[RFC] Make archival asynchronous (#11296)

* Make archival asynchronous

The prime benefit being sought here is for large archives to not
clog up the rendering process and cause unsightly proxy timeouts.
As a secondary benefit, archive-in-progress is moved out of the
way into a /tmp file so that new archival requests for the same
commit will not get fulfilled based on an archive that isn't yet
finished.

This asynchronous system is fairly primitive; request comes in, we'll
spawn off a new goroutine to handle it, then we'll mark it as done.
Status requests will see if the file exists in the final location,
and report the archival as done when it exists.

Fixes #11265

* Archive links: drop initial delay to three-quarters of a second

Some, or perhaps even most, archives will not take all that long to archive.
The archive process starts as soon as the download button is initially
clicked, so in theory they could be done quite quickly.  Drop the initial
delay down to three-quarters of a second to make it more responsive in the
common case of the archive being quickly created.

* archiver: restructure a little bit to facilitate testing

This introduces two sync.Cond pointers to the archiver package. If they're
non-nil when we go to process a request, we'll wait until signalled (at all)
to proceed. The tests will then create the sync.Cond so that it can signal
at-will and sanity-check the state of the queue at different phases.

The author believes that nil-checking these two sync.Cond pointers on every
archive processing will introduce minimal overhead with no impact on
maintainability.

* gofmt nit: no space around binary + operator

* services: archiver: appease golangci-lint, lock queueMutex

Locking/unlocking the queueMutex is allowed, but not required, for
Cond.Signal() and Cond.Broadcast().  The magic at play here is just a little
too much for golangci-lint, as we take the address of queueMutex and this is
mostly used in archiver.go; the variable still gets flagged as unused.

* archiver: tests: fix several timing nits

Once we've signaled a cond var, it may take some small amount of time for
the goroutines released to hit the spot we're wanting them to be at. Give
them an appropriate amount of time.

* archiver: tests: no underscore in var name, ungh

* archiver: tests: Test* is run in a separate context than TestMain

We must setup the mutex/cond variables at the beginning of any test that's
going to use it, or else these will be nil when the test is actually ran.

* archiver: tests: hopefully final tweak

Things got shuffled around such that we carefully build up and release
requests from the queue, so we can validate the state of the queue at each
step. Fix some assertions that no longer hold true as fallout.

* repo: Download: restore some semblance of previous behavior

When archival was made async, the GET endpoint was only useful if a previous
POST had initiated the download. This commit restores the previous behavior,
to an extent; we'll now submit the archive request there and return a
"202 Accepted" to indicate that it's processing if we didn't manage to
complete the request within ~2 seconds of submission.

This lets a client directly GET the archive, and gives them some indication
that they may attempt to GET it again at a later time.

* archiver: tests: simplify a bit further

We don't need to risk failure and use time.ParseDuration to get 2 *
time.Second.

else if isn't really necessary if the conditions are simple enough and lead
to the same result.

* archiver: tests: resolve potential source of flakiness

Increase all timeouts to 10 seconds; these aren't hard-coded sleeps, so
there's no guarantee we'll actually take that long. If we need longer to
not have a false-positive, then so be it.

While here, various assert.{Not,}Equal arguments are flipped around so that
the wording in error output reflects reality, where the expected argument is
second and actual third.

* archiver: setup infrastructure for notifying consumers of completion

This API will *not* allow consumers to subscribe to specific requests being
completed, just *any* request being completed. The caller is responsible for
determining if their request is satisfied and waiting again if needed.

* repo: archive: make GET endpoint synchronous again

If the request isn't complete, this endpoint will now submit the request and
wait for completion using the new API. This may still be susceptible to
timeouts for larger repos, but other endpoints now exist that the web
interface will use to negotiate its way through larger archive processes.

* archiver: tests: amend test to include WaitForCompletion()

This is a trivial one, so go ahead and include it.

* archiver: tests: fix test by calling NewContext()

The mutex is otherwise uninitialized, so we need to ensure that we're
actually initializing it if we plan to test it.

* archiver: tests: integrate new WaitForCompletion a little better

We can use this to wait for archives to come in, rather than spinning and
hoping with a timeout.

* archiver: tests: combine numQueued declaration with next-instruction assignment

* routers: repo: reap unused archiving flag from DownloadStatus()

This had some planned usage before, indicating whether this request
initiated the archival process or not. After several rounds of refactoring,
this use was deemed not necessary for much of anything and got boiled down
to !complete in all cases.

* services: archiver: restructure to use a channel

We now offer two forms of waiting for a request:
- WaitForCompletion: wait for completion with no timeout
- TimedWaitForCompletion: wait for completion with timeout

In both cases, we wait for the given request's cchan to close; in the latter
case, we do so with the caller-provided timeout. This completely removes the
need for busy-wait loops in Download/InitiateDownload, as it's fairly clean
to wait on a channel with timeout.

* services: archiver: use defer to unlock now that we can

This previously carried the lock into the goroutine, but an intermediate
step just added the request to archiveInProgress outside of the new
goroutine and removed the need for the goroutine to start out with it.

* Revert "archiver: tests: combine numQueued declaration with next-instruction assignment"

This reverts commit bcc5214023.

Revert "archiver: tests: integrate new WaitForCompletion a little better"

This reverts commit 9fc8bedb56.

Revert "archiver: tests: fix test by calling NewContext()"

This reverts commit 709c35685e.

Revert "archiver: tests: amend test to include WaitForCompletion()"

This reverts commit 75261f56bc.

* archiver: tests: first attempt at WaitForCompletion() tests

* archiver: tests: slight improvement, less busy-loop

Just wait for the requests to complete in order, instead of busy-waiting
with a timeout.  This is slightly less fragile.

While here, reverse the arguments of a nearby assert.Equal() so that
expected/actual are correct in any test output.

* archiver: address lint nits

* services: archiver: only close the channel once

* services: archiver: use a struct{} for the wait channel

This makes it obvious that the channel is only being used as a signal,
rather than anything useful being piped through it.

* archiver: tests: fix expectations

Move the close of the channel into doArchive() itself; notably, before these
goroutines move on to waiting on the Release cond.

The tests are adjusted to reflect that we can't WaitForCompletion() after
they've already completed, as WaitForCompletion() doesn't indicate that
they've been released from the queue yet.

* archiver: tests: set cchan to nil for comparison

* archiver: move ctx.Error's back into the route handlers

We shouldn't be setting this in a service, we should just be validating the
request that we were handed.

* services: archiver: use regex to match a hash

This makes sure we don't try and use refName as a hash when it's clearly not
one, e.g. heads/pull/foo.

* routers: repo: remove the weird /archive/status endpoint

We don't need to do this anymore, we can just continue POSTing to the
archive/* endpoint until we're told the download's complete. This avoids a
potential naming conflict, where a ref could start with "status/"

* archiver: tests: bump reasonable timeout to 15s

* archiver: tests: actually release timedReq

* archiver: tests: run through inFlight instead of manually checking

While we're here, add a test for manually re-processing an archive that's
already been complete. Re-open the channel and mark it incomplete, so that
doArchive can just mark it complete again.

* initArchiveLinks: prevent default behavior from clicking

* archiver: alias gitea's context, golang context import pending

* archiver: simplify logic, just reconstruct slices

While the previous logic was perhaps slightly more efficient, the
new variant's readability is much improved.

* archiver: don't block shutdown on waiting for archive

The technique established launches a goroutine to do the wait,
which will close a wait channel upon termination. For the timeout
case, we also send back a value indicating whether the timeout was
hit or not.

The timeouts are expected to be relatively small, but still a multi-
second delay to shutdown due to this could be unfortunate.

* archiver: simplify shutdown logic

We can just grab the shutdown channel from the graceful manager instead of
constructing a channel to halt the caller and/or pass a result back.

