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Ethereum: Json analyze with jq andvm.ffi/ffi

When working with data that has been returned from a CAST call, parsing from JSON can be a crucial step towards extracting relevant information. However, if you use the command line tool from JQ or the FFI module (Foreign Function Interface)VM.FFI on Ethereum, you can encounter problems with Parsen from JSON without any obvious mistakes.

In this article we will examine why these methods fail and provide an alternative approach for the desired result.

Why does it fail?

The main problem is how jq andvm.ffi/ffi json data interpret. By default, both tools expect a well -shaped JSON string or object as input. If your cast call returns invalid JSON, these tools increase an error.

In order to overcome this restriction, we can use the “JSON scheme” library to validate the incoming JSON data before we try to analyze it with JQ '. This approach ensures that our data meet the expected formats before trying to extract certain fields.

The solution: UseJsonschemaand vm.Parsejson

We will use the "JSON scheme" library that offers a robust possibility to validate JSON data for a predefined scheme. In addition, we usevm.Parsejson, which enables us to analyze JSON signs directly in C ++ objects.

Here is a sample implementation:

CPP

#include

#include

#include // on the assumption that JSONSCHEMA is installed and linked

// Define our JSON object

Structural data {

Std :: String id;

Std :: Vector Status;

};

int main () {

// sample data from a single call

Json :: value jsondata = json :: arrayvalue;

Jsondata ["id"]. Assstring ("Example ID");

For (size_t i = 0; i

JSON :: VALUE FIELD (Jsondata [i]);

if (field.isobject ()) {

Json :: value status (field);

if (status.isarray ()) {

Status [0] .asstring ("example status");

}

}

}

// validate the JSON data for a scheme

JSONSCHEMAS SHICHE;

schema.loadfromjsonvalue (jsondata);

Std :: String expectation status = "example status";

if (! schema.validate (expectation status)) {

Std :: Cerr << "Invalid Json: expected 'status' to be an array with an element." << STD :: ENDL;

Return 1; // Give back an exit code much zero to display errors

}

// Now we can safely analyze the JSON data with VM.Parsejson

attempt {

Data to Parseeddata;

vm.Parsejson (jsondata.tostostyledstring (), Parseddata);

Std :: cout << "parsed data: id =" << parseddata.id << ", status = [" << parseddata.status [0] << "]" << std :: endl;

} Catch (Const Std :: Exception & e) {

Std :: Cerr << "An error analyze json:" << e.what () << std :: endl;

Return 1; // Give back an exit code much zero to display errors

}

Return 0;

}

In this example, we define our “data structure” with the fields of “ID” and “Status”. Then we create an example -Json object from a occupation call, validate it against a scheme with Json scheme and surely analyze the JSON data with the vm.Parsejson.

Note that in a real scenario you should ensure that your JSON data correspond to the expected format by checking for validation errors or additional checks such as JSON syntax rules.

Diploma

While JQ andvm.ffi/ffican process some JSON inputs, they may not be suitable in all cases. By usingJSONSCHEMEand VM.PARSEJSON` you can create a robust solution for the parsing of JSON data from Cast -Calls on Ethereum.

Remember to always validate your JSON data before trying to analyze them and make sure that the expected structure will be maintained during the entire analysis process.

Feel free to ask whether you have any questions or need further clarification!

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