odb: Prevent stream_finalize_write() from overwriting

Now that #1785 is merged, git_odb_stream_finalize_write() calculates the object id before invoking the odb backend.

This commit gives a chance to the backend to check if it already knows this object.

1 files changed, 28 insertions, 0 deletions

diff --git a/tests-clar/object/blob/fromchunks.c b/tests-clar/object/blob/fromchunks.c
index 9fe62daef..03ed4efb4 100644
--- a/tests-clar/object/blob/fromchunks.c
+++ b/tests-clar/object/blob/fromchunks.c
@@ -53,6 +53,34 @@ void test_object_blob_fromchunks__can_create_a_blob_from_a_in_memory_chunk_provi
 	git_object_free(blob);
 }
 
+void test_object_blob_fromchunks__doesnot_overwrite_an_already_existing_object(void)
+{
+	git_buf path = GIT_BUF_INIT;
+	git_buf content = GIT_BUF_INIT;
+	git_oid expected_oid, oid;
+	int howmany = 7;
+	
+	cl_git_pass(git_oid_fromstr(&expected_oid, "321cbdf08803c744082332332838df6bd160f8f9"));
+
+	cl_git_pass(git_blob_create_fromchunks(&oid, repo, NULL, text_chunked_source_cb, &howmany));
+
+	/* Let's replace the content of the blob file storage with something else... */
+	cl_git_pass(git_buf_joinpath(&path, git_repository_path(repo), "objects/32/1cbdf08803c744082332332838df6bd160f8f9"));
+	cl_git_pass(p_unlink(git_buf_cstr(&path)));
+	cl_git_mkfile(git_buf_cstr(&path), "boom");
+
+	/* ...request a creation of the same blob... */
+	howmany = 7;
+	cl_git_pass(git_blob_create_fromchunks(&oid, repo, NULL, text_chunked_source_cb, &howmany));
+
+	/* ...and ensure the content of the faked blob file hasn't been altered */
+	cl_git_pass(git_futils_readbuffer(&content, git_buf_cstr(&path)));
+	cl_assert(!git__strcmp("boom", git_buf_cstr(&content)));
+
+	git_buf_free(&path);
+	git_buf_free(&content);
+}
+
 #define GITATTR "* text=auto\n" \
 	"*.txt text\n" \
 	"*.data binary\n"