otautil/rangeset.cpp

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * 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.
 */

#include "otautil/rangeset.h"

#include <limits.h>
#include <stddef.h>

#include <algorithm>
#include <string>
#include <utility>
#include <vector>

#include <android-base/logging.h>
#include <android-base/parseint.h>
#include <android-base/stringprintf.h>
#include <android-base/strings.h>

RangeSet::RangeSet(std::vector<Range>&& pairs) {
  blocks_ = 0;
  if (pairs.empty()) {
    LOG(ERROR) << "Invalid number of tokens";
    return;
  }

  for (const auto& range : pairs) {
    if (!PushBack(range)) {
      Clear();
      return;
    }
  }
}

RangeSet RangeSet::Parse(const std::string& range_text) {
  std::vector<std::string> pieces = android::base::Split(range_text, ",");
  if (pieces.size() < 3) {
    LOG(ERROR) << "Invalid range text: " << range_text;
    return {};
  }

  size_t num;
  if (!android::base::ParseUint(pieces[0], &num, static_cast<size_t>(INT_MAX))) {
    LOG(ERROR) << "Failed to parse the number of tokens: " << range_text;
    return {};
  }
  if (num == 0) {
    LOG(ERROR) << "Invalid number of tokens: " << range_text;
    return {};
  }
  if (num % 2 != 0) {
    LOG(ERROR) << "Number of tokens must be even: " << range_text;
    return {};
  }
  if (num != pieces.size() - 1) {
    LOG(ERROR) << "Mismatching number of tokens: " << range_text;
    return {};
  }

  std::vector<Range> pairs;
  for (size_t i = 0; i < num; i += 2) {
    size_t first;
    size_t second;
    if (!android::base::ParseUint(pieces[i + 1], &first, static_cast<size_t>(INT_MAX)) ||
        !android::base::ParseUint(pieces[i + 2], &second, static_cast<size_t>(INT_MAX))) {
      return {};
    }
    pairs.emplace_back(first, second);
  }
  return RangeSet(std::move(pairs));
}

bool RangeSet::PushBack(Range range) {
  if (range.first >= range.second) {
    LOG(ERROR) << "Empty or negative range: " << range.first << ", " << range.second;
    return false;
  }
  size_t sz = range.second - range.first;
  if (blocks_ >= SIZE_MAX - sz) {
    LOG(ERROR) << "RangeSet size overflow";
    return false;
  }

  ranges_.push_back(std::move(range));
  blocks_ += sz;
  return true;
}

void RangeSet::Clear() {
  ranges_.clear();
  blocks_ = 0;
}

std::vector<RangeSet> RangeSet::Split(size_t groups) const {
  if (ranges_.empty() || groups == 0) return {};

  if (blocks_ < groups) {
    groups = blocks_;
  }

  // Evenly distribute blocks, with the first few groups possibly containing one more.
  size_t mean = blocks_ / groups;
  std::vector<size_t> blocks_per_group(groups, mean);
  std::fill_n(blocks_per_group.begin(), blocks_ % groups, mean + 1);

  std::vector<RangeSet> result;

  // Forward iterate Ranges and fill up each group with the desired number of blocks.
  auto it = ranges_.cbegin();
  Range range = *it;
  for (const auto& blocks : blocks_per_group) {
    RangeSet buffer;
    size_t needed = blocks;
    while (needed > 0) {
      size_t range_blocks = range.second - range.first;
      if (range_blocks > needed) {
        // Split the current range and don't advance the iterator.
        buffer.PushBack({ range.first, range.first + needed });
        range.first = range.first + needed;
        break;
      }
      buffer.PushBack(range);
      it++;
      if (it != ranges_.cend()) {
        range = *it;
      }
      needed -= range_blocks;
    }
    result.push_back(std::move(buffer));
  }
  return result;
}

std::string RangeSet::ToString() const {
  if (ranges_.empty()) {
    return "";
  }
  std::string result = std::to_string(ranges_.size() * 2);
  for (const auto& r : ranges_) {
    result += android::base::StringPrintf(",%zu,%zu", r.first, r.second);
  }

  return result;
}

// Get the block number for the i-th (starting from 0) block in the RangeSet.
size_t RangeSet::GetBlockNumber(size_t idx) const {
  CHECK_LT(idx, blocks_) << "Out of bound index " << idx << " (total blocks: " << blocks_ << ")";

  for (const auto& range : ranges_) {
    if (idx < range.second - range.first) {
      return range.first + idx;
    }
    idx -= (range.second - range.first);
  }

