[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/filecache/compilationcache.go

@@ -0,0 +1,42 @@
+package filecache
+
+import (
+	"crypto/sha256"
+	"io"
+)
+
+// Cache allows the compiler engine to skip compilation of wasm to machine code
+// where doing so is redundant for the same wasm binary and version of wazero.
+//
+// This augments the default in-memory cache of compiled functions, by
+// decoupling it from a wazero.Runtime instance. Concretely, a runtime loses
+// its cache once closed. This cache allows the runtime to rebuild its
+// in-memory cache quicker, significantly reducing first-hit penalty on a hit.
+//
+// See New for the example implementation.
+type Cache interface {
+	// Get is called when the runtime is trying to get the cached compiled functions.
+	// Implementations are supposed to return compiled function in io.Reader with ok=true
+	// if the key exists on the cache. In the case of not-found, this should return
+	// ok=false with err=nil. content.Close() is automatically called by
+	// the caller of this Get.
+	//
+	// Note: the returned content won't go through the validation pass of Wasm binary
+	// which is applied when the binary is compiled from scratch without cache hit.
+	Get(key Key) (content io.ReadCloser, ok bool, err error)
+	//
+	// Add is called when the runtime is trying to add the new cache entry.
+	// The given `content` must be un-modified, and returned as-is in Get method.
+	//
+	// Note: the `content` is ensured to be safe through the validation phase applied on the Wasm binary.
+	Add(key Key, content io.Reader) (err error)
+	//
+	// Delete is called when the cache on the `key` returned by Get is no longer usable, and
+	// must be purged. Specifically, this is called happens when the wazero's version has been changed.
+	// For example, that is when there's a difference between the version of compiling wazero and the
+	// version of the currently used wazero.
+	Delete(key Key) (err error)
+}
+
+// Key represents the 256-bit unique identifier assigned to each cache entry.
+type Key = [sha256.Size]byte

vendor/github.com/tetratelabs/wazero/internal/filecache/file_cache.go

@@ -0,0 +1,76 @@
+package filecache
+
+import (
+	"encoding/hex"
+	"errors"
+	"io"
+	"os"
+	"path"
+	"path/filepath"
+)
+
+// New returns a new Cache implemented by fileCache.
+func New(dir string) Cache {
+	return newFileCache(dir)
+}
+
+func newFileCache(dir string) *fileCache {
+	return &fileCache{dirPath: dir}
+}
+
+// fileCache persists compiled functions into dirPath.
+//
+// Note: this can be expanded to do binary signing/verification, set TTL on each entry, etc.
+type fileCache struct {
+	dirPath string
+}
+
+func (fc *fileCache) path(key Key) string {
+	return path.Join(fc.dirPath, hex.EncodeToString(key[:]))
+}
+
+func (fc *fileCache) Get(key Key) (content io.ReadCloser, ok bool, err error) {
+	f, err := os.Open(fc.path(key))
+	if errors.Is(err, os.ErrNotExist) {
+		return nil, false, nil
+	} else if err != nil {
+		return nil, false, err
+	} else {
+		return f, true, nil
+	}
+}
+
+func (fc *fileCache) Add(key Key, content io.Reader) (err error) {
+	path := fc.path(key)
+	dirPath, fileName := filepath.Split(path)
+
+	file, err := os.CreateTemp(dirPath, fileName+".*.tmp")
+	if err != nil {
+		return
+	}
+	defer func() {
+		file.Close()
+		if err != nil {
+			_ = os.Remove(file.Name())
+		}
+	}()
+	if _, err = io.Copy(file, content); err != nil {
+		return
+	}
+	if err = file.Sync(); err != nil {
+		return
+	}
+	if err = file.Close(); err != nil {
+		return
+	}
+	err = os.Rename(file.Name(), path)
+	return
+}
+
+func (fc *fileCache) Delete(key Key) (err error) {
+	err = os.Remove(fc.path(key))
+	if errors.Is(err, os.ErrNotExist) {
+		err = nil
+	}
+	return
+}