** The actual header in the wal-index consists of two copies of this
** object.
*/
struct WalIndexHdr {
  u32 iChange;                    /* Counter incremented each transaction */
  u16 bigEndCksum;                /* True if checksums in WAL are big-endian */
  u16 szPage;                     /* Database page size in bytes */
    u32 mxFrame;                    /* Index of last valid frame in the WAL */
  u32 nPage;                      /* Size of database in pages */
  u32 aFrameCksum[2];             /* Checksum of last frame in log */
  u32 aSalt[2];                   /* Two salt values copied from WAL header */
  u32 aCksum[2];                  /* Checksum over all prior fields */
};

/*
................................................................................
** that this thread is running recovery.  If unable to establish
** the necessary locks, this routine returns SQLITE_BUSY.
*/
static int walIndexRecover(Wal *pWal){
  int rc;                         /* Return Code */
  i64 nSize;                      /* Size of log file */
  u32 aFrameCksum[2] = {0, 0};















  rc = walLockExclusive(pWal, WAL_ALL_BUT_WRITE, SQLITE_SHM_NLOCK-1);
  if( rc ){
    return rc;
  }
  WALTRACE(("WAL%p: recovery begin...\n", pWal));

  memset(&pWal->hdr, 0, sizeof(WalIndexHdr));

................................................................................
    ** checkpointers.
    */
    memset((void *)walCkptInfo(pWal), 0, sizeof(WalCkptInfo));
  }

recovery_error:
  WALTRACE(("WAL%p: recovery %s\n", pWal, rc ? "failed" : "ok"));
  walUnlockExclusive(pWal, WAL_ALL_BUT_WRITE, SQLITE_SHM_NLOCK-1);
  return rc;
}

/*
** Close an open wal-index.
*/
static void walIndexClose(Wal *pWal, int isDelete){

** The actual header in the wal-index consists of two copies of this
** object.
*/
struct WalIndexHdr {
  u32 iChange;                    /* Counter incremented each transaction */
  u16 bigEndCksum;                /* True if checksums in WAL are big-endian */
  u16 szPage;                     /* Database page size in bytes */
  u32 mxFrame;                    /* Index of last valid frame in the WAL */
  u32 nPage;                      /* Size of database in pages */
  u32 aFrameCksum[2];             /* Checksum of last frame in log */
  u32 aSalt[2];                   /* Two salt values copied from WAL header */
  u32 aCksum[2];                  /* Checksum over all prior fields */
};

/*
................................................................................
** that this thread is running recovery.  If unable to establish
** the necessary locks, this routine returns SQLITE_BUSY.
*/
static int walIndexRecover(Wal *pWal){
  int rc;                         /* Return Code */
  i64 nSize;                      /* Size of log file */
  u32 aFrameCksum[2] = {0, 0};
  int iLock;                      /* Lock offset to lock for checkpoint */
  int nLock;                      /* Number of locks to hold */

  /* Obtain an exclusive lock on all byte in the locking range not already
  ** locked by the caller. The caller is guaranteed to have locked the
  ** WAL_WRITE_LOCK byte, and may have also locked the WAL_CKPT_LOCK byte.
  ** If successful, the same bytes that are locked here are unlocked before
  ** this function returns.
  */
  assert( pWal->ckptLock==1 || pWal->ckptLock==0 );
  assert( WAL_ALL_BUT_WRITE==WAL_WRITE_LOCK+1 );
  assert( WAL_CKPT_LOCK==WAL_ALL_BUT_WRITE );
  assert( pWal->writeLock );
  iLock = WAL_ALL_BUT_WRITE + pWal->ckptLock;
  nLock = SQLITE_SHM_NLOCK - iLock;
  rc = walLockExclusive(pWal, iLock, nLock);
  if( rc ){
    return rc;
  }
  WALTRACE(("WAL%p: recovery begin...\n", pWal));

  memset(&pWal->hdr, 0, sizeof(WalIndexHdr));

