base/containers/buffer_iterator_unittest.cc

// Copyright 2019 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/containers/buffer_iterator.h"

#include <string.h>

#include <limits>
#include <optional>
#include <vector>

#include "base/compiler_specific.h"
#include "base/containers/span.h"
#include "testing/gtest/include/gtest/gtest.h"

namespace base {
namespace {

struct TestStruct {
  uint32_t one;
  uint8_t two, three, four, five;
};

bool operator==(const TestStruct& lhs, const TestStruct& rhs) {
  return lhs.one == rhs.one && lhs.two == rhs.two;
}

TestStruct CreateTestStruct() {
  return {0xabcdef12, 0x34, 0x56, 0x78, 0x90};
}

TEST(BufferIteratorTest, Object) {
  TestStruct expected = CreateTestStruct();

  char buffer[sizeof(TestStruct)];
  UNSAFE_TODO(memcpy(buffer, &expected, sizeof(buffer)));

  {
    // Read the object.
    BufferIterator<char> iterator(buffer);
    const TestStruct* actual = iterator.Object<TestStruct>();
    EXPECT_EQ(expected, *actual);
  }
  {
    // Iterator's view of the data is not large enough to read the object.
    BufferIterator<char> iterator(
        span<char>(buffer).first<sizeof(buffer) - 1u>());
    const TestStruct* actual = iterator.Object<TestStruct>();
    EXPECT_FALSE(actual);
  }
}

TEST(BufferIteratorTest, MutableObject) {
  TestStruct expected = CreateTestStruct();

  char buffer[sizeof(TestStruct)];

  BufferIterator<char> iterator(buffer);

  {
    // Write the object.
    *iterator.MutableObject<TestStruct>() = expected;
  }

  // Rewind the iterator.
  iterator.Seek(0);

  {
    // Read the object back.
    const TestStruct* actual = iterator.Object<TestStruct>();
    EXPECT_EQ(expected, *actual);
  }
}

TEST(BufferIteratorTest, ObjectDoesNotFit) {
  char buffer[64];
  BufferIterator<char> iterator(buffer);

  auto* pointer = iterator.Object<uint64_t>();
  EXPECT_TRUE(pointer);

  iterator.Seek(iterator.total_size() - 1);

  auto* invalid_pointer = iterator.Object<uint64_t>();
  EXPECT_FALSE(invalid_pointer);
}

TEST(BufferIteratorTest, Span) {
  TestStruct expected = CreateTestStruct();

  std::vector<char> buffer(sizeof(TestStruct) * 3);

  {
    // Load the span with data.
    BufferIterator<char> iterator(buffer);
    span<TestStruct> span = iterator.MutableSpan<TestStruct>(3);
    for (auto& ts : span) {
      UNSAFE_TODO(memcpy(&ts, &expected, sizeof(expected)));
    }
  }
  {
    // Read the data back out.
    BufferIterator<char> iterator(buffer);

    const TestStruct* actual = iterator.Object<TestStruct>();
    EXPECT_EQ(expected, *actual);

    actual = iterator.Object<TestStruct>();
    EXPECT_EQ(expected, *actual);

    actual = iterator.Object<TestStruct>();
    EXPECT_EQ(expected, *actual);

    EXPECT_EQ(iterator.total_size(), iterator.position());
  }
  {
    // Cannot create spans larger than there are data for.
    BufferIterator<char> iterator(buffer);
    span<const TestStruct> span = iterator.Span<TestStruct>(4);
    EXPECT_TRUE(span.empty());
  }
}

TEST(BufferIteratorTest, FixedSpan) {
  TestStruct expected = CreateTestStruct();

  std::vector<char> buffer(sizeof(TestStruct) * 3);

