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Icon LinkJSON ABI Format

The JSON of an ABI is the human-readable representation of the interface of a Sway contract.

Icon LinkNotation

Before describing the format of the JSON ABI, we provide some definitions that will make the JSON ABI spec easier to read.

Given the example below: 

struct Foo { x: bool }
struct Bar<T> { y: T }
 
fn baz(input1: Foo, input2: Bar<u64>); // an ABI function

we define the following expressions:

  • type declaration: the declaration or definition of a type which can be generic. struct Foo { .. } and struct Bar<T> { .. } in the example above are both type declarations.
  • type application: the application or use of a type. Foo and Bar<u64> in fn baz(input1: Foo, input2: Bar<u64>); in the example above are both applications of the type declarations struct Foo { .. } and struct Bar<T> { .. } respectively.
  • type parameter: a generic parameter used in a type declaration. T in struct Bar<T> in the example above is a type parameter.
  • type argument: an application of a type parameter used in a type application. u64 in input2: Bar<u64> in the example above is a type argument.

Icon LinkJSON ABI Spec

The ABI of a contract is represented as a JSON object containing the following properties:

  • "types": an array describing all the type declarations used (or transitively used) in the ABI. Each type declaration is a JSON object that contains the following properties:
    • "typeId": a unique integer ID.
    • "type": a string representation of the type declaration. The section JSON ABI Format for Each Possible Type Declaration specifies the format for each possible type.
    • "components": an array of the components of a given type, if any, and null otherwise. Each component is a type application represented as a JSON object that contains the following properties:
      • "name": the name of the component.
      • "type": the type declaration ID of the type of the component.
      • "typeArguments": an array of the type arguments used when applying the type of the component, if the type is generic, and null otherwise. Each type argument is a type application represented as a JSON object that contains the following properties:
        • "type": the type declaration ID of the type of the type argument.
        • "typeArguments": an array of the type arguments used when applying the type of the type argument, if the type is generic, and null otherwise. The format of the elements of this array recursively follows the rules described in this section.
    • "typeParameters": an array of type IDs of the type parameters of the type, if the type is generic, and null otherwise. Each type parameter is a type declaration and is represented as described in Generic Type Parameter .
  • "functions": an array describing all the functions in the ABI. Each function is a JSON object that contains the following properties:
    • "name": the name of the function
    • "inputs": an array of objects that represents the inputs to the function (i.e. its parameters). Each input is a type application represented as a JSON object that contains the following properties:
      • "name": the name of the input.
      • "type": the type declaration ID of the type of the input.
      • "typeArguments": an array of the type arguments used when applying the type of the input, if the type is generic, and null otherwise. Each type argument is a type application represented as a JSON object that contains the following properties:
        • "type": the type declaration ID of the type of the type argument.
        • "typeArguments": an array of the type arguments used when applying the type of the type argument, if the type is generic, and null otherwise. The format of the elements of this array recursively follows the rules described in this section.
    • "output": an object representing the output of the function (i.e. its return value). The output is a type application, which is a JSON object that contains the following properties:
      • "type": the type declaration ID of the type of the output.
      • "typeArguments": an array of the type arguments used when applying the type of the output, if the type is generic, and null otherwise. Each type argument is a type application represented as a JSON object that contains the following properties:
        • "type": the type declaration ID of the type of the type argument.
        • "typeArguments": an array of the type arguments used when applying the type of the type argument, if the type is generic, and null otherwise. The format of the elements of this array recursively follows the rules described in this section.
    • "attributes": an optional array of attributes. Each attribute is explained in the dedicated section and is represented as a JSON object that contains the following properties:
      • "name": the name of the attribute.
      • "arguments": an array of attribute arguments.
  • "loggedTypes": an array describing all instances of log or logd in the contract's bytecode. Each instance is a JSON object that contains the following properties:
    • "logId": a unique integer ID. The log and logd instructions must set their $rB register to that ID.
    • "loggedType": a type application represented as a JSON object that contains the following properties:
      • "type": the type declaration ID of the type of the value being logged.
      • "typeArguments": an array of the type arguments used when applying the type of the value being logged, if the type is generic, and null otherwise. Each type argument is a type application represented as a JSON object that contains the following properties:
        • "type": the type declaration ID of the type of the type argument.
        • "typeArguments": an array of the type arguments used when applying the type of the type argument, if the type is generic, and null otherwise. The format of the elements of this array recursively follows the rules described in this section.
  • "messagesTypes": an array describing all instances of smo in the contract's bytecode. Each instance is a JSON object that contains the following properties:
    • "messageDataType": a type application represented as a JSON object that contains the following properties:
      • "type": the type declaration ID of the type of the message data being sent.
      • "typeArguments": an array of the type arguments used when applying the type of the message data being sent, if the type is generic, and null otherwise. Each type argument is a type application represented as a JSON object that contains the following properties:
        • "type": the type declaration ID of the type of the type argument.
        • "typeArguments": an array of the type arguments used when applying the type of the type argument, if the type is generic, and null otherwise. The format of the elements of this array recursively follows the rules described in this section.
  • "configurables": an array describing all configurable variables used in the contract. Each configurable variable is represented as a JSON object that contains the following properties:
    • "name": the name of the configurable variable.
    • "configurableType": a type application represented as a JSON object that contains the following properties:
      • "type": the type declaration ID of the type of the configurable variable.
      • "typeArguments": an array of the type arguments used when applying the type of the configurable variable, if the type is generic, and null otherwise. Each type argument is a type application represented as a JSON object that contains the following properties:
        • "type": the type declaration ID of the type of the type argument.
        • "typeArguments": an array of the type arguments used when applying the type of the type argument, if the type is generic, and null otherwise. The format of the elements of this array recursively follows the rules described in this section.
    • "offset": the specific offset within the contract's bytecode, in bytes, to the data section entry for the configurable variable.

