Re: [PATCH v2 7/8] update-ref: support multiple simultaneous updates

> Add a --stdin signature to read update instructions from standard input
> and apply multiple ref updates together.  Use an input format that
> supports any update that could be specified via the command-line,
> including object names like 'branch:path with space'.
> 
> Signed-off-by: Brad King <brad.king@kitware.com>
> ---
>  Documentation/git-update-ref.txt |   21 ++++++-
>  builtin/update-ref.c             |  121 +++++++++++++++++++++++++++++++++++++-
>  2 files changed, 140 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/git-update-ref.txt b/Documentation/git-update-ref.txt
> index 0df13ff..295d0bb 100644
> --- a/Documentation/git-update-ref.txt
> +++ b/Documentation/git-update-ref.txt
> @@ -8,7 +8,7 @@ git-update-ref - Update the object name stored in a ref safely
>  SYNOPSIS
>  --------
>  [verse]
> -'git update-ref' [-m <reason>] (-d <ref> [<oldvalue>] | [--no-deref] <ref> <newvalue> [<oldvalue>])
> +'git update-ref' [-m <reason>] (-d <ref> [<oldvalue>] | [--no-deref] <ref> <newvalue> [<oldvalue>] | --stdin)
>  
>  DESCRIPTION
>  -----------
> @@ -58,6 +58,25 @@ archive by creating a symlink tree).
>  With `-d` flag, it deletes the named <ref> after verifying it
>  still contains <oldvalue>.
>  
> +With `--stdin`, update-ref reads instructions from standard input and
> +performs all modifications together.  Empty lines are ignored.
> +Each non-empty line is parsed as whitespace-separated arguments.
> +Use single-quotes to enclose whitespace and backslashes and an
> +unquoted backslash to escape a single quote.  Specify updates with
> +lines of the form:
> +
> +	[--no-deref] [--] <ref> <newvalue> [<oldvalue>]
> +
> +Lines of any other format or a repeated <ref> produce an error.
> +Specify a zero <newvalue> to delete a ref and/or a zero <oldvalue>
> +to make sure that a ref not exist.  Use either 40 "0" or the
> +empty string (written as '') to specify a zero value.
> +
> +If all <ref>s can be locked with matching <oldvalue>s
> +simultaneously all modifications are performed.  Otherwise, no

> +modifications are performed.  Note that while each individual
> +<ref> is updated or deleted atomically, a concurrent reader may
> +still see a subset of the modifications.
>  
>  Logging Updates
>  ---------------
> diff --git a/builtin/update-ref.c b/builtin/update-ref.c
> index 51d2684..eb8db85 100644
> --- a/builtin/update-ref.c
> +++ b/builtin/update-ref.c
> @@ -6,19 +6,129 @@
>  static const char * const git_update_ref_usage[] = {
>  	N_("git update-ref [options] -d <refname> [<oldval>]"),
>  	N_("git update-ref [options]    <refname> <newval> [<oldval>]"),
> +	N_("git update-ref [options] --stdin"),
>  	NULL
>  };
>  
> +static const char blank[] = " \t\r\n";
> +
> +static int updates_size;
> +static int updates_count;
> +static struct ref_update *updates;
> +
> +static const char* update_refs_stdin_next_arg(const char* next,
> +					      struct strbuf *arg)
> +{
> +	/* Skip leading whitespace: */
> +	while (isspace(*next))
> +		++next;
> +
> +	/* Return NULL when no argument is found: */
> +	if (!*next)
> +		return NULL;
> +
> +	/* Parse the argument: */
> +	strbuf_reset(arg);
> +	for (;;) {
> +		char c = *next;
> +		if (!c || isspace(c))
> +			break;
> +		++next;
> +		if (c == '\'') {
> +			size_t len = strcspn(next, "'");

