[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/tetratelabs/wazero/internal/wasm/module_instance.go

@@ -0,0 +1,251 @@
+package wasm
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/tetratelabs/wazero/api"
+	"github.com/tetratelabs/wazero/sys"
+)
+
+// FailIfClosed returns a sys.ExitError if CloseWithExitCode was called.
+func (m *ModuleInstance) FailIfClosed() (err error) {
+	if closed := m.Closed.Load(); closed != 0 {
+		switch closed & exitCodeFlagMask {
+		case exitCodeFlagResourceClosed:
+		case exitCodeFlagResourceNotClosed:
+			// This happens when this module is closed asynchronously in CloseModuleOnCanceledOrTimeout,
+			// and the closure of resources have been deferred here.
+			_ = m.ensureResourcesClosed(context.Background())
+		}
+		return sys.NewExitError(uint32(closed >> 32)) // Unpack the high order bits as the exit code.
+	}
+	return nil
+}
+
+// CloseModuleOnCanceledOrTimeout take a context `ctx`, which might be a Cancel or Timeout context,
+// and spawns the Goroutine to check the context is canceled ot deadline exceeded. If it reaches
+// one of the conditions, it sets the appropriate exit code.
+//
+// Callers of this function must invoke the returned context.CancelFunc to release the spawned Goroutine.
+func (m *ModuleInstance) CloseModuleOnCanceledOrTimeout(ctx context.Context) context.CancelFunc {
+	// Creating an empty channel in this case is a bit more efficient than
+	// creating a context.Context and canceling it with the same effect. We
+	// really just need to be notified when to stop listening to the users
+	// context. Closing the channel will unblock the select in the goroutine
+	// causing it to return an stop listening to ctx.Done().
+	cancelChan := make(chan struct{})
+	go m.closeModuleOnCanceledOrTimeout(ctx, cancelChan)
+	return func() { close(cancelChan) }
+}
+
+// closeModuleOnCanceledOrTimeout is extracted from CloseModuleOnCanceledOrTimeout for testing.
+func (m *ModuleInstance) closeModuleOnCanceledOrTimeout(ctx context.Context, cancelChan <-chan struct{}) {
+	select {
+	case <-ctx.Done():
+		select {
+		case <-cancelChan:
+			// In some cases by the time this goroutine is scheduled, the caller
+			// has already closed both the context and the cancelChan. In this
+			// case go will randomize which branch of the outer select to enter
+			// and we don't want to close the module.
+		default:
+			// This is the same logic as CloseWithCtxErr except this calls closeWithExitCodeWithoutClosingResource
+			// so that we can defer the resource closure in FailIfClosed.
+			switch {
+			case errors.Is(ctx.Err(), context.Canceled):
+				// TODO: figure out how to report error here.
+				_ = m.closeWithExitCodeWithoutClosingResource(sys.ExitCodeContextCanceled)
+			case errors.Is(ctx.Err(), context.DeadlineExceeded):
+				// TODO: figure out how to report error here.
+				_ = m.closeWithExitCodeWithoutClosingResource(sys.ExitCodeDeadlineExceeded)
+			}
+		}
+	case <-cancelChan:
+	}
+}
+
+// CloseWithCtxErr closes the module with an exit code based on the type of
+// error reported by the context.
+//
+// If the context's error is unknown or nil, the module does not close.
+func (m *ModuleInstance) CloseWithCtxErr(ctx context.Context) {
+	switch {
+	case errors.Is(ctx.Err(), context.Canceled):
+		// TODO: figure out how to report error here.
+		_ = m.CloseWithExitCode(ctx, sys.ExitCodeContextCanceled)
+	case errors.Is(ctx.Err(), context.DeadlineExceeded):
+		// TODO: figure out how to report error here.
+		_ = m.CloseWithExitCode(ctx, sys.ExitCodeDeadlineExceeded)
+	}
+}
+
+// Name implements the same method as documented on api.Module
+func (m *ModuleInstance) Name() string {
+	return m.ModuleName
+}
+
+// String implements the same method as documented on api.Module
+func (m *ModuleInstance) String() string {
+	return fmt.Sprintf("Module[%s]", m.Name())
+}
+
+// Close implements the same method as documented on api.Module.
+func (m *ModuleInstance) Close(ctx context.Context) (err error) {
+	return m.CloseWithExitCode(ctx, 0)
+}
+
+// CloseWithExitCode implements the same method as documented on api.Module.
+func (m *ModuleInstance) CloseWithExitCode(ctx context.Context, exitCode uint32) (err error) {
+	if !m.setExitCode(exitCode, exitCodeFlagResourceClosed) {
+		return nil // not an error to have already closed
+	}
+	_ = m.s.deleteModule(m)
+	return m.ensureResourcesClosed(ctx)
+}
+
+// IsClosed implements the same method as documented on api.Module.
+func (m *ModuleInstance) IsClosed() bool {
+	return m.Closed.Load() != 0
+}
+
+func (m *ModuleInstance) closeWithExitCodeWithoutClosingResource(exitCode uint32) (err error) {
+	if !m.setExitCode(exitCode, exitCodeFlagResourceNotClosed) {
+		return nil // not an error to have already closed
+	}
+	_ = m.s.deleteModule(m)
+	return nil
+}
+
+// closeWithExitCode is the same as CloseWithExitCode besides this doesn't delete it from Store.moduleList.
