SQLite

  aFrame = (u8 *)sqlite3_malloc64(szFrame);
  if( aFrame==0 ){
    rc = SQLITE_NOMEM_BKPT;
    goto begin_unlocked_out;
  }
  aData = &aFrame[WAL_FRAME_HDRSIZE];

  /* Check to see if a complete transaction has been appended to the
  ** wal file since the heap-memory wal-index was created. If so, the
  ** heap-memory wal-index is discarded and WAL_RETRY returned to
  ** the caller.  */
  aSaveCksum[0] = pWal->hdr.aFrameCksum[0];
  aSaveCksum[1] = pWal->hdr.aFrameCksum[1];
  for(iOffset=walFrameOffset(pWal->hdr.mxFrame+1, pWal->hdr.szPage); 
      iOffset+szFrame<=szWal; 
      iOffset+=szFrame
  ){
    u32 pgno;                   /* Database page number for frame */

        ** So retry opening this read transaction.  */
        rc = WAL_RETRY;
      }
      break;
    }
    if( !walDecodeFrame(pWal, &pgno, &nTruncate, aData, aFrame) ) break;

    /* If nTruncate is non-zero, then a complete transaction has been
    ** appended to this wal file. Set rc to WAL_RETRY and break out of
    ** the loop.  */
    if( nTruncate ){
      rc = WAL_RETRY;
      break;
    }
  }
  pWal->hdr.aFrameCksum[0] = aSaveCksum[0];
  pWal->hdr.aFrameCksum[1] = aSaveCksum[1];

#
# This file contains tests for using WAL databases in read-only mode.
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
source $testdir/lock_common.tcl
source $testdir/wal_common.tcl
set ::testprefix walro2

# These tests are only going to work on unix.
#
if {$::tcl_platform(platform) != "unix"} {
  finish_test
  return
}

    sql3 { SELECT * FROM t1 }
  } {a b c d e f g h}
  do_test 2.3.2 {
    sql3 { INSERT INTO t1 VALUES('i', 'j') }
    code3 { db3 close }
    sql1 { COMMIT } 
  } {}

  do_test 2.3.3 {
    sql1 { SELECT * FROM t1 }
  } {a b c d e f g h i j}


  #-----------------------------------------------------------------------
  # 3.1.*: That a readonly_shm connection can read a database file if both
  #        the *-wal and *-shm files are zero bytes in size.
  #
  # 3.2.*: That it flushes the cache if, between transactions on a db with a
  #        zero byte *-wal file, some other connection modifies the db, then
  #        does "PRAGMA wal_checkpoint=truncate" to truncate the wal file
  #        back to zero bytes in size.
  #
  # 3.3.*: That, if between transactions some other process wraps the wal
  #        file, the readonly_shm client reruns recovery.
  #
  catch { code1 { db close } }
  catch { code2 { db2 close } }
  catch { code3 { db3 close } }
  do_test 3.1.0 {
    list [file exists test.db-wal] [file exists test.db-shm]
  } {0 0}
  do_test 3.1.1 {
    close [open test.db-wal w]
    close [open test.db-shm w]
    code1 {
      sqlite3 db file:test.db?readonly_shm=1
    }
    sql1 { SELECT * FROM t1 }
  } {a b c d e f g h}

  do_test 3.2.0 {
    list [file size test.db-wal] [file size test.db-shm]
  } {0 0}
  do_test 3.2.1 {
    code2 { sqlite3 db2 test.db }
    sql2 { INSERT INTO t1 VALUES(1, 2) ; PRAGMA wal_checkpoint=truncate }
    code2 { db2 close }
    sql1 { SELECT * FROM t1 }
  } {a b c d e f g h 1 2}
  do_test 3.2.2 {
    list [file size test.db-wal] [file size test.db-shm]
  } {0 32768}

  do_test 3.3.0 {
    code2 { sqlite3 db2 test.db }
    sql2 { 
      INSERT INTO t1 VALUES(3, 4);
      INSERT INTO t1 VALUES(5, 6);
      INSERT INTO t1 VALUES(7, 8);
      INSERT INTO t1 VALUES(9, 10);
    }
    code2 { db2 close }
    code1 { db close }
    list [file size test.db-wal] [file size test.db-shm]
  } [list [wal_file_size 4 1024] 32768]
  do_test 3.3.1 {
    code1 { sqlite3 db file:test.db?readonly_shm=1 }
    sql1 { SELECT * FROM t1 }
  } {a b c d e f g h 1 2 3 4 5 6 7 8 9 10}
  do_test 3.3.2 {
    code2 { sqlite3 db2 test.db }
    sql2 { 
      PRAGMA wal_checkpoint; 
      DELETE FROM t1;
      INSERT INTO t1 VALUES('i', 'ii');
    }
    code2 { db2 close }
    list [file size test.db-wal] [file size test.db-shm]
  } [list [wal_file_size 4 1024] 32768]
  do_test 3.3.3 {
    sql1 { SELECT * FROM t1 }
  } {i ii}

}

finish_test