fuzz: reorganise the path for existing oss-fuzz fuzzers

In order to provide a better organisation for oss-fuzz fuzzers and
to avoid top-level clustters in the git repository when more fuzzers
are introduced, move the existing fuzzer-related sources to their
own oss-fuzz/ hierarchy.  Grouping the fuzzers into their own
directory, separate their application on fuzz-testing from the core
functionalities of the git code, prvides better and tidier structure
the oss-fuzz fuzzing library to manage, locate, build and execute
those fuzzers for fuzz-testing purposes in future development.

Signed-off-by: Arthur Chan <arthur.chan@adalogics.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

oss-fuzz/.gitignore

@@ -0,0 +1,3 @@
+fuzz-commit-graph
+fuzz-pack-headers
+fuzz-pack-idx

oss-fuzz/fuzz-commit-graph.c

@@ -0,0 +1,19 @@
+#include "commit-graph.h"
+#include "repository.h"
+
+struct commit_graph *parse_commit_graph(struct repository *r,
+					void *graph_map, size_t graph_size);
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+{
+	struct commit_graph *g;
+
+	initialize_the_repository();
+	g = parse_commit_graph(the_repository, (void *)data, size);
+	repo_clear(the_repository);
+	free_commit_graph(g);
+
+	return 0;
+}

oss-fuzz/fuzz-pack-headers.c

@@ -0,0 +1,14 @@
+#include "packfile.h"
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+{
+	enum object_type type;
+	unsigned long len;
+
+	unpack_object_header_buffer((const unsigned char *)data,
+				    (unsigned long)size, &type, &len);
+
+	return 0;
+}

oss-fuzz/fuzz-pack-idx.c

@@ -0,0 +1,13 @@
+#include "object-store.h"
+#include "packfile.h"
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+{
+	struct packed_git p;
+
+	load_idx("fuzz-input", GIT_SHA1_RAWSZ, (void *)data, size, &p);
+
+	return 0;
+}