Re: [PATCH v8 5/6] transport: add client support for object-info

>
> From: Calvin Wan <calvinwan@google.com>
>
> Sometimes, it is beneficial to retrieve information about an object
> without downloading it entirely. The server-side logic for this
> functionality was implemented in commit "a2ba162cda (object-info:
> support for retrieving object info, 2021-04-20)."
>
> This commit introduces client functions to interact with the server.
>
> Currently, the client supports requesting a list of object IDs with
> the ‘size’ feature from a v2 server. If the server does not advertise
> this feature (i.e., transfer.advertiseobjectinfo is set to false),
> the client will return an error and exit.
>
> Helped-by: Jonathan Tan <jonathantanmy@google.com>
> Helped-by: Christian Couder <chriscool@tuxfamily.org>
> Signed-off-by: Calvin Wan <calvinwan@google.com>
> Signed-off-by: Eric Ju  <eric.peijian@gmail.com>
> ---
>  Makefile            |  1 +
>  fetch-object-info.c | 92 +++++++++++++++++++++++++++++++++++++++++++++
>  fetch-object-info.h | 18 +++++++++
>  fetch-pack.c        |  3 ++
>  fetch-pack.h        |  2 +
>  transport-helper.c  | 11 +++++-
>  transport.c         | 28 +++++++++++++-
>  transport.h         | 11 ++++++
>  8 files changed, 163 insertions(+), 3 deletions(-)
>  create mode 100644 fetch-object-info.c
>  create mode 100644 fetch-object-info.h
>
> diff --git a/Makefile b/Makefile
> index 3fa4bf0d06..70e9ec0464 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1020,6 +1020,7 @@ LIB_OBJS += ewah/ewah_rlw.o
>  LIB_OBJS += exec-cmd.o
>  LIB_OBJS += fetch-negotiator.o
>  LIB_OBJS += fetch-pack.o
> +LIB_OBJS += fetch-object-info.o
>  LIB_OBJS += fmt-merge-msg.o
>  LIB_OBJS += fsck.o
>  LIB_OBJS += fsmonitor.o
> diff --git a/fetch-object-info.c b/fetch-object-info.c
> new file mode 100644
> index 0000000000..2aa9f2b70d
> --- /dev/null
> +++ b/fetch-object-info.c
> @@ -0,0 +1,92 @@
> +#include "git-compat-util.h"
> +#include "gettext.h"
> +#include "hex.h"
> +#include "pkt-line.h"
> +#include "connect.h"
> +#include "oid-array.h"
> +#include "object-store-ll.h"
> +#include "fetch-object-info.h"
> +#include "string-list.h"
> +
> +/**
> + * send_object_info_request sends git-cat-file object-info command and its
> + * arguments into the request buffer.
> + */
> +static void send_object_info_request(const int fd_out, struct object_info_args *args)
> +{
> +       struct strbuf req_buf = STRBUF_INIT;
> +
> +       write_command_and_capabilities(&req_buf, "object-info", args->server_options);
> +
> +       if (unsorted_string_list_has_string(args->object_info_options, "size"))
> +               packet_buf_write(&req_buf, "size");
> +
> +       if (args->oids) {
> +               for (size_t i = 0; i < args->oids->nr; i++)
> +                       packet_buf_write(&req_buf, "oid %s", oid_to_hex(&args->oids->oid[i]));
> +       }
> +
> +       packet_buf_flush(&req_buf);
> +       if (write_in_full(fd_out, req_buf.buf, req_buf.len) < 0)
> +               die_errno(_("unable to write request to remote"));
> +
> +       strbuf_release(&req_buf);
> +}
> +
> +/**
> + * fetch_object_info sends git-cat-file object-info command into the request buf
> + * and read the results from packets.
> + */
> +int fetch_object_info(const enum protocol_version version, struct object_info_args *args,
> +                     struct packet_reader *reader, struct object_info *object_info_data,
> +                     const int stateless_rpc, const int fd_out)
> +{
> +       int size_index = -1;
> +
> +       switch (version) {
> +       case protocol_v2:
> +               if (!server_supports_v2("object-info"))
> +                       die(_("object-info capability is not enabled on the server"));
> +               send_object_info_request(fd_out, args);
> +               break;
> +       case protocol_v1:
> +       case protocol_v0:
> +               die(_("wrong protocol version. expected v2"));

> +       case protocol_unknown_version:
> +               BUG("unknown protocol version");
> +       }
> +
> +       for (size_t i = 0; i < args->object_info_options->nr; i++) {
> +               if (packet_reader_read(reader) != PACKET_READ_NORMAL) {
> +                       check_stateless_delimiter(stateless_rpc, reader, "stateless delimiter expected");
> +                       return -1;
> +               }
> +               if (unsorted_string_list_has_string(args->object_info_options, reader->line)) {
> +                       if (!strcmp(reader->line, "size")) {
> +                               size_index = i;
> +                               for (size_t j = 0; j < args->oids->nr; j++)
> +                                       object_info_data[j].sizep = xcalloc(1, sizeof(long));
> +                       }
> +                       continue;
> +               }
> +               return -1;
> +       }