Merge branch 'ps/cat-file-remote-object-info' into jch

The 'remote-object-info' command has been added to 'git cat-file
--batch-command', allowing clients to request object metadata
(currently size) from a remote server via protocol v2 without
downloading the entire object. Format placeholders are dynamically
filtered on the client based on server-advertised capabilities,
returning empty strings for inapplicable or unsupported fields.

* ps/cat-file-remote-object-info:
  cat-file: make remote-object-info allow-list dynamic
  cat-file: validate remote atoms with an allow-list
  cat-file: add remote-object-info to batch-command
  transport: add client support for object-info
  serve: advertise object-info feature
  fetch-pack: move fetch initialization
  connect: make write_fetch_command_and_capabilities() more generic
  fetch-pack: move write_fetch_command_and_capabilities() to connect.c
  fetch-pack: drop static advertise_sid variable
  fetch-pack: fix hash_algo variable type
  t1006: split test utility functions into new 'lib-cat-file.sh'
  cat-file: declare loop counter inside for()
  transport-helper: fix memory leak of helper on disconnect

Author: gitster

Documentation/git-cat-file.adoc

@@ -169,6 +169,13 @@ info <object>::
 	Print object info for object reference `<object>`. This corresponds to the
 	output of `--batch-check`.
 
+remote-object-info <remote> <object>...::
+	Print object info for object references `<object>` at specified
+	`<remote>` without downloading objects from the remote.
+	Raise an error when the `object-info` capability is not supported by the remote.
+	Raise an error when no object references are provided.
+	This command may be combined with `--buffer`.
+
 flush::
 	Used with `--buffer` to execute all preceding commands that were issued
 	since the beginning or since the last flush was issued. When `--buffer`
@@ -301,7 +308,8 @@ one per line, and print information based on the command given. With
 `--batch-command`, the `info` command followed by an object will print
 information about the object the same way `--batch-check` would, and the
 `contents` command followed by an object prints contents in the same way
-`--batch` would.
+`--batch` would. The `remote-object-info` command followed by a remote and
+objects IDs prints object info from the remote without downloading the objects.
 
 You can specify the information shown for each object by using a custom
 `<format>`. The `<format>` is copied literally to stdout for each
@@ -324,24 +332,27 @@ newline. The available atoms are:
 	reports).
 
 `objectsize:disk`::
-	The size, in bytes, that the object takes up on disk. See the
-	note about on-disk sizes in the `CAVEATS` section below.
+	The size, in bytes, that the object takes up on disk.
 
 `deltabase`::
 	If the object is stored as a delta on-disk, this expands to the
 	full hex representation of the delta base object name.
-	Otherwise, expands to the null OID (all zeroes). See `CAVEATS`
-	below.
-
+	Otherwise, expands to the null OID (all zeroes).
 `rest`::
 	If this atom is used in the output string, input lines are split
 	at the first whitespace boundary. All characters before that
 	whitespace are considered to be the object name; characters
 	after that first run of whitespace (i.e., the "rest" of the
 	line) are output in place of the `%(rest)` atom.
 
+The command `remote-object-info` only supports the `%(objectname)` and
+`%(objectsize)` placeholders. See `CAVEATS` below for more information.
+
 If no format is specified, the default format is `%(objectname)
-%(objecttype) %(objectsize)`.
+%(objecttype) %(objectsize)`, except for `remote-object-info` commands which
+use `%(objectname) %(objectsize)` because "%(objecttype)" is not supported yet.
+WARNING: When "%(objecttype)" is supported, the default format WILL be unified,
+so DO NOT RELY on the current default format to stay the same!!!
 
 If `--batch` is specified, or if `--batch-command` is used with the `contents`
 command, the object information is followed by the object contents (consisting
@@ -438,6 +449,10 @@ scripting purposes.
 CAVEATS
 -------
 
+Note that since only `%(objectname)` and `%(objectsize)` are currently
+supported by the `remote-object-info` command. Using any other placeholder in
+the format string will return an empty string in its position.
+
 Note that the sizes of objects on disk are reported accurately, but care
 should be taken in drawing conclusions about which refs or objects are
 responsible for disk usage. The size of a packed non-delta object may be

Documentation/gitprotocol-v2.adoc

@@ -568,21 +568,26 @@ An `object-info` request takes the following arguments:
 
 	oid <oid>
 	Indicates to the server an object which the client wants to obtain
-	information for.
+	information for. They must be full object IDs.
 
 The response of `object-info` is a list of the requested object ids
 and associated requested information, each separated by a single space.
 
 	output = info flush-pkt
 
-	info = PKT-LINE(attrs) LF)
+	info = PKT-LINE(attrs LF)
 		*PKT-LINE(obj-info LF)
 
 	attrs = attr | attrs SP attrs
 
+	obj-size = 1*DIGIT
+
 	attr = "size"
 
-	obj-info = obj-id SP obj-size
+	obj-info = obj-id SP [obj-size]
+
+	If the server does not recognize the object id, the response will be
+	`obj-id SP` regardless of the number of attributes requested.
 
 bundle-uri
 ~~~~~~~~~~

Makefile

@@ -1170,6 +1170,7 @@ 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