* Style issues

* Fix mis-merge

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Lauris BH <lauris@nix.lv>

integrations/api_repo_test.go

@@ -77,9 +77,9 @@ func TestAPISearchRepo(t *testing.T) {
 		expectedResults
 	}{
 		{name: "RepositoriesMax50", requestURL: "/api/v1/repos/search?limit=50&private=false", expectedResults: expectedResults{
-			nil:   {count: 27},
+			nil:   {count: 28},
-			user:  {count: 27},
+			user:  {count: 28},
-			user2: {count: 27}},
+			user2: {count: 28}},
 		},
 		{name: "RepositoriesMax10", requestURL: "/api/v1/repos/search?limit=10&private=false", expectedResults: expectedResults{
 			nil:   {count: 10},

integrations/gitea-repositories-meta/user27/repo49.git/HEAD

@@ -0,0 +1 @@
+ref: refs/heads/master

integrations/gitea-repositories-meta/user27/repo49.git/config

@@ -0,0 +1,6 @@
+[core]
+	repositoryformatversion = 0
+	filemode = false
+	bare = true
+	symlinks = false
+	ignorecase = true

integrations/gitea-repositories-meta/user27/repo49.git/description

@@ -0,0 +1 @@
+Unnamed repository; edit this file 'description' to name the repository.

integrations/gitea-repositories-meta/user27/repo49.git/hooks/applypatch-msg.sample

@@ -0,0 +1,15 @@
+#!/bin/sh
+#
+# An example hook script to check the commit log message taken by
+# applypatch from an e-mail message.
+#
+# The hook should exit with non-zero status after issuing an
+# appropriate message if it wants to stop the commit.  The hook is
+# allowed to edit the commit message file.
+#
+# To enable this hook, rename this file to "applypatch-msg".
+
+. git-sh-setup
+commitmsg="$(git rev-parse --git-path hooks/commit-msg)"
+test -x "$commitmsg" && exec "$commitmsg" ${1+"$@"}
+:

integrations/gitea-repositories-meta/user27/repo49.git/hooks/commit-msg.sample

@@ -0,0 +1,24 @@
+#!/bin/sh
+#
+# An example hook script to check the commit log message.
+# Called by "git commit" with one argument, the name of the file
+# that has the commit message.  The hook should exit with non-zero
+# status after issuing an appropriate message if it wants to stop the
+# commit.  The hook is allowed to edit the commit message file.
+#
+# To enable this hook, rename this file to "commit-msg".
+
+# Uncomment the below to add a Signed-off-by line to the message.
+# Doing this in a hook is a bad idea in general, but the prepare-commit-msg
+# hook is more suited to it.
+#
+# SOB=$(git var GIT_AUTHOR_IDENT | sed -n 's/^\(.*>\).*$/Signed-off-by: \1/p')
+# grep -qs "^$SOB" "$1" || echo "$SOB" >> "$1"
+
+# This example catches duplicate Signed-off-by lines.
+
+test "" = "$(grep '^Signed-off-by: ' "$1" |
+	 sort | uniq -c | sed -e '/^[ 	]*1[ 	]/d')" || {
+	echo >&2 Duplicate Signed-off-by lines.
+	exit 1
+}

integrations/gitea-repositories-meta/user27/repo49.git/hooks/fsmonitor-watchman.sample

@@ -0,0 +1,114 @@
+#!/usr/bin/perl
+
+use strict;
+use warnings;
+use IPC::Open2;
+
+# An example hook script to integrate Watchman
+# (https://facebook.github.io/watchman/) with git to speed up detecting
+# new and modified files.
+#
+# The hook is passed a version (currently 1) and a time in nanoseconds
+# formatted as a string and outputs to stdout all files that have been
+# modified since the given time. Paths must be relative to the root of
+# the working tree and separated by a single NUL.
+#
+# To enable this hook, rename this file to "query-watchman" and set
+# 'git config core.fsmonitor .git/hooks/query-watchman'
+#
+my ($version, $time) = @ARGV;
+
+# Check the hook interface version
+
+if ($version == 1) {
+	# convert nanoseconds to seconds
+	$time = int $time / 1000000000;
+} else {
+	die "Unsupported query-fsmonitor hook version '$version'.\n" .
+	    "Falling back to scanning...\n";
+}
+
+my $git_work_tree;
+if ($^O =~ 'msys' || $^O =~ 'cygwin') {
+	$git_work_tree = Win32::GetCwd();
+	$git_work_tree =~ tr/\\/\//;
+} else {
+	require Cwd;
+	$git_work_tree = Cwd::cwd();
+}
+
+my $retry = 1;
+
+launch_watchman();
+
+sub launch_watchman {
+
+	my $pid = open2(\*CHLD_OUT, \*CHLD_IN, 'watchman -j --no-pretty')
+	    or die "open2() failed: $!\n" .
+	    "Falling back to scanning...\n";
+
+	# In the query expression below we're asking for names of files that
+	# changed since $time but were not transient (ie created after
+	# $time but no longer exist).
+	#
+	# To accomplish this, we're using the "since" generator to use the
+	# recency index to select candidate nodes and "fields" to limit the
+	# output to file names only. Then we're using the "expression" term to
+	# further constrain the results.
+	#
+	# The category of transient files that we want to ignore will have a
+	# creation clock (cclock) newer than $time_t value and will also not
+	# currently exist.
+
+	my $query = <<"	END";
+		["query", "$git_work_tree", {
+			"since": $time,
+			"fields": ["name"],
+			"expression": ["not", ["allof", ["since", $time, "cclock"], ["not", "exists"]]]
+		}]
+	END
+
+	print CHLD_IN $query;
+	close CHLD_IN;
+	my $response = do {local $/; <CHLD_OUT>};
+
+	die "Watchman: command returned no output.\n" .
+	    "Falling back to scanning...\n" if $response eq "";
+	die "Watchman: command returned invalid output: $response\n" .
+	    "Falling back to scanning...\n" unless $response =~ /^\{/;
+
+	my $json_pkg;
+	eval {
+		require JSON::XS;
+		$json_pkg = "JSON::XS";
+		1;
+	} or do {
+		require JSON::PP;
+		$json_pkg = "JSON::PP";
+	};
+
+	my $o = $json_pkg->new->utf8->decode($response);
+
+	if ($retry > 0 and $o->{error} and $o->{error} =~ m/unable to resolve root .* directory (.*) is not watched/) {
+		print STDERR "Adding '$git_work_tree' to watchman's watch list.\n";
+		$retry--;
+		qx/watchman watch "$git_work_tree"/;
+		die "Failed to make watchman watch '$git_work_tree'.\n" .
+		    "Falling back to scanning...\n" if $? != 0;
+
+		# Watchman will always return all files on the first query so
+		# return the fast "everything is dirty" flag to git and do the
+		# Watchman query just to get it over with now so we won't pay
+		# the cost in git to look up each individual file.
+		print "/\0";
+		eval { launch_watchman() };
+		exit 0;
+	}
+
+	die "Watchman: $o->{error}.\n" .
+	    "Falling back to scanning...\n" if $o->{error};
+
+	binmode STDOUT, ":utf8";
+	local $, = "\0";
+	print @{$o->{files}};
+}

integrations/gitea-repositories-meta/user27/repo49.git/hooks/post-receive

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+data=$(cat)
+exitcodes=""
+hookname=$(basename $0)
+GIT_DIR=${GIT_DIR:-$(dirname $0)}
+
+for hook in ${GIT_DIR}/hooks/${hookname}.d/*; do
+test -x "${hook}" && test -f "${hook}" || continue
+echo "${data}" | "${hook}"
+exitcodes="${exitcodes} $?"
+done
+
+for i in ${exitcodes}; do
+[ ${i} -eq 0 ] || exit ${i}
+done

integrations/gitea-repositories-meta/user27/repo49.git/hooks/post-receive.d/gitea

@@ -0,0 +1,2 @@
+#!/usr/bin/env bash
+"$GITEA_ROOT/gitea" hook --config="$GITEA_ROOT/$GITEA_CONF" post-receive

integrations/gitea-repositories-meta/user27/repo49.git/hooks/post-update.sample

@@ -0,0 +1,8 @@
+#!/bin/sh
+#
+# An example hook script to prepare a packed repository for use over
+# dumb transports.
+#
+# To enable this hook, rename this file to "post-update".
+
+exec git update-server-info

integrations/gitea-repositories-meta/user27/repo49.git/hooks/pre-applypatch.sample

@@ -0,0 +1,14 @@
+#!/bin/sh
+#
+# An example hook script to verify what is about to be committed
+# by applypatch from an e-mail message.
+#
+# The hook should exit with non-zero status after issuing an
+# appropriate message if it wants to stop the commit.
+#
+# To enable this hook, rename this file to "pre-applypatch".
+
+. git-sh-setup
+precommit="$(git rev-parse --git-path hooks/pre-commit)"
+test -x "$precommit" && exec "$precommit" ${1+"$@"}
+:

integrations/gitea-repositories-meta/user27/repo49.git/hooks/pre-commit.sample

@@ -0,0 +1,49 @@
+#!/bin/sh
+#
+# An example hook script to verify what is about to be committed.
+# Called by "git commit" with no arguments.  The hook should
+# exit with non-zero status after issuing an appropriate message if
+# it wants to stop the commit.
+#
+# To enable this hook, rename this file to "pre-commit".
+
+if git rev-parse --verify HEAD >/dev/null 2>&1
+then
+	against=HEAD
+else
+	# Initial commit: diff against an empty tree object
+	against=$(git hash-object -t tree /dev/null)
+fi
+
+# If you want to allow non-ASCII filenames set this variable to true.
+allownonascii=$(git config --bool hooks.allownonascii)
+
+# Redirect output to stderr.
+exec 1>&2
+
+# Cross platform projects tend to avoid non-ASCII filenames; prevent
+# them from being added to the repository. We exploit the fact that the
+# printable range starts at the space character and ends with tilde.
+if [ "$allownonascii" != "true" ] &&
+	# Note that the use of brackets around a tr range is ok here, (it's
+	# even required, for portability to Solaris 10's /usr/bin/tr), since
+	# the square bracket bytes happen to fall in the designated range.
+	test $(git diff --cached --name-only --diff-filter=A -z $against |
+	  LC_ALL=C tr -d '[ -~]\0' | wc -c) != 0
+then
+	cat <<\EOF
+Error: Attempt to add a non-ASCII file name.
+
+This can cause problems if you want to work with people on other platforms.
+
+To be portable it is advisable to rename the file.
+
+If you know what you are doing you can disable this check using:
+
+  git config hooks.allownonascii true
+EOF
+	exit 1
+fi
+
+# If there are whitespace errors, print the offending file names and fail.
+exec git diff-index --check --cached $against --

