message: [psbt] add file size limit
diff: @@ -39,6 +39,10 @@ static constexpr uint8_t PSBT_OUT_BIP32_DERIVATION = 0x02;
  // as a 0 length key which indicates that this is the separator. The separator has no value.
  static constexpr uint8_t PSBT_SEPARATOR = 0x00;
  +// BIP 174 does not specify a maximum file size, but we set a limit anyway
  +// to prevent reading a stream indefinately and running out of memory.
  +const std::streamsize MAX_FILE_SIZE_PSBT = 100000000; // 100 MiB
  +
  /** A structure for PSBTs which contain per-input information */
  struct PSBTInput
  {
  