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promisor-remote: lazy-fetch objects in subprocess
Teach Git to lazy-fetch missing objects in a subprocess instead of doing it in-process. This allows any fatal errors that occur during the fetch to be isolated and converted into an error return value, instead of causing the current command being run to terminate. Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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‎Documentation/technical/partial-clone.txt‎

Lines changed: 3 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -171,20 +171,13 @@ additional flag.
171171
Fetching Missing Objects
172172
------------------------
173173

174-
- Fetching of objects is done using the existing transport mechanism using
175-
transport_fetch_refs(), setting a new transport option
176-
TRANS_OPT_NO_DEPENDENTS to indicate that only the objects themselves are
177-
desired, not any object that they refer to.
178-
+
179-
Because some transports invoke fetch_pack() in the same process, fetch_pack()
180-
has been updated to not use any object flags when the corresponding argument
181-
(no_dependents) is set.
174+
- Fetching of objects is done by invoking a "git fetch" subprocess.
182175

183176
- The local repository sends a request with the hashes of all requested
184-
objects as "want" lines, and does not perform any packfile negotiation.
177+
objects, and does not perform any packfile negotiation.
185178
It then receives a packfile.
186179

187-
- Because we are reusing the existing fetch-pack mechanism, fetching
180+
- Because we are reusing the existing fetch mechanism, fetching
188181
currently fetches all objects referred to by the requested objects, even
189182
though they are not necessary.
190183

‎promisor-remote.c‎

Lines changed: 21 additions & 25 deletions
Original file line numberDiff line numberDiff line change
@@ -3,6 +3,7 @@
33
#include "promisor-remote.h"
44
#include "config.h"
55
#include "transport.h"
6+
#include "strvec.h"
67

78
static char *repository_format_partial_clone;
89
static const char *core_partial_clone_filter_default;
@@ -12,39 +13,34 @@ void set_repository_format_partial_clone(char *partial_clone)
1213
repository_format_partial_clone = xstrdup_or_null(partial_clone);
1314
}
1415

15-
static int fetch_refs(const char *remote_name, struct ref *ref)
16-
{
17-
struct remote *remote;
18-
struct transport *transport;
19-
int res;
20-
21-
remote = remote_get(remote_name);
22-
if (!remote->url[0])
23-
die(_("Remote with no URL"));
24-
transport = transport_get(remote, remote->url[0]);
25-
26-
transport_set_option(transport, TRANS_OPT_FROM_PROMISOR, "1");
27-
transport_set_option(transport, TRANS_OPT_NO_DEPENDENTS, "1");
28-
res = transport_fetch_refs(transport, ref);
29-
30-
return res;
31-
}
32-
3316
static int fetch_objects(const char *remote_name,
3417
const struct object_id *oids,
3518
int oid_nr)
3619
{
37-
struct ref *ref = NULL;
20+
struct child_process child = CHILD_PROCESS_INIT;
3821
int i;
22+
FILE *child_in;
23+
24+
child.git_cmd = 1;
25+
child.in = -1;
26+
strvec_pushl(&child.args, "-c", "fetch.negotiationAlgorithm=noop",
27+
"fetch", remote_name, "--no-tags",
28+
"--no-write-fetch-head", "--recurse-submodules=no",
29+
"--filter=blob:none", "--stdin", NULL);
30+
if (start_command(&child))
31+
die(_("promisor-remote: unable to fork off fetch subprocess"));
32+
child_in = xfdopen(child.in, "w");
3933

4034
for (i = 0; i < oid_nr; i++) {
41-
struct ref *new_ref = alloc_ref(oid_to_hex(&oids[i]));
42-
oidcpy(&new_ref->old_oid, &oids[i]);
43-
new_ref->exact_oid = 1;
44-
new_ref->next = ref;
45-
ref = new_ref;
35+
if (fputs(oid_to_hex(&oids[i]), child_in) < 0)
36+
die_errno(_("promisor-remote: could not write to fetch subprocess"));
37+
if (fputc('\n', child_in) < 0)
38+
die_errno(_("promisor-remote: could not write to fetch subprocess"));
4639
}
47-
return fetch_refs(remote_name, ref);
40+
41+
if (fclose(child_in) < 0)
42+
die_errno(_("promisor-remote: could not close stdin to fetch subprocess"));
43+
return finish_command(&child) ? -1 : 0;
4844
}
4945