................................................................................
    ** checkpointers.
    */
    memset((void *)walCkptInfo(pWal), 0, sizeof(WalCkptInfo));
  }

recovery_error:
  WALTRACE(("WAL%p: recovery %s\n", pWal, rc ? "failed" : "ok"));
  walUnlockExclusive(pWal, iLock, nLock);
  return rc;
}

/*
** Close an open wal-index.
*/
static void walIndexClose(Wal *pWal, int isDelete){

source $testdir/tester.tcl
source $testdir/lock_common.tcl
ifcapable !wal {finish_test ; return }

proc set_tvfs_hdr {file args} {

  # Set $nHdr to the number of bytes in the wal-index header:
  set nHdr 80
  set nInt [expr {$nHdr/4}]

  if {[llength $args]>1} {
    return -code error {wrong # args: should be "set_tvfs_hdr fileName ?val?"}
  }

  set blob [tvfs shm $file]

  if {[llength $args]} {
    set ia [lindex $args 0]
    set tail [string range $blob [expr $nHdr*2] end]

    set blob [binary format i${nInt}i${nInt}a* $ia $ia $tail]
    tvfs shm $file $blob
  }

  binary scan $blob i${nInt} ints
  return $ints
}
................................................................................
    SELECT count(a), sum(a) FROM t1;
  }
} {4 10}
do_test wal2-1.1 {
  execsql { SELECT count(a), sum(a) FROM t1 } db2
} {4 10}










foreach {tn iInsert res wal_index_hdr_mod wal_locks} {
         2    5   {5 15}    0             {READ RECOVER READ UNLOCK}
         3    6   {6 21}    1             {READ RECOVER READ UNLOCK}
         4    7   {7 28}    2             {READ RECOVER READ UNLOCK}
         5    8   {8 36}    3             {READ RECOVER READ UNLOCK}
         6    9   {9 45}    4             {READ RECOVER READ UNLOCK}
         7   10   {10 55}   5             {READ RECOVER READ UNLOCK}
         8   11   {11 66}   6             {READ RECOVER READ UNLOCK}
         9   12   {12 78}   7             {READ RECOVER READ UNLOCK}
        10   13   {13 91}   8             {READ RECOVER READ UNLOCK}
        11   14   {14 105}  9             {READ RECOVER READ UNLOCK}
        12   15   {15 120}  -1            {READ UNLOCK}
} {

  do_test wal2-1.$tn.1 {
    execsql { INSERT INTO t1 VALUES($iInsert) }

    set ::locks [list]
    set ::cb_done 0

................................................................................
    proc tvfs_cb {method args} {
      if {$::cb_done == 0 && $method == "xShmGet"} {
        set ::cb_done 1
        if {$::wal_index_hdr_mod >= 0} {
          incr_tvfs_hdr [lindex $args 0] $::wal_index_hdr_mod 1
        }
      }

      if {$method == "xShmLock"} { lappend ::locks [lindex $args 2] }
      return SQLITE_OK
    }

    execsql { SELECT count(a), sum(a) FROM t1 } db2
  } $res

................................................................................
# it simply drops back to a READ lock and proceeds. But because the
# header is out-of-date, the reader reads the out-of-date snapshot.
#
# After this, the header is corrupted again and the reader is allowed
# to run recovery. This time, it sees an up-to-date snapshot of the
# database file.
#





do_test wal2-2.0 {

  testvfs tvfs tvfs_cb
  proc tvfs_cb {method args} {
    if {$method == "xShmOpen"} { set ::shm_file [lindex $args 0] }
    return SQLITE_OK
  }
................................................................................
        if {$::wal_index_hdr_mod >= 0} {
          incr_tvfs_hdr $::shm_file $::wal_index_hdr_mod 1
        }
      }
      if {$method == "xShmLock"} {
        set lock [lindex $args 2]
        lappend ::locks $lock
        if {$lock == "RECOVER"} {
          set_tvfs_hdr $::shm_file $::oldhdr
        }
      }
      return SQLITE_OK
    }

