[PATCH 1/2] cat-file: force flush of stdout on empty string

From: John Cai via GitGitGadget <gitgitgadget@gmail.com>
Date: Nov 5, 2021, 21:56 UTC
Message-ID: <2d687baeed82e7b90d383bad8e209f50e0ce8c87.1636149400.git.gitgitgadget@gmail.com>
In-Reply-To: <pull.1124.git.git.1636149400.gitgitgadget@gmail.com>

From: John Cai <johncai86@gmail.com>

When in --buffer mode, it is very useful for the caller to have control over when the buffer is flushed. Currently there is no convenient way to signal for the buffer to be flushed. One workaround is to provide any nonexisting commit to git-cat-file's stdin, in which case the buffer will be flushed and a "$FOO missing" message will be displayed. However, this is not an ideal workaround.

Instead, this commit teaches git-cat-file to look for an empty string in stdin, which will trigger a flush of stdout.

Signed-off-by: John Cai <johncai86@gmail.com>
---
 builtin/cat-file.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index 86fc03242b8..4d17f30f24e 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -405,6 +405,11 @@ static void batch_one_object(const char *obj_name,
 	int flags = opt->follow_symlinks ? GET_OID_FOLLOW_SYMLINKS : 0;
 	enum get_oid_result result;
 
+	if (opt->buffer_output && obj_name[0] == '\0') {
+		fflush(stdout);
+		return;
+	}
+
 	result = get_oid_with_context(the_repository, obj_name,
 				      flags, &data->oid, &ctx);
 	if (result != FOUND) {
@@ -609,7 +614,11 @@ static int batch_objects(struct batch_options *opt)
 			data.rest = p;
 		}
 
-		batch_one_object(input.buf, &output, opt, &data);
+		 /*
+		  * When in buffer mode and input.buf is an empty string,
+		  * flush to stdout.
+		  */
+		 batch_one_object(input.buf, &output, opt, &data);
 	}
 
 	strbuf_release(&input);

-- 
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