Note: This JSON should be both human-readable and parsable by the tooling around the FuelVM and the Sway programming language. There is a detailed specification for the binary encoding backing this readable descriptor. The Function Selector Encoding section specifies the encoding for the function being selected to be executed and each of the argument types.

Icon LinkAttributes Semantics

Attribute nameAttribute argumentsSemantics
storageread and/or writeSpecifies if a function reads or writes to/from storage
payableNoneSpecifies if a function can accept coins: a function without payable attribute must not accept coins
testNoneSpecifies if a function is a unit test
inlinenever or always, but not bothSpecifies if a function should be inlined during code generation
doc-commentStringDocumentation comment
docNot defined yetNot defined yet

Icon LinkA Simple Example

Below is a simple example showing how the JSON ABI for an example that does not use generic or complex types. We will later go over more complex examples. 

abi MyContract {
    fn first_function(arg: u64) -> bool;
    fn second_function(arg: b256);
}

the JSON representation of this ABI looks like: 

{
  "types": [
    {
      "typeId": 0,
      "type": "()",
      "components": [],
      "typeParameters": null
    },
    {
      "typeId": 1,
      "type": "b256",
      "components": null,
      "typeParameters": null
    },
    {
      "typeId": 2,
      "type": "bool",
      "components": null,
      "typeParameters": null
    },
    {
      "typeId": 3,
      "type": "u64",
      "components": null,
      "typeParameters": null
    }
  ],
  "functions": [
    {
      "inputs": [
        {
          "name": "arg",
          "type": 3,
          "typeArguments": null
        }
      ],
      "name": "first_function",
      "output": {
        "type": 2,
        "typeArguments": null
      }
    },
    {
      "inputs": [
        {
          "name": "arg",
          "type": 1,
          "typeArguments": null
        }
      ],
      "name": "second_function",
      "output": {
        "type": 0,
        "typeArguments": null
      }
    }
  ],
  "loggedTypes": []
}

Icon LinkJSON ABI Format for Each Possible Type Declaration

Below is a list of the JSON ABI formats for each possible type declaration:

Icon Link() 

{
  "typeId": <id>,
  "type": "()",
  "components": null,
  "typeParameters": null
}

Icon Linkbool 

{
  "typeId": <id>,
  "type": "bool",
  "components": null,
  "typeParameters": null
}

Icon Linku8 

{
  "typeId": <id>,
  "type": "u8",
  "components": null,
  "typeParameters": null
}

Icon Linku16 

{
  "typeId": <id>,
  "type": "u16",
  "components": null,
  "typeParameters": null
}

Icon Linku32 

{
  "typeId": <id>,
  "type": "u32",
  "components": null,
  "typeParameters": null
}

Icon Linku64 

{
  "typeId": <id>,
  "type": "u64",
  "components": null,
  "typeParameters": null
}

Icon Linkb256 

{
  "typeId": <id>,
  "type": "b256",
  "components": null,
  "typeParameters": null
}

Icon Linkstruct 

{
  "typeId": <id>,
  "type": "struct <struct_name>",
  "components": [
    {
      "name": "<field1_name>",
      "type": <field1_type_id>,
      "typeArguments": [
        {
          "type": <type_arg1_type_id>,
          "typeArguments": ...
        },
        {
          "type": <type_arg2_type_id>,
          "typeArguments": ...
        },
        ...
      ]
    },
    {
      "name": "<field2_name>",
      "type": <field2_type_id>,
      "typeArguments": [
        {
          "type": <type_arg1_type_id>,
          "typeArguments": ...
        },
        {
          "type": <type_arg2_type_id>,
          "typeArguments": ...
        },
        ...
      ]
    },
    ...
  ],
  "typeParameters": [
    <type_param1_type_id>,
    <type_param2_type_id>,
    ...
  ]
}

