NEP: 14 Title: NeoContract ABI Author: Erik Zhang <[email protected]> Type: Standard Status: Final Created: 2020-03-25 Replaces: 3
An Application Binary Interface (ABI) is the interface between two program modules, one of which is often a library and/or operating system and the other one is usually an application created by a regular programmer.
This NEP describes the ABI standards for NEO smart contracts.
NEO smart contract system is designed to be mutually invocable between contracts. To achieve this, we need a mechanism for exposing the interface of smart contracts. With NeoContract ABI, developers can easily create programs to invoke smart contracts or write clients that automatically access contract functionalities.
We assume the Application Binary Interface (ABI) is strongly typed, known at compilation time and static. No introspection mechanism will be provided. We assert that all contracts will have the interface definitions of any contracts they call available at compile-time.
This specification does not address contracts whose interface is dynamic or otherwise known only at run-time. Should these cases become important they can be adequately handled as facilities built within the NEO ecosystem.
The NeoContract ABI is defined by JSON format, which has the following basic structure, where some of the top-level objects can have any number of child objects:
{
"methods": [],
"events": []
}
methods is an array of Method objects which describe the details of each method in the contract.
events is an array of Event objects which describe the details of each event in the contract.
Method object has the following structure:
{
"name": "transfer",
"offset": 0,
"safe": false,
"parameters": [],
"returntype": "Boolean"
}
name is the name of the method, which can be any valid identifier.
offset is the offset of this method in the script.
safe indicates if it's safe to call this method. If a method is marked as safe, the user interface will not give any warnings when it is called by any other contract.
parameters is an array of Parameter objects which describe the details of each parameter in the method.
returntype indicates the return type of the method. It can be one of the following values: Any, Signature, Boolean, Integer, Hash160, Hash256, ByteArray, PublicKey, String, Array, Map, InteropInterface, Void.
Event object has the following structure:
{
"name": "refund",
"parameters": []
}
name is the name of the event, which can be any valid identifier.
parameters is an array of Parameter objects which describe the details of each parameter in the event.
Parameter object has the following structure:
{
"name": "from",
"type": "Hash160"
}
name is the name of the parameter, which can be any valid identifier.
type indicates the type of the parameter. It can be one of the following values: Any, Signature, Boolean, Integer, Hash160, Hash256, ByteArray, PublicKey, String, Array, Map, InteropInterface.
ParameterType enum has the following values:
| name | description |
|---|---|
| Signature | A signature of a transaction or block which is generated by the user. |
| Boolean |
A boolean value can be either true or false.
|
| Integer | An arbitrarily large integer whose value in theory has no upper or lower bounds. |
| Hash160 | A 160-bits integer. |
| Hash256 | A 256-bits integer. |
| ByteArray | A byte array. |
| PublicKey | An ECC public key which is encoded with compressed mode. |
| String | A string which is encoded in UTF-8. |
| Array | An array of objects. The type of elements can be any value of ParameterType. |
| Map | A map of objects. The type of elements inside the key/value collection can be any value of ParameterType. |
| InteropInterface | An interface which is returned by interop services. |
| Any | Any means that the method will return a value of uncertain type. |
| Void | Void means that the method has no return value. This value cannot be the type of a parameter. |