static void send_request(int fd, struct strbuf *buf)
{
	if (args.stateless_rpc) {
		send_sideband(fd, -1, buf->buf, buf->len, LARGE_PACKET_MAX);
		packet_flush(fd);
	} else
		safe_write(fd, buf->buf, buf->len);
}

static void send_request(struct fetch_pack_args *args,
			 int fd, struct strbuf *buf)
{
	if (args->stateless_rpc) {
		send_sideband(fd, -1, buf->buf, buf->len, LARGE_PACKET_MAX);
		packet_flush(fd);
	} else
		write_or_die(fd, buf->buf, buf->len);
}

static void error_clnt(const char *fmt, ...)
{
	struct strbuf buf = STRBUF_INIT;
	va_list params;

	va_start(params, fmt);
	strbuf_vaddf(&buf, fmt, params);
	va_end(params);
	send_sideband(1, 3, buf.buf, buf.len, LARGE_PACKET_MAX);
	die("sent error to the client: %s", buf.buf);
}

static ssize_t process_input(int child_fd, int band)
{
	char buf[16384];
	ssize_t sz = read(child_fd, buf, sizeof(buf));
	if (sz < 0) {
		if (errno != EAGAIN && errno != EINTR)
			error_clnt("read error: %s\n", strerror(errno));
		return sz;
	}
	send_sideband(1, band, buf, sz, LARGE_PACKET_MAX);
	return sz;
}

static void error_clnt(const char *fmt, ...)
{
	char buf[1024];
	va_list params;
	int len;

	va_start(params, fmt);
	len = vsprintf(buf, fmt, params);
	va_end(params);
	send_sideband(1, 3, buf, len, LARGE_PACKET_MAX);
	die("sent error to the client: %s", buf);
}

static int copy_to_sideband(int in, int out, void *arg)
{
	char data[128];
	while (1) {
		ssize_t sz = xread(in, data, sizeof(data));
		if (sz <= 0)
			break;
		send_sideband(1, 2, data, sz, use_sideband);
	}
	close(in);
	return 0;
}

static ssize_t send_client_data(int fd, const char *data, ssize_t sz)
{
	if (use_sideband)
		return send_sideband(1, fd, data, sz, use_sideband);
	if (fd == 3)
		/* emergency quit */
		fd = 2;
	if (fd == 2) {
		/* XXX: are we happy to lose stuff here? */
		xwrite(fd, data, sz);
		return sz;
	}
	return safe_write(fd, data, sz);
}

static void send_client_data(int fd, const char *data, ssize_t sz)
{
	if (use_sideband) {
		send_sideband(1, fd, data, sz, use_sideband);
		return;
	}
	if (fd == 3)
		/* emergency quit */
		fd = 2;
	if (fd == 2) {
		/* XXX: are we happy to lose stuff here? */
		xwrite(fd, data, sz);
		return;
	}
	write_or_die(fd, data, sz);
}

static void report_message(const char *prefix, const char *err, va_list params)
{
	int sz = strlen(prefix);
	char msg[4096];

	strncpy(msg, prefix, sz);
	sz += vsnprintf(msg + sz, sizeof(msg) - sz, err, params);
	if (sz > (sizeof(msg) - 1))
		sz = sizeof(msg) - 1;
	msg[sz++] = '\n';

	if (use_sideband)
		send_sideband(1, 2, msg, sz, use_sideband);
	else
		xwrite(2, msg, sz);
}

static void report(struct command *commands, const char *unpack_status)
{
	struct command *cmd;
	struct strbuf buf = STRBUF_INIT;

	packet_buf_write(&buf, "unpack %s\n",
			 unpack_status ? unpack_status : "ok");
	for (cmd = commands; cmd; cmd = cmd->next) {
		if (!cmd->error_string)
			packet_buf_write(&buf, "ok %s\n",
					 cmd->ref_name);
		else
			packet_buf_write(&buf, "ng %s %s\n",
					 cmd->ref_name, cmd->error_string);
	}
	packet_buf_flush(&buf);

	if (use_sideband)
		send_sideband(1, 1, buf.buf, buf.len, use_sideband);
	else
		safe_write(1, buf.buf, buf.len);
	strbuf_release(&buf);
}

