Ripple uses a node store, where objects are keyed by a 32byte hash value.
These keys are created by hashing a binary representation of the whole object prefixed with a name-spacing sequence of bytes, unique to each class of object. As such, a method of consistently producing a binary sequence from a given object was required.
Objects have fields, which are a pairing of a type and a name. Names are simply ordinals used to look up preassigned names in a per type table. The type ordinal, similarly, is used to lookup a given class.
In ripple-lib-java the type equates to a SerializedType, with types such as 32
bit unsigned integer, variable length byte strings and even arrays of objects.
The fields have an ordinal quality, and can be deterministically sorted,
important for consistent binary representation.
There are also container types: An STObject, short for SerializedType Object,
is an associative container of fields to other SerializedTypes (even an STObject
itself). An STArray is an array of STObjects with a single Field, mapped to an
STObject, containing an arbitrary amount of Field -> SerializedType pairs. (See
notes below on differences to C++ implementation)
Following is a survey of some of the classes, sorted somewhat topologically.
The following json representation of metadata related to a finalized transaction can be used as a concrete example and will be referenced later.
/**
*
* # Transaction Meta JSON
*
* {
* "TransactionResult": "tesSUCCESS",
*
* {@link com.ripple.core.types.known.tx.result.TransactionResult}
* {@link com.ripple.core.fields.Field.TransactionResult}
* {@link com.ripple.core.coretypes.uint.UInt8}
*
* "TransactionIndex": 0,
*
* {@link com.ripple.core.types.known.tx.result.TransactionMeta#transactionIndex}
* {@link com.ripple.core.coretypes.uint.UInt32}
*
* "AffectedNodes": [
*
* {@link com.ripple.core.types.known.tx.result.TransactionMeta#affectedNodes}
*
* {
* "CreatedNode": {
*
* {@link com.ripple.core.types.known.tx.result.AffectedNode}
* {@link com.ripple.core.types.known.tx.result.AffectedNode#isCreatedNode()}
*
* "NewFields": {
*
* {@link com.ripple.core.types.known.tx.result.AffectedNode#nodeAsFinal()}
*
* "Sequence": 103929,
*
* {@link com.ripple.core.fields.Field#Sequence}
*
*
* "TakerGets": {
*
* {@link com.ripple.core.coretypes.Amount}
*
* "currency": "ILS",
*
* {@link com.ripple.core.coretypes.Currency}
*
* "value": "1694.768",
*
* {@link com.ripple.core.coretypes.AccountID}
*
* "issuer": "rNPRNzBB92BVpAhhZr4iXDTveCgV5Pofm9"
*
* {@link java.math.BigDecimal}
*
* },
*
*
* "Account": "raD5qJMAShLeHZXf9wjUmo6vRK4arj9cF3",
*
* {@link com.ripple.core.coretypes.AccountID}
*
* "BookDirectory": "62A3338CAF2E1BEE510FC33DE1863C56948E962CCE173CA55C14BE8A20D7F000",
*
* {@link com.ripple.core.coretypes.Quality#fromBookDirectory}
*
* "TakerPays": "98957503520",
*
* {@link com.ripple.core.coretypes.Amount}
* {@link com.ripple.core.coretypes.Amount#isNative()}
*
* "OwnerNode": "000000000000000E"
*
* {@link com.ripple.core.types.known.sle.entries.Offer#ownerNodeDirectoryIndex}
* },
*
* "LedgerIndex": "3596CE72C902BAFAAB56CC486ACAF9B4AFC67CF7CADBB81A4AA9CBDC8C5CB1AA",
*
* {@link com.ripple.core.coretypes.hash.Hash256#index}
*
* "LedgerEntryType": "Offer"
*
* {@link com.ripple.core.serialized.enums.LedgerEntryType}
* {@link com.ripple.core.types.known.sle.entries.Offer}
* }
* },
*
*
* {
* "CreatedNode": {
*
* {@link com.ripple.core.types.known.tx.result.AffectedNode}
* {@link com.ripple.core.types.known.tx.result.AffectedNode#isCreatedNode()}
