[PATCH] protocol-caps.c: fix memory leak in send_info()

Fix a memory leak in a2ba162cda (object-info: support for retrieving
object info, 2021-04-20) which appears to have been based on a
misunderstanding of how the pkt-line.c API works. There is no need to
strdup() input to packet_writer_write(), it's just a printf()-like
format function.

This fixes a potentially large memory leak, since the number of OID
lines the "object-info" call can be arbitrarily large (or a small one
if the request is small).

This makes t5701-git-serve.sh pass again under SANITIZE=leak, as it
did before a2ba162cda2.

Signed-off-by: Ævar Arnfjörð Bjarmason <redacted>
---

This was originally submitted as part of the SANITIZE=leak series as
https://lore.kernel.org/git/patch-3.4-b7fb5d5a56-20210714T172251Z-avarab@gmail.com/ (local)

In its v3 I stopped doing these leak fixes & test changes, let's just
consider this separately. We'll eventually want to add SANITIZE=leak
whitelisting to the relevant test if and when my SANITIZE=leak series
goes in, but we can just do that then along with adding various other
tests.

Range-diff:
1:  720852eee0b ! 1:  9acbc21cdd3 SANITIZE tests: fix memory leaks in t5701*, add to whitelist
    @@ Metadata
     Author: Ævar Arnfjörð Bjarmason [off-list ref]
     
      ## Commit message ##
    -    SANITIZE tests: fix memory leaks in t5701*, add to whitelist
    +    protocol-caps.c: fix memory leak in send_info()
     
         Fix a memory leak in a2ba162cda (object-info: support for retrieving
         object info, 2021-04-20) which appears to have been based on a
    -    misunderstanding of how the pkt-line.c API works, there is no need to
    -    strdup() input to, it's just a printf()-like format function.
    +    misunderstanding of how the pkt-line.c API works. There is no need to
    +    strdup() input to packet_writer_write(), it's just a printf()-like
    +    format function.
     
         This fixes a potentially large memory leak, since the number of OID
         lines the "object-info" call can be arbitrarily large (or a small one
         if the request is small).
     
    +    This makes t5701-git-serve.sh pass again under SANITIZE=leak, as it
    +    did before a2ba162cda2.
    +
         Signed-off-by: Ævar Arnfjörð Bjarmason [off-list ref]
     
      ## protocol-caps.c ##
    @@ protocol-caps.c: static void send_info(struct repository *r, struct packet_write
      }
      
      int cap_object_info(struct repository *r, struct strvec *keys,
    -
    - ## t/t5701-git-serve.sh ##
    -@@ t/t5701-git-serve.sh: test_description='test protocol v2 server commands'
    - GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
    - export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
    - 
    -+GIT_TEST_SANITIZE_LEAK=true
    - . ./test-lib.sh
    - 
    - test_expect_success 'test capability advertisement' '

 protocol-caps.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/protocol-caps.c b/protocol-caps.c
index 13a9e63a04a..901b6795e42 100644
--- a/protocol-caps.c
+++ b/protocol-caps.c

@@ -69,9 +69,10 @@ static void send_info(struct repository *r, struct packet_writer *writer,
 			}
 		}
 
-		packet_writer_write(writer, "%s",
-				    strbuf_detach(&send_buffer, NULL));
+		packet_writer_write(writer, "%s", send_buffer.buf);
+		strbuf_reset(&send_buffer);
 	}
+	strbuf_release(&send_buffer);
 }
 
 int cap_object_info(struct repository *r, struct strvec *keys,

-- 
2.33.0.805.g739b16c2189