    execsql { SELECT count(a), sum(a) FROM t1 } db2
  } $res0

  do_test wal2-2.$tn.3 {
    set ::locks
  } {READ RECOVER READ UNLOCK}

  do_test wal2-2.$tn.4 {
    set ::locks [list]
    set ::cb_done 0
    proc tvfs_cb {method args} {
      if {$::cb_done == 0 && $method == "xShmGet"} {
        set ::cb_done 1
................................................................................
  } $res1
}
db close
db2 close
tvfs delete
file delete -force test.db test.db-wal test.db-journal



#-------------------------------------------------------------------------
# This test case - wal2-3.* - tests the response of the library to an
# SQLITE_BUSY when attempting to obtain a READ or RECOVER lock.
#
#   wal2-3.0 - 2: SQLITE_BUSY when obtaining a READ lock
#   wal2-3.3 - 6: SQLITE_BUSY when obtaining a RECOVER lock
#
................................................................................
} {4 10}
do_test wal2-3.5 {
  list [info exists ::sabotage] [info exists ::locked]
} {0 0}
db close
tvfs delete
file delete -force test.db test.db-wal test.db-journal



#-------------------------------------------------------------------------
# Test that a database connection using a VFS that does not support the
# xShmXXX interfaces cannot open a WAL database.
#
do_test wal2-4.1 {
  sqlite3 db test.db
................................................................................
} {0 {{need xShmOpen to see this}}}
db close
tvfs delete

#-------------------------------------------------------------------------
# Test that if a database connection is forced to run recovery before it
# can perform a checkpoint, it does not transition into RECOVER state.




#
do_test wal2-5.1 {
  proc tvfs_cb {method args} {
    set ::shm_file [lindex $args 0]
    if {$method == "xShmLock"} { lappend ::locks [lindex $args 2] }
    return $::tvfs_cb_return
  }

source $testdir/tester.tcl
source $testdir/lock_common.tcl
ifcapable !wal {finish_test ; return }

proc set_tvfs_hdr {file args} {

  # Set $nHdr to the number of bytes in the wal-index header:
  set nHdr 40
  set nInt [expr {$nHdr/4}]

  if {[llength $args]>1} {
    return -code error {wrong # args: should be "set_tvfs_hdr fileName ?val?"}
  }

  set blob [tvfs shm $file]

  if {[llength $args]} {
    set ia [lindex $args 0]

    binary scan $blob a[expr $nHdr*2]a* dummy tail
    set blob [binary format i${nInt}i${nInt}a* $ia $ia $tail]
    tvfs shm $file $blob
  }

  binary scan $blob i${nInt} ints
  return $ints
}
................................................................................
    SELECT count(a), sum(a) FROM t1;
  }
} {4 10}
do_test wal2-1.1 {
  execsql { SELECT count(a), sum(a) FROM t1 } db2
} {4 10}

set RECOVER [list                                      \
  {0 1 lock exclusive}   {1 7 lock exclusive}          \
  {1 7 unlock exclusive} {0 1 unlock exclusive}        \
]
set READ [list                                         \
  {4 1 lock exclusive} {4 1 unlock exclusive}          \
  {4 1 lock shared}    {4 1 unlock shared}             \
]

foreach {tn iInsert res wal_index_hdr_mod wal_locks} "
         2    5   {5 15}    0             {$RECOVER $READ}
         3    6   {6 21}    1             {$RECOVER $READ}
         4    7   {7 28}    2             {$RECOVER $READ}
         5    8   {8 36}    3             {$RECOVER $READ}
         6    9   {9 45}    4             {$RECOVER $READ}
         7   10   {10 55}   5             {$RECOVER $READ}
         8   11   {11 66}   6             {$RECOVER $READ}
         9   12   {12 78}   7             {$RECOVER $READ}
        10   13   {13 91}   8             {$RECOVER $READ}
        11   14   {14 105}  9             {$RECOVER $READ}
        12   15   {15 120}  -1            {$READ}
" {

