streambase.h

lucene in java大家一定听说过了

/*------------------------------------------------------------------------------
* Copyright (C) 2003-2006 Jos van den Oever
* 
* Distributable under the terms of either the Apache License (Version 2.0) or 
* the GNU Lesser General Public License, as specified in the COPYING file.
------------------------------------------------------------------------------*/
#ifndef STREAMBASE_H
#define STREAMBASE_H

#include <string>

#define INT32MAX 0x7FFFFFFFL

namespace jstreams {

enum StreamStatus { Ok, Eof, Error };

/**
 * @short Base class for stream read access to many different file types.
 * 
 * This class is based on the interface java.io.InputStream. It allows
 * for uniform access to streamed resources.
 * The main difference with the java equivalent is a performance improvement.
 * When reading data, data is not copied into a buffer provided by the caller,
 * but a pointer to the read data is provided. This makes this interface especially
 * useful for deriving from it and implementing filterers or transformers.
 */
// java mapping: long=int64, int=int32, byte=uint8_t
template <class T>
class StreamBase {
protected:
    int64_t size;
    int64_t position;
    std::string error;
    StreamStatus status;
public:
    StreamBase() :size(-1), position(0), status(Ok){ }
    virtual ~StreamBase(){}
    /**
     * Return a string representation of the last error that has occurred.
     * If no error has occurred, an empty string is returned.
     **/
    const char* getError() const { return error.c_str(); }
    StreamStatus getStatus() const { return status; }
    int64_t getPosition() const { return position; }
    int64_t getSize() const { return size; }
    /** 
     * @brief Reads @p ntoread characters from the stream and sets \a start to
     * the first character that was read.
     *
     * If @p ntoread is @c 0, then at least one character will be read.
     *
     * @param start Pointer passed by reference that will be set to point to
     *              the retrieved array of characters. If the end of the stream
     *              is encountered or an error occurs, the value of @p start
     *              is undefined.
     * @return the number of characters that were read. If 0 is returned, the
     *         end of the stream has been reached. If -1 is returned, an error
     *         has occured.
     **/
 //   virtual int32_t read(const T*& start) = 0;
    /** 
     * @brief Reads characters from the stream and sets \a start to
     * the first character that was read.
     *
     * If @p ntoread is @c 0, then at least one character will be read.
     *
     * @param start Pointer passed by reference that will be set to point to
     *              the retrieved array of characters. If the end of the stream
     *              is encountered or an error occurs, the value of @p start
     *              is undefined.
     * @param ntoread The number of characters to read from the stream. If
     *                @p is @c 0 the stream reads at least 1 character.
     * @return the number of characters that were read. If -1 is returned, the
     *         end of the stream has been reached. If -2 is returned, an error
     *         has occured.
     **/
    virtual int32_t read(const T*& start, int32_t min, int32_t max) = 0;
    /**
     * Same as read(const T*& start, int32_t ntoread), but may read more.
     **/
//    virtual int32_t readAtLeast(const T*& start, int32_t ntoread) = 0;
    /* the available value may be greater than the actual value if
      the encoding is a variable one (such as utf8 or unicode) */
    /**
     * Skip @param ntoskip bytes. Unless an error occurs or the end of file is
     * encountered, this amount of bytes is skipped.
     * The optional @param skipped can be use to find out how many bites were skipped.
     * If the end of stream is reached, Eof is returned.
     * If an error occured, Error is returned.
     **/
    virtual int64_t skip(int64_t ntoskip);
     /**
      * \short Marks the current position in this input stream.
      * A subsequent call to the reset method repositions this stream at the
      * last marked position so that subsequent reads re-read the same bytes.
      *
      * The readlimit arguments tells this input stream to allow that many
      * bytes to be read before the mark position gets invalidated.
      * The stream somehow remembers all the bytes read after the call to mark
      * and stands ready to supply those same bytes again if and whenever the
      * method reset is called. However, the stream is not required to remember
      * any data at all if more than readlimit bytes are read from the stream
      * before reset is called.
      *
      * When calling the method mark more than once at the same position in the
      * stream, the call with the largest value for \p readlimit is defining.
      **/
    virtual int64_t mark(int32_t readlimit) = 0;
      /**
       * \short Repositions this stream to given requested position.
       * The general contract of reset is:
       * - Reset is guaranteed to work after a successfull call to read(),
       *   when new position is in the range of the data returned by read().
       *   This means that @p pos must lie between than the position
       *   corresponding to the @p start parameter (x) of the @r read function
       *   and the position corresponding to the last position in the returned
       *   buffer (x + @p nread).
       * if If the method mark has not been called since the stream was created,
       *   or the number of bytes read from the stream since mark was last
       *   called is larger than the argument to mark at that last call, then
       *   Error is returned.
       * - Otherwise the stream is reset to a state such that all the bytes
       *   read since the most recent call to mark (or since the start of the
       *   file, if mark has not been called) will be resupplied to subsequent
       *   callers of the read method, followed by any bytes that otherwise
       *   would have been the next input data as of the time of the call to
       *   reset.
       **/
    virtual int64_t reset(int64_t pos) = 0;
};
#define SKIPSTEP 1024
template <class T>
int64_t
StreamBase<T>::skip(int64_t ntoskip) {
    const T *begin;
    int32_t nread;
    int64_t skipped = 0;
    while (ntoskip) {
        int32_t step = (int32_t)((ntoskip > SKIPSTEP) ?SKIPSTEP :ntoskip);
        nread = read(begin, 1, step);
        if (nread < -1 ) {
            // an error occurred
            return nread;
        } else if (nread < 1) {
            ntoskip = 0;
        } else {
            skipped += nread;
            ntoskip -= nread;
        }
    }
    return skipped;
}

} // end namespace jstreams

#endif