docs(java): standardizing fury java spec

docs/protocols/README.md

@@ -1,4 +1,4 @@
 # Serialization Protocols
-- For Java Object Graph Protocol, see [java_object_graph_format](java_object_graph.md) doc.
-- For Cross Language Object Graph Protocol, see [xlang_object_graph_format](./xlang_object_graph.md) doc.
-- For Row Format Protocol, see [row format](./row_format.md) doc.
+- For Java Object Graph Protocol, see [java_object_graph_format_spec](java_object_graph_spec.md) doc.
+- For Cross Language Object Graph Protocol, see [xlang_object_graph_format_spec](./xlang_object_graph.md) doc.
+- For Row Format Protocol, see [row format_spec](./row_format.md) doc.

docs/protocols/java_object_graph.md → docs/protocols/java_object_graph_spec.md

@@ -2,15 +2,26 @@
 
 ## Spec overview
 
-The data are serialized using little endian order overall. If bytes swap is costly, the byte order will be encoded as a
-flag in data.
+Fury Java Serialization is an automatic object serialization framework that supports reference and polymorphism. Fury
+will
+convert an object from/to fury java serialization binary format. Fury has two core concepts for java serialization:
+
+- **Fury Java Binary format**
+- Framework to convert object to/from Fury Java Binary format
 
-The overall format are:
+The serialization format is a dynamic binary format. The dynamics and reference/polymorphism support make Fury flexible,
+much more easy to use, but
+also introduce more complexities compared to static serialization frameworks. So the format will be more complex.
+
+Here is the overall format:
 
 ```
 | fury header | object ref meta | object class meta | object value data |
 ```
 
+The data are serialized using little endian order overall. If bytes swap is costly, the byte order will be encoded as a
+flag in data.
+
 ## Fury header
 
 Fury header consists starts one byte:
@@ -53,8 +64,12 @@ If schema consistent mode is enabled globally or enabled for current class, clas
 
 - If class is registered, it will be written as a little-endian unsigned int: `class_id << 1` using fury unsigned int
   format.
-- If class is not registered, fury will write one byte `0b1` first, the little bit is different first bit of encoded
-  class id, which is `0`. Fury can use this information to determine whether read class by class id.
+- If class is not registered, fury will write one byte `0b01/0b11` first, then write class name.
+    - The higher bit will be 1 if the class is an
+      array, and written class will be the component class. This can reduce array class name cost if component class is
+      serialized before.
+    - The little bit is different first bit of
+      encoded class id, which is `0`. Fury can use this information to determine whether read class by class id.
     - If meta share mode is enabled, class will be written as a unsigned int.
     - If meta share mode is not enabled, class will be written as two enumerated string:
         - package name.
@@ -69,19 +84,49 @@ If schema evolution mode is enabled globally or enabled for current class, class
 - If meta share mode is enabled, class will be written as a unsigned int.
 
 ## Meta share
+
 > This mode will forbid streaming writing since it needs to look back for update the offset after the whole object graph
 > writing and mete collecting is finished.
-> TODO: We have plan to streamline meta writing but not started yet.
+> We have plan to streamline meta writing but haven't started yet.
 
 ### Schema consistent
 
+Class will be encoded as an enumerated string by full class name.
 
 ### Schema evolution
 
+Class meta format:
+
+```
+| meta header: hash + num classes | current class meta | parent class meta | ... |
+```
+
+#### Meta header
+
+Meta header is a 64 bits number value encoded in little endian order.
+
+- Lowest 4 digits `0b0000~0b1111` are used to record num classes. `0b1111` is preserved to indicate that Fury need to
+  read more bytes for length using Fury unsigned int encoding. If current class doesn't has parent class, or parent
+  class doesn't have fields to serialize, or we're in a context which serialize fields of current class
+  only( `ObjectStreamSerializer#SlotInfo` is an example),
+- Other 60 bits is used to store murmur hash of `flags + all layers class meta`. num classes will be 0.
+
+#### Single layer class meta
+
+```
+| enumerated class name string | unsigned int: num fields | field info: type info + field name | next field info | ... |
+```
+
+Type info of custom type field will be written as an one-byte flag instead of inline its meta, because the field value may be null, and Fury can reduce this field type meta writing if object of this type is serialized to in current object graph.
+
+Field order are left as implementation details, which is not exposed to specification, the deserialization need to
+resort fields based on Fury field comparator. In this way, fury can compute statistics for field names or types and
+using a more compact encoding.
 
