a similar .have system in fetch-pack, but it
does not suffer from the same problem. For each alternate
ref we consider in fetch-pack, we actually open the object
and mark it with the SEEN flag, so duplicates are
automatically culled.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

The foreach_alt_odb function triggers a callback for each
alternate object db we have, with room for a single void
pointer as data. Currently, we always call refs_from_alternate_cb
as the callback function, and then pass another callback (to
receive each ref individually) as the void pointer.

This has two problems:

  1. C technically forbids stuffing a function pointer into
     a "void *". In practice, this probably doesn't matter
     on any architectures git runs on, but it never hurts to
     follow the letter of the law.

  2. There is no room for an extra data pointer. Indeed, the
     alternate_ref_fn that refs_from_alternate_cb calls
     takes a void* for data, but we always pass it NULL.

Instead, let's properly stuff our function pointer into a
data struct, which also leaves room for an extra
caller-supplied data pointer. And to keep things simple for
existing callers, let's make a for_each_alternate_ref
function that takes care of creating the extra struct.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>