/*
 * Make a pack stream and spit it out into file descriptor fd
 */
static int pack_objects(int fd, struct ref *refs, struct extra_have_objects *extra, struct send_pack_args *args)
{
	/*
	 * The child becomes pack-objects --revs; we feed
	 * the revision parameters to it via its stdin and
	 * let its stdout go back to the other end.
	 */
	const char *argv[] = {
		"pack-objects",
		"--all-progress-implied",
		"--revs",
		"--stdout",
		NULL,
		NULL,
		NULL,
		NULL,
		NULL,
	};
	struct child_process po;
	int i;

	i = 4;
	if (args->use_thin_pack)
		argv[i++] = "--thin";
	if (args->use_ofs_delta)
		argv[i++] = "--delta-base-offset";
	if (args->quiet)
		argv[i++] = "-q";
	if (args->progress)
		argv[i++] = "--progress";
	memset(&po, 0, sizeof(po));
	po.argv = argv;
	po.in = -1;
	po.out = args->stateless_rpc ? -1 : fd;
	po.git_cmd = 1;
	if (start_command(&po))
		die_errno("git pack-objects failed");

	/*
	 * We feed the pack-objects we just spawned with revision
	 * parameters by writing to the pipe.
	 */
	for (i = 0; i < extra->nr; i++)
		if (!feed_object(extra->array[i], po.in, 1))
			break;

	while (refs) {
		if (!is_null_sha1(refs->old_sha1) &&
		    !feed_object(refs->old_sha1, po.in, 1))
			break;
		if (!is_null_sha1(refs->new_sha1) &&
		    !feed_object(refs->new_sha1, po.in, 0))
			break;
		refs = refs->next;
	}

	close(po.in);

	if (args->stateless_rpc) {
		char *buf = xmalloc(LARGE_PACKET_MAX);
		while (1) {
			ssize_t n = xread(po.out, buf, LARGE_PACKET_MAX);
			if (n <= 0)
				break;
			send_sideband(fd, -1, buf, n, LARGE_PACKET_MAX);
		}
		free(buf);
		close(po.out);
		po.out = -1;
	}

	if (finish_command(&po))
		return -1;
	return 0;
}

int send_pack(struct send_pack_args *args,
	      int fd[], struct child_process *conn,
	      struct ref *remote_refs,
	      struct extra_have_objects *extra_have)
{
	int in = fd[0];
	int out = fd[1];
	struct strbuf req_buf = STRBUF_INIT;
	struct ref *ref;
	int new_refs;
	int allow_deleting_refs = 0;
	int status_report = 0;
	int use_sideband = 0;
	unsigned cmds_sent = 0;
	int ret;
	struct async demux;

	/* Does the other end support the reporting? */
	if (server_supports("report-status"))
		status_report = 1;
	if (server_supports("delete-refs"))
		allow_deleting_refs = 1;
	if (server_supports("ofs-delta"))
		args->use_ofs_delta = 1;
	if (server_supports("side-band-64k"))
		use_sideband = 1;

	if (!remote_refs) {
		fprintf(stderr, "No refs in common and none specified; doing nothing.\n"
			"Perhaps you should specify a branch such as 'master'.\n");
		return 0;
	}

	/*
	 * Finally, tell the other end!
	 */
	new_refs = 0;
	for (ref = remote_refs; ref; ref = ref->next) {
		if (!ref->peer_ref && !args->send_mirror)
			continue;

		/* Check for statuses set by set_ref_status_for_push() */
		switch (ref->status) {
		case REF_STATUS_REJECT_NONFASTFORWARD:
		case REF_STATUS_UPTODATE:
			continue;
		default:
			; /* do nothing */
		}

		if (ref->deletion && !allow_deleting_refs) {
			ref->status = REF_STATUS_REJECT_NODELETE;
			continue;
		}

		if (!ref->deletion)
			new_refs++;

		if (args->dry_run) {
			ref->status = REF_STATUS_OK;
		} else {
			char *old_hex = sha1_to_hex(ref->old_sha1);
			char *new_hex = sha1_to_hex(ref->new_sha1);

			if (!cmds_sent && (status_report || use_sideband)) {
				packet_buf_write(&req_buf, "%s %s %s%c%s%s",
					old_hex, new_hex, ref->name, 0,
					status_report ? " report-status" : "",
					use_sideband ? " side-band-64k" : "");
			}
			else
				packet_buf_write(&req_buf, "%s %s %s",
					old_hex, new_hex, ref->name);
			ref->status = status_report ?
				REF_STATUS_EXPECTING_REPORT :
				REF_STATUS_OK;
			cmds_sent++;
		}
	}

	if (args->stateless_rpc) {
		if (!args->dry_run && cmds_sent) {
			packet_buf_flush(&req_buf);
			send_sideband(out, -1, req_buf.buf, req_buf.len, LARGE_PACKET_MAX);
		}
	} else {
		safe_write(out, req_buf.buf, req_buf.len);
		packet_flush(out);
	}
	strbuf_release(&req_buf);

	if (use_sideband && cmds_sent) {
		memset(&demux, 0, sizeof(demux));
		demux.proc = sideband_demux;
		demux.data = fd;
		demux.out = -1;
		if (start_async(&demux))
			die("send-pack: unable to fork off sideband demultiplexer");
		in = demux.out;
	}
//.........这里部分代码省略.........