5046
static struct promisor_remote *promisors;

‎t/t0410-partial-clone.sh‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -214,7 +214,7 @@ test_expect_success 'fetching of missing objects works with ref-in-want enabled'
214214
rm -rf repo/.git/objects/* &&
215215
rm -f trace &&
216216
GIT_TRACE_PACKET="$(pwd)/trace" git -C repo cat-file -p "$HASH" &&
217-
grep "git< fetch=.*ref-in-want" trace
217+
grep "fetch< fetch=.*ref-in-want" trace
218218
'
219219

220220
test_expect_success 'fetching of missing objects from another promisor remote' '

‎t/t4067-diff-partial-clone.sh‎

Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -20,7 +20,7 @@ test_expect_success 'git show batches blobs' '
2020
# Ensure that there is exactly 1 negotiation by checking that there is
2121
# only 1 "done" line sent. ("done" marks the end of negotiation.)
2222
GIT_TRACE_PACKET="$(pwd)/trace" git -C client show HEAD &&
23-
grep "git> done" trace >done_lines &&
23+
grep "fetch> done" trace >done_lines &&
2424
test_line_count = 1 done_lines
2525
'
2626

@@ -44,7 +44,7 @@ test_expect_success 'diff batches blobs' '
4444
# Ensure that there is exactly 1 negotiation by checking that there is
4545
# only 1 "done" line sent. ("done" marks the end of negotiation.)
4646
GIT_TRACE_PACKET="$(pwd)/trace" git -C client diff HEAD^ HEAD &&
47-
grep "git> done" trace >done_lines &&
47+
grep "fetch> done" trace >done_lines &&
4848
test_line_count = 1 done_lines
4949
'
5050

@@ -127,7 +127,7 @@ test_expect_success 'diff with rename detection batches blobs' '
127127
# only 1 "done" line sent. ("done" marks the end of negotiation.)
128128
GIT_TRACE_PACKET="$(pwd)/trace" git -C client diff --raw -M HEAD^ HEAD >out &&
129129
grep ":100644 100644.*R[0-9][0-9][0-9].*b.*c" out &&
130-
grep "git> done" trace >done_lines &&
130+
grep "fetch> done" trace >done_lines &&
131131
test_line_count = 1 done_lines
132132
'
133133

@@ -175,7 +175,7 @@ test_expect_success 'diff --break-rewrites fetches only if necessary, and batche
175175
# by checking that there is only 1 "done" line sent. ("done" marks the
176176
# end of negotiation.)
177177
GIT_TRACE_PACKET="$(pwd)/trace" git -C client diff --break-rewrites --raw -M HEAD^ HEAD &&
178-
grep "git> done" trace >done_lines &&
178+
grep "fetch> done" trace >done_lines &&
179179
test_line_count = 1 done_lines
180180
'
181181

‎t/t5300-pack-object.sh‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -528,7 +528,7 @@ test_expect_success 'prefetch objects' '
528528
TWO=$(git -C server rev-parse three_branch^) &&
529529
git -C client fetch --filter=blob:none origin "$TWO" &&
530530
GIT_TRACE_PACKET=$(pwd)/trace git -C client push origin "$TWO":refs/heads/two_branch &&
531-
grep "git> done" trace >donelines &&
531+
grep "fetch> done" trace >donelines &&
532532
test_line_count = 1 donelines
533533
'
534534

‎t/t5601-clone.sh‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -704,7 +704,7 @@ test_expect_success 'batch missing blob request during checkout' '
704704
# Ensure that there is only one negotiation by checking that there is
705705
# only "done" line sent. ("done" marks the end of negotiation.)
706706
GIT_TRACE_PACKET="$(pwd)/trace" git -C client checkout HEAD^ &&
707-
grep "git> done" trace >done_lines &&
707+
grep "fetch> done" trace >done_lines &&
708708
test_line_count = 1 done_lines
709709
'
710710

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