bundle-uri: store fetch.bundleCreationToken

When a bundle list specifies the "creationToken" heuristic, the Git
client downloads the list and then starts downloading bundles in
descending creationToken order. This process stops as soon as all
downloaded bundles can be applied to the repository (because all
required commits are present in the repository or in the downloaded
bundles).

When checking the same bundle list twice, this strategy requires
downloading the bundle with the maximum creationToken again, which is
wasteful. The creationToken heuristic promises that the client will not
have a use for that bundle if its creationToken value is at most the
previous creationToken value.

To prevent these wasteful downloads, create a fetch.bundleCreationToken
config setting that the Git client sets after downloading bundles. This
value allows skipping that maximum bundle download when this config
value is the same value (or larger).

To test that this works correctly, we can insert some "duplicate"
fetches into existing tests and demonstrate that only the bundle list is
downloaded.

The previous logic for downloading bundles by creationToken worked even
if the bundle list was empty, but now we have logic that depends on the
first entry of the list. Terminate early in the (non-sensical) case of
an empty bundle list.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 46 insertions, 2 deletions

diff --git a/bundle-uri.c b/bundle-uri.c
index 7a1b6d94bf..d6f7df7350 100644
--- a/bundle-uri.c
+++ b/bundle-uri.c
@@ -481,6 +481,8 @@ static int fetch_bundles_by_token(struct repository *r,
 {
 	int cur;
 	int move_direction = 0;
+	const char *creationTokenStr;
+	uint64_t maxCreationToken = 0, newMaxCreationToken = 0;
 	struct bundle_list_context ctx = {
 		.r = r,
 		.list = list,
@@ -494,9 +496,28 @@ static int fetch_bundles_by_token(struct repository *r,
 
 	for_all_bundles_in_list(list, append_bundle, &bundles);
 
+	if (!bundles.nr) {
+		free(bundles.items);
+		return 0;
+	}
+
 	QSORT(bundles.items, bundles.nr, compare_creation_token_decreasing);
 
 	/*
+	 * If fetch.bundleCreationToken exists, parses to a uint64t, and
+	 * is not strictly smaller than the maximum creation token in the
+	 * bundle list, then do not download any bundles.
+	 */
+	if (!repo_config_get_value(r,
+				   "fetch.bundlecreationtoken",
+				   &creationTokenStr) &&
+	    sscanf(creationTokenStr, "%"PRIu64, &maxCreationToken) == 1 &&
+	    bundles.items[0]->creationToken <= maxCreationToken) {
+		free(bundles.items);
+		return 0;
+	}
+
+	/*
 	 * Attempt to download and unbundle the minimum number of bundles by
 	 * creationToken in decreasing order. If we fail to unbundle (after
 	 * a successful download) then move to the next non-downloaded bundle
@@ -516,6 +537,16 @@ static int fetch_bundles_by_token(struct repository *r,
 	cur = 0;
 	while (cur >= 0 && cur < bundles.nr) {
 		struct remote_bundle_info *bundle = bundles.items[cur];
+
+		/*
+		 * If we need to dig into bundles below the previous
+		 * creation token value, then likely we are in an erroneous
+		 * state due to missing or invalid bundles. Halt the process
+		 * instead of continuing to download extra data.
+		 */
+		if (bundle->creationToken <= maxCreationToken)
+			break;
+
 		if (!bundle->file) {
 			/*
 			 * Not downloaded yet. Try downloading.
@@ -555,6 +586,9 @@ static int fetch_bundles_by_token(struct repository *r,
 				 */
 				move_direction = -1;
 				bundle->unbundled = 1;
+
+				if (bundle->creationToken > newMaxCreationToken)
+					newMaxCreationToken = bundle->creationToken;
 			}
 		}
 
@@ -569,14 +603,24 @@ move:
 		cur += move_direction;
 	}
 
-	free(bundles.items);
-
 	/*
 	 * We succeed if the loop terminates because 'cur' drops below
 	 * zero. The other case is that we terminate because 'cur'
 	 * reaches the end of the list, so we have a failure no matter
 	 * which bundles we apply from the list.
 	 */
+	if (cur < 0) {
+		struct strbuf value = STRBUF_INIT;
+		strbuf_addf(&value, "%"PRIu64"", newMaxCreationToken);
+		if (repo_config_set_multivar_gently(ctx.r,
+						    "fetch.bundleCreationToken",
+						    value.buf, NULL, 0))
+			warning(_("failed to store maximum creation token"));
+
+		strbuf_release(&value);
+	}
+
+	free(bundles.items);
 	return cur >= 0;
 }