 ## Enumerated String
 
-Enumerated string are mainly used to encode class name and field names. The format consists of header and binary.
+Enumerated string are mainly used to encode meta string such class name and field names. The format consists of header
+and binary.
 
 Header are written using little endian order, Fury can read this flag first to determine how to deserialize the data.
 
@@ -95,6 +140,16 @@ If string hasn't been written before, the data will be written as follows:
 | unsigned int: string binary size + 1bit: not written before | 61bits: murmur hash + 3 bits encoding flags | string binary |
 ```
 
+Murmur hash can be omitted if caller pass a flag. In such cases, the format will be:
+
+```
+| unsigned int: string binary size + 1bit: not written before | 8 bits encoding flags | string binary |
+```
+
+5 bits in `8 bits encoding flags` will be left empty.
+
+Encoding flags:
+
 | Encoding Flag | Pattern                                                   | Encoding Action                                                                                                                     |
 |---------------|-----------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------|
 | 0             | every char is in `a-z._$\|`                               | `LOWER_SPECIAL`                                                                                                                     |
@@ -104,7 +159,9 @@ If string hasn't been written before, the data will be written as follows:
 | 4             | any utf-8 char                                            | use `UTF-8` encoding                                                                                                                |
 
 #### Write by ref
+
 If string has been written before, the data will be written as follows:
+
 ```
 | unsigned int: written string id + 1bit: written before |
 ```
@@ -186,8 +243,12 @@ String binary encoding:
 
 Format:
 
-- one byte for encoding: 0 for `latin`, 1 for `utf-16`, 2 for `utf-8`.
-- positive varint for encoded string binary length.
+```
+| header: size + encoding | binary data |
+```
+
+- `size + encoding` will be concat as a long and encoded as a unsigned var long. The little 2 bits is used for encoding:
+  0 for `latin`, 1 for `utf-16`, 2 for `utf-8`.
 - encoded string binary data based on encoding: `latin/utf-16/utf-8`.
 
 Which encoding to choose:
@@ -200,7 +261,7 @@ Which encoding to choose:
 
 ### Collection
 
-> All collection serializer must extends `io.fury.serializer.collection.CollectionSerializer`.
+> All collection serializer must extends `AbstractCollectionSerializer`.
 
 Format:
 
@@ -220,11 +281,11 @@ In most cases, all collection elements are same type and not null, elements head
 information to avoid the cost of writing it for every elements. Specifically, there are four kinds of information
 which will be encoded by elements header, each use one bit:
 
-- Whether track elements ref, use first bit `0b1` of header to flag it.
-- Whether collection has null, use second bit `0b10` of header to flag it. If ref tracking is enabled for this
+- If track elements ref, use first bit `0b1` of header to flag it.
+- If collection has null, use second bit `0b10` of header to flag it. If ref tracking is enabled for this
   element type, this flag is invalid.
-- Whether collection elements type is not declare type, use 3rd bit `0b100` of header to flag it.
-- Whether collection elements type different, use 4rd bit `0b1000` of header to flag it.
+- If collection elements type is not declare type, use 3rd bit `0b100` of header to flag it.
+- If collection elements type different, use 4rd bit `0b1000` of header to flag it.
 
 By default, all bits are unset, which means all elements won't track ref, all elements are same type,, not null and the
 actual element is the declare type in custom class field.
@@ -233,24 +294,144 @@ actual element is the declare type in custom class field.
 
 Based on the elements header, the serialization of elements data may skip `ref flag`/`null flag`/`element class info`.
 
-`io.fury.serializer.collection.CollectionSerializer#write/read` can be taken as an example.
+`CollectionSerializer#write/read` can be taken as an example.
 
 ### Array
 
 #### Primitive array
 
+Primitive array are taken as a binary buffer, serialization will just write the length of array size as an unsigned int,
+then copy the whole buffer into the stream.
+
+Such serialization won't compress the array. If users want to compress primitive array, users need to register custom
+serializers for such types.
+
 #### Object array
 
+Object array is serialized using collection format. Object component type will be taken as collection element generic
