104 lines
3.3 KiB
Markdown
104 lines
3.3 KiB
Markdown
GM Serialization
|
|
=====
|
|
|
|
Serialization helpers for the Gajumaru.
|
|
|
|
Build
|
|
-----
|
|
|
|
$ rebar3 compile
|
|
|
|
|
|
Test
|
|
----
|
|
|
|
$ rebar3 eunit
|
|
|
|
Dynamic encoding
|
|
----
|
|
|
|
The module `gmser_dyn` offers dynamic encoding support, encoding most 'regular'
|
|
Erlang data types into an internal RLP representation.
|
|
|
|
Main API:
|
|
* `encode(term()) -> iolist()`
|
|
* `encode_typed(template(), term()) -> iolist()`
|
|
* `decode(iolist()) -> term()`
|
|
|
|
* `serialize(term()) -> binary()`
|
|
* `serialize_typed(template(), term()) -> binary()`
|
|
* `deserialize(binary()) -> term()`
|
|
|
|
The basic types supported by the encoder are:
|
|
* `non_neg_integer()` (`int` , code: 248)
|
|
* `binary()` (`binary`, code: 249)
|
|
* `boolean()` (`bool` , code: 250)
|
|
* `list()` (`list` , code: 251)
|
|
* `map()` (`map` , code: 252)
|
|
* `tuple()` (`tuple` , code: 253)
|
|
* `gmser_id:id()` (`id` , code: 254)
|
|
* `atom()` (`label` , code: 255)
|
|
|
|
When encoding `map` types, the map elements are first sorted.
|
|
|
|
When specifying a map type for template-driven encoding, use
|
|
the `#{items => [{Key, Value}]}` construct.
|
|
|
|
Labels
|
|
----
|
|
|
|
Labels correspond to (existing) atoms in Erlang.
|
|
Decoding of a label results in a call to `binary_to_existing_atom/2`, so will
|
|
fail if the corresponding atom does not already exist.
|
|
|
|
It's possible to cache labels for more compact encoding.
|
|
Note that when caching labels, the same cache mapping needs to be used on the
|
|
decoder side.
|
|
|
|
Labels are encoded as `[<<255>>, << AtomToBinary/binary >>]`.
|
|
If a cached label is used, the encoding becomes `[<<255>, [Ix]]`, where
|
|
`Ix` is the integer-encoded index value of the cached label.
|
|
|
|
Examples
|
|
----
|
|
|
|
Dynamically encoded objects have the basic structure `[<<0>>,V,Obj]`, where `V` is the
|
|
integer-coded version, and `Obj` is the top-level encoding on the form `[Tag,Data]`.
|
|
|
|
```erlang
|
|
E = fun(T) -> io:fwrite("~w~n", [gmser_dyn:encode(T)]) end.
|
|
|
|
E(17) -> [<<0>>,<<1>>,[<<248>>,<<17>>]]
|
|
E(<<"abc">>) -> [<<0>>,<<1>>,[<<249>>,<<97,98,99>>]]
|
|
E(true) -> [<<0>>,<<1>>,[<<250>>,<<1>>]]
|
|
E(false) -> [<<0>>,<<1>>,[<<250>>,<<0>>]]
|
|
E([1,2]) -> [<<0>>,<<1>>,[<<251>>,[[<<248>>,<<1>>],[<<248>>,<<2>>]]]]
|
|
E({1,2}) -> [<<0>>,<<1>>,[<<253>>,[[<<248>>,<<1>>],[<<248>>,<<2>>]]]]
|
|
E(#{a=>1, b=>2}) ->
|
|
[<<0>>,<<1>>,[<<252>>,[[[<<255>>,<<97>>],[<<248>>,<<1>>]],[[<<255>>,<<98>>],[<<248>>,<<2>>]]]]]
|
|
E(gmser_id:create(account,<<1:256>>)) ->
|
|
[<<0>>,<<1>>,[<<254>>,<<1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1>>]]
|
|
```
|
|
|
|
Note that tuples and list are encoded the same way, except for the initial type tag.
|
|
Maps are encoded as `[<Map>, [KV1, KV2, ...]]`, where `[KV1, KV2, ...]` is the sorted
|
|
list of key-value tuples from `map:to_list(Map)`, but with the `tuple` type tag omitted.
|
|
|
|
Template-driven encoding
|
|
----
|
|
|
|
Templates can be provided to the encoder by either naming an already registered
|
|
type, or by passing a template directly. The template will then be enforced, and
|
|
used to slightly compress the encoding.
|
|
|
|
In the following example, as the encoder knows that `{11,12}` is encoded as a
|
|
tuple of two integers, it can omit the inner type tags.
|
|
|
|
```erlang
|
|
ET = fun(Type,Term) -> io:fwrite("~w~n", [gmser_dyn:encode_typed(Type,Term)]) end.
|
|
|
|
ET({int,int}, {11,12}) ->[<<0>>,<<1>>,[<<253>>,[<<11>>,<<12>>]]]
|
|
ET({int,int}, {11,a}) ->
|
|
** exception error: {illegal,int,a} ...
|
|
```
|