Persistent Playground: Explore OPFS support

[adamziel]

This commit explores a custom OPFS filesystem backend for Playground to avoid losing changes after a page refresh.

Status: Playground works in read-only mode. Writing and reading entire files and directories works, but there's something off with seeking. For example, inserting a post yields General error: 10 disk I/O error.

I could not reproduce it with a simple fseek() call from PHP, unfortunately.

Perhaps this Emscripten PR contains some clues: https://github.com/emscripten-core/emscripten/pull/16307/files#diff-6558aa76b3879121168686cc9b281ffcf4828c11d7f5aaa325231d744c276d1dR72

Solves #19

cc @dmsnell

[adamziel]

There's no touch() method, but I still don't like this hack

[adamziel]

console.log output looks like this:

php_8_0.js?t=1686587334137:366 .ht.sqlite-journal llseek {position: 4620, offset: 4620, whence: 0}
php_8_0.js?t=1686587334137:340 .ht.sqlite-journal write {offset: 20648152, length: 4096, position: 4620, canOwn: undefined}
php_8_0.js?t=1686587334137:366 .ht.sqlite-journal llseek {position: 8716, offset: 8716, whence: 0}
php_8_0.js?t=1686587334137:340 .ht.sqlite-journal write {offset: 7049180, length: 4, position: 8716, canOwn: undefined}
php_8_0.js?t=1686587334137:366 .ht.sqlite llseek {position: 200704, offset: 192512, whence: 0}
php_8_0.js?t=1686587334137:321 .ht.sqlite read {offset: 20643896, length: 4096, position: 192512}
php_8_0.js?t=1686587334137:366 .ht.sqlite-journal llseek {position: 8720, offset: 8720, whence: 0}
php_8_0.js?t=1686587334137:340 .ht.sqlite-journal write {offset: 7049176, length: 4, position: 8720, canOwn: undefined}
php_8_0.js?t=1686587334137:366 .ht.sqlite-journal llseek {position: 8724, offset: 8724, whence: 0}
php_8_0.js?t=1686587334137:340 .ht.sqlite-journal write {offset: 20643896, length: 4096, position: 8724, canOwn: undefined}
php_8_0.js?t=1686587334137:366 .ht.sqlite-journal llseek {position: 12820, offset: 12820, whence: 0}
php_8_0.js?t=1686587334137:340 .ht.sqlite-journal write {offset: 7049180, length: 4, position: 12820, canOwn: undefined}

[adamziel]

This code works, how weird! Must be something specific to $wpdb interaction with SQLite

// Create SQLite database, create a table, insert, update, select some data
$sqlite = new SQLite3('test.sqlite');
// start a transaction
$sqlite->exec('BEGIN');
$sqlite->exec('CREATE TABLE test (id INTEGER PRIMARY KEY, name TEXT)');
$sqlite->exec('INSERT INTO test (name) VALUES ("test")');
$sqlite->exec('UPDATE test SET name = "test2" WHERE id = 1');
// commit
$sqlite->exec('COMMIT');
var_dump($sqlite->querySingle('SELECT name FROM test WHERE id = 1'));

[adamziel]

Minimal reproduction:

<?php
$sqlite = new SQLite3('/wordpress/wp-content/database/.ht.sqlite');
$sqlite->exec("INSERT INTO wp_options (option_name, option_value) VALUES ('a', 'b');");
var_dump($sqlite->lastErrorCode());

It's the SQLITE_IOERR error constant:

SQLITE_PRIVATE const char *sqlite3ErrStr(int rc){
  static const char* const aMsg[] = {
    /* SQLITE_OK          */ "not an error",
    /* SQLITE_ERROR       */ "SQL logic error",
    /* SQLITE_INTERNAL    */ 0,
    /* SQLITE_PERM        */ "access permission denied",
    /* SQLITE_ABORT       */ "query aborted",
    /* SQLITE_BUSY        */ "database is locked",
    /* SQLITE_LOCKED      */ "database table is locked",
    /* SQLITE_NOMEM       */ "out of memory",
    /* SQLITE_READONLY    */ "attempt to write a readonly database",
    /* SQLITE_INTERRUPT   */ "interrupted",
    /* SQLITE_IOERR       */ "disk I/O error",

It can be returned only by these two SQLite functions:

static int findInodeInfo(
  unixFile *pFile,               /* Unix file with file desc used in the key */
  unixInodeInfo **ppInode        /* Return the unixInodeInfo object here */
);

static int proxyGetHostID(unsigned char *pHostID, int *pError)

The first one is particularly suspicious since SQLITE_IOERR happens on rc = osFstat(fd, &statbuf); failure

[adamziel]

Closing – this PR uses the old webkit Filesystem spec and is a dead-end. A follow-up should use the same cross-browser API as #547 and wrap all the newly async PHP functions (like stat()) in Asyncify.