iLast = pWal->hdr.iLastPg;
  nSegment = (iLast >> 8) + 1;
  nFinal = (iLast & 0x000000FF);

  nByte = sizeof(WalIterator) + (nSegment-1)*sizeof(struct WalSegment) + 512;
  p = (WalIterator *)sqlite3_malloc(nByte);
  if( !p ){
    return SQLITE_NOMEM;
  }

  if( p ){
    memset(p, 0, nByte);
    p->nSegment = nSegment;

    for(i=0; i<nSegment-1; i++){
      p->aSegment[i].aDbPage = &aData[walIndexEntry(i*256+1)];
      p->aSegment[i].aIndex = (u8 *)&aData[walIndexEntry(i*256+1)+256];
    }
................................................................................
      pFinal->aIndex[i] = i;
    }
    walMergesort8(pFinal->aDbPage, aTmp, pFinal->aIndex, &nFinal);
    p->nFinal = nFinal;
  }

  *pp = p;
  return SQLITE_OK;
}

/* 
** Free a log iterator allocated by walIteratorInit().
*/
static void walIteratorFree(WalIterator *p){
  sqlite3_free(p);

  iLast = pWal->hdr.iLastPg;
  nSegment = (iLast >> 8) + 1;
  nFinal = (iLast & 0x000000FF);

  nByte = sizeof(WalIterator) + (nSegment-1)*sizeof(struct WalSegment) + 512;
  p = (WalIterator *)sqlite3_malloc(nByte);
  if( !p ){
    rc = SQLITE_NOMEM;
  }else{


    memset(p, 0, nByte);
    p->nSegment = nSegment;

    for(i=0; i<nSegment-1; i++){
      p->aSegment[i].aDbPage = &aData[walIndexEntry(i*256+1)];
      p->aSegment[i].aIndex = (u8 *)&aData[walIndexEntry(i*256+1)+256];
    }
................................................................................
      pFinal->aIndex[i] = i;
    }
    walMergesort8(pFinal->aDbPage, aTmp, pFinal->aIndex, &nFinal);
    p->nFinal = nFinal;
  }

  *pp = p;
  return rc;
}

/* 
** Free a log iterator allocated by walIteratorInit().
*/
static void walIteratorFree(WalIterator *p){
  sqlite3_free(p);

# 2010 May 5
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this file is testing the operation of the library in
# "PRAGMA journal_mode=WAL" mode.
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
source $testdir/lock_common.tcl
ifcapable !wal {finish_test ; return }

proc set_tvfs_hdr {file args} {
  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 blob [binary format i8a* [lindex $args 0] [string range $blob 32 end]]
    tvfs shm $file $blob
  }

  binary scan $blob i8 ints
  return $ints
}

proc incr_tvfs_hdr {file idx incrval} {
  set ints [set_tvfs_hdr $file]
  set v [lindex $ints $idx]
  incr v $incrval
  lset ints $idx $v
  set_tvfs_hdr $file $ints
}


#-------------------------------------------------------------------------
# Test case wal2-1.*:
#
# Set up a small database containing a single table. The database is not
# checkpointed during the test - all content resides in the log file.
#
# Two connections are established to the database file - a writer ([db])
# and a reader ([db2]). For each of the 8 integer fields in the wal-index
# header (6 fields and 2 checksum values), do the following:
#
#   1. Modify the database using the writer.
#
#   2. Attempt to read the database using the reader. Before the reader
#      has a chance to snapshot the wal-index header, increment one
#      of the the integer fields (so that the reader ends up with a corrupted
#      header).
#
#   3. Check that the reader recovers the wal-index and reads the correct
#      database content.
#
do_test wal2-1.0 {
  proc tvfs_cb {method args} { return SQLITE_OK }
  testvfs tvfs tvfs_cb

  sqlite3 db  test.db -vfs tvfs
  sqlite3 db2 test.db -vfs tvfs

  execsql {
    PRAGMA journal_mode = WAL;
    CREATE TABLE t1(a);
  } db2
  execsql {
    INSERT INTO t1 VALUES(1);
    INSERT INTO t1 VALUES(2);
    INSERT INTO t1 VALUES(3);
    INSERT INTO t1 VALUES(4);
    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}   -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

  do_test wal2-1.$tn.2 {
    set ::locks
  } $wal_locks
}
db close
db2 close
tvfs delete
file delete -force test.db test.db-wal test.db-journal