Icon Linkenum 

{
  "typeId": <id>,
  "type": "enum <enum_name>",
  "components": [
    {
      "name": "<variant1_name>",
      "type": <variant1_type_id>,
      "typeArguments": [
        {
          "type": <type_arg1_type_id>,
          "typeArguments": ...
        },
        {
          "type": <type_arg2_type_id>,
          "typeArguments": ...
        },
        ...
      ]
    },
    {
      "name": "<variant2_name>",
      "type": <variant2_type_id>,
      "typeArguments": [
        {
          "type": <type_arg1_type_id>,
          "typeArguments": ...
        },
        {
          "type": <type_arg2_type_id>,
          "typeArguments": ...
        },
        ...
      ]
    },
    ...
  ],
  "typeParameters": [
    <type_param1_type_id>,
    <type_param2_type_id>,
    ...
  ]
}

Icon Linkstr[<n>] 

{
  "typeId": <id>,
  "type": "str[<n>]",
  "components": null,
  "typeParameters": null
}

<n> is the length of the string.

Icon Linkarray 

{
  "typeId": <id>,
  "type": "[_; <n>]",
  "components": [
    {
      "name": "__array_element",
      "type": "<element_type>",
      "typeArguments": ...
    }
    {
      "name": "__array_element",
      "type": <element_type_id>,
      "typeArguments": [
        {
          "type": <type_arg1_type_id>,
          "typeArguments": ...
        },
        {
          "type": <type_arg2_type_id>,
          "typeArguments": ...
        },
        ...
      ]
    },
 
  ],
  "typeParameters": null
}
  • <n> is the size of the array.

Icon Linktuple 

{
  "typeId": <id>,
  "type": "(_, _, ...)",
  "components": [
    {
      "name": "__tuple_element",
      "type": <field1_type_id>,
      "typeArguments": [
        {
          "type": <type_arg1_type_id>,
          "typeArguments": ...
        },
        {
          "type": <type_arg2_type_id>,
          "typeArguments": ...
        },
        ...
      ]
    },
    {
      "name": "__tuple_element",
      "type": <field2_type_id>,
      "typeArguments": [
        {
          "type": <type_arg1_type_id>,
          "typeArguments": ...
        },
        {
          "type": <type_arg2_type_id>,
          "typeArguments": ...
        },
        ...
      ]
    },
    ...
  ],
  "typeParameters": null
}

Icon LinkGeneric Type Parameter 

{
  "typeId": <id>,
  "type": "generic <name>",
  "components": null,
  "typeParameters": null
}

<name> is the name of the generic parameter as specified in the struct or enum declaration that uses it.

Icon LinkSome Complex Examples

Icon LinkAn Example with Non-Generic Custom Types

Given the following ABI declaration: 

enum MyEnum {
    Foo: u64,
    Bar: bool,
}
 
struct MyStruct {
    bim: u64,
    bam: MyEnum,
}
 
abi MyContract {
    /// this is a doc comment
    #[payable, storage(read, write)]
    fn complex_function(
arg1: ([str[5]; 3], bool, b256),
arg2: MyStruct,
    );
}

its JSON representation would look like: 

