| 144 | } |
| 145 | |
| 146 | Result<std::string> EncodeMetadata(const KeyValueMetadata& metadata) { |
| 147 | ARROW_ASSIGN_OR_RAISE(auto npairs, DowncastMetadataSize(metadata.size())); |
| 148 | std::string exported; |
| 149 | |
| 150 | // Pre-compute total string size |
| 151 | size_t total_size = 4; |
| 152 | for (int32_t i = 0; i < npairs; ++i) { |
| 153 | total_size += 8 + metadata.key(i).length() + metadata.value(i).length(); |
| 154 | } |
| 155 | exported.resize(total_size); |
| 156 | |
| 157 | char* data_start = &exported[0]; |
| 158 | char* data = data_start; |
| 159 | auto write_int32 = [&](int32_t v) -> void { |
| 160 | memcpy(data, &v, 4); |
| 161 | data += 4; |
| 162 | }; |
| 163 | auto write_string = [&](const std::string& s) -> Status { |
| 164 | ARROW_ASSIGN_OR_RAISE(auto len, DowncastMetadataSize(s.length())); |
| 165 | write_int32(len); |
| 166 | if (len > 0) { |
| 167 | memcpy(data, s.data(), len); |
| 168 | data += len; |
| 169 | } |
| 170 | return Status::OK(); |
| 171 | }; |
| 172 | |
| 173 | write_int32(npairs); |
| 174 | for (int32_t i = 0; i < npairs; ++i) { |
| 175 | RETURN_NOT_OK(write_string(metadata.key(i))); |
| 176 | RETURN_NOT_OK(write_string(metadata.value(i))); |
| 177 | } |
| 178 | DCHECK_EQ(static_cast<size_t>(data - data_start), total_size); |
| 179 | return exported; |
| 180 | } |
| 181 | |
| 182 | struct SchemaExporter { |
| 183 | Status ExportField(const Field& field) { |