static int copy_to_sideband(int in, int out, void *arg)
{
	char data[128];
	int keepalive_active = 0;

	if (keepalive_in_sec <= 0)
		use_keepalive = KEEPALIVE_NEVER;
	if (use_keepalive == KEEPALIVE_ALWAYS)
		keepalive_active = 1;

	while (1) {
		ssize_t sz;

		if (keepalive_active) {
			struct pollfd pfd;
			int ret;

			pfd.fd = in;
			pfd.events = POLLIN;
			ret = poll(&pfd, 1, 1000 * keepalive_in_sec);

			if (ret < 0) {
				if (errno == EINTR)
					continue;
				else
					break;
			} else if (ret == 0) {
				/* no data; send a keepalive packet */
				static const char buf[] = "0005\1";
				write_or_die(1, buf, sizeof(buf) - 1);
				continue;
			} /* else there is actual data to read */
		}

		sz = xread(in, data, sizeof(data));
		if (sz <= 0)
			break;

		if (use_keepalive == KEEPALIVE_AFTER_NUL && !keepalive_active) {
			const char *p = memchr(data, '\0', sz);
			if (p) {
				/*
				 * The NUL tells us to start sending keepalives. Make
				 * sure we send any other data we read along
				 * with it.
				 */
				keepalive_active = 1;
				send_sideband(1, 2, data, p - data, use_sideband);
				send_sideband(1, 2, p + 1, sz - (p - data + 1), use_sideband);
				continue;
			}
		}

		/*
		 * Either we're not looking for a NUL signal, or we didn't see
		 * it yet; just pass along the data.
		 */
		send_sideband(1, 2, data, sz, use_sideband);
	}
	close(in);
	return 0;
}

/*
 * Make a pack stream and spit it out into file descriptor fd
 */
static int pack_objects(int fd, struct ref *refs, struct sha1_array *extra, struct send_pack_args *args)
{
	/*
	 * The child becomes pack-objects --revs; we feed
	 * the revision parameters to it via its stdin and
	 * let its stdout go back to the other end.
	 */
	const char *argv[] = {
		"pack-objects",
		"--all-progress-implied",
		"--revs",
		"--stdout",
		NULL,
		NULL,
		NULL,
		NULL,
		NULL,
		NULL,
	};
	struct child_process po = CHILD_PROCESS_INIT;
	FILE *po_in;
	int i;

	i = 4;
	if (args->use_thin_pack)
		argv[i++] = "--thin";
	if (args->use_ofs_delta)
		argv[i++] = "--delta-base-offset";
	if (args->quiet || !args->progress)
		argv[i++] = "-q";
	if (args->progress)
		argv[i++] = "--progress";
	if (is_repository_shallow())
		argv[i++] = "--shallow";
	po.argv = argv;
	po.in = -1;
	po.out = args->stateless_rpc ? -1 : fd;
	po.git_cmd = 1;
	if (start_command(&po))
		die_errno("git pack-objects failed");

	/*
	 * We feed the pack-objects we just spawned with revision
	 * parameters by writing to the pipe.
	 */
	po_in = xfdopen(po.in, "w");
	for (i = 0; i < extra->nr; i++)
		feed_object(extra->sha1[i], po_in, 1);

	while (refs) {
		if (!is_null_oid(&refs->old_oid))
			feed_object(refs->old_oid.hash, po_in, 1);
		if (!is_null_oid(&refs->new_oid))
			feed_object(refs->new_oid.hash, po_in, 0);
		refs = refs->next;
	}

	fflush(po_in);
	if (ferror(po_in))
		die_errno("error writing to pack-objects");
	fclose(po_in);

	if (args->stateless_rpc) {
		char *buf = xmalloc(LARGE_PACKET_MAX);
		while (1) {
			ssize_t n = xread(po.out, buf, LARGE_PACKET_MAX);
			if (n <= 0)
				break;
			send_sideband(fd, -1, buf, n, LARGE_PACKET_MAX);
		}
		free(buf);
		close(po.out);
		po.out = -1;
	}

	if (finish_command(&po))
		return -1;
	return 0;
}

//.........这里部分代码省略.........
		else
			ref->status = REF_STATUS_EXPECTING_REPORT;
	}