*
* "NewFields": {
*
* {@link com.ripple.core.types.known.tx.result.AffectedNode#nodeAsFinal()}
*
* "RootIndex": "62A3338CAF2E1BEE510FC33DE1863C56948E962CCE173CA55C14BE8A20D7F000",
*
* com.ripple.core.coretypes.hash.Hash256#index
*
* "TakerGetsIssuer": "92D705968936C419CE614BF264B5EEB1CEA47FF4",
*
* {@link com.ripple.core.coretypes.Currency}
* {@link com.ripple.core.coretypes.hash.Hash160}
* {@link com.ripple.core.fields.Field#TakerGetsIssuer}
*
* "ExchangeRate": "5C14BE8A20D7F000",
*
* {@link com.ripple.core.coretypes.Quality#fromBookDirectory}
*
* "TakerGetsCurrency": "000000000000000000000000494C530000000000"
*
* {@link com.ripple.core.coretypes.Currency}
* {@link com.ripple.core.coretypes.hash.Hash160}
* {@link com.ripple.core.fields.Field#TakerGetsCurrency}
*
* },
*
* "LedgerIndex": "62A3338CAF2E1BEE510FC33DE1863C56948E962CCE173CA55C14BE8A20D7F000",
*
* {@link com.ripple.core.coretypes.hash.Hash256#index}
*
* "LedgerEntryType": "DirectoryNode"
*
* {@link com.ripple.core.types.known.sle.entries.DirectoryNode}
* {@link com.ripple.core.serialized.enums.LedgerEntryType#DirectoryNode}
* }
* },
*
* {
* "ModifiedNode": {
*
* {@link com.ripple.core.types.known.tx.result.AffectedNode}
* {@link com.ripple.core.types.known.tx.result.AffectedNode#isModifiedNode()}
*
* "FinalFields": {
*
* {@link com.ripple.core.types.known.tx.result.AffectedNode#nodeAsFinal()}
*
* "RootIndex": "801C5AFB5862D4666D0DF8E5BE1385DC9B421ED09A4269542A07BC0267584B64",
*
* {@link com.ripple.core.types.known.sle.entries.DirectoryNode#rootIndex}
*
* "Flags": 0,
* "Owner": "raD5qJMAShLeHZXf9wjUmo6vRK4arj9cF3",
*
* {@link com.ripple.core.coretypes.hash.Index#ownerDirectory}
*
* "IndexPrevious": "0000000000000000"
*
* {@link com.ripple.core.types.known.sle.entries.DirectoryNode#hasPreviousIndex}
* {@link com.ripple.core.types.known.sle.entries.DirectoryNode#prevIndex}
* },
*
* "LedgerIndex": "AB03F8AA02FFA4635E7CE2850416AEC5542910A2B4DBE93C318FEB08375E0DB5",
*
* "LedgerEntryType": "DirectoryNode"
* }
* },
* {
* "ModifiedNode": {
*
* {@link com.ripple.core.types.known.tx.result.AffectedNode}
* {@link com.ripple.core.types.known.tx.result.AffectedNode#isModifiedNode()}
*
* "FinalFields": {
*
* {@link com.ripple.core.types.known.tx.result.AffectedNode#nodeAsFinal()}
*
* "Sequence": 103930,
* "Flags": 0,
* "Account": "raD5qJMAShLeHZXf9wjUmo6vRK4arj9cF3",
* "OwnerCount": 9,
* "Balance": "106861218302"
*
* {@link com.ripple.core.coretypes.Amount}
* },
*
* "LedgerIndex": "CF23A37E39A571A0F22EC3E97EB0169936B520C3088963F16C5EE4AC59130B1B",
*
* {@link com.ripple.core.coretypes.hash.Index#accountRoot}
*
* "LedgerEntryType": "AccountRoot",
*
* {@link com.ripple.core.types.known.sle.entries.AccountRoot}
* {@link com.ripple.core.serialized.enums.LedgerEntryType#AccountRoot}
*
* "PreviousFields": {
*
* {@link com.ripple.core.types.known.tx.result.AffectedNode#nodeAsPrevious()}
*
* "Sequence": 103929,
* "OwnerCount": 8,
* "Balance": "106861218312"
* },
*
* "PreviousTxnID": "DE15F43F4A73C4F6CB1C334D9E47BDE84467C0902796BB81D4924885D1C11E6D",
*
* {@link com.ripple.core.types.known.tx.Transaction#hash}
*
* "PreviousTxnLgrSeq": 3225338
*
* {@link com.ripple.core.coretypes.uint.UInt32}
* }
* }
* ]
* }
*/-
Note that ALL field names are, by convention, upper case (in fact field names (index, hash) may be lower cased but are not serialized)
-
The
AffectedNodesis an STArray. As stated, the immediate children each contain only a single key (or Field)- CreatedNode
- ModifiedNode
Moving on.
