refactor: Improve txRaw decoder code (#9769)

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## Description

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ref: #9754 (review)

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(cherry picked from commit 3771ebd)

# Conflicts:
#	x/auth/tx/decoder.go

x/auth/tx/decoder.go

@@ -11,6 +11,15 @@ import (
 // DefaultTxDecoder returns a default protobuf TxDecoder using the provided Marshaler.
 func DefaultTxDecoder(cdc codec.ProtoCodecMarshaler) sdk.TxDecoder {
 	return func(txBytes []byte) (sdk.Tx, error) {
+<<<<<<< HEAD
+=======
+		// Make sure txBytes follow ADR-027.
+		err := rejectNonADR027TxRaw(txBytes)
+		if err != nil {
+			return nil, sdkerrors.Wrap(sdkerrors.ErrTxDecode, err.Error())
+		}
+
+>>>>>>> 3771ebdf2 (refactor: Improve txRaw decoder code (#9769))
 		var raw tx.TxRaw
 
 		// reject all unknown proto fields in the root TxRaw
@@ -79,3 +88,85 @@ func DefaultJSONTxDecoder(cdc codec.ProtoCodecMarshaler) sdk.TxDecoder {
 		}, nil
 	}
 }
+<<<<<<< HEAD
+=======
+
+// rejectNonADR027TxRaw rejects txBytes that do not follow ADR-027. This is NOT
+// a generic ADR-027 checker, it only applies decoding TxRaw. Specifically, it
+// only checks that:
+// - field numbers are in ascending order (1, 2, and potentially multiple 3s),
+// - and varints are as short as possible.
+// All other ADR-027 edge cases (e.g. default values) are not applicable with
+// TxRaw.
+func rejectNonADR027TxRaw(txBytes []byte) error {
+	// Make sure all fields are ordered in ascending order with this variable.
+	prevTagNum := protowire.Number(0)
+
+	for len(txBytes) > 0 {
+		tagNum, wireType, m := protowire.ConsumeTag(txBytes)
+		if m < 0 {
+			return fmt.Errorf("invalid length; %w", protowire.ParseError(m))
+		}
+		// TxRaw only has bytes fields.
+		if wireType != protowire.BytesType {
+			return fmt.Errorf("expected %d wire type, got %d", protowire.BytesType, wireType)
+		}
+		// Make sure fields are ordered in ascending order.
+		if tagNum < prevTagNum {
+			return fmt.Errorf("txRaw must follow ADR-027, got tagNum %d after tagNum %d", tagNum, prevTagNum)
+		}
+		prevTagNum = tagNum
+
+		// All 3 fields of TxRaw have wireType == 2, so their next component
+		// is a varint, so we can safely call ConsumeVarint here.
+		// Byte structure: <varint of bytes length><bytes sequence>
+		// Inner  fields are verified in `DefaultTxDecoder`
+		lengthPrefix, m := protowire.ConsumeVarint(txBytes[m:])
+		if m < 0 {
+			return fmt.Errorf("invalid length; %w", protowire.ParseError(m))
+		}
+		// We make sure that this varint is as short as possible.
+		n := varintMinLength(lengthPrefix)
+		if n != m {
+			return fmt.Errorf("length prefix varint for tagNum %d is not as short as possible, read %d, only need %d", tagNum, m, n)
+		}
+
+		// Skip over the bytes that store fieldNumber and wireType bytes.
+		_, _, m = protowire.ConsumeField(txBytes)
+		if m < 0 {
+			return fmt.Errorf("invalid length; %w", protowire.ParseError(m))
+		}
+		txBytes = txBytes[m:]
+	}
+
+	return nil
+}
+
+// varintMinLength returns the minimum number of bytes necessary to encode an
+// uint using varint encoding.
+func varintMinLength(n uint64) int {
+	switch {
+	// Note: 1<<N == 2**N.
+	case n < 1<<(7):
+		return 1
+	case n < 1<<(7*2):
+		return 2
+	case n < 1<<(7*3):
+		return 3
+	case n < 1<<(7*4):
+		return 4
+	case n < 1<<(7*5):
+		return 5
+	case n < 1<<(7*6):
+		return 6
+	case n < 1<<(7*7):
+		return 7
+	case n < 1<<(7*8):
+		return 8
+	case n < 1<<(7*9):
+		return 9
+	default:
+		return 10
+	}
+}
+>>>>>>> 3771ebdf2 (refactor: Improve txRaw decoder code (#9769))