> +			if (!next[len])
> +				die("unterminated single-quote: '%s", next);
> +			strbuf_add(arg, next, len);
> +			next += len + 1;
> +			continue;
> +		}
> +		if (c == '\\') {
> +			if (*next == '\'')
> +				c = *next++;
> +			else
> +				die("unquoted backslash not escaping "
> +				    "single-quote: \\%s", next);
> +		}
> +		strbuf_addch(arg, c);
> +	}
> +	return next;
> +}
> +
> +static void update_refs_stdin(const char *line)
> +{
> +	int options = 1, flags = 0, argc = 0;
> +	char *argv[3] = {0, 0, 0};
> +	struct strbuf arg = STRBUF_INIT;
> +	struct ref_update *update;
> +	const char *next = line;
> +
> +	/* Skip blank lines: */
> +	if (!line[0])
> +		return;
> +
> +	/* Parse arguments on this line: */
> +	while ((next = update_refs_stdin_next_arg(next, &arg)) != NULL) {
> +		if (options && arg.buf[0] == '-')
> +			if (!strcmp(arg.buf, "--no-deref"))
> +				flags |= REF_NODEREF;
> +			else if (!strcmp(arg.buf, "--"))
> +				options = 0;
> +			else
> +				die("unknown option %s", arg.buf);
> +		else if (argc >= 3)
> +			die("too many arguments on line: %s", line);
> +		else {
> +			argv[argc++] = xstrdup(arg.buf);
> +			options = 0;
> +		}
> +	}
> +	strbuf_release(&arg);
> +
> +	/* Allocate and zero-init a struct ref_update: */
> +	if (updates_count == updates_size) {
> +		updates_size = updates_size ? (updates_size * 2) : 16;
> +		updates = xrealloc(updates, sizeof(*updates) * updates_size);
> +		memset(updates + updates_count, 0,
> +		       sizeof(*updates) * (updates_size - updates_count));
> +	}

> +	update = &updates[updates_count++];
> +	update->flags = flags;
> +
> +	/* Set the update ref_name: */
> +	if (!argv[0])
> +		die("no ref on line: %s", line);
> +	if (check_refname_format(argv[0], REFNAME_ALLOW_ONELEVEL))
> +		die("invalid ref format on line: %s", line);
> +	update->ref_name = argv[0];
> +	argv[0] = 0;
> +
> +	/* Set the update new_sha1 and, if specified, old_sha1: */
> +	if (!argv[1])
> +		die("missing new value on line: %s", line);
> +	if (*argv[1] && get_sha1(argv[1], update->new_sha1))
> +		die("invalid new value on line: %s", line);
> +	if (argv[2]) {
> +		update->have_old = 1;
> +		if (*argv[2] && get_sha1(argv[2], update->old_sha1))
> +			die("invalid old value on line: %s", line);
> +	}
> +
> +	while (argc > 0)
> +		free(argv[--argc]);
> +}
> +
>  int cmd_update_ref(int argc, const char **argv, const char *prefix)
>  {
>  	const char *refname, *oldval, *msg = NULL;
>  	unsigned char sha1[20], oldsha1[20];
> -	int delete = 0, no_deref = 0, flags = 0;
> +	int delete = 0, no_deref = 0, read_stdin = 0, flags = 0;
> +	struct strbuf line = STRBUF_INIT;
>  	struct option options[] = {
>  		OPT_STRING( 'm', NULL, &msg, N_("reason"), N_("reason of the update")),
>  		OPT_BOOLEAN('d', NULL, &delete, N_("delete the reference")),
>  		OPT_BOOLEAN( 0 , "no-deref", &no_deref,
>  					N_("update <refname> not the one it points to")),
> +		OPT_BOOLEAN( 0 , "stdin", &read_stdin, N_("read updates from stdin")),
>  		OPT_END(),
>  	};
>  
> @@ -28,6 +138,15 @@ int cmd_update_ref(int argc, const char **argv, const char *prefix)
>  	if (msg && !*msg)
>  		die("Refusing to perform update with empty message.");
>  
> +	if (read_stdin) {
> +		if (delete || no_deref || argc > 0)
> +			usage_with_options(git_update_ref_usage, options);
> +		while (strbuf_getline(&line, stdin, '\n') != EOF)
> +			update_refs_stdin(line.buf);
> +		strbuf_release(&line);
> +		return update_refs(msg, updates, updates_count, DIE_ON_ERR);
> +	}
> +
>  	if (delete) {
>  		if (argc < 1 || argc > 2)
>  			usage_with_options(git_update_ref_usage, options);
>