com
└── ripple
├── serialized
├── core
│
├── enums
│ ├── LedgerEntryType
│ ├── EngineResult
│ └── TransactionType
- In the json above look at the TransactionResult field. Note that it has a Type of of UINT8, yet clearly it's represented in json as a string.
This is a simple Java enum(eration) of the various types. eg.
UINT32(2)
This definition implies giving the static ordinal 2 to the UINT32 type.
Consider the following definition of a field
QualityIn(20, Type.UINT32)
As stated before a Field has name and type ordinals, but it also has an implied symbolic string representation (as seen used in the json above)
The string name can be looked up via a code, which is an integer created by
shifting the type ordinal 16 bits to the left and ORing it with the name.
See: com.ripple.core.fields.Field#fromCode
This is simply an interface for returning a Field. We know that a Field implies a Type and a name and there's a set amount of them. For each concrete class implementation of a given Type, we create a XXXfield class that implements HasField
eg.
protected abstract static class STArrayField implements HasField{}
public static STArrayField starrayField(final Field f) {
return new STArrayField(){ @Override public Field getField() {return f;}};
}Then we can create static members on the concrete class
static public STArrayField AffectedNodes = starrayField(Field.AffectedNodes);
static public STArrayField Signatures = starrayField(Field.Signatures);
static public STArrayField Template = starrayField(Field.Template);Later this is used create an api that looks as so
if (transactionType() == TransactionType.Payment && meta.has(STArray.AffectedNodes)) {
STArray affected = meta.get(STArray.AffectedNodes);
for (STObject node : affected) {
if (node.has(STObject.CreatedNode)) {
STObject created = node.get(STObject.CreatedNode);This is implemented by overloading get()
public STArray get(STArray.STArrayField f) {
return (STArray) fields.get(f.getField());
}public interface SerializedType {
Object toJSON();
byte[] toBytes();
String toHex();
void toBytesSink(BytesSink to);
Type type();
}A dynamic array of byte[]. Used by TypeTranslators to avoid needless copying (see fromParser(parser, hint)).
Responsible for decoding Fields and VL encoded structures.
Handles converting a SerializedType instances to/from json, binary and other non SerializedType values.
Has methods like fromHex, fromBytes, which delegate to fromParser.
Responsible for encoding Fields/SerializeType into binary.
-
In the C++ implementation of serialized objects, an STObject can, itself, be assigned a Field, which is stored outside of the associative structure.
This is problematic when storing as json. Consider this pseudocode.
>>> so = STObject() >>> so.name = "FieldName" >>> so["FieldOfDreams"] = "A Kevin Costner Movie" >>> sa = STArray([so])
How could
sabe declared as json?>>> [{"FieldName" : {"FieldOfDreams": "A Kevin Costner Movie"}}]This is in fact how rippled works. There is no 1:1 mapping of STObject to {}
In ripple-lib(-java)? there is, and single key children of STArrays are enforced.
-
Ripple uses 32 byte hashes for object indexes, taking half of a SHA512 hash, which is ~%33 faster than SHA256.
-
Simply using google protocol buffers was considered inadequate link