message: Factor out checksum checking from descriptor parsing
diff: @@ -910,22 +910,29 @@ std::unique_ptr<DescriptorImpl> InferScript(const CScript& script, ParseScriptCo
  } // namespace
  -std::unique_ptr<Descriptor> Parse(const std::string& descriptor, FlatSigningProvider& out, bool require_checksum)
  +/** Check a descriptor checksum, and update desc to be the checksum-less part. */
  +bool CheckChecksum(Span<const char>& sp, bool require_checksum, std::string* out_checksum = nullptr)
  {
  - Span<const char> sp(descriptor.data(), descriptor.size());
  -
  - // Checksum checks
  auto check_split = Split(sp, '#');
  - if (check_split.size() > 2) return nullptr; // Multiple '#' symbols
  - if (check_split.size() == 1 && require_checksum) return nullptr; // Missing checksum
  + if (check_split.size() > 2) return false; // Multiple '#' symbols
  + if (check_split.size() == 1 && require_checksum) return false; // Missing checksum
  if (check_split.size() == 2) {
  - if (check_split[1].size() != 8) return nullptr; // Unexpected length for checksum
  + if (check_split[1].size() != 8) return false; // Unexpected length for checksum
  + }
  auto checksum = DescriptorChecksum(check_split[0]);
  - if (checksum.empty()) return nullptr; // Invalid characters in payload
  - if (!std::equal(checksum.begin(), checksum.end(), check_split[1].begin())) return nullptr; // Checksum mismatch
  + if (checksum.empty()) return false; // Invalid characters in payload
  + if (check_split.size() == 2) {
  + if (!std::equal(checksum.begin(), checksum.end(), check_split[1].begin())) return false; // Checksum mismatch
  }
  + if (out_checksum) *out_checksum = std::move(checksum);
  sp = check_split[0];
  + return true;
  +}
  +std::unique_ptr<Descriptor> Parse(const std::string& descriptor, FlatSigningProvider& out, bool require_checksum)
  +{
  + Span<const char> sp(descriptor.data(), descriptor.size());
  + if (!CheckChecksum(sp, require_checksum)) return nullptr;
  auto ret = ParseScript(sp, ParseScriptContext::TOP, out);
  if (sp.size() == 0 && ret) return std::unique_ptr<Descriptor>(std::move(ret));
  return nullptr;
  