integrations/gitea-repositories-meta/user27/repo49.git/hooks/pre-push.sample

@@ -0,0 +1,53 @@
+#!/bin/sh
+
+# An example hook script to verify what is about to be pushed.  Called by "git
+# push" after it has checked the remote status, but before anything has been
+# pushed.  If this script exits with a non-zero status nothing will be pushed.
+#
+# This hook is called with the following parameters:
+#
+# $1 -- Name of the remote to which the push is being done
+# $2 -- URL to which the push is being done
+#
+# If pushing without using a named remote those arguments will be equal.
+#
+# Information about the commits which are being pushed is supplied as lines to
+# the standard input in the form:
+#
+#   <local ref> <local sha1> <remote ref> <remote sha1>
+#
+# This sample shows how to prevent push of commits where the log message starts
+# with "WIP" (work in progress).
+
+remote="$1"
+url="$2"
+
+z40=0000000000000000000000000000000000000000
+
+while read local_ref local_sha remote_ref remote_sha
+do
+	if [ "$local_sha" = $z40 ]
+	then
+		# Handle delete
+		:
+	else
+		if [ "$remote_sha" = $z40 ]
+		then
+			# New branch, examine all commits
+			range="$local_sha"
+		else
+			# Update to existing branch, examine new commits
+			range="$remote_sha..$local_sha"
+		fi
+
+		# Check for WIP commit
+		commit=`git rev-list -n 1 --grep '^WIP' "$range"`
+		if [ -n "$commit" ]
+		then
+			echo >&2 "Found WIP commit in $local_ref, not pushing"
+			exit 1
+		fi
+	fi
+done
+
+exit 0

integrations/gitea-repositories-meta/user27/repo49.git/hooks/pre-rebase.sample

@@ -0,0 +1,169 @@
+#!/bin/sh
+#
+# Copyright (c) 2006, 2008 Junio C Hamano
+#
+# The "pre-rebase" hook is run just before "git rebase" starts doing
+# its job, and can prevent the command from running by exiting with
+# non-zero status.
+#
+# The hook is called with the following parameters:
+#
+# $1 -- the upstream the series was forked from.
+# $2 -- the branch being rebased (or empty when rebasing the current branch).
+#
+# This sample shows how to prevent topic branches that are already
+# merged to 'next' branch from getting rebased, because allowing it
+# would result in rebasing already published history.
+
+publish=next
+basebranch="$1"
+if test "$#" = 2
+then
+	topic="refs/heads/$2"
+else
+	topic=`git symbolic-ref HEAD` ||
+	exit 0 ;# we do not interrupt rebasing detached HEAD
+fi
+
+case "$topic" in
+refs/heads/??/*)
+	;;
+*)
+	exit 0 ;# we do not interrupt others.
+	;;
+esac
+
+# Now we are dealing with a topic branch being rebased
+# on top of master.  Is it OK to rebase it?
+
+# Does the topic really exist?
+git show-ref -q "$topic" || {
+	echo >&2 "No such branch $topic"
+	exit 1
+}
+
+# Is topic fully merged to master?
+not_in_master=`git rev-list --pretty=oneline ^master "$topic"`
+if test -z "$not_in_master"
+then
+	echo >&2 "$topic is fully merged to master; better remove it."
+	exit 1 ;# we could allow it, but there is no point.
+fi
+
+# Is topic ever merged to next?  If so you should not be rebasing it.
+only_next_1=`git rev-list ^master "^$topic" ${publish} | sort`
+only_next_2=`git rev-list ^master           ${publish} | sort`
+if test "$only_next_1" = "$only_next_2"
+then
+	not_in_topic=`git rev-list "^$topic" master`
+	if test -z "$not_in_topic"
+	then
+		echo >&2 "$topic is already up to date with master"
+		exit 1 ;# we could allow it, but there is no point.
+	else
+		exit 0
+	fi
+else
+	not_in_next=`git rev-list --pretty=oneline ^${publish} "$topic"`
+	/usr/bin/perl -e '
+		my $topic = $ARGV[0];
+		my $msg = "* $topic has commits already merged to public branch:\n";
+		my (%not_in_next) = map {
+			/^([0-9a-f]+) /;
+			($1 => 1);
+		} split(/\n/, $ARGV[1]);
+		for my $elem (map {
+				/^([0-9a-f]+) (.*)$/;
+				[$1 => $2];
+			} split(/\n/, $ARGV[2])) {
+			if (!exists $not_in_next{$elem->[0]}) {
+				if ($msg) {
+					print STDERR $msg;
+					undef $msg;
+				}
+				print STDERR " $elem->[1]\n";
+			}
+		}
+	' "$topic" "$not_in_next" "$not_in_master"
+	exit 1
+fi
+
+<<\DOC_END
+
+This sample hook safeguards topic branches that have been
+published from being rewound.
+
+The workflow assumed here is:
+
+ * Once a topic branch forks from "master", "master" is never
+   merged into it again (either directly or indirectly).
+
+ * Once a topic branch is fully cooked and merged into "master",
+   it is deleted.  If you need to build on top of it to correct
+   earlier mistakes, a new topic branch is created by forking at
+   the tip of the "master".  This is not strictly necessary, but
+   it makes it easier to keep your history simple.
+
+ * Whenever you need to test or publish your changes to topic
+   branches, merge them into "next" branch.
+
+The script, being an example, hardcodes the publish branch name
+to be "next", but it is trivial to make it configurable via
+$GIT_DIR/config mechanism.
+
+With this workflow, you would want to know:
+
+(1) ... if a topic branch has ever been merged to "next".  Young
+    topic branches can have stupid mistakes you would rather
+    clean up before publishing, and things that have not been
+    merged into other branches can be easily rebased without
+    affecting other people.  But once it is published, you would
+    not want to rewind it.
+
+(2) ... if a topic branch has been fully merged to "master".
+    Then you can delete it.  More importantly, you should not
+    build on top of it -- other people may already want to
+    change things related to the topic as patches against your
+    "master", so if you need further changes, it is better to
+    fork the topic (perhaps with the same name) afresh from the
+    tip of "master".
+
+Let's look at this example:
+
+		   o---o---o---o---o---o---o---o---o---o "next"
+		  /       /           /           /
+		 /   a---a---b A     /           /
+		/   /               /           /
+	       /   /   c---c---c---c B         /
+	      /   /   /             \         /
+	     /   /   /   b---b C     \       /
+	    /   /   /   /             \     /
+    ---o---o---o---o---o---o---o---o---o---o---o "master"
+
+
+A, B and C are topic branches.
+
+ * A has one fix since it was merged up to "next".
+
+ * B has finished.  It has been fully merged up to "master" and "next",
+   and is ready to be deleted.
+
+ * C has not merged to "next" at all.
+
+We would want to allow C to be rebased, refuse A, and encourage
+B to be deleted.
+
+To compute (1):
+
+	git rev-list ^master ^topic next
+	git rev-list ^master        next
+
+	if these match, topic has not merged in next at all.
+
+To compute (2):
+
+	git rev-list master..topic
+
+	if this is empty, it is fully merged to "master".
+
+DOC_END

integrations/gitea-repositories-meta/user27/repo49.git/hooks/pre-receive

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+data=$(cat)
+exitcodes=""
+hookname=$(basename $0)
+GIT_DIR=${GIT_DIR:-$(dirname $0)}
+
+for hook in ${GIT_DIR}/hooks/${hookname}.d/*; do
+test -x "${hook}" && test -f "${hook}" || continue
+echo "${data}" | "${hook}"
+exitcodes="${exitcodes} $?"
+done
+
+for i in ${exitcodes}; do
+[ ${i} -eq 0 ] || exit ${i}
+done

integrations/gitea-repositories-meta/user27/repo49.git/hooks/pre-receive.d/gitea

@@ -0,0 +1,2 @@
+#!/usr/bin/env bash
+"$GITEA_ROOT/gitea" hook --config="$GITEA_ROOT/$GITEA_CONF" pre-receive

integrations/gitea-repositories-meta/user27/repo49.git/hooks/pre-receive.sample

@@ -0,0 +1,24 @@
+#!/bin/sh
+#
+# An example hook script to make use of push options.
+# The example simply echoes all push options that start with 'echoback='
+# and rejects all pushes when the "reject" push option is used.
+#
+# To enable this hook, rename this file to "pre-receive".
+
+if test -n "$GIT_PUSH_OPTION_COUNT"
+then
+	i=0
+	while test "$i" -lt "$GIT_PUSH_OPTION_COUNT"
+	do
+		eval "value=\$GIT_PUSH_OPTION_$i"
+		case "$value" in
+		echoback=*)
+			echo "echo from the pre-receive-hook: ${value#*=}" >&2
+			;;
+		reject)
+			exit 1
+		esac
+		i=$((i + 1))
+	done
+fi

integrations/gitea-repositories-meta/user27/repo49.git/hooks/prepare-commit-msg.sample

