A library to aid in the generation and construction of JSON for smart contract development.

Use the library to generate RFC-7159 compliant JSON from within a smart contract.

• Solidity 0.8+

$ npm install solidity-json-writer

Once installed, you can use the library by importing it:

pragma solidity ^0.8.0;

import "solidity-json-writer/contracts/JsonWriter.sol";

contract ExampleContract {
    
    using JsonWriter for JsonWriter.Json;

    function generateJSON() external pure returns (string memory) {
        JsonWriter.Json memory writer;

        writer = writer.writeStartObject();
        writer = writer.writeStringProperty("Product", "PC");
        writer = writer.writeUintProperty("YearsOld", 5);
        writer = writer.writeIntProperty("LowestTemp", -30);
        writer = writer.writeStringProperty("CPU", "Intel");
        writer = writer.writeStartArray("Drives");
        writer = writer.writeStringValue("500 gigabyte SSD");
        writer = writer.writeStringValue("2 terabyte hard drive");
        writer = writer.writeEndArray();
        writer = writer.writeEndObject();

        return writer.value;
    }
}

Output:

{"Product": "PC","YearsOld": 5,"LowestTemp": -30,"CPU": "Intel","Drives": ["500 gigabyte SSD","2 terabyte hard drive"]}

Note: In order to optimize gas, the JSON generated within the smart contract is not pretty-printed.

Pretty-printed output:

{
    "Product": "PC",
    "YearsOld": 5,
    "LowestTemp": -30,
    "CPU": "Intel",
    "Drives": [
	"500 gigabyte SSD", 
	"2 terabyte hard drive"
    ]
}

When using the library to generate JSON for ERC-721 metadata, there are a few things to take into account:

1. If the generated JSON for metadata does not contain RFC-3986 reserved characters, data:application/json, should be prepended to that JSON.
2. If the metadata does contain reserved characters, prepend data:application/json;base64 and then encode the generated JSON as base64.

JsonWriter supports the following Solidity primitives:

• address
• bool
• int
• string
• uint

Although the concept of null does not exist within Solidity, JsonWriter is capable of generating properties and values of null.

The full API documentation for JsonWriter can be found in the docs.

JsonWriter is released under the MIT License.