[RFC PATCH 06/13] bundle-uri client: add transfer.injectBundleURI support

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Add the ability to inject "fake" bundle URIs into the newly supported
bundle-uri dialog. As discussed in the added documentation this allows
us to pretend as though the remote supports bundle URIs.

This will be useful both for ad-hoc testing, and for the real use-case
of retrofitting bundle URI support on-the-fly, i.e. to have:

	git -c transfer.injectBundleURI "file://$(pwd)/local.bdl" \
	clone https://example.com/git.git"

Be similar in spirit to:

	git clone --reference local-clone.git --disassociate \
	https://example.com/git.git"

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 Documentation/config/transfer.txt     | 20 ++++++++++++
 t/lib-t5730-protocol-v2-bundle-uri.sh | 46 +++++++++++++++++++++++++++
 transport.c                           | 33 +++++++++++++++++++
 3 files changed, 99 insertions(+)

diff --git a/Documentation/config/transfer.txt b/Documentation/config/transfer.txt
index 505126a780..a9aff7f982 100644
--- a/Documentation/config/transfer.txt
+++ b/Documentation/config/transfer.txt
@@ -73,3 +73,23 @@ transfer.unpackLimit::
 transfer.advertiseSID::
 	Boolean. When true, client and server processes will advertise their
 	unique session IDs to their remote counterpart. Defaults to false.
+
+transfer.injectBundleURI::
+	Allows for the injection of `bundle-uri` lines into the
+	protocol v2 transport dialog (see `protocol.version` in
+	linkgit:git-config[1]). See `bundle-uri` in
+	link:technical/protocol-v2.html[the Git Wire Protocol, Version
+	2] documentation for what the format looks like.
++
+Can be given more than once, each key being injected as one line into
+the dialog.
++
+This is useful for testing the `bundle-uri` facility, and to e.g. use
+linkgit:git-clone[1] to clone from a server which does not support
+`bundle-uri`, but where the clone can benefit from getting some or
+most of the data from a static bundle retrieved from elsewhere.
++
+Impacts any command that uses the transport to communicate with remote
+linkgit:git-upload-pack[1] processes, e.g. linkgit:git-clone[1],
+linkgit:git-fetch[1] and the linkgit:git-ls-remote-bundle-uri[1]
+inspection command, this includes the `file://` protocol.
diff --git a/t/lib-t5730-protocol-v2-bundle-uri.sh b/t/lib-t5730-protocol-v2-bundle-uri.sh
index fccf7ccaa2..e5d17f6a81 100644
--- a/t/lib-t5730-protocol-v2-bundle-uri.sh
+++ b/t/lib-t5730-protocol-v2-bundle-uri.sh
@@ -270,3 +270,49 @@ test_expect_success "ls-remote-bundle-uri --[no-]quiet with $T5730_PROTOCOL:// u
 	test_must_be_empty err &&
 	test_cmp out.expect out.actual
 '
+
+test_expect_success "ls-remote-bundle-uri with -c transfer.injectBundleURI using with $T5730_PROTOCOL:// using protocol v2" '
+	test_when_finished "rm -f log" &&
+
+	test_config -C "$T5730_PARENT" uploadpack.bundleURI \
+		"$T5730_BUNDLE_URI_ESCAPED" &&
+
+	cat >expect <<-\EOF &&
+	https://injected.example.com/fake-1.bdl
+	https://injected.example.com/fake-2.bdl
+	EOF
+	GIT_TRACE_PACKET="$PWD/log" \
+	git \
+		-c protocol.version=2 \
+		-c transfer.injectBundleURI="https://injected.example.com/fake-1.bdl" \
+		-c transfer.injectBundleURI="https://injected.example.com/fake-2.bdl" \
+		ls-remote-bundle-uri \
+		"$T5730_URI" \
+		>actual 2>err &&
+	test_cmp expect actual &&
+	test_path_is_missing log
+'
+
+test_expect_success "ls-remote-bundle-uri with bad -c transfer.injectBundleURI protocol v2 with $T5730_PROTOCOL://" '
+	test_when_finished "rm -f log" &&
+
+	test_config -C "$T5730_PARENT" uploadpack.bundleURI \
+		"$T5730_BUNDLE_URI_ESCAPED" &&
+
+	cat >err.expect <<-\EOF &&
+	error: bad (empty) transfer.injectBundleURI
+	error: could not get the bundle-uri list
+	EOF
+
+	test_must_fail env \
+		GIT_TRACE_PACKET="$PWD/log" \
+		git \
+		-c protocol.version=2 \
+		-c transfer.injectBundleURI \
+		ls-remote-bundle-uri \
+		"$T5730_URI" \
+		>out 2>err.actual &&
+	test_must_be_empty out &&
+	test_cmp err.expect err.actual &&
+	test_path_is_missing log
+'
diff --git a/transport.c b/transport.c
index 286c96269d..bd8a914652 100644
--- a/transport.c
+++ b/transport.c
@@ -1501,14 +1501,47 @@ int transport_fetch_refs(struct transport *transport, struct ref *refs)
 	return rc;
 }
 
+struct config_cb {
+	struct transport *transport;
+	int configured;
+	int ret;
+};
+
+static int bundle_uri_config(const char *var, const char *value, void *data)
+{
+	struct config_cb *cb = data;
+	struct transport *transport = cb->transport;
+	struct string_list *uri = &transport->bundle_uri;
+
+	if (!strcmp(var, "transfer.injectbundleuri")) {
+		cb->configured = 1;
+		if (!value)
+			cb->ret = error(_("bad (empty) transfer.injectBundleURI"));
+		else if (bundle_uri_parse_line(uri, value) < 0)
+			cb->ret = error(_("bad transfer.injectBundleURI: '%s'"),
+					value);
+		return 0;
+	}
+	return 0;
+}
+
 int transport_get_remote_bundle_uri(struct transport *transport, int quiet)
 {
 	const struct transport_vtable *vtable = transport->vtable;
+	struct config_cb cb = {
+		.transport = transport,
+	};
 
 	/* Lazily configured */
 	if (transport->got_remote_bundle_uri++)
 		return 0;
 
+	git_config(bundle_uri_config, &cb);
+
+	/* Our own config can fake it up with transport.injectBundleURI */
+	if (cb.configured)
+		return cb.ret;
+
 	/*
 	 * This is intentionally below the transport.injectBundleURI,
 	 * we want to be able to inject into protocol v0, or into the
-- 
2.33.0.rc0.646.g585563e77f