@@ -0,0 +1,42 @@
+#!/bin/sh
+#
+# An example hook script to prepare the commit log message.
+# Called by "git commit" with the name of the file that has the
+# commit message, followed by the description of the commit
+# message's source.  The hook's purpose is to edit the commit
+# message file.  If the hook fails with a non-zero status,
+# the commit is aborted.
+#
+# To enable this hook, rename this file to "prepare-commit-msg".
+
+# This hook includes three examples. The first one removes the
+# "# Please enter the commit message..." help message.
+#
+# The second includes the output of "git diff --name-status -r"
+# into the message, just before the "git status" output.  It is
+# commented because it doesn't cope with --amend or with squashed
+# commits.
+#
+# The third example adds a Signed-off-by line to the message, that can
+# still be edited.  This is rarely a good idea.
+
+COMMIT_MSG_FILE=$1
+COMMIT_SOURCE=$2
+SHA1=$3
+
+/usr/bin/perl -i.bak -ne 'print unless(m/^. Please enter the commit message/..m/^#$/)' "$COMMIT_MSG_FILE"
+
+# case "$COMMIT_SOURCE,$SHA1" in
+#  ,|template,)
+#    /usr/bin/perl -i.bak -pe '
+#       print "\n" . `git diff --cached --name-status -r`
+# 	 if /^#/ && $first++ == 0' "$COMMIT_MSG_FILE" ;;
+#  *) ;;
+# esac
+
+# SOB=$(git var GIT_COMMITTER_IDENT | sed -n 's/^\(.*>\).*$/Signed-off-by: \1/p')
+# git interpret-trailers --in-place --trailer "$SOB" "$COMMIT_MSG_FILE"
+# if test -z "$COMMIT_SOURCE"
+# then
+#   /usr/bin/perl -i.bak -pe 'print "\n" if !$first_line++' "$COMMIT_MSG_FILE"
+# fi

integrations/gitea-repositories-meta/user27/repo49.git/hooks/update

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+exitcodes=""
+hookname=$(basename $0)
+GIT_DIR=${GIT_DIR:-$(dirname $0)}
+
+for hook in ${GIT_DIR}/hooks/${hookname}.d/*; do
+test -x "${hook}" && test -f "${hook}" || continue
+"${hook}" $1 $2 $3
+exitcodes="${exitcodes} $?"
+done
+
+for i in ${exitcodes}; do
+[ ${i} -eq 0 ] || exit ${i}
+done

integrations/gitea-repositories-meta/user27/repo49.git/hooks/update.d/gitea

@@ -0,0 +1,2 @@
+#!/usr/bin/env bash
+"$GITEA_ROOT/gitea" hook --config="$GITEA_ROOT/$GITEA_CONF" update $1 $2 $3

integrations/gitea-repositories-meta/user27/repo49.git/hooks/update.sample

@@ -0,0 +1,128 @@
+#!/bin/sh
+#
+# An example hook script to block unannotated tags from entering.
+# Called by "git receive-pack" with arguments: refname sha1-old sha1-new
+#
+# To enable this hook, rename this file to "update".
+#
+# Config
+# ------
+# hooks.allowunannotated
+#   This boolean sets whether unannotated tags will be allowed into the
+#   repository.  By default they won't be.
+# hooks.allowdeletetag
+#   This boolean sets whether deleting tags will be allowed in the
+#   repository.  By default they won't be.
+# hooks.allowmodifytag
+#   This boolean sets whether a tag may be modified after creation. By default
+#   it won't be.
+# hooks.allowdeletebranch
+#   This boolean sets whether deleting branches will be allowed in the
+#   repository.  By default they won't be.
+# hooks.denycreatebranch
+#   This boolean sets whether remotely creating branches will be denied
+#   in the repository.  By default this is allowed.
+#
+
+# --- Command line
+refname="$1"
+oldrev="$2"
+newrev="$3"
+
+# --- Safety check
+if [ -z "$GIT_DIR" ]; then
+	echo "Don't run this script from the command line." >&2
+	echo " (if you want, you could supply GIT_DIR then run" >&2
+	echo "  $0 <ref> <oldrev> <newrev>)" >&2
+	exit 1
+fi
+
+if [ -z "$refname" -o -z "$oldrev" -o -z "$newrev" ]; then
+	echo "usage: $0 <ref> <oldrev> <newrev>" >&2
+	exit 1
+fi
+
+# --- Config
+allowunannotated=$(git config --bool hooks.allowunannotated)
+allowdeletebranch=$(git config --bool hooks.allowdeletebranch)
+denycreatebranch=$(git config --bool hooks.denycreatebranch)
+allowdeletetag=$(git config --bool hooks.allowdeletetag)
+allowmodifytag=$(git config --bool hooks.allowmodifytag)
+
+# check for no description
+projectdesc=$(sed -e '1q' "$GIT_DIR/description")
+case "$projectdesc" in
+"Unnamed repository"* | "")
+	echo "*** Project description file hasn't been set" >&2
+	exit 1
+	;;
+esac
+
+# --- Check types
+# if $newrev is 0000...0000, it's a commit to delete a ref.
+zero="0000000000000000000000000000000000000000"
+if [ "$newrev" = "$zero" ]; then
+	newrev_type=delete
+else
+	newrev_type=$(git cat-file -t $newrev)
+fi
+
+case "$refname","$newrev_type" in
+	refs/tags/*,commit)
+		# un-annotated tag
+		short_refname=${refname##refs/tags/}
+		if [ "$allowunannotated" != "true" ]; then
+			echo "*** The un-annotated tag, $short_refname, is not allowed in this repository" >&2
+			echo "*** Use 'git tag [ -a | -s ]' for tags you want to propagate." >&2
+			exit 1
+		fi
+		;;
+	refs/tags/*,delete)
+		# delete tag
+		if [ "$allowdeletetag" != "true" ]; then
+			echo "*** Deleting a tag is not allowed in this repository" >&2
+			exit 1
+		fi
+		;;
+	refs/tags/*,tag)
+		# annotated tag
+		if [ "$allowmodifytag" != "true" ] && git rev-parse $refname > /dev/null 2>&1
+		then
+			echo "*** Tag '$refname' already exists." >&2
+			echo "*** Modifying a tag is not allowed in this repository." >&2
+			exit 1
+		fi
+		;;
+	refs/heads/*,commit)
+		# branch
+		if [ "$oldrev" = "$zero" -a "$denycreatebranch" = "true" ]; then
+			echo "*** Creating a branch is not allowed in this repository" >&2
+			exit 1
+		fi
+		;;
+	refs/heads/*,delete)
+		# delete branch
+		if [ "$allowdeletebranch" != "true" ]; then
+			echo "*** Deleting a branch is not allowed in this repository" >&2
+			exit 1
+		fi
+		;;
+	refs/remotes/*,commit)
+		# tracking branch
+		;;
+	refs/remotes/*,delete)
+		# delete tracking branch
+		if [ "$allowdeletebranch" != "true" ]; then
+			echo "*** Deleting a tracking branch is not allowed in this repository" >&2
+			exit 1
+		fi
+		;;
+	*)
+		# Anything else (is there anything else?)
+		echo "*** Update hook: unknown type of update to ref $refname of type $newrev_type" >&2
+		exit 1
+		;;
+esac
+
+# --- Finished
+exit 0

integrations/gitea-repositories-meta/user27/repo49.git/info/exclude

@@ -0,0 +1,6 @@
+# git ls-files --others --exclude-from=.git/info/exclude
+# Lines that start with '#' are comments.
+# For a project mostly in C, the following would be a good set of
+# exclude patterns (uncomment them if you want to use them):
+# *.[oa]
+# *~

integrations/gitea-repositories-meta/user27/repo49.git/info/refs

@@ -0,0 +1 @@
+aacbdfe9e1c4b47f60abe81849045fa4e96f1d75	refs/heads/master

integrations/gitea-repositories-meta/user27/repo49.git/objects/info/packs

@@ -0,0 +1 @@
+

integrations/gitea-repositories-meta/user27/repo49.git/refs/heads/master

@@ -0,0 +1 @@
+aacbdfe9e1c4b47f60abe81849045fa4e96f1d75

models/fixtures/repository.yml

@@ -680,3 +680,16 @@
   num_pulls: 1
   is_mirror: false
   status: 0
+
+-
+  id: 49
+  owner_id: 27
+  owner_name: user27
+  lower_name: repo49
+  name: repo49
+  is_private: false
+  num_stars: 0
+  num_forks: 0
+  num_issues: 0
+  is_mirror: false
+  status: 0

models/fixtures/user.yml

@@ -469,7 +469,7 @@
   is_admin: false
   avatar: avatar27
   avatar_email: user27@example.com
-  num_repos: 2
+  num_repos: 3
 
