Solidity ABI
Explanations and correlations of Solidity's ABI compared to OrbiterSDK's C++ approach.
Sparq is a native blockchain, which means it has no EVM. However, the vast majority of the smart contract ecossystem operates and depends on Solidity - not only the contracts themselves but also the data they share across each other.
The ABI namespace, declared in contract/abi.h
, contains several functions for Solidity ABI-related operations, for managing and manipulating data in Solidity format.
This is only an overview, check the Doxygen docs for more details on how those classes work.
Solidity types
The Types enum contains the supported Solidity data types in the ABI. Each value has an intrinsic equivalency with both the Solidity data type and the native C++ data type that it represents. BaseTypes is a std::variant
declared in utils.h
that abstracts all of the types in one typedef, for easier handling.
Replace the X in "uintX" and "intX" with the desired size number. The ABI supports every size from 8 to 256 (inclusive), in multiples of 8 (e.g. 8, 16, 24, 32, 40, 48, ..., until 256) - in other words, x <= 256 && x % 8 == 0
. Enums are encoded as uint8.
Enum | Solidity | C++ |
---|---|---|
intX | intX | intX_t |
intXArr | intX[] | std::vector<intX_t> |
uintX | uintX | uintX_t |
uintXArr | uintX[] | std::vector<uintX_t> |
address | address | Address |
addressArr | address[] | std::vector |
boolean | bool | bool |
booleanArr | bool[] | std::vector |
bytes | bytes | Bytes |
bytesArr | bytes[] | std::vector |
string | string | std::string |
stringArr | string[] | std::vector<std::string> |
enum | enum | uint8_t |
MethodDescription and EventDescription
The MethodDescription and EventDescription structs abstract, respectively, the structures for a given Solidity method and Solidity event, such as their name, type, inputs and outputs, state mutability, anonymity and indexations. Those are used extensively by ContractReflectionInterface
and JsonAbi
, to make it easier to pass data around when performing actions like registering the contract and generating ABI for events.
Encoding and decoding
Encoding and decoding ABI data is done by calling the ABI::Encoder::encodeData()
and ABI::Decoder::decodeData()
functions, respectively. The encode function asks for one or more native C++ types, returning a Bytes
object that is the encoded ABI string. The decode function asks for a Bytes
object with the ABI encoded data (and optionally an index for said data), returning a std::tuple
with the decoded native C++ types.
If encoding a function call, ABI::Encoder::encodeFunction()
(which encodes the functor - first 4 bytes of keccak(functionSignature)
) should be called first, then the encoded data should be appended with Utils::appendBytes()
.
Here's an example:
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