	/*
	 * Finally, tell the other end!
	 */
	for (ref = remote_refs; ref; ref = ref->next) {
		char *old_hex, *new_hex;

		if (args->dry_run || push_cert_nonce)
			continue;

		if (check_to_send_update(ref, args) < 0)
			continue;

		old_hex = oid_to_hex(&ref->old_oid);
		new_hex = oid_to_hex(&ref->new_oid);
		if (!cmds_sent) {
			packet_buf_write(&req_buf,
					 "%s %s %s%c%s",
					 old_hex, new_hex, ref->name, 0,
					 cap_buf.buf);
			cmds_sent = 1;
		} else {
			packet_buf_write(&req_buf, "%s %s %s",
					 old_hex, new_hex, ref->name);
		}
	}

	if (args->stateless_rpc) {
		if (!args->dry_run && (cmds_sent || is_repository_shallow())) {
			packet_buf_flush(&req_buf);
			send_sideband(out, -1, req_buf.buf, req_buf.len, LARGE_PACKET_MAX);
		}
	} else {
		write_or_die(out, req_buf.buf, req_buf.len);
		packet_flush(out);
	}
	strbuf_release(&req_buf);
	strbuf_release(&cap_buf);

	if (use_push_options) {
		struct string_list_item *item;
		struct strbuf sb = STRBUF_INIT;

		for_each_string_list_item(item, args->push_options)
			packet_buf_write(&sb, "%s", item->string);

		write_or_die(out, sb.buf, sb.len);
		packet_flush(out);
		strbuf_release(&sb);
	}

	if (use_sideband && cmds_sent) {
		memset(&demux, 0, sizeof(demux));
		demux.proc = sideband_demux;
		demux.data = fd;
		demux.out = -1;
		demux.isolate_sigpipe = 1;
		if (start_async(&demux))
			die("send-pack: unable to fork off sideband demultiplexer");
		in = demux.out;
	}

	if (need_pack_data && cmds_sent) {

/*
 * Make a pack stream and spit it out into file descriptor fd
 */
static int pack_objects(int fd, struct ref *refs, struct sha1_array *extra, struct send_pack_args *args)
{
	/*
	 * The child becomes pack-objects --revs; we feed
	 * the revision parameters to it via its stdin and
	 * let its stdout go back to the other end.
	 */
	const char *argv[] = {
		"pack-objects",
		"--all-progress-implied",
		"--revs",
		"--stdout",
		NULL,
		NULL,
		NULL,
		NULL,
		NULL,
		NULL,
	};
	struct child_process po = CHILD_PROCESS_INIT;
	FILE *po_in;
	int i;
	int rc;

	i = 4;
	if (args->use_thin_pack)
		argv[i++] = "--thin";
	if (args->use_ofs_delta)
		argv[i++] = "--delta-base-offset";
	if (args->quiet || !args->progress)
		argv[i++] = "-q";
	if (args->progress)
		argv[i++] = "--progress";
	if (is_repository_shallow())
		argv[i++] = "--shallow";
	po.argv = argv;
	po.in = -1;
	po.out = args->stateless_rpc ? -1 : fd;
	po.git_cmd = 1;
	if (start_command(&po))
		die_errno("git pack-objects failed");

	/*
	 * We feed the pack-objects we just spawned with revision
	 * parameters by writing to the pipe.
	 */
	po_in = xfdopen(po.in, "w");
	for (i = 0; i < extra->nr; i++)
		feed_object(extra->sha1[i], po_in, 1);

	while (refs) {
		if (!is_null_oid(&refs->old_oid))
			feed_object(refs->old_oid.hash, po_in, 1);
		if (!is_null_oid(&refs->new_oid))
			feed_object(refs->new_oid.hash, po_in, 0);
		refs = refs->next;
	}

	fflush(po_in);
	if (ferror(po_in))
		die_errno("error writing to pack-objects");
	fclose(po_in);

	if (args->stateless_rpc) {
		char *buf = xmalloc(LARGE_PACKET_MAX);
		while (1) {
			ssize_t n = xread(po.out, buf, LARGE_PACKET_MAX);
			if (n <= 0)
				break;
			send_sideband(fd, -1, buf, n, LARGE_PACKET_MAX);
		}
		free(buf);
		close(po.out);
		po.out = -1;
	}

	rc = finish_command(&po);
	if (rc) {
		/*
		 * For a normal non-zero exit, we assume pack-objects wrote
		 * something useful to stderr. For death by signal, though,
		 * we should mention it to the user. The exception is SIGPIPE
		 * (141), because that's a normal occurence if the remote end
		 * hangs up (and we'll report that by trying to read the unpack
		 * status).
		 */
		if (rc > 128 && rc != 141)
			error("pack-objects died of signal %d", rc - 128);
		return -1;
	}
	return 0;
}