 -
   id: 28

models/repo_list_test.go

@@ -187,10 +187,10 @@ func TestSearchRepository(t *testing.T) {
 			count: 14},
 		{name: "AllPublic/PublicRepositoriesOfUserIncludingCollaborative",
 			opts:  &SearchRepoOptions{ListOptions: ListOptions{Page: 1, PageSize: 10}, OwnerID: 15, AllPublic: true, Template: util.OptionalBoolFalse},
-			count: 25},
+			count: 26},
 		{name: "AllPublic/PublicAndPrivateRepositoriesOfUserIncludingCollaborative",
 			opts:  &SearchRepoOptions{ListOptions: ListOptions{Page: 1, PageSize: 10}, OwnerID: 15, Private: true, AllPublic: true, AllLimited: true, Template: util.OptionalBoolFalse},
-			count: 30},
+			count: 31},
 		{name: "AllPublic/PublicAndPrivateRepositoriesOfUserIncludingCollaborativeByName",
 			opts:  &SearchRepoOptions{Keyword: "test", ListOptions: ListOptions{Page: 1, PageSize: 10}, OwnerID: 15, Private: true, AllPublic: true},
 			count: 15},
@@ -199,7 +199,7 @@ func TestSearchRepository(t *testing.T) {
 			count: 13},
 		{name: "AllPublic/PublicRepositoriesOfOrganization",
 			opts:  &SearchRepoOptions{ListOptions: ListOptions{Page: 1, PageSize: 10}, OwnerID: 17, AllPublic: true, Collaborate: util.OptionalBoolFalse, Template: util.OptionalBoolFalse},
-			count: 25},
+			count: 26},
 		{name: "AllTemplates",
 			opts:  &SearchRepoOptions{ListOptions: ListOptions{Page: 1, PageSize: 10}, Template: util.OptionalBoolTrue},
 			count: 2},

routers/repo/repo.go

@@ -7,20 +7,17 @@ package repo
 
 import (
 	"fmt"
-	"os"
-	"path"
 	"strings"
+	"time"
 
 	"code.gitea.io/gitea/models"
 	"code.gitea.io/gitea/modules/auth"
 	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/context"
-	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
+	archiver_service "code.gitea.io/gitea/services/archiver"
 	repo_service "code.gitea.io/gitea/services/repository"
-
-	"github.com/unknwon/com"
 )
 
 const (
@@ -327,78 +324,49 @@ func RedirectDownload(ctx *context.Context) {
 	ctx.Error(404)
 }
 
-// Download download an archive of a repository
+// Download an archive of a repository
 func Download(ctx *context.Context) {
-	var (
+	uri := ctx.Params("*")
-		uri         = ctx.Params("*")
+	aReq := archiver_service.DeriveRequestFrom(ctx, uri)
-		refName     string
-		ext         string
-		archivePath string
-		archiveType git.ArchiveType
-	)
 
-	switch {
+	if aReq == nil {
-	case strings.HasSuffix(uri, ".zip"):
-		ext = ".zip"
-		archivePath = path.Join(ctx.Repo.GitRepo.Path, "archives/zip")
-		archiveType = git.ZIP
-	case strings.HasSuffix(uri, ".tar.gz"):
-		ext = ".tar.gz"
-		archivePath = path.Join(ctx.Repo.GitRepo.Path, "archives/targz")
-		archiveType = git.TARGZ
-	default:
-		log.Trace("Unknown format: %s", uri)
 		ctx.Error(404)
 		return
 	}
-	refName = strings.TrimSuffix(uri, ext)
 
-	if !com.IsDir(archivePath) {
+	downloadName := ctx.Repo.Repository.Name + "-" + aReq.GetArchiveName()
-		if err := os.MkdirAll(archivePath, os.ModePerm); err != nil {
+	complete := aReq.IsComplete()
-			ctx.ServerError("Download -> os.MkdirAll(archivePath)", err)
+	if !complete {
-			return
+		aReq = archiver_service.ArchiveRepository(aReq)
-		}
+		complete = aReq.WaitForCompletion(ctx)
 	}
 
-	// Get corresponding commit.
+	if complete {
-	var (
+		ctx.ServeFile(aReq.GetArchivePath(), downloadName)
-		commit *git.Commit
-		err    error
-	)
-	gitRepo := ctx.Repo.GitRepo
-	if gitRepo.IsBranchExist(refName) {
-		commit, err = gitRepo.GetBranchCommit(refName)
-		if err != nil {
-			ctx.ServerError("GetBranchCommit", err)
-			return
-		}
-	} else if gitRepo.IsTagExist(refName) {
-		commit, err = gitRepo.GetTagCommit(refName)
-		if err != nil {
-			ctx.ServerError("GetTagCommit", err)
-			return
-		}
-	} else if len(refName) >= 4 && len(refName) <= 40 {
-		commit, err = gitRepo.GetCommit(refName)
-		if err != nil {
-			ctx.NotFound("GetCommit", nil)
-			return
-		}
 	} else {
-		ctx.NotFound("Download", nil)
+		ctx.Error(404)
-		return
-	}
-
-	archivePath = path.Join(archivePath, base.ShortSha(commit.ID.String())+ext)
-	if !com.IsFile(archivePath) {
-		if err := commit.CreateArchive(ctx.Req.Context(), archivePath, git.CreateArchiveOpts{
-			Format: archiveType,
-			Prefix: setting.Repository.PrefixArchiveFiles,
-		}); err != nil {
-			ctx.ServerError("Download -> CreateArchive "+archivePath, err)
-			return
 	}
 }
 
-	ctx.ServeFile(archivePath, ctx.Repo.Repository.Name+"-"+refName+ext)
+// InitiateDownload will enqueue an archival request, as needed.  It may submit
+// a request that's already in-progress, but the archiver service will just
+// kind of drop it on the floor if this is the case.
+func InitiateDownload(ctx *context.Context) {
+	uri := ctx.Params("*")
+	aReq := archiver_service.DeriveRequestFrom(ctx, uri)
+
+	if aReq == nil {
+		ctx.Error(404)
+		return
+	}
+
+	complete := aReq.IsComplete()
+	if !complete {
+		aReq = archiver_service.ArchiveRepository(aReq)
+		complete, _ = aReq.TimedWaitForCompletion(ctx, 2*time.Second)
+	}
+
+	ctx.JSON(200, map[string]interface{}{
+		"complete": complete,
+	})
 }

routers/routes/routes.go

@@ -1000,7 +1000,10 @@ func RegisterRoutes(m *macaron.Macaron) {
 			m.Get("/:period", repo.ActivityAuthors)
 		}, context.RepoRef(), repo.MustBeNotEmpty, context.RequireRepoReaderOr(models.UnitTypeCode))
 
-		m.Get("/archive/*", repo.MustBeNotEmpty, reqRepoCodeReader, repo.Download)
+		m.Group("/archive", func() {
+			m.Get("/*", repo.Download)
+			m.Post("/*", repo.InitiateDownload)
+		}, repo.MustBeNotEmpty, reqRepoCodeReader)
 
 		m.Group("/branches", func() {
 			m.Get("", repo.Branches)

