chore: refresh gramsrv public release

internal/compat/layerwire/fallback.go

@@ -0,0 +1,138 @@
+package layerwire
+
+import "github.com/gotd/td/bin"
+
+// Hand-written transforms for the message subtree: structural changes that are
+// not pure field drops, and 227-only constructors that older clients cannot
+// decode. By-abstract-type fallbacks auto-cover future variants of the same
+// class (e.g. a new MessageAction added in a later layer still degrades to
+// messageActionEmpty). See docs/layer-compat-220-227-design.md §5.2.
+
+const (
+	messageActionEmptyID   = 0xb6aef7b0 // messageActionEmpty = MessageAction
+	messageEntityUnknownID = 0xbb92ba95 // messageEntityUnknown offset:int length:int = MessageEntity
+	pageBlockUnsupportedID = 0x13567e8a // pageBlockUnsupported = PageBlock
+	textEmptyID            = 0xdc3d824f // textEmpty = RichText
+)
+
+func init() {
+	structuralTransforms["pollAnswerVoters"] = transcodePollAnswerVoters
+
+	// 227-only constructors degrade to a class member every supported layer has.
+	// Each target carries no body, so the replacement is a bare id (a new
+	// variant inside a Vector keeps its slot — no element drop needed).
+	newTypeFallbacksByType["MessageAction"] = replaceWithBare(messageActionEmptyID)
+	newTypeFallbacksByType["PageBlock"] = replaceWithBare(pageBlockUnsupportedID)
+	newTypeFallbacksByType["RichText"] = replaceWithBare(textEmptyID)
+	newTypeFallbacksByType["MessageEntity"] = fallbackMessageEntity
+}
+
+// replaceWithBare consumes the canonical (227-only) object and emits a
+// bodyless constructor id the target layer understands.
+func replaceWithBare(id uint32) fallbackFunc {
+	return func(cl *ctorLayout, in, out *bin.Buffer, layer int) error {
+		if err := canonical.skipObject(in); err != nil {
+			return err
+		}
+		out.PutID(id)
+		return nil
+	}
+}
+
+// peerVectorField is a synthetic Vector<Peer> layout used to consume the
+// canonical recent_voters field.
+var peerVectorField = fieldLayout{
+	kind:    kindVector,
+	flagBit: -1,
+	elem:    &fieldLayout{kind: kindObject, typeName: "Peer", flagBit: -1},
+}
+
+// transcodePollAnswerVoters downgrades pollAnswerVoters: canonical (227) made
+// voters conditional (flags.2?int) and added recent_voters (flags.2?Vector<Peer>);
+// older layers carry voters as a plain int. The leading CRC is already consumed.
+//
+//	227: flags:# chosen:flags.0?true correct:flags.1?true option:bytes
+//	     voters:flags.2?int recent_voters:flags.2?Vector<Peer>
+//	<=226: flags:# chosen:flags.0?true correct:flags.1?true option:bytes voters:int
+func transcodePollAnswerVoters(cl *ctorLayout, target uint32, in, out *bin.Buffer, layer int) error {
+	flags, err := in.Uint32()
+	if err != nil {
+		return err
+	}
+	option, err := in.Bytes()
+	if err != nil {
+		return err
+	}
+	var voters int
+	if flags&(1<<2) != 0 {
+		if voters, err = in.Int(); err != nil {
+			return err
+		}
+		if err := canonical.skipValue(in, &peerVectorField); err != nil {
+			return err
+		}
+	}
+	out.PutID(target)
+	out.PutUint32(flags & 0b11) // retain chosen/correct, clear the moved bit 2
+	out.PutBytes(option)
+	out.PutInt(voters)
+	return nil
+}
+
+// fallbackMessageEntity replaces any 227-only MessageEntity with
+// messageEntityUnknown, preserving offset/length so text positions stay valid.
+func fallbackMessageEntity(cl *ctorLayout, in, out *bin.Buffer, layer int) error {
+	id, err := in.PeekID()
+	if err != nil {
+		return err
+	}
+	if err := in.ConsumeID(id); err != nil {
+		return err
+	}
+	offset, length, err := canonical.decodeOffsetLength(in, cl)
+	if err != nil {
+		return err
+	}
+	out.PutID(messageEntityUnknownID)
+	out.PutInt(offset)
+	out.PutInt(length)
+	return nil
+}
+
+// decodeOffsetLength walks a constructor body (no leading CRC) per the canonical
+// layout, returning its offset/length int fields and discarding the rest.
+func (m *schemaModel) decodeOffsetLength(in *bin.Buffer, cl *ctorLayout) (offset, length int, err error) {
+	var flags map[string]uint32
+	for i := range cl.fields {
+		f := &cl.fields[i]
+		if f.isFlags {
+			v, e := in.Uint32()
+			if e != nil {
+				return 0, 0, e
+			}
+			if flags == nil {
+				flags = make(map[string]uint32, 2)
+			}
+			flags[f.name] = v
+			continue
+		}
+		if f.conditional() && flags[f.flagName]&(1<<uint(f.flagBit)) == 0 {
+			continue
+		}
+		switch {
+		case f.kind == kindInt && f.name == "offset":
+			if offset, err = in.Int(); err != nil {
+				return
+			}
+		case f.kind == kindInt && f.name == "length":
+			if length, err = in.Int(); err != nil {
+				return
+			}
+		default:
+			if err = m.skipValue(in, f); err != nil {
+				return
+			}
+		}
+	}
+	return
+}