{
  "types": [
    {
      "typeId": 0,
      "type": "()",
      "components": [],
      "typeParameters": null
    },
    {
      "typeId": 1,
      "type": "(_, _, _)",
      "components": [
        {
          "name": "__tuple_element",
          "type": 2,
          "typeArguments": null
        },
        {
          "name": "__tuple_element",
          "type": 4,
          "typeArguments": null
        },
        {
          "name": "__tuple_element",
          "type": 3,
          "typeArguments": null
        }
      ],
      "typeParameters": null
    },
    {
      "typeId": 2,
      "type": "[_; 3]",
      "components": [
        {
          "name": "__array_element",
          "type": 6,
          "typeArguments": null
        }
      ],
      "typeParameters": null
    },
    {
      "typeId": 3,
      "type": "b256",
      "components": null,
      "typeParameters": null
    },
    {
      "typeId": 4,
      "type": "bool",
      "components": null,
      "typeParameters": null
    },
    {
      "typeId": 5,
      "type": "enum MyEnum",
      "components": [
        {
          "name": "Foo",
          "type": 8,
          "typeArguments": null
        },
        {
          "name": "Bar",
          "type": 4,
          "typeArguments": null
        }
      ],
      "typeParameters": null
    },
    {
      "typeId": 6,
      "type": "str[5]",
      "components": null,
      "typeParameters": null
    },
    {
      "typeId": 7,
      "type": "struct MyStruct",
      "components": [
        {
          "name": "bim",
          "type": 8,
          "typeArguments": null
        },
        {
          "name": "bam",
          "type": 5,
          "typeArguments": null
        }
      ],
      "typeParameters": null
    },
    {
      "typeId": 8,
      "type": "u64",
      "components": null,
      "typeParameters": null
    }
  ],
  "functions": [
    {
      "inputs": [
        {
          "name": "arg1",
          "type": 1,
          "typeArguments": null
        },
        {
          "name": "arg2",
          "type": 7,
          "typeArguments": null
        }
      ],
      "name": "complex_function",
      "output": {
        "type": 0,
        "typeArguments": null
      },
      "attributes": [
        {
          "name": "doc-comment",
          "arguments": [" this is a doc comment"]
        },
        {
          "name": "payable",
        },
        {
          "name": "storage",
          "arguments": ["read", "write"]
        }
      ]
    }
  ],
  "loggedTypes": []
}

Icon LinkAn Example with Generic Types

Given the following ABI declaration: 

enum MyEnum<T, U> {
    Foo: T,
    Bar: U,
}
struct MyStruct<W> {
    bam: MyEnum<W, W>,
}
 
abi MyContract {
    fn complex_function(
arg1: MyStruct<b256>,
    );
}

its JSON representation would look like: 

{
  "types": [
    {
      "typeId": 0,
      "type": "()",
      "components": [],
      "typeParameters": null
    },
    {
      "typeId": 1,
      "type": "b256",
      "components": null,
      "typeParameters": null
    },
    {
      "typeId": 2,
      "type": "enum MyEnum",
      "components": [
        {
          "name": "Foo",
          "type": 3,
          "typeArguments": null
        },
        {
          "name": "Bar",
          "type": 4,
          "typeArguments": null
        }
      ],
      "typeParameters": [3, 4]
    },
    {
      "typeId": 3,
      "type": "generic T",
      "components": null,
      "typeParameters": null
    },
    {
      "typeId": 4,
      "type": "generic U",
      "components": null,
      "typeParameters": null
    },
    {
      "typeId": 5,
      "type": "generic W",
      "components": null,
      "typeParameters": null
    },
    {
      "typeId": 6,
      "type": "struct MyStruct",
      "components": [
        {
          "name": "bam",
          "type": 2,
          "typeArguments": [
            {
              "type": 5,
              "typeArguments": null
            },
            {
              "type": 5,
              "typeArguments": null
            }
          ]
        }
      ],
      "typeParameters": [5]
    }
  ],
  "functions": [
    {
      "inputs": [
        {
          "name": "arg1",
          "type": 6,
          "typeArguments": [
            {
              "type": 1,
              "typeArguments": null
            }
          ]
        }
      ],
      "name": "complex_function",
      "output": {
        "type": 0,
        "typeArguments": null
      }
    }
  ],
  "loggedTypes": []
}

Icon LinkAn Example with Logs

Given the following contract: 

struct MyStruct<W> {
    x: W,
}
 
abi MyContract {
    fn logging();
}
 
...
 
fn logging() {
    log(MyStruct { x: 42 });
    log(MyStruct { x: true });
}

its JSON representation would look like: 

{
  "types": [
    {
      "typeId": 0,
      "type": "()",
      "components": [],
      "typeParameters": null
    },
    {
      "typeId": 1,
      "type": "bool",
      "components": null,
      "typeParameters": null
    },
    {
      "typeId": 2,
      "type": "generic W",
      "components": null,
      "typeParameters": null
    },
    {
      "typeId": 3,
      "type": "struct MyStruct",
      "components": [
        {
          "name": "x",
          "type": 2,
          "typeArguments": null
        }
      ],
      "typeParameters": [2]
    },
    {
      "typeId": 4,
      "type": "u64",
      "components": null,
      "typeParameters": null
    }
  ],
  "functions": [
    {
      "inputs": [],
      "name": "logging",
      "output": {
        "type": 0,
        "typeArguments": null
      }
    }
  ],
  "loggedTypes": [
    {
      "logId": 0,
      "loggedType": {
        "type": 3,
        "typeArguments": [
          {
            "type": 4,
            "typeArguments": null
          }
        ]
      }
    },
    {
      "logId": 1,
      "loggedType": {
        "type": 3,
        "typeArguments": [
          {
            "type": 1,
            "typeArguments": null
          }
        ]
      }
    }
  ]
}

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