services/archiver/archiver.go

@@ -0,0 +1,310 @@
+// Copyright 2020 The Gitea Authors.
+// All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package archiver
+
+import (
+	"io"
+	"io/ioutil"
+	"os"
+	"path"
+	"regexp"
+	"strings"
+	"sync"
+	"time"
+
+	"code.gitea.io/gitea/modules/base"
+	"code.gitea.io/gitea/modules/context"
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/graceful"
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/setting"
+
+	"github.com/unknwon/com"
+)
+
+// ArchiveRequest defines the parameters of an archive request, which notably
+// includes the specific repository being archived as well as the commit, the
+// name by which it was requested, and the kind of archive being requested.
+// This is entirely opaque to external entities, though, and mostly used as a
+// handle elsewhere.
+type ArchiveRequest struct {
+	uri             string
+	repo            *git.Repository
+	refName         string
+	ext             string
+	archivePath     string
+	archiveType     git.ArchiveType
+	archiveComplete bool
+	commit          *git.Commit
+	cchan           chan struct{}
+}
+
+var archiveInProgress []*ArchiveRequest
+var archiveMutex sync.Mutex
+
+// SHA1 hashes will only go up to 40 characters, but SHA256 hashes will go all
+// the way to 64.
+var shaRegex = regexp.MustCompile(`^[0-9a-f]{4,64}$`)
+
+// These facilitate testing, by allowing the unit tests to control (to some extent)
+// the goroutine used for processing the queue.
+var archiveQueueMutex *sync.Mutex
+var archiveQueueStartCond *sync.Cond
+var archiveQueueReleaseCond *sync.Cond
+
+// GetArchivePath returns the path from which we can serve this archive.
+func (aReq *ArchiveRequest) GetArchivePath() string {
+	return aReq.archivePath
+}
+
+// GetArchiveName returns the name of the caller, based on the ref used by the
+// caller to create this request.
+func (aReq *ArchiveRequest) GetArchiveName() string {
+	return aReq.refName + aReq.ext
+}
+
+// IsComplete returns the completion status of this request.
+func (aReq *ArchiveRequest) IsComplete() bool {
+	return aReq.archiveComplete
+}
+
+// WaitForCompletion will wait for this request to complete, with no timeout.
+// It returns whether the archive was actually completed, as the channel could
+// have also been closed due to an error.
+func (aReq *ArchiveRequest) WaitForCompletion(ctx *context.Context) bool {
+	select {
+	case <-aReq.cchan:
+	case <-ctx.Req.Context().Done():
+	}
+
+	return aReq.IsComplete()
+}
+
+// TimedWaitForCompletion will wait for this request to complete, with timeout
+// happening after the specified Duration.  It returns whether the archive is
+// now complete and whether we hit the timeout or not.  The latter may not be
+// useful if the request is complete or we started to shutdown.
+func (aReq *ArchiveRequest) TimedWaitForCompletion(ctx *context.Context, dur time.Duration) (bool, bool) {
+	timeout := false
+	select {
+	case <-time.After(dur):
+		timeout = true
+	case <-aReq.cchan:
+	case <-ctx.Req.Context().Done():
+	}
+
+	return aReq.IsComplete(), timeout
+}
+
+// The caller must hold the archiveMutex across calls to getArchiveRequest.
+func getArchiveRequest(repo *git.Repository, commit *git.Commit, archiveType git.ArchiveType) *ArchiveRequest {
+	for _, r := range archiveInProgress {
+		// Need to be referring to the same repository.
+		if r.repo.Path == repo.Path && r.commit.ID == commit.ID && r.archiveType == archiveType {
+			return r
+		}
+	}
+	return nil
+}
+
+// DeriveRequestFrom creates an archival request, based on the URI.  The
+// resulting ArchiveRequest is suitable for being passed to ArchiveRepository()
+// if it's determined that the request still needs to be satisfied.
+func DeriveRequestFrom(ctx *context.Context, uri string) *ArchiveRequest {
+	if ctx.Repo == nil || ctx.Repo.GitRepo == nil {
+		log.Trace("Repo not initialized")
+		return nil
+	}
+	r := &ArchiveRequest{
+		uri:  uri,
+		repo: ctx.Repo.GitRepo,
+	}
+
+	switch {
+	case strings.HasSuffix(uri, ".zip"):
+		r.ext = ".zip"
+		r.archivePath = path.Join(r.repo.Path, "archives/zip")
+		r.archiveType = git.ZIP
+	case strings.HasSuffix(uri, ".tar.gz"):
+		r.ext = ".tar.gz"
+		r.archivePath = path.Join(r.repo.Path, "archives/targz")
+		r.archiveType = git.TARGZ
+	default:
+		log.Trace("Unknown format: %s", uri)
+		return nil
+	}
+
+	r.refName = strings.TrimSuffix(r.uri, r.ext)
+	if !com.IsDir(r.archivePath) {
+		if err := os.MkdirAll(r.archivePath, os.ModePerm); err != nil {
+			ctx.ServerError("Download -> os.MkdirAll(archivePath)", err)
+			return nil
+		}
+	}
+
+	// Get corresponding commit.
+	var (
+		err error
+	)
+	if r.repo.IsBranchExist(r.refName) {
+		r.commit, err = r.repo.GetBranchCommit(r.refName)
+		if err != nil {
+			ctx.ServerError("GetBranchCommit", err)
+			return nil
+		}
+	} else if r.repo.IsTagExist(r.refName) {
+		r.commit, err = r.repo.GetTagCommit(r.refName)
+		if err != nil {
+			ctx.ServerError("GetTagCommit", err)
+			return nil
+		}
+	} else if shaRegex.MatchString(r.refName) {
+		r.commit, err = r.repo.GetCommit(r.refName)
+		if err != nil {
+			ctx.NotFound("GetCommit", nil)
+			return nil
+		}
+	} else {
+		ctx.NotFound("DeriveRequestFrom", nil)
+		return nil
+	}
+
+	archiveMutex.Lock()
+	defer archiveMutex.Unlock()
+	if rExisting := getArchiveRequest(r.repo, r.commit, r.archiveType); rExisting != nil {
+		return rExisting
+	}
+
+	r.archivePath = path.Join(r.archivePath, base.ShortSha(r.commit.ID.String())+r.ext)
+	r.archiveComplete = com.IsFile(r.archivePath)
+	return r
+}
+
+func doArchive(r *ArchiveRequest) {
+	var (
+		err         error
+		tmpArchive  *os.File
+		destArchive *os.File
+	)
+
+	// Close the channel to indicate to potential waiters that this request
+	// has finished.
+	defer close(r.cchan)
+
+	// It could have happened that we enqueued two archival requests, due to
+	// race conditions and difficulties in locking.  Do one last check that
+	// the archive we're referring to doesn't already exist.  If it does exist,
+	// then just mark the request as complete and move on.
+	if com.IsFile(r.archivePath) {
+		r.archiveComplete = true
+		return
+	}
+
+	// Create a temporary file to use while the archive is being built.  We
+	// will then copy it into place (r.archivePath) once it's fully
+	// constructed.
+	tmpArchive, err = ioutil.TempFile("", "archive")
+	if err != nil {
+		log.Error("Unable to create a temporary archive file! Error: %v", err)
+		return
+	}
+	defer func() {
+		tmpArchive.Close()
+		os.Remove(tmpArchive.Name())
+	}()
+
+	if err = r.commit.CreateArchive(graceful.GetManager().ShutdownContext(), tmpArchive.Name(), git.CreateArchiveOpts{
+		Format: r.archiveType,
+		Prefix: setting.Repository.PrefixArchiveFiles,
+	}); err != nil {
+		log.Error("Download -> CreateArchive "+tmpArchive.Name(), err)
+		return
+	}
+
+	// Now we copy it into place
+	if destArchive, err = os.Create(r.archivePath); err != nil {
+		log.Error("Unable to open archive " + r.archivePath)
+		return
+	}
+	_, err = io.Copy(destArchive, tmpArchive)
+	destArchive.Close()
+	if err != nil {
+		log.Error("Unable to write archive " + r.archivePath)
+		return
+	}
+
+	// Block any attempt to finalize creating a new request if we're marking
+	r.archiveComplete = true
+}
+
+// ArchiveRepository satisfies the ArchiveRequest being passed in.  Processing
+// will occur in a separate goroutine, as this phase may take a while to
+// complete.  If the archive already exists, ArchiveRepository will not do
+// anything.  In all cases, the caller should be examining the *ArchiveRequest
+// being returned for completion, as it may be different than the one they passed
+// in.
+func ArchiveRepository(request *ArchiveRequest) *ArchiveRequest {
+	// We'll return the request that's already been enqueued if it has been
+	// enqueued, or we'll immediately enqueue it if it has not been enqueued
+	// and it is not marked complete.
+	archiveMutex.Lock()
+	defer archiveMutex.Unlock()
+	if rExisting := getArchiveRequest(request.repo, request.commit, request.archiveType); rExisting != nil {
+		return rExisting
+	}
+	if request.archiveComplete {
+		return request
+	}
+
+	request.cchan = make(chan struct{})
+	archiveInProgress = append(archiveInProgress, request)
+	go func() {
+		// Wait to start, if we have the Cond for it.  This is currently only
+		// useful for testing, so that the start and release of queued entries
+		// can be controlled to examine the queue.
+		if archiveQueueStartCond != nil {
+			archiveQueueMutex.Lock()
+			archiveQueueStartCond.Wait()
+			archiveQueueMutex.Unlock()
+		}
+
+		// Drop the mutex while we process the request.  This may take a long
+		// time, and it's not necessary now that we've added the reequest to
+		// archiveInProgress.
+		doArchive(request)
+
+		if archiveQueueReleaseCond != nil {
+			archiveQueueMutex.Lock()
+			archiveQueueReleaseCond.Wait()
+			archiveQueueMutex.Unlock()
+		}
+
+		// Purge this request from the list.  To do so, we'll just take the
+		// index at which we ended up at and swap the final element into that
+		// position, then chop off the now-redundant final element.  The slice
+		// may have change in between these two segments and we may have moved,
+		// so we search for it here.  We could perhaps avoid this search
+		// entirely if len(archiveInProgress) == 1, but we should verify
+		// correctness.
+		archiveMutex.Lock()
+		defer archiveMutex.Unlock()
+
+		idx := -1
+		for _idx, req := range archiveInProgress {
+			if req == request {
+				idx = _idx
+				break
+			}
+		}
+		if idx == -1 {
+			log.Error("ArchiveRepository: Failed to find request for removal.")
+			return
+		}
+		archiveInProgress = append(archiveInProgress[:idx], archiveInProgress[idx+1:]...)
+	}()
+
+	return request
+}