+func (m *ModuleInstance) closeWithExitCode(ctx context.Context, exitCode uint32) (err error) {
+	if !m.setExitCode(exitCode, exitCodeFlagResourceClosed) {
+		return nil // not an error to have already closed
+	}
+	return m.ensureResourcesClosed(ctx)
+}
+
+type exitCodeFlag = uint64
+
+const exitCodeFlagMask = 0xff
+
+const (
+	// exitCodeFlagResourceClosed indicates that the module was closed and resources were already closed.
+	exitCodeFlagResourceClosed = 1 << iota
+	// exitCodeFlagResourceNotClosed indicates that the module was closed while resources are not closed yet.
+	exitCodeFlagResourceNotClosed
+)
+
+func (m *ModuleInstance) setExitCode(exitCode uint32, flag exitCodeFlag) bool {
+	closed := flag | uint64(exitCode)<<32 // Store exitCode as high-order bits.
+	return m.Closed.CompareAndSwap(0, closed)
+}
+
+// ensureResourcesClosed ensures that resources assigned to ModuleInstance is released.
+// Only one call will happen per module, due to external atomic guards on Closed.
+func (m *ModuleInstance) ensureResourcesClosed(ctx context.Context) (err error) {
+	if closeNotifier := m.CloseNotifier; closeNotifier != nil { // experimental
+		closeNotifier.CloseNotify(ctx, uint32(m.Closed.Load()>>32))
+		m.CloseNotifier = nil
+	}
+
+	if sysCtx := m.Sys; sysCtx != nil { // nil if from HostModuleBuilder
+		err = sysCtx.FS().Close()
+		m.Sys = nil
+	}
+
+	if mem := m.MemoryInstance; mem != nil {
+		if mem.expBuffer != nil {
+			mem.expBuffer.Free()
+			mem.expBuffer = nil
+		}
+	}
+
+	if m.CodeCloser != nil {
+		if e := m.CodeCloser.Close(ctx); err == nil {
+			err = e
+		}
+		m.CodeCloser = nil
+	}
+	return err
+}
+
+// Memory implements the same method as documented on api.Module.
+func (m *ModuleInstance) Memory() api.Memory {
+	return m.MemoryInstance
+}
+
+// ExportedMemory implements the same method as documented on api.Module.
+func (m *ModuleInstance) ExportedMemory(name string) api.Memory {
+	_, err := m.getExport(name, ExternTypeMemory)
+	if err != nil {
+		return nil
+	}
+	// We Assume that we have at most one memory.
+	return m.MemoryInstance
+}
+
+// ExportedMemoryDefinitions implements the same method as documented on
+// api.Module.
+func (m *ModuleInstance) ExportedMemoryDefinitions() map[string]api.MemoryDefinition {
+	// Special case as we currently only support one memory.
+	if mem := m.MemoryInstance; mem != nil {
+		// Now, find out if it is exported
+		for name, exp := range m.Exports {
+			if exp.Type == ExternTypeMemory {
+				return map[string]api.MemoryDefinition{name: mem.definition}
+			}
+		}
+	}
+	return map[string]api.MemoryDefinition{}
+}
+
+// ExportedFunction implements the same method as documented on api.Module.
+func (m *ModuleInstance) ExportedFunction(name string) api.Function {
+	exp, err := m.getExport(name, ExternTypeFunc)
+	if err != nil {
+		return nil
+	}
+	return m.Engine.NewFunction(exp.Index)
+}
+
+// ExportedFunctionDefinitions implements the same method as documented on
+// api.Module.
+func (m *ModuleInstance) ExportedFunctionDefinitions() map[string]api.FunctionDefinition {
+	result := map[string]api.FunctionDefinition{}
+	for name, exp := range m.Exports {
+		if exp.Type == ExternTypeFunc {
+			result[name] = m.Source.FunctionDefinition(exp.Index)
+		}
+	}
+	return result
+}
+
+// GlobalVal is an internal hack to get the lower 64 bits of a global.
+func (m *ModuleInstance) GlobalVal(idx Index) uint64 {
+	return m.Globals[idx].Val
+}
+
+// ExportedGlobal implements the same method as documented on api.Module.
+func (m *ModuleInstance) ExportedGlobal(name string) api.Global {
+	exp, err := m.getExport(name, ExternTypeGlobal)
+	if err != nil {
+		return nil
+	}
+	g := m.Globals[exp.Index]
+	if g.Type.Mutable {
+		return mutableGlobal{g: g}
+	}
+	return constantGlobal{g: g}
+}
+
+// NumGlobal implements experimental.InternalModule.
+func (m *ModuleInstance) NumGlobal() int {
+	return len(m.Globals)
+}
+
+// Global implements experimental.InternalModule.
+func (m *ModuleInstance) Global(idx int) api.Global {
+	return constantGlobal{g: m.Globals[idx]}
+}