zlib/examples/gzlog.h

   1 /* gzlog.h
   2   Copyright (C) 2004, 2008 Mark Adler, all rights reserved
   3   version 2.0, 25 Apr 2008
   4
   5   This software is provided 'as-is', without any express or implied
   6   warranty.  In no event will the author be held liable for any damages
   7   arising from the use of this software.
   8
   9   Permission is granted to anyone to use this software for any purpose,
  10   including commercial applications, and to alter it and redistribute it
  11   freely, subject to the following restrictions:
  12
  13   1. The origin of this software must not be misrepresented; you must not
  14      claim that you wrote the original software. If you use this software
  15      in a product, an acknowledgment in the product documentation would be
  16      appreciated but is not required.
  17   2. Altered source versions must be plainly marked as such, and must not be
  18      misrepresented as being the original software.
  19   3. This notice may not be removed or altered from any source distribution.
  20
  21   Mark Adler    madler@alumni.caltech.edu
  22  */
  23
  24 /* Version History:
  25    1.0  26 Nov 2004  First version
  26    2.0  25 Apr 2008  Complete redesign for recovery of interrupted operations
  27                      Interface changed slightly in that now path is a prefix
  28                      Compression now occurs as needed during gzlog_write()
  29                      gzlog_write() now always leaves the log file as valid gzip
  30  */
  31
  32 /*
  33    The gzlog object allows writing short messages to a gzipped log file,
  34    opening the log file locked for small bursts, and then closing it.  The log
  35    object works by appending stored (uncompressed) data to the gzip file until
  36    1 MB has been accumulated.  At that time, the stored data is compressed, and
  37    replaces the uncompressed data in the file.  The log file is truncated to
  38    its new size at that time.  After each write operation, the log file is a
  39    valid gzip file that can decompressed to recover what was written.
  40
  41    The gzlog operations can be interupted at any point due to an application or
  42    system crash, and the log file will be recovered the next time the log is
  43    opened with gzlog_open().
  44  */
  45
  46 #ifndef GZLOG_H
  47 #define GZLOG_H
  48
  49 /* gzlog object type */
  50 typedef void gzlog;
  51
  52 /* Open a gzlog object, creating the log file if it does not exist.  Return
  53    NULL on error.  Note that gzlog_open() could take a while to complete if it
  54    has to wait to verify that a lock is stale (possibly for five minutes), or
  55    if there is significant contention with other instantiations of this object
  56    when locking the resource.  path is the prefix of the file names created by
  57    this object.  If path is "foo", then the log file will be "foo.gz", and
  58    other auxiliary files will be created and destroyed during the process:
  59    "foo.dict" for a compression dictionary, "foo.temp" for a temporary (next)
  60    dictionary, "foo.add" for data being added or compressed, "foo.lock" for the
  61    lock file, and "foo.repairs" to log recovery operations performed due to
  62    interrupted gzlog operations.  A gzlog_open() followed by a gzlog_close()
  63    will recover a previously interrupted operation, if any. */
  64 gzlog *gzlog_open(char *path);
  65
  66 /* Write to a gzlog object.  Return zero on success, -1 if there is a file i/o
  67    error on any of the gzlog files (this should not happen if gzlog_open()
  68    succeeded, unless the device has run out of space or leftover auxiliary
  69    files have permissions or ownership that prevent their use), -2 if there is
  70    a memory allocation failure, or -3 if the log argument is invalid (e.g. if
  71    it was not created by gzlog_open()).  This function will write data to the
  72    file uncompressed, until 1 MB has been accumulated, at which time that data
  73    will be compressed.  The log file will be a valid gzip file upon successful
  74    return. */
  75 int gzlog_write(gzlog *log, void *data, size_t len);
  76
  77 /* Force compression of any uncompressed data in the log.  This should be used
  78    sparingly, if at all.  The main application would be when a log file will
  79    not be appended to again.  If this is used to compress frequently while
  80    appending, it will both significantly increase the execution time and
  81    reduce the compression ratio.  The return codes are the same as for
  82    gzlog_write(). */
  83 int gzlog_compress(gzlog *log);
  84
  85 /* Close a gzlog object.  Return zero on success, -3 if the log argument is
  86    invalid.  The log object is freed, and so cannot be referenced again. */
  87 int gzlog_close(gzlog *log);
  88
  89 #endif