[experiment] add alternative wasm sqlite3 implementation available via build-tag (#2863)

This allows for building GoToSocial with [SQLite transpiled to WASM](https://github.com/ncruces/go-sqlite3) and accessed through [Wazero](https://wazero.io/).

vendor/github.com/ncruces/go-sqlite3/vfs/os_windows.go

@@ -0,0 +1,186 @@
+//go:build !sqlite3_nosys
+
+package vfs
+
+import (
+	"math/rand"
+	"os"
+	"time"
+
+	"golang.org/x/sys/windows"
+)
+
+func osGetSharedLock(file *os.File) _ErrorCode {
+	// Acquire the PENDING lock temporarily before acquiring a new SHARED lock.
+	rc := osReadLock(file, _PENDING_BYTE, 1, 0)
+	if rc == _OK {
+		// Acquire the SHARED lock.
+		rc = osReadLock(file, _SHARED_FIRST, _SHARED_SIZE, 0)
+
+		// Release the PENDING lock.
+		osUnlock(file, _PENDING_BYTE, 1)
+	}
+	return rc
+}
+
+func osGetReservedLock(file *os.File) _ErrorCode {
+	// Acquire the RESERVED lock.
+	return osWriteLock(file, _RESERVED_BYTE, 1, 0)
+}
+
+func osGetPendingLock(file *os.File, block bool) _ErrorCode {
+	var timeout time.Duration
+	if block {
+		timeout = -1
+	}
+
+	// Acquire the PENDING lock.
+	return osWriteLock(file, _PENDING_BYTE, 1, timeout)
+}
+
+func osGetExclusiveLock(file *os.File, wait bool) _ErrorCode {
+	var timeout time.Duration
+	if wait {
+		timeout = time.Millisecond
+	}
+
+	// Release the SHARED lock.
+	osUnlock(file, _SHARED_FIRST, _SHARED_SIZE)
+
+	// Acquire the EXCLUSIVE lock.
+	rc := osWriteLock(file, _SHARED_FIRST, _SHARED_SIZE, timeout)
+
+	if rc != _OK {
+		// Reacquire the SHARED lock.
+		osReadLock(file, _SHARED_FIRST, _SHARED_SIZE, 0)
+	}
+	return rc
+}
+
+func osDowngradeLock(file *os.File, state LockLevel) _ErrorCode {
+	if state >= LOCK_EXCLUSIVE {
+		// Release the EXCLUSIVE lock.
+		osUnlock(file, _SHARED_FIRST, _SHARED_SIZE)
+
+		// Reacquire the SHARED lock.
+		if rc := osReadLock(file, _SHARED_FIRST, _SHARED_SIZE, 0); rc != _OK {
+			// This should never happen.
+			// We should always be able to reacquire the read lock.
+			return _IOERR_RDLOCK
+		}
+	}
+
+	// Release the PENDING and RESERVED locks.
+	if state >= LOCK_RESERVED {
+		osUnlock(file, _RESERVED_BYTE, 1)
+	}
+	if state >= LOCK_PENDING {
+		osUnlock(file, _PENDING_BYTE, 1)
+	}
+	return _OK
+}
+
+func osReleaseLock(file *os.File, state LockLevel) _ErrorCode {
+	// Release all locks.
+	if state >= LOCK_RESERVED {
+		osUnlock(file, _RESERVED_BYTE, 1)
+	}
+	if state >= LOCK_SHARED {
+		osUnlock(file, _SHARED_FIRST, _SHARED_SIZE)
+	}
+	if state >= LOCK_PENDING {
+		osUnlock(file, _PENDING_BYTE, 1)
+	}
+	return _OK
+}
+
+func osCheckReservedLock(file *os.File) (bool, _ErrorCode) {
+	// Test the RESERVED lock.
+	rc := osLock(file, 0, _RESERVED_BYTE, 1, 0, _IOERR_CHECKRESERVEDLOCK)
+	if rc == _BUSY {
+		return true, _OK
+	}
+	if rc == _OK {
+		// Release the RESERVED lock.
+		osUnlock(file, _RESERVED_BYTE, 1)
+	}
+	return false, rc
+}
+
+func osUnlock(file *os.File, start, len uint32) _ErrorCode {
+	err := windows.UnlockFileEx(windows.Handle(file.Fd()),
+		0, len, 0, &windows.Overlapped{Offset: start})
+	if err == windows.ERROR_NOT_LOCKED {
+		return _OK
+	}
+	if err != nil {
+		return _IOERR_UNLOCK
+	}
+	return _OK
+}
+
+func osLock(file *os.File, flags, start, len uint32, timeout time.Duration, def _ErrorCode) _ErrorCode {
+	var err error
+	switch {
+	case timeout == 0:
+		err = osLockEx(file, flags|windows.LOCKFILE_FAIL_IMMEDIATELY, start, len)
+	case timeout < 0:
+		err = osLockEx(file, flags, start, len)
+	default:
+		before := time.Now()
+		for {
+			err = osLockEx(file, flags|windows.LOCKFILE_FAIL_IMMEDIATELY, start, len)
+			if errno, _ := err.(windows.Errno); errno != windows.ERROR_LOCK_VIOLATION {
+				break
+			}
+			if timeout < time.Since(before) {
+				break
+			}
+			osSleep(time.Duration(rand.Int63n(int64(time.Millisecond))))
+		}
+	}
+	return osLockErrorCode(err, def)
+}
+
+func osLockEx(file *os.File, flags, start, len uint32) error {
+	return windows.LockFileEx(windows.Handle(file.Fd()), flags,
+		0, len, 0, &windows.Overlapped{Offset: start})
+}
+
+func osReadLock(file *os.File, start, len uint32, timeout time.Duration) _ErrorCode {
+	return osLock(file, 0, start, len, timeout, _IOERR_RDLOCK)
+}
+
+func osWriteLock(file *os.File, start, len uint32, timeout time.Duration) _ErrorCode {
+	return osLock(file, windows.LOCKFILE_EXCLUSIVE_LOCK, start, len, timeout, _IOERR_LOCK)
+}
+
+func osLockErrorCode(err error, def _ErrorCode) _ErrorCode {
+	if err == nil {
+		return _OK
+	}
+	if errno, ok := err.(windows.Errno); ok {
+		// https://devblogs.microsoft.com/oldnewthing/20140905-00/?p=63
+		switch errno {
+		case
+			windows.ERROR_LOCK_VIOLATION,
+			windows.ERROR_IO_PENDING,
+			windows.ERROR_OPERATION_ABORTED:
+			return _BUSY
+		}
+	}
+	return def
+}
+
+func osSleep(d time.Duration) {
+	if d > 0 {
+		period := max(1, d/(5*time.Millisecond))
+		if period < 16 {
+			windows.TimeBeginPeriod(uint32(period))
+		}
+		time.Sleep(d)
+		if period < 16 {
+			windows.TimeEndPeriod(uint32(period))
+		}
+	}
+}