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