Re: [PATCH 2/2] builtin/cat-file.c: support NUL-delimited input with `-z`

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Hi Taylor

Thanks for working on this, I've been annoyed by the lack of a "-z" option but never got round to doing anything about it.

On 23/07/2022 00:29, Taylor Blau wrote:
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.

I wonder if this should also change the output delimiter from NL to NUL.

printf 'HEAD:does\nnot\nexist\000' | bin-wrappers/git cat-file --batch-check -z

prints

HEAD:does
not
exist missing

If it was terminated by a NUL rather than a newline it would be much easier to parse.

Best Wishes

Phillip

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@xxxxxxxxxxxx>
---
  Documentation/git-cat-file.txt |  7 +++++-
  builtin/cat-file.c             | 28 ++++++++++++++++++++---
  t/t1006-cat-file.sh            | 42 +++++++++++++++++++++++++++++++++-
  3 files changed, 72 insertions(+), 5 deletions(-)

diff --git a/Documentation/git-cat-file.txt b/Documentation/git-cat-file.txt
index 24a811f0ef..3515350ed6 100644
--- a/Documentation/git-cat-file.txt
+++ b/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
  ------
diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index f42782e955..c3602d15df 100644
--- a/builtin/cat-file.c
+++ b/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)) {
-		int i;
+	while (1) {
+		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)
diff --git a/t/t1006-cat-file.sh b/t/t1006-cat-file.sh
index 01c0535765..23b8942edb 100755
--- a/t/t1006-cat-file.sh
+++ b/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
  '



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