src/StoreSwapLogData.h

   1 /*
   2  * Copyright (C) 1996-2021 The Squid Software Foundation and contributors
   3  *
   4  * Squid software is distributed under GPLv2+ license and includes
   5  * contributions from numerous individuals and organizations.
   6  * Please see the COPYING and CONTRIBUTORS files for details.
   7  */
   8
   9 #ifndef SQUID_STORESWAPLOGDATA_H
  10 #define SQUID_STORESWAPLOGDATA_H
  11
  12 /**
  13  \defgroup FileFormatSwapStateAPI swap.state File Structure
  14  \ingroup FileSystems
  15  \section ImplementationNotes Implementation Notes
  16  \par
  17  *      When writing an object to disk, we must first write the meta data.
  18  *      This is done with a couple of functions.  First, storeSwapMetaPack()
  19  *      takes a StoreEntry as a parameter and returns a tlv linked
  20  *      list.  Second, storeSwapMetaPack() converts the tlv list
  21  *      into a character buffer that we can write.
  22  *
  23  \note  MemObject has a MemObject::swap_hdr_sz.
  24  *      This value is the size of that character buffer; the size of the
  25  *      swap file meta data.  The StoreEntry has a member
  26  *      StoreEntry::swap_file_sz that represents the size of the disk file.
  27  *      Thus, the size of the object "content" is
  28  \code    StoreEntry->swap_file_sz  - MemObject->swap_hdr_sz;    \endcode
  29  \note The swap file content includes the HTTP reply headers and the HTTP reply body (if any).
  30  *
  31  \par
  32  *      When reading a swap file, there is a similar process to extract
  33  *      the swap meta data.  First, storeSwapMetaUnpack() converts a
  34  *      character buffer into a tlv linked list.  It also tells us
  35  *      the value for MemObject->swap_hdr_sz.
  36  */
  37
  38 #include "md5.h"
  39 #include "mem/forward.h"
  40 #include "store/forward.h"
  41
  42 /// maintains a 24-bit checksum over integer fields
  43 class SwapChecksum24
  44 {
  45 public:
  46     SwapChecksum24() { raw[0] = raw[1] = raw[2] = 0; }
  47
  48     bool operator ==(const SwapChecksum24 &o) const {
  49         return raw[0] == o.raw[0] && raw[1] == o.raw[1] && raw[2] == o.raw[2];
  50     }
  51
  52     bool operator !=(const SwapChecksum24 &o) const {
  53         return !(*this == o);
  54     }
  55
  56     /// compute and store checksum based on three 32bit integers
  57     void set(uint32_t f1, uint32_t f2, uint32_t f3);
  58
  59     /// compute and store checksum based on int32_t and uint64_t integers
  60     void set(int32_t f1, uint64_t f2);
  61
  62     // printing for debugging
  63     std::ostream &print(std::ostream &os) const;
  64
  65 private:
  66     uint8_t raw[3]; // designed to follow "op" members, in padding space
  67 };
  68
  69 inline std::ostream &
  70 operator <<(std::ostream &os, const SwapChecksum24 &sum)
  71 {
  72     return sum.print(os);
  73 }
  74
  75 /**
  76  \ingroup FielFormatSwapStateAPI
  77  *
  78  \par
  79  * Defines the structure of a binary swap.state file entry for UFS stores.
  80  * TODO: Move to fs/ufs
  81  *
  82  \note StoreSwapLogData entries are written in native machine byte order
  83  *     They are not necessarily portable across architectures.
  84  */
  85 class StoreSwapLogData
  86 {
  87     MEMPROXY_CLASS(StoreSwapLogData);
  88
  89 public:
  90     /// type to use for storing time-related members; must be signed
  91     typedef int64_t SwappedTime;
  92
  93     /// consistency self-check: whether the data appears to make sense
  94     bool sane() const;
  95
  96     /// call this before storing the log entry
  97     void finalize();
  98
  99     /**
 100      * Either SWAP_LOG_ADD when an object is added to the disk storage,
 101      * or SWAP_LOG_DEL when an object is deleted.
 102      */
 103     uint8_t op = 0;
 104
 105     /**
 106      * Fingerprint to weed out bogus/corrupted swap.state entries.
 107      */
 108     SwapChecksum24 checksum; // follows "op" because compiler will pad anyway
 109
 110     /**
 111      * The 32-bit file number which maps to a pathname.
 112      * Only the low 24-bits are relevant. The high 8-bits are
 113      * used as an index to an array of storage directories, and
 114      * are set at run time because the order of storage directories
 115      * may change over time.
 116      */
 117     sfileno swap_filen = 0;
 118
 119     /**
 120      * A Unix time value that represents the time when
 121      * the origin server generated this response. If the response
 122      * has a valid Date: header, this timestamp corresponds
 123      * to that time. Otherwise, it is set to the Squid process time
 124      * when the response is read (as soon as the end of headers are found).
 125      */
 126     SwappedTime timestamp = 0;
 127
 128     /**
 129      * The last time that a client requested this object.
 130      */
 131     SwappedTime lastref = 0;
 132
 133     /**
 134      * The value of the response's Expires: header, if any.
 135      * If the response does not have an Expires: header, this
 136      * is set to -1.
 137      * If the response has an invalid (unparsable)
 138      * Expires: header, it is also set to -1.  There are some cases
 139      * where Squid sets expires to -2. This happens for the
 140      * internal "netdb" object and for FTP URL responses.
 141      */
 142     SwappedTime expires = 0;
 143
 144     /**
 145      * The value of the response's Last-modified: header, if any.
 146      * This is set to -1 if there is no Last-modified: header,
 147      * or if it is unparsable.
 148      */
 149     SwappedTime lastmod = 0;
 150
 151     /**
 152      * This is the number of bytes that the object occupies on
 153      * disk. It includes the Squid "swap file header".
 154      */
 155     uint64_t swap_file_sz = 0;
 156
 157     /**
 158      * The number of times that this object has been accessed (referenced).
 159      * Since its a 16-bit quantity, it is susceptible to overflow
 160      * if a single object is accessed 65,536 times before being replaced.
 161      */
 162     uint16_t refcount;
 163
 164     /**
 165      * A copy of the StoreEntry flags field. Used as a sanity
 166      * check when rebuilding the cache at startup. Objects that
 167      * have the KEY_PRIVATE flag set are not added back to the cache.
 168      */
 169     uint16_t flags = 0;
 170
 171     /**
 172      * The 128-bit MD5 hash for this object.
 173      */
 174     unsigned char key[SQUID_MD5_DIGEST_LENGTH] = {};
 175 };
 176
 177 /// \ingroup FileFormatSwapStateAPI
 178 /// Swap log starts with this binary structure.
 179 class StoreSwapLogHeader
 180 {
 181 public:
 182     // sets default values for this Squid version; loaded values may differ
 183     StoreSwapLogHeader();
 184
 185     /// consistency self-check: whether the data appears to make sense
 186     bool sane() const;
 187
 188     /// number of bytes after the log header before the first log entry
 189     size_t gapSize() const;
 190
 191     uint8_t op;
 192     SwapChecksum24 checksum; // follows "op" because compiler will pad anyway
 193     int32_t version;
 194     int32_t record_size;
 195 };
 196
 197 #endif /* SQUID_STORESWAPLOGDATA_H */
 198