lnav/src/line_buffer.hh

/**
 * Copyright (c) 2007-2012, Timothy Stack
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer.
 * * Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 * * Neither the name of Timothy Stack nor the names of its contributors
 * may be used to endorse or promote products derived from this software
 * without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ''AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * @file line_buffer.hh
 */

#ifndef __line_buffer_hh
#define __line_buffer_hh

#include <errno.h>
#include <sys/types.h>
#include <unistd.h>
#include <zlib.h>

#include <exception>

#include "lnav_log.hh"
#include "auto_fd.hh"
#include "auto_mem.hh"
#include "shared_buffer.hh"

struct line_value {
    char *lv_start;
    size_t lv_len;
    bool lv_partial;

    void terminate() {
        this->lv_start[this->lv_len] = '\0';
    };
};

/**
 * Buffer for reading whole lines out of file descriptors.  The class presents
 * a stateless interface, callers specify the offset where a line starts and
 * the class takes care of caching the surrounding range and locating the
 * delimiter.
 *
 * XXX A bit of a wheel reinvention, but I'm not sure how well the libraries
 * handle non-blocking I/O...
 */
class line_buffer {
public:
    class error
        : public std::exception {
public:
        error(int err)
            : e_err(err) { };

        int e_err;
    };

    /** Construct an empty line_buffer. */
    line_buffer();

    virtual ~line_buffer();

    /** @param fd The file descriptor that data should be pulled from. */
    void set_fd(auto_fd &fd) throw (error);

    /** @return The file descriptor that data should be pulled from. */
    int get_fd() const { return this->lb_fd; };

    time_t get_file_time() const { return this->lb_file_time; };

    /**
     * @return The size of the file or the amount of data pulled from a pipe.
     */
    ssize_t get_file_size() const { return this->lb_file_size; };

    bool is_compressed() const {
        return this->lb_gz_file != NULL || this->lb_bz_file;
    };

    off_t get_read_offset(off_t off) const
    {
        if (this->lb_gz_file) {
            return this->lb_gz_offset;
        }
        else{
            return off;
        }
    };

    /**
     * Read up to the end of file or a given delimiter.
     *
     * @param offset_inout The offset in the file to start reading from.  On
     * return, it contains the offset where the next line should start or one
     * past the size of the file.
     * @param len_out On return, contains the length of the line, not including
     * the delimiter.
     * @param delim The character that splits lines in the input, defaults to a
     * line feed.
     * @return The address in the internal buffer where the line starts.  The
     * line is not NULL-terminated, but this method ensures there is room to NULL
     * terminate the line.  If any modifications are made to the line, such as
     * NULL termination, the invalidate() must be called before re-reading the
     * line to refresh the buffer.
     */
    bool read_line(off_t &offset_inout, line_value &lv,
        bool include_delim = false)
        throw (error);

    bool read_line(off_t &offset_inout, shared_buffer_ref &sbr, line_value *lv = NULL)
        throw (error);

    bool read_range(off_t offset, size_t len, shared_buffer_ref &sbr)
        throw (error);

    /**
     * Signal that the contents of the internal buffer have been modified and
     * any attempts to re-read the currently cached line(s) should trigger
     * another read from the file.
     */
    void invalidate()
    {
        this->lb_file_offset += this->lb_buffer_size;
        this->lb_buffer_size  = 0;
        this->lb_file_size    = -1;
        log_info("invalidate %p", this);
    };

    /** Release any resources held by this object. */
    void reset()
    {
        this->lb_fd.reset();

        this->lb_file_offset      = 0;
        this->lb_file_size        = (size_t)-1;
        this->lb_buffer_size      = 0;
        this->lb_last_line_offset = -1;
    };

    /** Check the invariants for this object. */
    bool invariant(void)
    {
        require(this->lb_buffer != NULL);
        require(this->lb_buffer_size <= this->lb_buffer_max);

        return true;
    };

private:

    /**
     * @param off The file offset to check for in the buffer.
     * @return True if the given offset is cached in the buffer.
     */
    bool in_range(off_t off) const
    {
        return this->lb_file_offset <= off &&
               off < (int)(this->lb_file_offset + this->lb_buffer_size);
    };

    void resize_buffer(size_t new_max) throw (error);

    /**
     * Ensure there is enough room in the buffer to cache a range of data from
     * the file.  First, this method will check to see if there is enough room
     * from where 'start' begins in the buffer to the maximum buffer size.  If
     * this is not enough, the currently cached data at 'start' will be moved
     * to the beginning of the buffer, overwriting any cached data earlier in
     * the file.  Finally, if this is still not enough, the buffer will be
     * reallocated to make more room.
     *
     * @param start The file offset of the start of the line.
     * @param max_length The amount of data to be cached in the buffer.
     */
    void ensure_available(off_t start, size_t max_length) throw (error);

    /**
     * Fill the buffer with the given range of data from the file.
     *
     * @param start The file offset where data should start to be read from the
     * file.
     * @param max_length The maximum amount of data to read from the file.
     * @return True if any data was read from the file.
     */
    bool fill_range(off_t start, size_t max_length) throw (error);

    /**
     * After a successful fill, the cached data can be retrieved with this
     * method.
     *
     * @param start The file offset to retrieve cached data for.
     * @param avail_out On return, the amount of data currently cached at the
     * given offset.
     * @return A pointer to the start of the cached data in the internal
     * buffer.
     */
    char *get_range(off_t start, size_t &avail_out)
    {
        off_t buffer_offset = start - this->lb_file_offset;
        char *retval;

        require(buffer_offset >= 0);

        retval    = &this->lb_buffer[buffer_offset];
        avail_out = this->lb_buffer_size - buffer_offset;

        return retval;
    };

    shared_buffer lb_share_manager;

    auto_fd lb_fd;              /*< The file to read data from. */
    gzFile  lb_gz_file;         /*< File handle for gzipped files. */
    bool    lb_bz_file;         /*< Flag set for bzip2 compressed files. */
    off_t   lb_gz_offset;       /*< The offset into the compressed file. */

    auto_mem<char> lb_buffer;   /*< The internal buffer where data is cached */

    ssize_t lb_file_size;       /*<
                                 * The size of the file.  When lb_fd refers to
                                 * a pipe, this is set to the amount of data
                                 * read from the pipe when EOF is reached.
                                 */
    off_t lb_file_offset;       /*<
                                 * Data cached in the buffer comes from this
                                 * offset in the file.
                                 */
    time_t lb_file_time;
    ssize_t lb_buffer_size;     /*< The amount of cached data in the buffer. */
    ssize_t lb_buffer_max;      /*< The size of the buffer memory. */
    bool   lb_seekable;         /*< Flag set for seekable file descriptors. */
    off_t  lb_last_line_offset; /*< */
};
#endif