builtin/cat-file.c: support NUL-delimited input with `-z`

When callers are using `cat-file` via one of the stdin-driven `--batch`
modes, all input is newline-delimited. This presents a problem when
callers wish to ask about, e.g. tree-entries that have a newline
character present in their filename.

To support this niche scenario, introduce a new `-z` mode to the
`--batch`, `--batch-check`, and `--batch-command` suite of options that
instructs `cat-file` to treat its input as NUL-delimited, allowing the
individual commands themselves to have newlines present.

The refactoring here is slightly unfortunate, since we turn loops like:

    while (strbuf_getline(&buf, stdin) != EOF)

into:

    while (1) {
        int ret;
        if (opt->nul_terminated)
            ret = strbuf_getline_nul(&input, stdin);
        else
            ret = strbuf_getline(&input, stdin);

        if (ret == EOF)
            break;
    }

It's tempting to think that we could use `strbuf_getwholeline()` and
specify either `\n` or `\0` as the terminating character. But for input
on platforms that include a CR character preceeding the LF, this
wouldn't quite be the same, since `strbuf_getline(...)` will trim any
trailing CR, while `strbuf_getwholeline(&buf, stdin, '\n')` will not.

In the future, we could clean this up further by introducing a variant
of `strbuf_getwholeline()` that addresses the aforementioned gap, but
that approach felt too heavy-handed for this pair of uses.

Some tests are added in t1006 to ensure that `cat-file` produces the
same output in `--batch`, `--batch-check`, and `--batch-command` modes
with and without the new `-z` option.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-cat-file.txt

@@ -14,7 +14,7 @@ SYNOPSIS
 'git cat-file' (-t | -s) [--allow-unknown-type] <object>
 'git cat-file' (--batch | --batch-check | --batch-command) [--batch-all-objects]
 	     [--buffer] [--follow-symlinks] [--unordered]
-	     [--textconv | --filters]
+	     [--textconv | --filters] [-z]
 'git cat-file' (--textconv | --filters)
 	     [<rev>:<path|tree-ish> | --path=<path|tree-ish> <rev>]
 
@@ -207,6 +207,11 @@ respectively print:
 	/etc/passwd
 --
 
+-z::
+	Only meaningful with `--batch`, `--batch-check`, or
+	`--batch-command`; input is NUL-delimited instead of
+	newline-delimited.
+
 
 OUTPUT
 ------

builtin/cat-file.c

@@ -31,6 +31,7 @@ struct batch_options {
 	int all_objects;
 	int unordered;
 	int transform_mode; /* may be 'w' or 'c' for --filters or --textconv */
+	int nul_terminated;
 	const char *format;
 };
 
@@ -614,12 +615,20 @@ static void batch_objects_command(struct batch_options *opt,
 	struct queued_cmd *queued_cmd = NULL;
 	size_t alloc = 0, nr = 0;
 
-	while (!strbuf_getline(&input, stdin)) {
+	while (1) {
-		int i;
+		int i, ret;
 		const struct parse_cmd *cmd = NULL;
 		const char *p = NULL, *cmd_end;
 		struct queued_cmd call = {0};
 
+		if (opt->nul_terminated)
+			ret = strbuf_getline_nul(&input, stdin);
+		else
+			ret = strbuf_getline(&input, stdin);
+
+		if (ret)
+			break;
+
 		if (!input.len)
 			die(_("empty command in input"));
 		if (isspace(*input.buf))
@@ -763,7 +772,16 @@ static int batch_objects(struct batch_options *opt)
 		goto cleanup;
 	}
 
-	while (strbuf_getline(&input, stdin) != EOF) {
+	while (1) {
+		int ret;
+		if (opt->nul_terminated)
+			ret = strbuf_getline_nul(&input, stdin);
+		else
+			ret = strbuf_getline(&input, stdin);
+
+		if (ret == EOF)
+			break;
+
 		if (data.split_on_whitespace) {
 			/*
 			 * Split at first whitespace, tying off the beginning
@@ -866,6 +884,7 @@ int cmd_cat_file(int argc, const char **argv, const char *prefix)
 			N_("like --batch, but don't emit <contents>"),
 			PARSE_OPT_OPTARG | PARSE_OPT_NONEG,
 			batch_option_callback),
+		OPT_BOOL('z', NULL, &batch.nul_terminated, N_("stdin is NUL-terminated")),
 		OPT_CALLBACK_F(0, "batch-command", &batch, N_("format"),
 			N_("read commands from stdin"),
 			PARSE_OPT_OPTARG | PARSE_OPT_NONEG,
@@ -921,6 +940,9 @@ int cmd_cat_file(int argc, const char **argv, const char *prefix)
 	else if (batch.all_objects)
 		usage_msg_optf(_("'%s' requires a batch mode"), usage, options,
 			       "--batch-all-objects");
+	else if (batch.nul_terminated)
+		usage_msg_optf(_("'%s' requires a batch mode"), usage, options,
+			       "-z");
 