#-------------------------------------------------------------------------
# This test case is very similar to the previous one, except, after
# the reader reads the corrupt wal-index header, but before it has
# a chance to re-read it under the cover of the RECOVER lock, the
# wal-index header is replaced with a valid, but out-of-date, header.
#
# Because the header checksum looks Ok, the reader does not run recovery,
# 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
  }

  sqlite3 db  test.db -vfs tvfs
  sqlite3 db2 test.db -vfs tvfs

  execsql {
    PRAGMA journal_mode = WAL;
    CREATE TABLE t1(a);
  } db2
  execsql {
    INSERT INTO t1 VALUES(1);
    INSERT INTO t1 VALUES(2);
    INSERT INTO t1 VALUES(3);
    INSERT INTO t1 VALUES(4);
    SELECT count(a), sum(a) FROM t1;
  }
} {4 10}
do_test wal2-2.1 {
  execsql { SELECT count(a), sum(a) FROM t1 } db2
} {4 10}

foreach {tn iInsert res0 res1 wal_index_hdr_mod} {
         2    5   {4 10}   {5 15}    0
         3    6   {5 15}   {6 21}    1
         4    7   {6 21}   {7 28}    2
         5    8   {7 28}   {8 36}    3
         6    9   {8 36}   {9 45}    4
         7   10   {9 45}   {10 55}   5
         8   11   {10 55}  {11 66}   6
         9   12   {11 66}  {12 78}   7
} {
  do_test wal2-1.$tn.1 {
    set oldhdr [set_tvfs_hdr $::shm_file]
    execsql { INSERT INTO t1 VALUES($iInsert) }
    execsql { SELECT count(a), sum(a) FROM t1 }
  } $res1

  do_test wal2-2.$tn.2 {
    set ::locks [list]
    set ::cb_done 0
    proc tvfs_cb {method args} {
      if {$::cb_done == 0 && $method == "xShmGet"} {
        set ::cb_done 1
        if {$::wal_index_hdr_mod >= 0} {
          incr_tvfs_hdr $::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 && $method == "xShmGet"} {
        set ::cb_done 1
        if {$::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
      }
      return SQLITE_OK
    }

    execsql { SELECT count(a), sum(a) FROM t1 } db2
  } $res1
}
db close
db2 close
tvfs delete
file delete -force test.db test.db-wal test.db-journal

finish_test

  sqlite3 db test.db
  sqlite3_extended_result_codes db 1
  sqlite3_db_config_lookaside db 0 0 0
} -sqlbody {
  SELECT count(*) FROM x;
}











# A [testvfs] callback for the VFS created by [do_shmfault_test]. This
# callback injects SQLITE_IOERR faults into methods for which an entry
# in array ::shmfault_ioerr_methods is defined. For example, to enable
# errors in xShmOpen:
#
#   set ::shmfault_ioerr_methods(xShmOpen) 1
................................................................................
  set ::shmfault_ioerr_countdown 1
  set ::shmfault_ioerr_methods(xShmGet) 1
  db close
  unset ::shmfault_ioerr_methods(xShmGet)
  if {[file exists test.db-wal]==0} {error "Failed to create WAL file!"}

  sqlite3 db test.db -vfs shmfault
breakpoint
} -sqlbody {
  SELECT count(*) FROM t1;
}

finish_test

  sqlite3 db test.db
  sqlite3_extended_result_codes db 1
  sqlite3_db_config_lookaside db 0 0 0
} -sqlbody {
  SELECT count(*) FROM x;
}

do_ioerr_test walfault-ioerr-1 -sqlprep {
  PRAGMA auto_vacuum = 1;
  PRAGMA journal_mode = WAL;
  CREATE TABLE abc(a PRIMARY KEY);
  INSERT INTO abc VALUES(randomblob(1500));
} -sqlbody {
  DELETE FROM abc;
  PRAGMA wal_checkpoint;
}

# A [testvfs] callback for the VFS created by [do_shmfault_test]. This
# callback injects SQLITE_IOERR faults into methods for which an entry
# in array ::shmfault_ioerr_methods is defined. For example, to enable
# errors in xShmOpen:
#
#   set ::shmfault_ioerr_methods(xShmOpen) 1
................................................................................
  set ::shmfault_ioerr_countdown 1
  set ::shmfault_ioerr_methods(xShmGet) 1
  db close
  unset ::shmfault_ioerr_methods(xShmGet)
  if {[file exists test.db-wal]==0} {error "Failed to create WAL file!"}

  sqlite3 db test.db -vfs shmfault

} -sqlbody {
  SELECT count(*) FROM t1;
}

finish_test