how to transform OpaqueExtrinsic to get the variables within the transaciton?

Question

I'm writing a custom BlockImport and I need to decode the transactions within the block,as we know a transaction is simply a pallet method call for example store_value(value), but at the point where I'm verifying a block all I got is OpaqueExtrinsic which is the transaction encoded.

How can I take that extrinsic and retrieve the parameter value that was passed when the user called my pallet extrinsic store_value(value)?

Extra: in the following code I'm just iterating over all the block extrinsics:

if let Some(block_extrinsics) = &block.body {
    let mut block_extrinsics = block_extrinsics.iter();
    block_extrinsics.next();
    for extrinsic in block_extrinsics {
             // what to do next ¯\_(ツ)_/¯
    }
}

Answer 1

Substrate is build in the way that the runtime and the node are separate from each other. The node should not be able to interpret transaction as the runtime can upgrade at any point, which may also changes the transaction encoding. A proper solution here would be to define your own runtime api. Something like:

sp_api::decl_runtime_apis! {
    trait CheckExtrinsics<Block: BlockT> {
        fn contains_special_extrinsics(extrinsics: Vec<Block::Extrinsic>) -> bool;
    }
}

Then in your code you run this:

if let Some(block_extrinsics) = &block.body
{
    if client.runtime_api().contains_special_extrinsics(block_extrinsics.clone())? {
        // do something
    }
}

In your runtime you then need to implement the runtime api in whatever way you want.