assert( db->pDfltColl!=0 );

  /* Also add a UTF-8 case-insensitive collation sequence. */
  createCollation(db, "NOCASE", SQLITE_UTF8, SQLITE_COLL_NOCASE, 0,
                  nocaseCollatingFunc, 0);

  /* Parse the filename/URI argument. */

  rc = sqlite3ParseUri(
      zVfs, zFilename, &flags, &btflags, &db->pVfs, &zOpen, &zErrMsg);
  if( rc!=SQLITE_OK ){
    if( rc==SQLITE_NOMEM ) db->mallocFailed = 1;
    sqlite3Error(db, rc, zErrMsg ? "%s" : 0, zErrMsg);
    sqlite3_free(zErrMsg);
    goto opendb_out;
  }

  /* Open the backend database driver */
  db->openFlags = flags;
  rc = sqlite3BtreeOpen(db->pVfs, zOpen, db, &db->aDb[0].pBt, btflags,
                        flags | SQLITE_OPEN_MAIN_DB);
  if( rc!=SQLITE_OK ){
    if( rc==SQLITE_IOERR_NOMEM ){
      rc = SQLITE_NOMEM;
    }
    sqlite3Error(db, rc, 0);

  assert( db->pDfltColl!=0 );

  /* Also add a UTF-8 case-insensitive collation sequence. */
  createCollation(db, "NOCASE", SQLITE_UTF8, SQLITE_COLL_NOCASE, 0,
                  nocaseCollatingFunc, 0);

  /* Parse the filename/URI argument. */
  db->openFlags = flags;
  rc = sqlite3ParseUri(
      zVfs, zFilename, &flags, &btflags, &db->pVfs, &zOpen, &zErrMsg);
  if( rc!=SQLITE_OK ){
    if( rc==SQLITE_NOMEM ) db->mallocFailed = 1;
    sqlite3Error(db, rc, zErrMsg ? "%s" : 0, zErrMsg);
    sqlite3_free(zErrMsg);
    goto opendb_out;
  }

  /* Open the backend database driver */

  rc = sqlite3BtreeOpen(db->pVfs, zOpen, db, &db->aDb[0].pBt, btflags,
                        flags | SQLITE_OPEN_MAIN_DB);
  if( rc!=SQLITE_OK ){
    if( rc==SQLITE_IOERR_NOMEM ){
      rc = SQLITE_NOMEM;
    }
    sqlite3Error(db, rc, 0);

**
** Mutexes are created using [sqlite3_mutex_alloc()].
*/
typedef struct sqlite3_mutex sqlite3_mutex;

/*
** CAPI3REF: OS Interface Object

**
** An instance of the sqlite3_vfs object defines the interface between
** the SQLite core and the underlying operating system.  The "vfs"
** in the name of the object stands for "virtual file system".
**
** The value of the iVersion field is initially 1 but may be larger in
** future versions of SQLite.  Additional fields may be appended to this

**
** Mutexes are created using [sqlite3_mutex_alloc()].
*/
typedef struct sqlite3_mutex sqlite3_mutex;

/*
** CAPI3REF: OS Interface Object
** KEYWORDS: VFS VFSes
**
** An instance of the sqlite3_vfs object defines the interface between
** the SQLite core and the underlying operating system.  The "vfs"
** in the name of the object stands for "virtual file system".
**
** The value of the iVersion field is initially 1 but may be larger in
** future versions of SQLite.  Additional fields may be appended to this

sqlite3 db test.db
db close
foreach {tn uri flags error} {
  1   {file:test.db?mode=ro}   ro    {not an error}
  2   {file:test.db?mode=ro}   rw    {not an error}
  3   {file:test.db?mode=ro}   rwc   {not an error}

  4   {file:test.db?mode=rw}   ro    {access permission denied}
  5   {file:test.db?mode=rw}   rw    {not an error}
  6   {file:test.db?mode=rw}   rwc   {not an error}

  7   {file:test.db?mode=rwc}  ro    {access permission denied}
  8   {file:test.db?mode=rwc}  rw    {access permission denied}
  9   {file:test.db?mode=rwc}  rwc   {not an error}
} {
  set f(ro)  [list SQLITE_OPEN_READONLY SQLITE_OPEN_URI]
  set f(rw)  [list SQLITE_OPEN_READWRITE SQLITE_OPEN_URI]
  set f(rwc) [list SQLITE_OPEN_READWRITE SQLITE_OPEN_CREATE SQLITE_OPEN_URI]

  set DB [sqlite3_open_v2 $uri $f($flags) ""]

sqlite3 db test.db
db close
foreach {tn uri flags error} {
  1   {file:test.db?mode=ro}   ro    {not an error}
  2   {file:test.db?mode=ro}   rw    {not an error}
  3   {file:test.db?mode=ro}   rwc   {not an error}

  4   {file:test.db?mode=rw}   ro    {access mode not allowed: rw}
  5   {file:test.db?mode=rw}   rw    {not an error}
  6   {file:test.db?mode=rw}   rwc   {not an error}

  7   {file:test.db?mode=rwc}  ro    {access mode not allowed: rwc}
  8   {file:test.db?mode=rwc}  rw    {access mode not allowed: rwc}
  9   {file:test.db?mode=rwc}  rwc   {not an error}
} {
  set f(ro)  [list SQLITE_OPEN_READONLY SQLITE_OPEN_URI]
  set f(rw)  [list SQLITE_OPEN_READWRITE SQLITE_OPEN_URI]
  set f(rwc) [list SQLITE_OPEN_READWRITE SQLITE_OPEN_CREATE SQLITE_OPEN_URI]

  set DB [sqlite3_open_v2 $uri $f($flags) ""]

#
#   1.*: That file names are correctly extracted from URIs.
#   2.*: That URI options (query parameters) are correctly extracted from URIs.
#   3.*: That specifying an unknown VFS causes an error.
#   4.*: Tests for specifying other options (other than "vfs").
#   5.*: Test using a different VFS with an attached database.
#   6.*: Test that authorities other than "" and localhost cause errors.

