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feat(java): type meta encoding for java (#1556)
## What does this PR do? This PR implements type meta encoding for java proposed in #1240 . The type meta encoding in xlang spec proposed in #1413 will be finished in another PR based on this PR. The spec has been updated too: type meta header ``` | 8 bytes meta header | meta size | variable bytes | variable bytes | variable bytes | +-------------------------------+-----------|--------------------+-------------------+----------------+ | 7 bytes hash + 1 bytes header | 1~2 bytes | current class meta | parent class meta | ... | ``` And the encoding for packge/class/field name has been updated to: ``` - Package name encoding(omitted when class is registered): - encoding algorithm: `UTF8/ALL_TO_LOWER_SPECIAL/LOWER_UPPER_DIGIT_SPECIAL` - Header: `6 bits size | 2 bits encoding flags`. The `6 bits size: 0~63` will be used to indicate size `0~62`, the value `63` the size need more byte to read, the encoding will encode `size - 62` as a varint next. - Class name encoding(omitted when class is registered): - encoding algorithm: `UTF8/LOWER_UPPER_DIGIT_SPECIAL/FIRST_TO_LOWER_SPECIAL/ALL_TO_LOWER_SPECIAL` - header: `6 bits size | 2 bits encoding flags`. The `6 bits size: 0~63` will be used to indicate size `1~64`, the value `63` the size need more byte to read, the encoding will encode `size - 63` as a varint next. - Field info: - header(8 bits): `3 bits size + 2 bits field name encoding + polymorphism flag + nullability flag + ref tracking flag`. Users can use annotation to provide those info. - 2 bits field name encoding: - encoding: `UTF8/ALL_TO_LOWER_SPECIAL/LOWER_UPPER_DIGIT_SPECIAL/TAG_ID` - If tag id is used, i.e. field name is written by an unsigned varint tag id. 2 bits encoding will be `11`. - size of field name: - The `3 bits size: 0~7` will be used to indicate length `1~7`, the value `6` the size read more bytes, the encoding will encode `size - 7` as a varint next. - If encoding is `TAG_ID`, then num_bytes of field name will be used to store tag id. - Field name: If type id is set, type id will be used instead. Otherwise meta string encoding length and data will be written instead. ``` ## Meta size Before this PR: ```java class org.apache.fury.benchmark.data.MediaContent 78 class org.apache.fury.benchmark.data.Media 208 class org.apache.fury.benchmark.data.Image 114 ``` With this PR: ```java class org.apache.fury.benchmark.data.MediaContent 53 class org.apache.fury.benchmark.data.Media 114 class org.apache.fury.benchmark.data.Image 68 ``` The size of class meta reduced by half, which is a great gain. The size can be reduded more if we introduce field name hash, but it's not related to this PR. We can discuss it in another PR. ## Related issues #1240 #203 #202 ## Does this PR introduce any user-facing change? <!-- If any user-facing interface changes, please [open an issue](https://github.com/apache/incubator-fury/issues/new/choose) describing the need to do so and update the document if necessary. --> - [ ] Does this PR introduce any public API change? - [ ] Does this PR introduce any binary protocol compatibility change? ## Benchmark <!-- When the PR has an impact on performance (if you don't know whether the PR will have an impact on performance, you can submit the PR first, and if it will have impact on performance, the code reviewer will explain it), be sure to attach a benchmark data here. -->
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