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Improve documentation of definitions.json (#80)

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* Add documentation about type_code

* Clarify "nth"

Co-authored-by: Nathan Nichols <natenichols@cox.net>
This commit is contained in:
Elliot Lee
2020-07-04 12:58:17 -07:00
parent cd0eb2b623
commit 7da60d30b5
1 changed files with 14 additions and 3 deletions
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17
packages/ripple-binary-codec/src/definitions/README.md
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@@ -2,7 +2,7 @@
## Types
These are the [types](https://xrpl.org/serialization.html#type-list) associated with a given Serialization Field
These are the [types](https://xrpl.org/serialization.html#type-list) associated with a given Serialization Field. Each type has an arbitrary [type_code](https://xrpl.org/serialization.html#type-codes), with lower codes sorting first.
## Ledger Entry Types
@@ -18,11 +18,22 @@ The key is the string defined in the rippled source code, such as "LedgerEntry",
### nth
nth is the `index` used to make an [`SField` field code](https://github.com/ripple/rippled/blob/eaff9a0e6aec0ad077f118501791c7684debcfd5/src/ripple/protocol/SField.h#L95-L98).
`nth` is the sort code, meaning "nth of type." It is is combined with the type code in order to construct the Field ID of this field. The Field ID is only used for sorting the fields. Since there are multiple fields with the same data type, the `nth` is used to deterministically order each field among other fields of the same data type.
Each field has a Field ID, which is used to sort fields that have the same type as one another with lower codes sorting first.
- [Field definitions](https://github.com/ripple/rippled/blob/72e6005f562a8f0818bc94803d222ac9345e1e40/src/ripple/protocol/impl/SField.cpp#L72-L266)
- [Constructing the `SField` field codes](https://github.com/ripple/rippled/blob/eaff9a0e6aec0ad077f118501791c7684debcfd5/src/ripple/protocol/SField.h#L95-L98)
For example, the `Account` field has sort code (nth) `1`, so it comes before the `Destination` field which has sort code `3`.
Sort code numbers are reused for fields of different types, but different fields of the same type never have the same sort code. When you combine the type code with the sort code, you get the field's unique _Field ID_.
The unique [Field ID](https://xrpl.org/serialization.html#field-ids) is prefixed before the field in the final serialized blob. The size of the Field ID is one to three bytes depending on the type code and the field codes it combines.
### isVLEncoded
If true, the field is Variable Length encoded. The variable-length encoded fields are `STI_VL`/`Blob`, `STI_ACCOUNT`/`AccountID`, and `STI_VECTOR256`/`Vector256`.
If true, the field is Variable Length encoded and [length-prefixed](https://xrpl.org/serialization.html#length-prefixing). The variable-length encoded fields are `STI_VL`/`Blob`, `STI_ACCOUNT`/`AccountID`, and `STI_VECTOR256`/`Vector256`.
### isSerialized