git_buf_grow_by: increase buf asize incrementally

Introduce `git_buf_grow_by` to incrementally increase the size of a
`git_buf`, performing an overflow calculation on the growth.

2 files changed, 30 insertions, 0 deletions

diff --git a/tests/buf/basic.c b/tests/buf/basic.c
index d558757a9..dcc0916d2 100644
--- a/tests/buf/basic.c
+++ b/tests/buf/basic.c
@@ -15,6 +15,26 @@ void test_buf_basic__resize(void)
 	git_buf_free(&buf1);
 }
 
+void test_buf_basic__resize_incremental(void)
+{
+	git_buf buf1 = GIT_BUF_INIT;
+
+	/* Presently, asking for 6 bytes will round up to 8. */
+	cl_git_pass(git_buf_puts(&buf1, "Hello"));
+	cl_assert_equal_i(5, buf1.size);
+	cl_assert_equal_i(8, buf1.asize);
+
+	/* Ensure an additional byte does not realloc. */
+	cl_git_pass(git_buf_grow_by(&buf1, 1));
+	cl_assert_equal_i(5, buf1.size);
+	cl_assert_equal_i(8, buf1.asize);
+
+	/* But requesting many does. */
+	cl_git_pass(git_buf_grow_by(&buf1, 16));
+	cl_assert_equal_i(5, buf1.size);
+	cl_assert(buf1.asize > 8);
+}
+
 void test_buf_basic__printf(void)
 {
 	git_buf buf2 = GIT_BUF_INIT;
diff --git a/tests/buf/oom.c b/tests/buf/oom.c
index 709439aa5..b9fd29cbb 100644
--- a/tests/buf/oom.c
+++ b/tests/buf/oom.c
@@ -29,3 +29,13 @@ void test_buf_oom__grow(void)
 
 	git_buf_free(&buf);
 }
+
+void test_buf_oom__grow_by(void)
+{
+	git_buf buf = GIT_BUF_INIT;
+
+	buf.size = SIZE_MAX-10;
+
+	cl_assert(git_buf_grow_by(&buf, 50) == -1);
+	cl_assert(git_buf_oom(&buf));
+}