#

set testprefix uri
db close
sqlite3_shutdown
sqlite3_config_uri 1

................................................................................
  set A(0) {1 {attempt to write a readonly database}}
  do_test 4.1.$tn.2 {
    sqlite3 db "file:test.db?mode=$mode"
    catchsql { INSERT INTO t1 VALUES(1, 2) }
  } $A($write_ok)

  set A(1) {0 {}}
  set A(0) {1 {access permission denied}}
  do_test 4.1.$tn.3 {
    list [catch {sqlite3 db "file:test.db?mode=$mode" -readonly 1} msg] $msg
  } $A($readonly_ok)
}

set orig [sqlite3_enable_shared_cache]
foreach {tn options sc_default is_shared} {
................................................................................
  do_test 6.$tn {
    set DB [sqlite3_open $uri]
    sqlite3_errmsg $DB
  } $res
  catch { sqlite3_close $DB }
}


finish_test

#
#   1.*: That file names are correctly extracted from URIs.
#   2.*: That URI options (query parameters) are correctly extracted from URIs.
#   3.*: That specifying an unknown VFS causes an error.
#   4.*: Tests for specifying other options (other than "vfs").
#   5.*: Test using a different VFS with an attached database.
#   6.*: Test that authorities other than "" and localhost cause errors.
#   7.*: Test that a read-write db can be attached to a read-only connection.
#

set testprefix uri
db close
sqlite3_shutdown
sqlite3_config_uri 1

................................................................................
  set A(0) {1 {attempt to write a readonly database}}
  do_test 4.1.$tn.2 {
    sqlite3 db "file:test.db?mode=$mode"
    catchsql { INSERT INTO t1 VALUES(1, 2) }
  } $A($write_ok)

  set A(1) {0 {}}
  set A(0) [list 1 "access mode not allowed: $mode"]
  do_test 4.1.$tn.3 {
    list [catch {sqlite3 db "file:test.db?mode=$mode" -readonly 1} msg] $msg
  } $A($readonly_ok)
}

set orig [sqlite3_enable_shared_cache]
foreach {tn options sc_default is_shared} {
................................................................................
  do_test 6.$tn {
    set DB [sqlite3_open $uri]
    sqlite3_errmsg $DB
  } $res
  catch { sqlite3_close $DB }
}

forcedelete test.db test.db2
do_test 7.1 {
  sqlite3 db test.db
  execsql {
    CREATE TABLE t1(a, b);
    INSERT INTO t1 VALUES(1, 2);
    ATTACH 'test.db2' AS aux;
    CREATE TABLE aux.t2(a, b);
    INSERT INTO t1 VALUES('a', 'b');
  }
  db close
} {}
do_test 7.2 {
  sqlite3 db file:test.db?mode=ro
  execsql { ATTACH 'file:test.db2?mode=rw' AS aux }
} {}
do_execsql_test  7.3 { 
  INSERT INTO t2 VALUES('c', 'd') 
} {}
do_catchsql_test 7.4 { 
  INSERT INTO t1 VALUES(3, 4) 
} {1 {attempt to write a readonly database}}

finish_test

    sql2 {
      PRAGMA wal_checkpoint;
      INSERT INTO t1 VALUES('k', 'l');
    }
    set {} {}
  } {}
  do_test 1.2.8 { sql1 "SELECT * FROM t1" } {a b c d e f g h i j k l}
}
































finish_test

    sql2 {
      PRAGMA wal_checkpoint;
      INSERT INTO t1 VALUES('k', 'l');
    }
    set {} {}
  } {}
  do_test 1.2.8 { sql1 "SELECT * FROM t1" } {a b c d e f g h i j k l}

  # Now check that if the readonly_shm option is not supplied, or if it
  # is set to zero, it is not possible to connect to the database without
  # read-write access to the shm.
  do_test 1.3.1 {
    code1 { db close }
    code1 { sqlite3 db test.db }
    csql1 { SELECT * FROM t1 }
  } {1 {unable to open database file}}

  # Also test that if the -shm file can be opened for read/write access,
  # it is, even if readonly_shm=1 is present in the URI.
  do_test 1.3.2.1 {
    code1 { db close }
    code2 { db2 close }
    file exists test.db-shm
  } {0}
  do_test 1.3.2.2 {
    code1 { sqlite3 db file:test.db?readonly_shm=1 }
    sql1 { SELECT * FROM t1 }
  } {a b c d e f g h i j k l}
  do_test 1.3.2.3 {
    code1 { db close }
    close [open test.db-shm w]
    file attributes test.db-shm -permissions r--r--r--
    code1 { sqlite3 db file:test.db?readonly_shm=1 }
    csql1 { SELECT * FROM t1 }
  } {1 {attempt to write a readonly database}}
  do_test 1.3.2.4 {
    code1 { sqlite3_extended_errcode db } 
  } {SQLITE_READONLY_RECOVERY}
}

finish_test