Re: [PATCH] fetch-pack: make packfile URIs work with transfer.fsckobjects

From: Junio C Hamano <gitster@pobox.com>
Date: Aug 14, 2020, 19:59 UTC
Message-ID: <xmqq8sehvw13.fsf@gitster.c.googlers.com>
In-Reply-To: <20200814193234.3072139-1-jonathantanmy@google.com>

Jonathan Tan <jonathantanmy@google.com> writes:

Show 6 quoted lines

> When fetching with packfile URIs and transfer.fsckobjects=1, use the
> --fsck-objects instead of the --strict flag when invoking index-pack so
> that links are not checked, only objects. This is because incomplete
> links are expected. (A subsequent connectivity check will be done when
> all the packs have been downloaded regardless of whether
> transfer.fsckobjects is set.)

Good reasoning. The change looks surprisingly small, thanks to the existing need already.

I realize that the code's quality (from readability and discoverability's point of view) has deteriorated in this area quite a lot over the past few years, though. The "from_promisor" field is set when fetch-pack is run with the corresponding command line option, but the option is documented nowhere, so it is not immediately obvious why the new need can be fulfilled by just piggybacking on the existing codepath. The meaning of the only_packfile parameter get_pack() takes is never explained anywhere, either.

Show 13 quoted lines

> diff --git a/fetch-pack.c b/fetch-pack.c
> index 7f20eca4f8..66631d0034 100644
> --- a/fetch-pack.c
> +++ b/fetch-pack.c
> @@ -892,7 +892,7 @@ static int get_pack(struct fetch_pack_args *args,
>  	    : transfer_fsck_objects >= 0
>  	    ? transfer_fsck_objects
>  	    : 0) {
> -		if (args->from_promisor)
> +		if (args->from_promisor || !only_packfile)
>  			/*
>  			 * We cannot use --strict in index-pack because it
>  			 * checks both broken objects and links, but we only

I think this is a good way to work around the "we do not have full set of objects until we grab out-of-line packfiles, but we process the in-protocol packdata before we grab them, so we cannot validate yet" problem. My guess is that "only_packfile" means "after reading this packfile, the repository should be fully complete and we can afford to check for connectivity", which would be always true for protocol below v2 that lack the packfile-uri extension (hence the call to get_pack() in do_fetch_pack() passes hardcoded 1 in this parameter). The v2 codepath in do_fetch_pack_v2() calls get_pack() with true only when there is no packfile-uri, so we loosen the validation when we know we will further grab one or more packfiles out of line.

Show 20 quoted lines

> +test_expect_success 'packfile-uri with transfer.fsckobjects' '
> +	P="$HTTPD_DOCUMENT_ROOT_PATH/http_parent" &&
> +	rm -rf "$P" http_child log &&
> +
> +	git init "$P" &&
> +	git -C "$P" config "uploadpack.allowsidebandall" "true" &&
> +
> +	echo my-blob >"$P/my-blob" &&
> +	git -C "$P" add my-blob &&
> +	git -C "$P" commit -m x &&
> +
> +	configure_exclusion "$P" my-blob >h &&
> +
> +	sane_unset GIT_TEST_SIDEBAND_ALL &&
> +	git -c protocol.version=2 -c transfer.fsckobjects=1 \
> +		-c fetch.uriprotocols=http,https \
> +		clone "$HTTPD_URL/smart/http_parent" http_child &&
> +
> +	# Ensure that there are exactly 4 files (2 .pack and 2 .idx).
> +	ls http_child/.git/objects/pack/* >filelist &&

Subtle but correct.

Show 17 quoted lines

> +	test_line_count = 4 filelist
> +'
> +
> +test_expect_success 'packfile-uri with transfer.fsckobjects fails on bad object' '
> +	P="$HTTPD_DOCUMENT_ROOT_PATH/http_parent" &&
> +	rm -rf "$P" http_child log &&
> +
> +	git init "$P" &&
> +	git -C "$P" config "uploadpack.allowsidebandall" "true" &&
> +
> +	cat >bogus-commit <<EOF &&
> +tree $EMPTY_TREE
> +author Bugs Bunny 1234567890 +0000
> +committer Bugs Bunny <bugs@bun.ni> 1234567890 +0000
> +
> +This commit object intentionally broken
> +EOF

Use <<-EOF for readablity, please.

Show 18 quoted lines

> +	BOGUS=$(git -C "$P" hash-object -t commit -w --stdin <bogus-commit) &&
> +	git -C "$P" branch bogus-branch "$BOGUS" &&
> +
> +	echo my-blob >"$P/my-blob" &&
> +	git -C "$P" add my-blob &&
> +	git -C "$P" commit -m x &&
> +
> +	configure_exclusion "$P" my-blob >h &&
> +
> +	sane_unset GIT_TEST_SIDEBAND_ALL &&
> +	test_must_fail git -c protocol.version=2 -c transfer.fsckobjects=1 \
> +		-c fetch.uriprotocols=http,https \
> +		clone "$HTTPD_URL/smart/http_parent" http_child 2>error &&
> +	test_i18ngrep "invalid author/committer line - missing email" error
> +'
> +
>  # DO NOT add non-httpd-specific tests here, because the last part of this
>  # test script is only executed when httpd is available and enabled.