  CHECK(false) << "Failed to find block number for index " << idx;
  return 0;  // Unreachable, but to make compiler happy.
}

// RangeSet has half-closed half-open bounds. For example, "3,5" contains blocks 3 and 4. So "3,5"
// and "5,7" are not overlapped.
bool RangeSet::Overlaps(const RangeSet& other) const {
  for (const auto& range : ranges_) {
    size_t start = range.first;
    size_t end = range.second;
    for (const auto& other_range : other.ranges_) {
      size_t other_start = other_range.first;
      size_t other_end = other_range.second;
      // [start, end) vs [other_start, other_end)
      if (!(other_start >= end || start >= other_end)) {
        return true;
      }
    }
  }
  return false;
}

// Ranges in the the set should be mutually exclusive; and they're sorted by the start block.
SortedRangeSet::SortedRangeSet(std::vector<Range>&& pairs) : RangeSet(std::move(pairs)) {
  std::sort(ranges_.begin(), ranges_.end());
}

void SortedRangeSet::Insert(const Range& to_insert) {
  SortedRangeSet rs({ to_insert });
  Insert(rs);
}

// Insert the input SortedRangeSet; keep the ranges sorted and merge the overlap ranges.
void SortedRangeSet::Insert(const SortedRangeSet& rs) {
  if (rs.size() == 0) {
    return;
  }
  // Merge and sort the two RangeSets.
  std::vector<Range> temp = std::move(ranges_);
  std::copy(rs.begin(), rs.end(), std::back_inserter(temp));
  std::sort(temp.begin(), temp.end());

  Clear();
  // Trim overlaps and insert the result back to ranges_.
  Range to_insert = temp.front();
  for (auto it = temp.cbegin() + 1; it != temp.cend(); it++) {
    if (it->first <= to_insert.second) {
      to_insert.second = std::max(to_insert.second, it->second);
    } else {
      ranges_.push_back(to_insert);
      blocks_ += (to_insert.second - to_insert.first);
      to_insert = *it;
    }
  }
  ranges_.push_back(to_insert);
  blocks_ += (to_insert.second - to_insert.first);
}

// Compute the block range the file occupies, and insert that range.
void SortedRangeSet::Insert(size_t start, size_t len) {
  Range to_insert{ start / kBlockSize, (start + len - 1) / kBlockSize + 1 };
  Insert(to_insert);
}

bool SortedRangeSet::Overlaps(size_t start, size_t len) const {
  RangeSet rs({ { start / kBlockSize, (start + len - 1) / kBlockSize + 1 } });
  return Overlaps(rs);
}

// Given an offset of the file, checks if the corresponding block (by considering the file as
// 0-based continuous block ranges) is covered by the SortedRangeSet. If so, returns the offset
// within this SortedRangeSet.
//
// For example, the 4106-th byte of a file is from block 1, assuming a block size of 4096-byte.
// The mapped offset within a SortedRangeSet("1-9 15-19") is 10.
//
// An offset of 65546 falls into the 16-th block in a file. Block 16 is contained as the 10-th
// item in SortedRangeSet("1-9 15-19"). So its data can be found at offset 40970 (i.e. 4096 * 10
// + 10) in a range represented by this SortedRangeSet.
size_t SortedRangeSet::GetOffsetInRangeSet(size_t old_offset) const {
  size_t old_block_start = old_offset / kBlockSize;
  size_t new_block_start = 0;
  for (const auto& range : ranges_) {
    // Find the index of old_block_start.
    if (old_block_start >= range.second) {
      new_block_start += (range.second - range.first);
    } else if (old_block_start >= range.first) {
      new_block_start += (old_block_start - range.first);
      return (new_block_start * kBlockSize + old_offset % kBlockSize);
    } else {
      CHECK(false) << "block_start " << old_block_start
                   << " is missing between two ranges: " << this->ToString();
      return 0;
    }
  }
  CHECK(false) << "block_start " << old_block_start
               << " exceeds the limit of current RangeSet: " << this->ToString();
  return 0;
}