+type.
+
 ### Map
 
+> All Map serializer must extends `AbstractMapSerializer`.
+
+Format:
+
+```
+| length(unsigned varint) | map header | key value pairs data |
+```
+
+#### Map header
+
+- For `HashMap/LinkedHashMap`, this will be empty.
+- For `TreeMap`, this will be `Comparator`
+- For other `Map`, this may be extra object field info.
+
+#### Map Key-Value data
+
+Map iteration is too expensive, Fury can't compute the header like for collection before since it introduce
+[considerable overhead](https://github.com/alipay/fury/issues/925).
+Users can use `MapFieldInfo` annotation to provide header in advance. Otherwise Fury will use first key-value pair to
+predict header optimistically, and update the chunk header if predict failed at some pair.
+
+Fury will serialize map chunk by chunk, every chunk
+has 127 pairs at most.
+
+```
++----------------+----------------+~~~~~~~~~~~~~~~~~+
+| chunk size: N  |    KV header   |   N*2 objects   |
++----------------+----------------+~~~~~~~~~~~~~~~~~+
+```
+
+KV header:
+
+- If track key ref, use first bit `0b1` of header to flag it.
+- If key has null, use second bit `0b10` of header to flag it. If ref tracking is enabled for this
+  key type, this flag is invalid.
+- If map key type is not declared type, use 3rd bit `0b100` of header to flag it.
+- If map key type different, use 4rd bit `0b1000` of header to flag it.
+- If track value ref, use 5rd bit `0b10000` of header to flag it.
+- If value has null, use 6rd bit `0b100000` of header to flag it. If ref tracking is enabled for this
+  value type, this flag is invalid.
+- If map value type is not declared type, use 7rd bit `0b1000000` of header to flag it.
+- If map value type different, use 8rd bit `0b10000000` of header to flag it.
+
+If streaming write is enabled, which means Fury can't update written `chunk size`. In such cases, map key-value data
+format will be:
+
+```
++----------------+~~~~~~~~~~~~~~~~~+
+|    KV header   |   N*2 objects   |
++----------------+~~~~~~~~~~~~~~~~~+
+```
+
+`KV header` will be header marked by `MapFieldInfo` in java. For languages such as golang, this can be computed in
+advance for non-interface type mostly.
+
 ### Enum
 
-Enum are serialized as an
+Enum are serialized as an unsigned var int. If the order of enum values change, the deserialized enum value may not be
+the value users expect. In such cases, users must register enum serializer by make it write enum value as a enumerated
+string with unique hash disabled.
 
 ### Object
 
+Object means object of `pojo/struct/bean` type.
+Object will be serialized by writing its fields data in fury order.
+
+Depends on schema compatibility, object will have different format.
+
+#### Field order
+
+Field will be ordered as following, every group of fields will have it's own order:
+
+- primitive fields: larger size type first, smaller later, variable size type last.
+- boxed primitive fields: same sort as primitive fields
+- final fields: same type together, then sort by field name lexicographically.
+- collection fields: same sort as final fields
+- map fields: same sort as final fields
+- other fields: same sort as final fields
+
+#### Schema consistent
+
+Object fields will be serialized one by one using following format:
+
+```
+Primitive field value:
++~~~~~~~~~~~~+
+| value data |
++~~~~~~~~~~~~+
+Boxed field value:
++-----------+~~~~~~~~~~~~~+
+| null flag | field value |
++-----------+~~~~~~~~~~~~~+
+field value of final type with ref tracking:
++===========+~~~~~~~~~~~~+
+| ref meta  | value data |
++===========+~~~~~~~~~~~~+
+field value of final type without ref tracking:
++-----------+~~~~~~~~~~~~~+
+| null flag | field value |
++-----------+~~~~~~~~~~~~~+
+field value of non-final type with ref tracking:
++===========+~~~~~~~~~~~~+~~~~~~~~~~~~+
+| ref meta  | class meta | value data |
++===========+~~~~~~~~~~~~+~~~~~~~~~~~~+
+field value of non-final type without ref tracking:
++-----------+~~~~~~~~~~~~+~~~~~~~~~~~~+
+| null flag | class meta | value data |
++-----------+~~~~~~~~~~~~+~~~~~~~~~~~~+
+```
+
+#### Schema evolution
+Schema evolution have similar format as schema consistent mode for object except:
+- For this object type itself, `schema consistent` mode will write class by id/name, but `schema evolution` mode will write class field names, types and other meta too, see [Class meta](#class-meta).
+- Class meta of `final custom type` need to be written too, because peer may not have this class defined. 
+
 ### Class
 
+Class will be serialized using class meta format.
+
 ## Implementation guidelines
 
 - Try to merge multiple bytes into an int/long write before writing to reduce memory IO and bound check cost.