 	/* Batch defaults */
 	if (batch.buffer_output < 0)

t/t1006-cat-file.sh

@@ -88,7 +88,8 @@ done
 
 for opt in --buffer \
 	--follow-symlinks \
-	--batch-all-objects
+	--batch-all-objects \
+	-z
 do
 	test_expect_success "usage: bad option combination: $opt without batch mode" '
 		test_incompatible_usage git cat-file $opt &&
@@ -100,6 +101,10 @@ echo_without_newline () {
     printf '%s' "$*"
 }
 
+echo_without_newline_nul () {
+	echo_without_newline "$@" | tr '\n' '\0'
+}
+
 strlen () {
     echo_without_newline "$1" | wc -c | sed -e 's/^ *//'
 }
@@ -398,6 +403,12 @@ test_expect_success '--batch with multiple sha1s gives correct format' '
 	test "$(maybe_remove_timestamp "$batch_output" 1)" = "$(maybe_remove_timestamp "$(echo_without_newline "$batch_input" | git cat-file --batch)" 1)"
 '
 
+test_expect_success '--batch, -z with multiple sha1s gives correct format' '
+	echo_without_newline_nul "$batch_input" >in &&
+	test "$(maybe_remove_timestamp "$batch_output" 1)" = \
+	"$(maybe_remove_timestamp "$(git cat-file --batch -z <in)" 1)"
+'
+
 batch_check_input="$hello_sha1
 $tree_sha1
 $commit_sha1
@@ -418,6 +429,24 @@ test_expect_success "--batch-check with multiple sha1s gives correct format" '
     "$(echo_without_newline "$batch_check_input" | git cat-file --batch-check)"
 '
 
+test_expect_success "--batch-check, -z with multiple sha1s gives correct format" '
+    echo_without_newline_nul "$batch_check_input" >in &&
+    test "$batch_check_output" = "$(git cat-file --batch-check -z <in)"
+'
+
+test_expect_success FUNNYNAMES '--batch-check, -z with newline in input' '
+	touch -- "newline${LF}embedded" &&
+	git add -- "newline${LF}embedded" &&
+	git commit -m "file with newline embedded" &&
+	test_tick &&
+
+	printf "HEAD:newline${LF}embedded" >in &&
+	git cat-file --batch-check -z <in >actual &&
+
+	echo "$(git rev-parse "HEAD:newline${LF}embedded") blob 0" >expect &&
+	test_cmp expect actual
+'
+
 batch_command_multiple_info="info $hello_sha1
 info $tree_sha1
 info $commit_sha1
@@ -436,6 +465,11 @@ test_expect_success '--batch-command with multiple info calls gives correct form
 	echo "$batch_command_multiple_info" >in &&
 	git cat-file --batch-command --buffer <in >actual &&
 
+	test_cmp expect actual &&
+
+	echo "$batch_command_multiple_info" | tr "\n" "\0" >in &&
+	git cat-file --batch-command --buffer -z <in >actual &&
+
 	test_cmp expect actual
 '
 
@@ -459,6 +493,12 @@ test_expect_success '--batch-command with multiple command calls gives correct f
 	echo "$batch_command_multiple_contents" >in &&
 	git cat-file --batch-command --buffer <in >actual_raw &&
 
+	remove_timestamp <actual_raw >actual &&
+	test_cmp expect actual &&
+
+	echo "$batch_command_multiple_contents" | tr "\n" "\0" >in &&
+	git cat-file --batch-command --buffer -z <in >actual_raw &&
+
 	remove_timestamp <actual_raw >actual &&
 	test_cmp expect actual
 '