+static void add_wants(const struct ref *wants, struct strbuf *req_buf)
+{
+ for ( ; wants ; wants = wants->next) {
+ const struct object_id *remote = &wants->old_oid;
+ const char *remote_hex;
+ struct object *o;
+
+ /*
+ * If that object is complete (i.e. it is an ancestor of a
+ * local ref), we tell them we have it but do not have to
+ * tell them about its ancestors, which they already know
+ * about.
+ *
+ * We use lookup_object here because we are only
+ * interested in the case we *know* the object is
+ * reachable and we have already scanned it.
+ */
+ if (((o = lookup_object(remote->hash)) != NULL) &&
+ (o->flags & COMPLETE)) {
+ continue;
+ }
+
+ remote_hex = oid_to_hex(remote);
+ packet_buf_write(req_buf, "want %s\n", remote_hex);
+ }
+}
+
+static void add_common(struct strbuf *req_buf, struct oidset *common)
+{
+ struct oidset_iter iter;
+ const struct object_id *oid;
+ oidset_iter_init(common, &iter);
+
+ while ((oid = oidset_iter_next(&iter))) {
+ packet_buf_write(req_buf, "have %s\n", oid_to_hex(oid));
+ }
+}
+
+static int add_haves(struct strbuf *req_buf, int *haves_to_send, int *in_vain)
+{
+ int ret = 0;
+ int haves_added = 0;
+ const struct object_id *oid;
+
+ while ((oid = get_rev())) {
+ packet_buf_write(req_buf, "have %s\n", oid_to_hex(oid));
+ if (++haves_added >= *haves_to_send)
+ break;
+ }
+
+ *in_vain += haves_added;
+ if (!haves_added || *in_vain >= MAX_IN_VAIN) {
+ /* Send Done */
+ packet_buf_write(req_buf, "done\n");
+ ret = 1;
+ }
+
+ /* Increase haves to send on next round */
+ *haves_to_send = next_flush(1, *haves_to_send);
+
+ return ret;
+}
+
+static int send_fetch_request(int fd_out, const struct fetch_pack_args *args,
+ const struct ref *wants, struct oidset *common,
+ int *haves_to_send, int *in_vain)
+{
+ int ret = 0;
+ struct strbuf req_buf = STRBUF_INIT;
+
+ if (server_supports_v2("fetch", 1))
+ packet_buf_write(&req_buf, "command=fetch");
+ if (server_supports_v2("agent", 0))
+ packet_buf_write(&req_buf, "agent=%s", git_user_agent_sanitized());
+
+ packet_buf_delim(&req_buf);
+ if (args->use_thin_pack)
+ packet_buf_write(&req_buf, "thin-pack");
+ if (args->no_progress)
+ packet_buf_write(&req_buf, "no-progress");
+ if (args->include_tag)
+ packet_buf_write(&req_buf, "include-tag");
+ if (prefer_ofs_delta)
+ packet_buf_write(&req_buf, "ofs-delta");
+
+ /* add wants */
+ add_wants(wants, &req_buf);
+
+ /* Add all of the common commits we've found in previous rounds */
+ add_common(&req_buf, common);
+
+ /* Add initial haves */
+ ret = add_haves(&req_buf, haves_to_send, in_vain);
+
+ /* Send request */
+ packet_buf_flush(&req_buf);
+ write_or_die(fd_out, req_buf.buf, req_buf.len);
+
+ strbuf_release(&req_buf);
+ return ret;
+}
+
+/*
+ * Processes a section header in a server's response and checks if it matches
+ * `section`. If the value of `peek` is 1, the header line will be peeked (and
+ * not consumed); if 0, the line will be consumed and the function will die if
+ * the section header doesn't match what was expected.
