[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/filename.go

@@ -0,0 +1,174 @@
+package vfs
+
+import (
+	"context"
+	"net/url"
+
+	"github.com/ncruces/go-sqlite3/internal/util"
+	"github.com/tetratelabs/wazero/api"
+)
+
+// Filename is used by SQLite to pass filenames
+// to the Open method of a VFS.
+//
+// https://sqlite.org/c3ref/filename.html
+type Filename struct {
+	ctx   context.Context
+	mod   api.Module
+	zPath uint32
+	flags OpenFlag
+	stack [2]uint64
+}
+
+// OpenFilename is an internal API users should not call directly.
+func OpenFilename(ctx context.Context, mod api.Module, id uint32, flags OpenFlag) *Filename {
+	if id == 0 {
+		return nil
+	}
+	return &Filename{
+		ctx:   ctx,
+		mod:   mod,
+		zPath: id,
+		flags: flags,
+	}
+}
+
+// String returns this filename as a string.
+func (n *Filename) String() string {
+	if n == nil || n.zPath == 0 {
+		return ""
+	}
+	return util.ReadString(n.mod, n.zPath, _MAX_PATHNAME)
+}
+
+// Database returns the name of the corresponding database file.
+//
+// https://sqlite.org/c3ref/filename_database.html
+func (n *Filename) Database() string {
+	return n.path("sqlite3_filename_database")
+}
+
+// Journal returns the name of the corresponding rollback journal file.
+//
+// https://sqlite.org/c3ref/filename_database.html
+func (n *Filename) Journal() string {
+	return n.path("sqlite3_filename_journal")
+}
+
+// Journal returns the name of the corresponding WAL file.
+//
+// https://sqlite.org/c3ref/filename_database.html
+func (n *Filename) WAL() string {
+	return n.path("sqlite3_filename_wal")
+}
+
+func (n *Filename) path(method string) string {
+	if n == nil || n.zPath == 0 {
+		return ""
+	}
+	n.stack[0] = uint64(n.zPath)
+	fn := n.mod.ExportedFunction(method)
+	if err := fn.CallWithStack(n.ctx, n.stack[:]); err != nil {
+		panic(err)
+	}
+	return util.ReadString(n.mod, uint32(n.stack[0]), _MAX_PATHNAME)
+}
+
+// DatabaseFile returns the main database [File] corresponding to a journal.
+//
+// https://sqlite.org/c3ref/database_file_object.html
+func (n *Filename) DatabaseFile() File {
+	if n == nil || n.zPath == 0 {
+		return nil
+	}
+	if n.flags&(OPEN_MAIN_DB|OPEN_MAIN_JOURNAL|OPEN_WAL) == 0 {
+		return nil
+	}
+
+	n.stack[0] = uint64(n.zPath)
+	fn := n.mod.ExportedFunction("sqlite3_database_file_object")
+	if err := fn.CallWithStack(n.ctx, n.stack[:]); err != nil {
+		panic(err)
+	}
+	file, _ := vfsFileGet(n.ctx, n.mod, uint32(n.stack[0])).(File)
+	return file
+}
+
+// URIParameter returns the value of a URI parameter.
+//
+// https://sqlite.org/c3ref/uri_boolean.html
+func (n *Filename) URIParameter(key string) string {
+	if n == nil || n.zPath == 0 {
+		return ""
+	}
+
+	uriKey := n.mod.ExportedFunction("sqlite3_uri_key")
+	n.stack[0] = uint64(n.zPath)
+	n.stack[1] = uint64(0)
+	if err := uriKey.CallWithStack(n.ctx, n.stack[:]); err != nil {
+		panic(err)
+	}
+
+	ptr := uint32(n.stack[0])
+	if ptr == 0 {
+		return ""
+	}
+
+	// Parse the format from:
+	// https://github.com/sqlite/sqlite/blob/b74eb0/src/pager.c#L4797-L4840
+	// This avoids having to alloc/free the key just to find a value.
+	for {
+		k := util.ReadString(n.mod, ptr, _MAX_NAME)
+		if k == "" {
+			return ""
+		}
+		ptr += uint32(len(k)) + 1
+
+		v := util.ReadString(n.mod, ptr, _MAX_NAME)
+		if k == key {
+			return v
+		}
+		ptr += uint32(len(v)) + 1
+	}
+}
+
+// URIParameters obtains values for URI parameters.
+//
+// https://sqlite.org/c3ref/uri_boolean.html
+func (n *Filename) URIParameters() url.Values {
+	if n == nil || n.zPath == 0 {
+		return nil
+	}
+
+	uriKey := n.mod.ExportedFunction("sqlite3_uri_key")
+	n.stack[0] = uint64(n.zPath)
+	n.stack[1] = uint64(0)
+	if err := uriKey.CallWithStack(n.ctx, n.stack[:]); err != nil {
+		panic(err)
+	}
+
+	ptr := uint32(n.stack[0])
+	if ptr == 0 {
+		return nil
+	}
+
+	var params url.Values
+
+	// Parse the format from:
+	// https://github.com/sqlite/sqlite/blob/b74eb0/src/pager.c#L4797-L4840
+	// This is the only way to support multiple valued keys.
+	for {
+		k := util.ReadString(n.mod, ptr, _MAX_NAME)
+		if k == "" {
+			return params
+		}
+		ptr += uint32(len(k)) + 1
+
+		v := util.ReadString(n.mod, ptr, _MAX_NAME)
+		if params == nil {
+			params = url.Values{}
+		}
+		params.Add(k, v)
+		ptr += uint32(len(v)) + 1
+	}
+}