diff: batch fetching of missing blobs

When running a command like "git show" or "git diff" in a partial clone,
batch all missing blobs to be fetched as one request.

This is similar to c0c578b33c ("unpack-trees: batch fetching of missing
blobs", 2017-12-08), but for another command.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/diff.c b/diff.c
index ec5c095199b3953cc74dabdfccf4536d4c6df831..c5fd9165f95e815fa2489671ec34bcfb6eb3c73c 100644 (file)
--- a/diff.c
+++ b/diff.c
@@ -25,6 +25,7 @@
 #include "packfile.h"
 #include "parse-options.h"
 #include "help.h"
+#include "fetch-object.h"
 
 #ifdef NO_FAST_WORKING_DIRECTORY
 #define FAST_WORKING_DIRECTORY 0
@@ -6366,8 +6367,41 @@ void diffcore_fix_diff_index(void)
        QSORT(q->queue, q->nr, diffnamecmp);
 }
 
+static void add_if_missing(struct repository *r,
+                          struct oid_array *to_fetch,
+                          const struct diff_filespec *filespec)
+{
+       if (filespec && filespec->oid_valid &&
+           oid_object_info_extended(r, &filespec->oid, NULL,
+                                    OBJECT_INFO_FOR_PREFETCH))
+               oid_array_append(to_fetch, &filespec->oid);
+}
+
 void diffcore_std(struct diff_options *options)
 {
+       if (options->repo == the_repository &&
+           repository_format_partial_clone) {
+               /*
+                * Prefetch the diff pairs that are about to be flushed.
+                */
+               int i;
+               struct diff_queue_struct *q = &diff_queued_diff;
+               struct oid_array to_fetch = OID_ARRAY_INIT;
+
+               for (i = 0; i < q->nr; i++) {
+                       struct diff_filepair *p = q->queue[i];
+                       add_if_missing(options->repo, &to_fetch, p->one);
+                       add_if_missing(options->repo, &to_fetch, p->two);
+               }
+               if (to_fetch.nr)
+                       /*
+                        * NEEDSWORK: Consider deduplicating the OIDs sent.
+                        */
+                       fetch_objects(repository_format_partial_clone,
+                                     to_fetch.oid, to_fetch.nr);
+               oid_array_clear(&to_fetch);
+       }
+
        /* NOTE please keep the following in sync with diff_tree_combined() */
        if (options->skip_stat_unmatch)
                diffcore_skip_stat_unmatch(options);

diff --git a/t/t4067-diff-partial-clone.sh b/t/t4067-diff-partial-clone.sh
new file mode 100755 (executable)
index 0000000..90c8fb2
--- /dev/null
+++ b/t/t4067-diff-partial-clone.sh
@@ -0,0 +1,103 @@
+#!/bin/sh
+
+test_description='behavior of diff when reading objects in a partial clone'
+
+. ./test-lib.sh
+
+test_expect_success 'git show batches blobs' '
+       test_when_finished "rm -rf server client trace" &&
+
+       test_create_repo server &&
+       echo a >server/a &&
+       echo b >server/b &&
+       git -C server add a b &&
+       git -C server commit -m x &&
+
+       test_config -C server uploadpack.allowfilter 1 &&
+       test_config -C server uploadpack.allowanysha1inwant 1 &&
+       git clone --bare --filter=blob:limit=0 "file://$(pwd)/server" client &&
+
+       # Ensure that there is exactly 1 negotiation by checking that there is
+       # only 1 "done" line sent. ("done" marks the end of negotiation.)
+       GIT_TRACE_PACKET="$(pwd)/trace" git -C client show HEAD &&
+       grep "git> done" trace >done_lines &&
+       test_line_count = 1 done_lines
+'
+
+test_expect_success 'diff batches blobs' '
+       test_when_finished "rm -rf server client trace" &&
+
+       test_create_repo server &&
+       echo a >server/a &&
+       echo b >server/b &&
+       git -C server add a b &&
+       git -C server commit -m x &&
+       echo c >server/c &&
+       echo d >server/d &&
+       git -C server add c d &&
+       git -C server commit -m x &&
+
+       test_config -C server uploadpack.allowfilter 1 &&
+       test_config -C server uploadpack.allowanysha1inwant 1 &&
+       git clone --bare --filter=blob:limit=0 "file://$(pwd)/server" client &&
+
+       # Ensure that there is exactly 1 negotiation by checking that there is
+       # only 1 "done" line sent. ("done" marks the end of negotiation.)
+       GIT_TRACE_PACKET="$(pwd)/trace" git -C client diff HEAD^ HEAD &&
+       grep "git> done" trace >done_lines &&
+       test_line_count = 1 done_lines
+'
+
+test_expect_success 'diff skips same-OID blobs' '
+       test_when_finished "rm -rf server client trace" &&
+
+       test_create_repo server &&
+       echo a >server/a &&
+       echo b >server/b &&
+       git -C server add a b &&
+       git -C server commit -m x &&
+       echo another-a >server/a &&
+       git -C server add a &&
+       git -C server commit -m x &&
+
+       test_config -C server uploadpack.allowfilter 1 &&
+       test_config -C server uploadpack.allowanysha1inwant 1 &&
+       git clone --bare --filter=blob:limit=0 "file://$(pwd)/server" client &&
+
+       echo a | git hash-object --stdin >hash-old-a &&
+       echo another-a | git hash-object --stdin >hash-new-a &&
+       echo b | git hash-object --stdin >hash-b &&
+
+       # Ensure that only a and another-a are fetched.
+       GIT_TRACE_PACKET="$(pwd)/trace" git -C client diff HEAD^ HEAD &&
+       grep "want $(cat hash-old-a)" trace &&
+       grep "want $(cat hash-new-a)" trace &&
+       ! grep "want $(cat hash-b)" trace
+'
+
+test_expect_success 'diff with rename detection batches blobs' '
+       test_when_finished "rm -rf server client trace" &&
+
+       test_create_repo server &&
+       echo a >server/a &&
+       printf "b\nb\nb\nb\nb\n" >server/b &&
+       git -C server add a b &&
+       git -C server commit -m x &&
+       rm server/b &&
+       printf "b\nb\nb\nb\nbX\n" >server/c &&
+       git -C server add c &&
+       git -C server commit -a -m x &&
+
+       test_config -C server uploadpack.allowfilter 1 &&
+       test_config -C server uploadpack.allowanysha1inwant 1 &&
+       git clone --bare --filter=blob:limit=0 "file://$(pwd)/server" client &&
+
+       # Ensure that there is exactly 1 negotiation by checking that there is
+       # only 1 "done" line sent. ("done" marks the end of negotiation.)
+       GIT_TRACE_PACKET="$(pwd)/trace" git -C client diff -M HEAD^ HEAD >out &&
+       grep "similarity index" out &&
+       grep "git> done" trace >done_lines &&
+       test_line_count = 1 done_lines
+'
+
+test_done