+ */
+static int process_section_header(struct packet_reader *reader,
+ const char *section, int peek)
+{
+ int ret;
+
+ if (packet_reader_peek(reader) != PACKET_READ_NORMAL)
+ die("error reading packet");
+
+ ret = !strcmp(reader->line, section);
+
+ if (!peek) {
+ if (!ret)
+ die("expected '%s', received '%s'",
+ section, reader->line);
+ packet_reader_read(reader);
+ }
+
+ return ret;
+}
+
+static int process_acks(struct packet_reader *reader, struct oidset *common)
+{
+ /* received */
+ int received_ready = 0;
+ int received_ack = 0;
+
+ process_section_header(reader, "acknowledgments", 0);
+ while (packet_reader_read(reader) == PACKET_READ_NORMAL) {
+ const char *arg;
+
+ if (!strcmp(reader->line, "NAK"))
+ continue;
+
+ if (skip_prefix(reader->line, "ACK ", &arg)) {
+ struct object_id oid;
+ if (!get_oid_hex(arg, &oid)) {
+ struct commit *commit;
+ oidset_insert(common, &oid);
+ commit = lookup_commit(&oid);
+ mark_common(commit, 0, 1);
+ }
+ continue;
+ }
+
+ if (!strcmp(reader->line, "ready")) {
+ clear_prio_queue(&rev_list);
+ received_ready = 1;
+ continue;
+ }
+
+ die("unexpected acknowledgment line: '%s'", reader->line);
+ }
+
+ if (reader->status != PACKET_READ_FLUSH &&
+ reader->status != PACKET_READ_DELIM)
+ die("error processing acks: %d", reader->status);
+
+ /* return 0 if no common, 1 if there are common, or 2 if ready */
+ return received_ready ? 2 : (received_ack ? 1 : 0);
+}
+
+enum fetch_state {
+ FETCH_CHECK_LOCAL = 0,
+ FETCH_SEND_REQUEST,
+ FETCH_PROCESS_ACKS,
+ FETCH_GET_PACK,
+ FETCH_DONE,
+};
+
+static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
+ int fd[2],
+ const struct ref *orig_ref,
+ struct ref **sought, int nr_sought,
+ char **pack_lockfile)
+{
+ struct ref *ref = copy_ref_list(orig_ref);
+ enum fetch_state state = FETCH_CHECK_LOCAL;
+ struct oidset common = OIDSET_INIT;
+ struct packet_reader reader;
+ int in_vain = 0;
+ int haves_to_send = INITIAL_FLUSH;
+ packet_reader_init(&reader, fd[0], NULL, 0,
+ PACKET_READ_CHOMP_NEWLINE);
+
+ while (state != FETCH_DONE) {
+ switch (state) {
+ case FETCH_CHECK_LOCAL:
+ sort_ref_list(&ref, ref_compare_name);
+ QSORT(sought, nr_sought, cmp_ref_by_name);
+
+ /* v2 supports these by default */
+ allow_unadvertised_object_request |= ALLOW_REACHABLE_SHA1;
+ use_sideband = 2;
+
+ if (marked)
+ for_each_ref(clear_marks, NULL);
+ marked = 1;
+
+ for_each_ref(rev_list_insert_ref_oid, NULL);
+ for_each_cached_alternate(insert_one_alternate_object);
+
+ /* Filter 'ref' by 'sought' and those that aren't local */
+ if (everything_local(args, &ref, sought, nr_sought))
+ state = FETCH_DONE;
+ else
+ state = FETCH_SEND_REQUEST;
+ break;
+ case FETCH_SEND_REQUEST:
+ if (send_fetch_request(fd[1], args, ref, &common,
+ &haves_to_send, &in_vain))
+ state = FETCH_GET_PACK;
+ else
+ state = FETCH_PROCESS_ACKS;
+ break;
+ case FETCH_PROCESS_ACKS:
+ /* Process ACKs/NAKs */
+ switch (process_acks(&reader, &common)) {
+ case 2:
+ state = FETCH_GET_PACK;
+ break;
+ case 1:
+ in_vain = 0;
+ /* fallthrough */
+ default:
+ state = FETCH_SEND_REQUEST;
+ break;
+ }
+ break;
+ case FETCH_GET_PACK:
+ /* get the pack */
+ process_section_header(&reader, "packfile", 0);
+ if (get_pack(args, fd, pack_lockfile))
+ die(_("git fetch-pack: fetch failed."));
+
+ state = FETCH_DONE;
+ break;
+ case FETCH_DONE:
+ continue;
+ }
+ }
+
+ oidset_clear(&common);
+ return ref;
+}
+