services/archiver/archiver_test.go

@@ -0,0 +1,221 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package archiver
+
+import (
+	"path/filepath"
+	"sync"
+	"testing"
+	"time"
+
+	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/modules/test"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/unknwon/com"
+)
+
+var queueMutex sync.Mutex
+
+func TestMain(m *testing.M) {
+	models.MainTest(m, filepath.Join("..", ".."))
+}
+
+func waitForCount(t *testing.T, num int) {
+	var numQueued int
+
+	// Wait for up to 10 seconds for the queue to be impacted.
+	timeout := time.Now().Add(10 * time.Second)
+	for {
+		numQueued = len(archiveInProgress)
+		if numQueued == num || time.Now().After(timeout) {
+			break
+		}
+	}
+
+	assert.Equal(t, num, len(archiveInProgress))
+}
+
+func releaseOneEntry(t *testing.T, inFlight []*ArchiveRequest) {
+	var nowQueued, numQueued int
+
+	numQueued = len(archiveInProgress)
+
+	// Release one, then wait up to 10 seconds for it to complete.
+	queueMutex.Lock()
+	archiveQueueReleaseCond.Signal()
+	queueMutex.Unlock()
+	timeout := time.Now().Add(10 * time.Second)
+	for {
+		nowQueued = len(archiveInProgress)
+		if nowQueued != numQueued || time.Now().After(timeout) {
+			break
+		}
+	}
+
+	// Make sure we didn't just timeout.
+	assert.NotEqual(t, numQueued, nowQueued)
+
+	// Also make sure that we released only one.
+	assert.Equal(t, numQueued-1, nowQueued)
+}
+
+func TestArchive_Basic(t *testing.T) {
+	assert.NoError(t, models.PrepareTestDatabase())
+
+	archiveQueueMutex = &queueMutex
+	archiveQueueStartCond = sync.NewCond(&queueMutex)
+	archiveQueueReleaseCond = sync.NewCond(&queueMutex)
+	defer func() {
+		archiveQueueMutex = nil
+		archiveQueueStartCond = nil
+		archiveQueueReleaseCond = nil
+	}()
+
+	ctx := test.MockContext(t, "user27/repo49")
+	firstCommit, secondCommit := "51f84af23134", "aacbdfe9e1c4"
+
+	bogusReq := DeriveRequestFrom(ctx, firstCommit+".zip")
+	assert.Nil(t, bogusReq)
+
+	test.LoadRepo(t, ctx, 49)
+	bogusReq = DeriveRequestFrom(ctx, firstCommit+".zip")
+	assert.Nil(t, bogusReq)
+
+	test.LoadGitRepo(t, ctx)
+	defer ctx.Repo.GitRepo.Close()
+
+	// Check a series of bogus requests.
+	// Step 1, valid commit with a bad extension.
+	bogusReq = DeriveRequestFrom(ctx, firstCommit+".dilbert")
+	assert.Nil(t, bogusReq)
+
+	// Step 2, missing commit.
+	bogusReq = DeriveRequestFrom(ctx, "dbffff.zip")
+	assert.Nil(t, bogusReq)
+
+	// Step 3, doesn't look like branch/tag/commit.
+	bogusReq = DeriveRequestFrom(ctx, "db.zip")
+	assert.Nil(t, bogusReq)
+
+	// Now two valid requests, firstCommit with valid extensions.
+	zipReq := DeriveRequestFrom(ctx, firstCommit+".zip")
+	assert.NotNil(t, zipReq)
+
+	tgzReq := DeriveRequestFrom(ctx, firstCommit+".tar.gz")
+	assert.NotNil(t, tgzReq)
+
+	secondReq := DeriveRequestFrom(ctx, secondCommit+".zip")
+	assert.NotNil(t, secondReq)
+
+	inFlight := make([]*ArchiveRequest, 3)
+	inFlight[0] = zipReq
+	inFlight[1] = tgzReq
+	inFlight[2] = secondReq
+
+	ArchiveRepository(zipReq)
+	waitForCount(t, 1)
+	ArchiveRepository(tgzReq)
+	waitForCount(t, 2)
+	ArchiveRepository(secondReq)
+	waitForCount(t, 3)
+
+	// Make sure sending an unprocessed request through doesn't affect the queue
+	// count.
+	ArchiveRepository(zipReq)
+
+	// Sleep two seconds to make sure the queue doesn't change.
+	time.Sleep(2 * time.Second)
+	assert.Equal(t, 3, len(archiveInProgress))
+
+	// Release them all, they'll then stall at the archiveQueueReleaseCond while
+	// we examine the queue state.
+	queueMutex.Lock()
+	archiveQueueStartCond.Broadcast()
+	queueMutex.Unlock()
+
+	// Iterate through all of the in-flight requests and wait for their
+	// completion.
+	for _, req := range inFlight {
+		req.WaitForCompletion(ctx)
+	}
+
+	for _, req := range inFlight {
+		assert.True(t, req.IsComplete())
+		assert.True(t, com.IsExist(req.GetArchivePath()))
+	}
+
+	arbitraryReq := inFlight[0]
+	// Reopen the channel so we don't double-close, mark it incomplete.  We're
+	// going to run it back through the archiver, and it should get marked
+	// complete again.
+	arbitraryReq.cchan = make(chan struct{})
+	arbitraryReq.archiveComplete = false
+	doArchive(arbitraryReq)
+	assert.True(t, arbitraryReq.IsComplete())
+
+	// Queues should not have drained yet, because we haven't released them.
+	// Do so now.
+	assert.Equal(t, 3, len(archiveInProgress))
+
+	zipReq2 := DeriveRequestFrom(ctx, firstCommit+".zip")
+	// This zipReq should match what's sitting in the queue, as we haven't
+	// let it release yet.  From the consumer's point of view, this looks like
+	// a long-running archive task.
+	assert.Equal(t, zipReq, zipReq2)
+
+	// We still have the other three stalled at completion, waiting to remove
+	// from archiveInProgress.  Try to submit this new one before its
+	// predecessor has cleared out of the queue.
+	ArchiveRepository(zipReq2)
+
+	// Make sure the queue hasn't grown any.
+	assert.Equal(t, 3, len(archiveInProgress))
+
+	// Make sure the queue drains properly
+	releaseOneEntry(t, inFlight)
+	assert.Equal(t, 2, len(archiveInProgress))
+	releaseOneEntry(t, inFlight)
+	assert.Equal(t, 1, len(archiveInProgress))
+	releaseOneEntry(t, inFlight)
+	assert.Equal(t, 0, len(archiveInProgress))
+
+	// Now we'll submit a request and TimedWaitForCompletion twice, before and
+	// after we release it.  We should trigger both the timeout and non-timeout
+	// cases.
+	var completed, timedout bool
+	timedReq := DeriveRequestFrom(ctx, secondCommit+".tar.gz")
+	assert.NotNil(t, timedReq)
+	ArchiveRepository(timedReq)
+
+	// Guaranteed to timeout; we haven't signalled the request to start..
+	completed, timedout = timedReq.TimedWaitForCompletion(ctx, 2*time.Second)
+	assert.Equal(t, false, completed)
+	assert.Equal(t, true, timedout)
+
+	queueMutex.Lock()
+	archiveQueueStartCond.Broadcast()
+	queueMutex.Unlock()
+
+	// Shouldn't timeout, we've now signalled it and it's a small request.
+	completed, timedout = timedReq.TimedWaitForCompletion(ctx, 15*time.Second)
+	assert.Equal(t, true, completed)
+	assert.Equal(t, false, timedout)
+
+	zipReq2 = DeriveRequestFrom(ctx, firstCommit+".zip")
+	// Now, we're guaranteed to have released the original zipReq from the queue.
+	// Ensure that we don't get handed back the released entry somehow, but they
+	// should remain functionally equivalent in all fields.  The exception here
+	// is zipReq.cchan, which will be non-nil because it's a completed request.
+	// It's fine to go ahead and set it to nil now.
+	zipReq.cchan = nil
+	assert.Equal(t, zipReq, zipReq2)
+	assert.False(t, zipReq == zipReq2)
+
+	// Same commit, different compression formats should have different names.
+	// Ideally, the extension would match what we originally requested.
+	assert.NotEqual(t, zipReq.GetArchiveName(), tgzReq.GetArchiveName())
+	assert.NotEqual(t, zipReq.GetArchiveName(), secondReq.GetArchiveName())
+}

