odb: test loose reading/writing large objects

Introduce a test for very large objects in the ODB.  Write a large
object (5 GB) and ensure that the write succeeds and provides us the
expected object ID.  Introduce a test that writes that file and
ensures that we can subsequently read it.

tests/odb/largefiles.c

+#include "clar_libgit2.h"
+#include "git2/odb_backend.h"
+
+static git_repository *repo;
+static git_odb *odb;
+
+void test_odb_largefiles__initialize(void)
+{
+	repo = cl_git_sandbox_init("testrepo.git");
+	cl_git_pass(git_repository_odb(&odb, repo));
+}
+
+void test_odb_largefiles__cleanup(void)
+{
+	git_odb_free(odb);
+	cl_git_sandbox_cleanup();
+}
+
+static void writefile(git_oid *oid)
+{
+	static git_odb_stream *stream;
+	git_buf buf = GIT_BUF_INIT;
+	size_t i;
+
+	for (i = 0; i < 3041; i++)
+		cl_git_pass(git_buf_puts(&buf, "Hello, world.\n"));
+
+	cl_git_pass(git_odb_open_wstream(&stream, odb, 5368709122, GIT_OBJ_BLOB));
+	for (i = 0; i < 126103; i++)
+		cl_git_pass(git_odb_stream_write(stream, buf.ptr, buf.size));
+
+	cl_git_pass(git_odb_stream_finalize_write(oid, stream));
+
+	git_odb_stream_free(stream);
+	git_buf_free(&buf);
+}
+
+void test_odb_largefiles__write_from_memory(void)
+{
+	git_oid expected, oid;
+	git_buf buf = GIT_BUF_INIT;
+	size_t i;
+
+#ifndef GIT_ARCH_64
+	cl_skip();
+#endif
+
+	if (!cl_is_env_set("GITTEST_INVASIVE_FS_SIZE"))
+		cl_skip();
+
+	if (!cl_is_env_set("GITTEST_INVASIVE_MEMORY"))
+		cl_skip();
+
+	for (i = 0; i < (3041*126103); i++)
+		cl_git_pass(git_buf_puts(&buf, "Hello, world.\n"));
+
+	git_oid_fromstr(&expected, "3fb56989cca483b21ba7cb0a6edb229d10e1c26c");
+	cl_git_pass(git_odb_write(&oid, odb, buf.ptr, buf.size, GIT_OBJ_BLOB));
+
+	cl_assert_equal_oid(&expected, &oid);
+}
+
+void test_odb_largefiles__streamwrite(void)
+{
+	git_oid expected, oid;
+
+	if (!cl_is_env_set("GITTEST_INVASIVE_FS_SIZE"))
+		cl_skip();
+
+	git_oid_fromstr(&expected, "3fb56989cca483b21ba7cb0a6edb229d10e1c26c");
+	writefile(&oid);
+
+	cl_assert_equal_oid(&expected, &oid);
+}
+
+void test_odb_largefiles__read_into_memory(void)
+{
+	git_oid oid;
+	git_odb_object *obj;
+
+#ifndef GIT_ARCH_64
+	cl_skip();
+#endif
+
+	if (!cl_is_env_set("GITTEST_INVASIVE_FS_SIZE"))
+		cl_skip();
+
+	if (!cl_is_env_set("GITTEST_INVASIVE_MEMORY"))
+		cl_skip();
+
+	writefile(&oid);
+	cl_git_pass(git_odb_read(&obj, odb, &oid));
+
+	git_odb_object_free(obj);
+}