Add function generating array of iovec with different FUSE structs

This commit adds a function in the newly created fuse_util library,
which accepts a variable number of arguments and data structures.

Fixes #3609

2 files changed, 73 insertions, 0 deletions

diff --git a/test/util/BUILD b/test/util/BUILD
index 2a17c33ee..b0c2c2a5a 100644
--- a/test/util/BUILD
+++ b/test/util/BUILD
@@ -46,6 +46,12 @@ cc_library(
 )
 
 cc_library(
+    name = "fuse_util",
+    testonly = 1,
+    hdrs = ["fuse_util.h"],
+)
+
+cc_library(
     name = "proc_util",
     testonly = 1,
     srcs = ["proc_util.cc"],
diff --git a/test/util/fuse_util.h b/test/util/fuse_util.h
new file mode 100644
index 000000000..5f5182b96
--- /dev/null
+++ b/test/util/fuse_util.h
@@ -0,0 +1,67 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef GVISOR_TEST_UTIL_FUSE_UTIL_H_
+#define GVISOR_TEST_UTIL_FUSE_UTIL_H_
+
+#include <sys/uio.h>
+
+#include <string>
+#include <vector>
+
+namespace gvisor {
+namespace testing {
+
+// The fundamental generation function with a single argument. If passed by
+// std::string or std::vector<char>, it will call specialized versions as
+// implemented below.
+template <typename T>
+std::vector<struct iovec> FuseGenerateIovecs(T &first) {
+  return {(struct iovec){.iov_base = &first, .iov_len = sizeof(first)}};
+}
+
+// If an argument is of type std::string, it must be used in read-only scenario.
+// Because we are setting up iovec, which contains the original address of a
+// data structure, we have to drop const qualification. Usually used with
+// variable-length payload data.
+template <typename T = std::string>
+std::vector<struct iovec> FuseGenerateIovecs(std::string &first) {
+  // Pad one byte for null-terminate c-string.
+  return {(struct iovec){.iov_base = const_cast<char *>(first.c_str()),
+                         .iov_len = first.size() + 1}};
+}
+
+// If an argument is of type std::vector<char>, it must be used in write-only
+// scenario and the size of the variable must be greater than or equal to the
+// size of the expected data. Usually used with variable-length payload data.
+template <typename T = std::vector<char>>
+std::vector<struct iovec> FuseGenerateIovecs(std::vector<char> &first) {
+  return {(struct iovec){.iov_base = first.data(), .iov_len = first.size()}};
+}
+
+// A helper function to set up an array of iovec struct for testing purpose.
+// Use variadic class template to generalize different numbers and different
+// types of FUSE structs.
+template <typename T, typename... Types>
+std::vector<struct iovec> FuseGenerateIovecs(T &first, Types &...args) {
+  auto first_iovec = FuseGenerateIovecs(first);
+  auto iovecs = FuseGenerateIovecs(args...);
+  first_iovec.insert(std::end(first_iovec), std::begin(iovecs),
+                     std::end(iovecs));
+  return first_iovec;
+}
+
+}  // namespace testing
+}  // namespace gvisor
+#endif  // GVISOR_TEST_UTIL_FUSE_UTIL_H_