fuzzers: use `git_buf_printf` instead of `snprintf`

The `snprintf` function does not exist on Win32, it only has
`_snprintf_s` available. Let's just avoid any cross-platform hassle and
use our own `git_buf` functionality instead.

fuzzers/packfile_fuzzer.c

@@ -16,6 +16,7 @@
 #include "git2.h"
 #include "git2/sys/mempack.h"
 #include "common.h"
+#include "buffer.h"
 
 static git_odb *odb = NULL;
 static git_odb_backend *mempack = NULL;
@@ -54,12 +55,11 @@ int LLVMFuzzerInitialize(int *argc, char ***argv)
 
 int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 {
-	git_indexer *indexer = NULL;
 	git_indexer_progress stats = {0, 0};
+	git_indexer *indexer = NULL;
+	git_buf path = GIT_BUF_INIT;
+	git_oid oid;
 	bool append_hash = false;
-	git_oid id;
-	char hash[GIT_OID_HEXSZ + 1] = {0};
-	char path[GIT_PATH_MAX];
 
 	if (size == 0)
 		return 0;
@@ -70,7 +70,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 	}
 	git_mempack_reset(mempack);
 
-	if (git_odb_write(&id, odb, base_obj, base_obj_len, GIT_OBJECT_BLOB) < 0) {
+	if (git_odb_write(&oid, odb, base_obj, base_obj_len, GIT_OBJECT_BLOB) < 0) {
 		fprintf(stderr, "Failed to add an object to the odb\n");
 		abort();
 	}
@@ -92,7 +92,6 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 	if (git_indexer_append(indexer, data, size, &stats) < 0)
 		goto cleanup;
 	if (append_hash) {
-		git_oid oid;
 		if (git_odb_hash(&oid, data, size, GIT_OBJECT_BLOB) < 0) {
 			fprintf(stderr, "Failed to compute the SHA1 hash\n");
 			abort();
@@ -104,19 +103,19 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
 	if (git_indexer_commit(indexer, &stats) < 0)
 		goto cleanup;
 
-	/*
-	 * We made it! We managed to produce a valid packfile.
-	 * Let's clean it up.
-	 */
-	git_oid_fmt(hash, git_indexer_hash(indexer));
-	printf("Generated packfile %s\n", hash);
-	snprintf(path, sizeof(path), "pack-%s.idx", hash);
-	p_unlink(path);
-	snprintf(path, sizeof(path), "pack-%s.pack", hash);
-	p_unlink(path);
+	if (git_buf_printf(&path, "pack-%s.idx", git_oid_tostr_s(git_indexer_hash(indexer))) < 0)
+		goto cleanup;
+	p_unlink(git_buf_cstr(&path));
+
+	git_buf_clear(&path);
+
+	if (git_buf_printf(&path, "pack-%s.pack", git_oid_tostr_s(git_indexer_hash(indexer))) < 0)
+		goto cleanup;
+	p_unlink(git_buf_cstr(&path));
 
 cleanup:
 	git_mempack_reset(mempack);
 	git_indexer_free(indexer);
+	git_buf_dispose(&path);
 	return 0;
 }