templates/repo/branch/list.tmpl

@@ -27,8 +27,8 @@
 							<div class="ui basic jump dropdown icon button poping up" data-content="{{$.i18n.Tr "repo.branch.download" ($.DefaultBranch)}}" data-variation="tiny inverted" data-position="top right">
 							  <i class="download icon"></i>
 							  <div class="menu">
-							    <a class="item" href="{{$.RepoLink}}/archive/{{EscapePound $.DefaultBranch}}.zip">{{svg "octicon-file-zip"}}&nbsp;ZIP</a>
+							    <a class="item archive-link" data-url="{{$.RepoLink}}/archive/{{EscapePound $.DefaultBranch}}.zip">{{svg "octicon-file-zip"}}&nbsp;ZIP</a>
-							    <a class="item" href="{{$.RepoLink}}/archive/{{EscapePound $.DefaultBranch}}.tar.gz">{{svg "octicon-file-zip"}}&nbsp;TAR.GZ</a>
+							    <a class="item archive-link" data-url="{{$.RepoLink}}/archive/{{EscapePound $.DefaultBranch}}.tar.gz">{{svg "octicon-file-zip"}}&nbsp;TAR.GZ</a>
 							  </div>
 							</div>
 						</td>
@@ -106,8 +106,8 @@
 											<div class="ui basic jump dropdown icon button poping up" data-content="{{$.i18n.Tr "repo.branch.download" (.Name)}}" data-variation="tiny inverted" data-position="top right">
 												<i class="download icon"></i>
 												<div class="menu">
-													<a class="item" href="{{$.RepoLink}}/archive/{{EscapePound .Name}}.zip">{{svg "octicon-file-zip"}}&nbsp;ZIP</a>
+													<a class="item archive-link" data-url="{{$.RepoLink}}/archive/{{EscapePound .Name}}.zip">{{svg "octicon-file-zip"}}&nbsp;ZIP</a>
-													<a class="item" href="{{$.RepoLink}}/archive/{{EscapePound .Name}}.tar.gz">{{svg "octicon-file-zip"}}&nbsp;TAR.GZ</a>
+													<a class="item archive-link" data-url="{{$.RepoLink}}/archive/{{EscapePound .Name}}.tar.gz">{{svg "octicon-file-zip"}}&nbsp;TAR.GZ</a>
 												</div>
 											</div>
 										{{end}}

templates/repo/home.tmpl

@@ -133,8 +133,8 @@
 						<div class="ui basic jump dropdown icon button poping up" data-content="{{.i18n.Tr "repo.download_archive"}}" data-variation="tiny inverted" data-position="top right">
 							{{svg "octicon-download"}}
 							<div class="menu">
-								<a class="item" href="{{$.RepoLink}}/archive/{{EscapePound $.BranchName}}.zip">{{svg "octicon-file-zip"}}&nbsp;ZIP</a>
+								<a class="item archive-link" data-url="{{$.RepoLink}}/archive/{{EscapePound $.BranchName}}.zip">{{svg "octicon-file-zip"}}&nbsp;ZIP</a>
-								<a class="item" href="{{$.RepoLink}}/archive/{{EscapePound $.BranchName}}.tar.gz">{{svg "octicon-file-zip"}}&nbsp;TAR.GZ</a>
+								<a class="item archive-link" data-url="{{$.RepoLink}}/archive/{{EscapePound $.BranchName}}.tar.gz">{{svg "octicon-file-zip"}}&nbsp;TAR.GZ</a>
 							</div>
 						</div>
 					</div>

templates/repo/release/list.tmpl

@@ -37,8 +37,8 @@
 								<div class="download df ac">
 									{{if $.Permission.CanRead $.UnitTypeCode}}
 										<a class="mr-3 mono" href="{{$.RepoLink}}/src/commit/{{.Sha1}}" rel="nofollow">{{svg "octicon-git-commit" 16 "mr-2"}}{{ShortSha .Sha1}}</a>
-										<a class="mr-3" href="{{$.RepoLink}}/archive/{{.TagName | EscapePound}}.zip" rel="nofollow">{{svg "octicon-file-zip" 16 "mr-2"}}ZIP</a>
+										<a class="archive-link mr-3" data-url="{{$.RepoLink}}/archive/{{.TagName | EscapePound}}.zip" rel="nofollow">{{svg "octicon-file-zip" 16 "mr-2"}}ZIP</a>
-										<a class="mr-3" href="{{$.RepoLink}}/archive/{{.TagName | EscapePound}}.tar.gz">{{svg "octicon-file-zip" 16 "mr-2"}}TAR.GZ</a>
+										<a class="archive-link mr-3" data-url="{{$.RepoLink}}/archive/{{.TagName | EscapePound}}.tar.gz">{{svg "octicon-file-zip" 16 "mr-2"}}TAR.GZ</a>
 										{{if (and $.CanCreateRelease $release.IsTag)}}
 											<a class="mr-3" href="{{$.RepoLink}}/releases/new?tag={{.TagName | EscapePound}}">{{svg "octicon-tag" 16 "mr-2"}}{{$.i18n.Tr "repo.release.new_release"}}</a>
 										{{end}}
@@ -99,8 +99,8 @@
 							<div class="download">
 							{{if $.Permission.CanRead $.UnitTypeCode}}
 								<a class="mono" href="{{$.RepoLink}}/src/commit/{{.Sha1}}" rel="nofollow">{{svg "octicon-git-commit" 16 "mr-2"}}{{ShortSha .Sha1}}</a>
-								<a href="{{$.RepoLink}}/archive/{{.TagName | EscapePound}}.zip" rel="nofollow">{{svg "octicon-file-zip"}}&nbsp;ZIP</a>
+								<a class="archive-link" data-url="{{$.RepoLink}}/archive/{{.TagName | EscapePound}}.zip" rel="nofollow">{{svg "octicon-file-zip"}}&nbsp;ZIP</a>
-								<a href="{{$.RepoLink}}/archive/{{.TagName | EscapePound}}.tar.gz">{{svg "octicon-file-zip"}}&nbsp;TAR.GZ</a>
+								<a class="archive-link" data-url="{{$.RepoLink}}/archive/{{.TagName | EscapePound}}.tar.gz">{{svg "octicon-file-zip"}}&nbsp;TAR.GZ</a>
 							{{end}}
 							</div>
 						{{else}}
@@ -143,10 +143,10 @@
 									<ul class="list">
 										{{if $.Permission.CanRead $.UnitTypeCode}}
 											<li>
-												<a href="{{$.RepoLink}}/archive/{{.TagName | EscapePound}}.zip" rel="nofollow"><strong>{{svg "octicon-file-zip" 16 "mr-2"}}{{$.i18n.Tr "repo.release.source_code"}} (ZIP)</strong></a>
+												<a class="archive-link" data-url="{{$.RepoLink}}/archive/{{.TagName | EscapePound}}.zip" rel="nofollow"><strong>{{svg "octicon-file-zip" 16 "mr-2"}}{{$.i18n.Tr "repo.release.source_code"}} (ZIP)</strong></a>
 											</li>
 											<li>
-												<a href="{{$.RepoLink}}/archive/{{.TagName | EscapePound}}.tar.gz"><strong>{{svg "octicon-file-zip" 16 "mr-2"}}{{$.i18n.Tr "repo.release.source_code"}} (TAR.GZ)</strong></a>
+												<a class="archive-link" data-url="{{$.RepoLink}}/archive/{{.TagName | EscapePound}}.tar.gz"><strong>{{svg "octicon-file-zip" 16 "mr-2"}}{{$.i18n.Tr "repo.release.source_code"}} (TAR.GZ)</strong></a>
 											</li>
 										{{end}}
 										{{if .Attachments}}

web_src/js/index.js

@@ -690,6 +690,54 @@ function initIssueComments() {
   });
 }
 
+function getArchive($target, url, first) {
+  $.ajax({
+    url,
+    type: 'POST',
+    data: {
+      _csrf: csrf,
+    },
+    complete(xhr) {
+      if (xhr.status === 200) {
+        if (!xhr.responseJSON) {
+          // XXX Shouldn't happen?
+          $target.closest('.dropdown').children('i').removeClass('loading');
+          return;
+        }
+
+        if (!xhr.responseJSON.complete) {
+          $target.closest('.dropdown').children('i').addClass('loading');
+          // Wait for only three quarters of a second initially, in case it's
+          // quickly archived.
+          setTimeout(() => {
+            getArchive($target, url, false);
+          }, first ? 750 : 2000);
+        } else {
+          // We don't need to continue checking.
+          $target.closest('.dropdown').children('i').removeClass('loading');
+          window.location.href = url;
+        }
+      }
+    }
+  });
+}
+
+function initArchiveLinks() {
+  if ($('.archive-link').length === 0) {
+    return;
+  }
+
+  $('.archive-link').on('click', function (event) {
+    const url = $(this).data('url');
+    if (typeof url === 'undefined') {
+      return;
+    }
+
+    event.preventDefault();
+    getArchive($(event.target), url, true);
+  });
+}
+
 async function initRepository() {
   if ($('.repository').length === 0) {
     return;
@@ -2462,6 +2510,7 @@ $(document).ready(async () => {
   initMarkdownAnchors();
   initCommentForm();
   initInstall();
+  initArchiveLinks();
   initRepository();
   initMigration();
   initWikiForm();