  {
    // Load the span with data.
    BufferIterator<char> iterator(buffer);
    auto span = iterator.MutableSpan<TestStruct, 3u>();
    static_assert(std::same_as<std::optional<base::span<TestStruct, 3u>>,
                               decltype(span)>);
    for (auto& ts : *span) {
      UNSAFE_TODO(memcpy(&ts, &expected, sizeof(expected)));
    }
  }
  {
    // Read the data back out.
    BufferIterator<char> iterator(buffer);

    const TestStruct* actual = iterator.Object<TestStruct>();
    EXPECT_EQ(expected, *actual);

    actual = iterator.Object<TestStruct>();
    EXPECT_EQ(expected, *actual);

    actual = iterator.Object<TestStruct>();
    EXPECT_EQ(expected, *actual);

    EXPECT_EQ(iterator.total_size(), iterator.position());
  }
  {
    // Cannot create spans larger than there are data for.
    BufferIterator<char> iterator(buffer);
    auto maybe_span = iterator.Span<TestStruct, 4u>();
    EXPECT_FALSE(maybe_span.has_value());
  }
}

TEST(BufferIteratorTest, SpanOverflow) {
  char buffer[64];

  BufferIterator<char> iterator(
      // SAFETY: This intentionally makes an incorrectly-sized span. The span
      // pointer, stored in the BufferIterator is never moved past the start in
      // this test, as that would cause Undefined Behaviour.
      UNSAFE_BUFFERS(span(buffer, std::numeric_limits<size_t>::max())));

  constexpr size_t kInvalidU64Size =
      (std::numeric_limits<size_t>::max() / sizeof(uint64_t)) + 1u;
  {
    span<const uint64_t> empty_span = iterator.Span<uint64_t>(kInvalidU64Size);
    EXPECT_TRUE(empty_span.empty());
  }
  {
    span<const uint64_t> empty_span =
        iterator.Span<uint64_t>(std::numeric_limits<size_t>::max());
    EXPECT_TRUE(empty_span.empty());
  }
}

TEST(BufferIteratorTest, Position) {
  char buffer[64];
  BufferIterator<char> iterator(buffer);
  EXPECT_EQ(sizeof(buffer), iterator.total_size());

  size_t position = iterator.position();
  EXPECT_EQ(0u, position);

  iterator.Object<uint8_t>();
  EXPECT_EQ(sizeof(uint8_t), iterator.position() - position);
  position = iterator.position();

  iterator.Object<uint32_t>();
  EXPECT_EQ(sizeof(uint32_t), iterator.position() - position);
  position = iterator.position();

  iterator.Seek(32);
  EXPECT_EQ(32u, iterator.position());

  EXPECT_EQ(sizeof(buffer), iterator.total_size());
}

TEST(BufferIteratorTest, CopyObject) {
  TestStruct expected = CreateTestStruct();

  constexpr int kNumCopies = 3;
  char buffer[sizeof(TestStruct) * kNumCopies];
  for (int i = 0; i < kNumCopies; i++) {
    as_writable_bytes(span(buffer))
        .subspan(i * sizeof(TestStruct))
        .copy_prefix_from(byte_span_from_ref(expected));
  }

  BufferIterator<char> iterator(buffer);
  std::optional<TestStruct> actual;
  for (int i = 0; i < kNumCopies; i++) {
    actual = iterator.CopyObject<TestStruct>();
    ASSERT_TRUE(actual.has_value());
    EXPECT_EQ(expected, *actual);
  }
  actual = iterator.CopyObject<TestStruct>();
  EXPECT_FALSE(actual.has_value());
}

TEST(BufferIteratorTest, SeekWithSizeConfines) {
  const char buffer[] = "vindicate";
  BufferIterator<const char> iterator(base::span_from_cstring(buffer));
  iterator.Seek(5);
  iterator.TruncateTo(3);
  EXPECT_TRUE(iterator.Span<char>(4).empty());

  std::string result;
  while (const char* c = iterator.Object<char>()) {
    result += *c;
  }
  EXPECT_EQ(result, "cat");
}

}  // namespace
}  // namespace base