cmds/incidentd/src/FdBuffer.h

/*
 * Copyright (C) 2016 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.
 */

#ifndef FD_BUFFER_H
#define FD_BUFFER_H

#include <utils/Errors.h>

#include <vector>

using namespace android;
using namespace std;

/**
 * Reads a file into a buffer, and then writes that data to an FdSet.
 */
class FdBuffer
{
public:
    FdBuffer();
    ~FdBuffer();

    /**
     * Read the data until the timeout is hit or we hit eof.
     * Returns NO_ERROR if there were no errors or if we timed out.
     * Will mark the file O_NONBLOCK.
     */
    status_t read(int fd, int64_t timeoutMs);

    /**
     * Read processed results by streaming data to a parsing process, e.g. incident helper.
     * The parsing process provides IO fds which are 'toFd' and 'fromFd'. The function
     * reads original data in 'fd' and writes to parsing process through 'toFd', then it reads
     * and stores the processed data from 'fromFd' in memory for later usage.
     * This function behaves in a streaming fashion in order to save memory usage.
     * Returns NO_ERROR if there were no errors or if we timed out.
     */
    status_t readProcessedDataInStream(int fd, int toFd, int fromFd, int64_t timeoutMs);

    /**
     * Whether we timed out.
     */
    bool timedOut() const { return mTimedOut; }

    /**
     * If more than 4 MB is read, we truncate the data and return success.
     * Downstream tools must handle truncated incident reports as best as possible
     * anyway because they could be cut off for a lot of reasons and it's best
     * to get as much useful information out of the system as possible. If this
     * happens, truncated() will return true so it can be marked. If the data is
     * exactly 4 MB, truncated is still set. Sorry.
     */
    bool truncated() const { return mTruncated; }

    /**
     * How much data was read.
     */
    size_t size() const;

    /**
     * Flush all the data to given file descriptor;
     */
    status_t flush(int fd) const;

    /**
     * How long the read took in milliseconds.
     */
    int64_t durationMs() const { return mFinishTime - mStartTime; }

    /**
     * Read data stored in FdBuffer
     */
    class iterator;
    friend class iterator;
    class iterator : public std::iterator<std::random_access_iterator_tag, uint8_t> {
    public:
        iterator(const FdBuffer& buffer, ssize_t index, ssize_t offset)
                : mFdBuffer(buffer), mIndex(index), mOffset(offset) {}
        iterator& operator=(iterator& other) const { return other; }
        iterator& operator+(size_t offset); // this is implemented in .cpp
        iterator& operator+=(size_t offset) { return *this + offset; }
        iterator& operator++() { return *this + 1; }
        iterator operator++(int) { return *this + 1; }
        bool operator==(iterator other) const {
            return mIndex == other.mIndex && mOffset == other.mOffset;
        }
        bool operator!=(iterator other) const { return !(*this == other); }
        int operator-(iterator other) const { return (int)bytesRead() - (int)other.bytesRead(); }
        reference operator*() const { return mFdBuffer.mBuffers[mIndex][mOffset]; }

        // return the snapshot of the current iterator
        iterator snapshot() const { return iterator(mFdBuffer, mIndex, mOffset); }
        // how many bytes are read
        size_t bytesRead() const;
        // random access could make the iterator out of bound
        bool outOfBound() const { return bytesRead() > mFdBuffer.size(); }
    private:
        const FdBuffer& mFdBuffer;
        size_t mIndex;
        size_t mOffset;
    };
    iterator begin() const { return iterator(*this, 0, 0); }
    iterator end() const;

private:
    vector<uint8_t*> mBuffers;
    int64_t mStartTime;
    int64_t mFinishTime;
    ssize_t mCurrentWritten;
    bool mTimedOut;
    bool mTruncated;
};

#endif // FD_BUFFER_H