  do_test wal2-1.$tn.1 {
    execsql { INSERT INTO t1 VALUES($iInsert) }

    set ::locks [list]
    set ::cb_done 0

................................................................................
    proc tvfs_cb {method args} {
      if {$::cb_done == 0 && $method == "xShmGet"} {
        set ::cb_done 1
        if {$::wal_index_hdr_mod >= 0} {
          incr_tvfs_hdr [lindex $args 0] $::wal_index_hdr_mod 1
        }
      }

      if {$method == "xShmLock"} { lappend ::locks [lindex $args 2] }
      return SQLITE_OK
    }

    execsql { SELECT count(a), sum(a) FROM t1 } db2
  } $res

................................................................................
# it simply drops back to a READ lock and proceeds. But because the
# header is out-of-date, the reader reads the out-of-date snapshot.
#
# After this, the header is corrupted again and the reader is allowed
# to run recovery. This time, it sees an up-to-date snapshot of the
# database file.
#
set WRITER [list 0 1 lock exclusive]
set LOCKS  [list \
  {0 1 lock exclusive} {0 1 unlock exclusive} \
  {4 1 lock shared}    {4 1 unlock shared}    \
]
do_test wal2-2.0 {

  testvfs tvfs tvfs_cb
  proc tvfs_cb {method args} {
    if {$method == "xShmOpen"} { set ::shm_file [lindex $args 0] }
    return SQLITE_OK
  }
................................................................................
        if {$::wal_index_hdr_mod >= 0} {
          incr_tvfs_hdr $::shm_file $::wal_index_hdr_mod 1
        }
      }
      if {$method == "xShmLock"} {
        set lock [lindex $args 2]
        lappend ::locks $lock
        if {$lock == $::WRITER} {
          set_tvfs_hdr $::shm_file $::oldhdr
        }
      }
      return SQLITE_OK
    }

    execsql { SELECT count(a), sum(a) FROM t1 } db2
  } $res0

  do_test wal2-2.$tn.3 {
    set ::locks
  } $LOCKS

  do_test wal2-2.$tn.4 {
    set ::locks [list]
    set ::cb_done 0
    proc tvfs_cb {method args} {
      if {$::cb_done == 0 && $method == "xShmGet"} {
        set ::cb_done 1
................................................................................
  } $res1
}
db close
db2 close
tvfs delete
file delete -force test.db test.db-wal test.db-journal


if 0 {
#-------------------------------------------------------------------------
# This test case - wal2-3.* - tests the response of the library to an
# SQLITE_BUSY when attempting to obtain a READ or RECOVER lock.
#
#   wal2-3.0 - 2: SQLITE_BUSY when obtaining a READ lock
#   wal2-3.3 - 6: SQLITE_BUSY when obtaining a RECOVER lock
#
................................................................................
} {4 10}
do_test wal2-3.5 {
  list [info exists ::sabotage] [info exists ::locked]
} {0 0}
db close
tvfs delete
file delete -force test.db test.db-wal test.db-journal

}

#-------------------------------------------------------------------------
# Test that a database connection using a VFS that does not support the
# xShmXXX interfaces cannot open a WAL database.
#
do_test wal2-4.1 {
  sqlite3 db test.db
................................................................................
} {0 {{need xShmOpen to see this}}}
db close
tvfs delete

#-------------------------------------------------------------------------
# Test that if a database connection is forced to run recovery before it
# can perform a checkpoint, it does not transition into RECOVER state.
#
# UPDATE: This has now changed. When running a checkpoint, if recovery is
# required the client grabs all exclusive locks (just as it would for a
# recovery performed as a pre-cursor to a normal database transaction).
#
do_test wal2-5.1 {
  proc tvfs_cb {method args} {
    set ::shm_file [lindex $args 0]
    if {$method == "xShmLock"} { lappend ::locks [lindex $args 2] }
    return $::tvfs_cb_return
  }