multipack: Introduce a parser for multi-pack-index files

This change is the first in a series to add support for git's
multi-pack-index. This should speed up large repositories significantly.

Part of: #5399

1 files changed, 76 insertions, 0 deletions

diff --git a/fuzzers/midx_fuzzer.c b/fuzzers/midx_fuzzer.c
new file mode 100644
index 000000000..e67873faa
--- /dev/null
+++ b/fuzzers/midx_fuzzer.c
@@ -0,0 +1,76 @@
+/*
+ * libgit2 multi-pack-index fuzzer target.
+ *
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+
+#include <stdio.h>
+
+#include "git2.h"
+
+#include "buffer.h"
+#include "common.h"
+#include "futils.h"
+#include "hash.h"
+#include "midx.h"
+
+int LLVMFuzzerInitialize(int *argc, char ***argv)
+{
+	GIT_UNUSED(argc);
+	GIT_UNUSED(argv);
+
+	if (git_libgit2_init() < 0) {
+		fprintf(stderr, "Failed to initialize libgit2\n");
+		abort();
+	}
+	return 0;
+}
+
+int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+{
+	git_midx_file idx = {{0}};
+	git_midx_entry e;
+	git_buf midx_buf = GIT_BUF_INIT;
+	git_oid oid = {{0}};
+	bool append_hash = false;
+
+	if (size < 4)
+		return 0;
+
+	/*
+	 * If the first byte in the stream has the high bit set, append the
+	 * SHA1 hash so that the packfile is somewhat valid.
+	 */
+	append_hash = *data & 0x80;
+	/* Keep a 4-byte alignment to avoid unaligned accesses. */
+	data += 4;
+	size -= 4;
+
+	if (append_hash) {
+		if (git_buf_init(&midx_buf, size + sizeof(oid)) < 0)
+			goto cleanup;
+		if (git_hash_buf(&oid, data, size) < 0) {
+			fprintf(stderr, "Failed to compute the SHA1 hash\n");
+			abort();
+		}
+		memcpy(midx_buf.ptr, data, size);
+		memcpy(midx_buf.ptr + size, &oid, sizeof(oid));
+	} else {
+		git_buf_attach_notowned(&midx_buf, (char *)data, size);
+	}
+
+	if (git_midx_parse(&idx, (const unsigned char *)git_buf_cstr(&midx_buf), git_buf_len(&midx_buf)) < 0)
+		goto cleanup;
+
+	/* Search for any oid, just to exercise that codepath. */
+	if (git_midx_entry_find(&e, &idx, &oid, GIT_OID_HEXSZ) < 0)
+		goto cleanup;
+
+cleanup:
+	git_midx_close(&idx);
+	git_buf_dispose(&midx_buf);
+	return 0;
+}