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078bd606c7
Add a new RPC / WS call for `server_definitions`, which returns an
SDK-compatible `definitions.json` (binary enum definitions) generated by
the server. This enables clients/libraries to dynamically work with new
fields and features, such as ones that may become available on side
chains. Clients query `server_definitions` on a node from the network
they want to work with, and immediately know how to speak that node's
binary "language", even if new features are added to it in the future
(as long as there are no new serialized types that the software doesn't
know how to serialize/deserialize).
Example:
```js
> {"command": "server_definitions"}
< {
"result": {
"FIELDS": [
[
"Generic",
{
"isSerialized": false,
"isSigningField": false,
"isVLEncoded": false,
"nth": 0,
"type": "Unknown"
}
],
[
"Invalid",
{
"isSerialized": false,
"isSigningField": false,
"isVLEncoded": false,
"nth": -1,
"type": "Unknown"
}
],
[
"ObjectEndMarker",
{
"isSerialized": false,
"isSigningField": true,
"isVLEncoded": false,
"nth": 1,
"type": "STObject"
}
],
...
```
Close #3657
---------
Co-authored-by: Richard Holland <richard.holland@starstone.co.nz>
protocol
Classes and functions for handling data and values associated with the XRP Ledger protocol.
Serialized Objects
Objects transmitted over the network must be serialized into a canonical format. The prefix "ST" refers to classes that deal with the serialized format.
The term "Tx" or "tx" is an abbreviation for "Transaction", a commonly occurring object type.
Optional Fields
Our serialized fields have some "type magic" to make optional fields easier to read:
- The operation
x[sfFoo]means "return the value of 'Foo' if it exists, or the default value if it doesn't." - The operation
x[~sfFoo]means "return the value of 'Foo' if it exists, or nothing if it doesn't." This usage of the tilde/bitwise NOT operator is not standard outside of therippledcodebase.- As a consequence of this,
x[~sfFoo] = y[~sfFoo]assigns the value of Foo from y to x, including omitting Foo from x if it doesn't exist in y.
- As a consequence of this,
Typically, for things that are guaranteed to exist, you use
x[sfFoo] and avoid having to deal with a container that may
or may not hold a value. For things not guaranteed to exist,
you use x[~sfFoo] because you want such a container. It
avoids having to look something up twice, once just to see if
it exists and a second time to get/set its value.
(Real example)
The source of this "type magic" is in SField.h.