why the subxt can not decode metadata

Question

Here is test demo, but always fail to run.

• Cargo.toml

[dependencies]
yew = { version = "0.20.0", features = ["csr"] }
gloo = "0.8.0"
wasm-bindgen-futures = "0.4.32"
subxt = { version="0.27.0", default-features = false, features = ["jsonrpsee-web"] }

• main.rs

use gloo::console::log;
// use sp_keyring::AccountKeyring;
use subxt::{OnlineClient, PolkadotConfig};
use wasm_bindgen_futures;
use yew::prelude::*;

#[subxt::subxt(runtime_metadata_path = "metadata.scale")]
pub mod polkadot {}

#[function_component(App)]
fn app() -> Html {
    wasm_bindgen_futures::spawn_local(async move {
        let api = OnlineClient::<PolkadotConfig>::new().await.unwrap();
        log!("hello world");
    });
    html! {
      <>
          <h1 class="text-3xl font-bold underline bg-slate-100">{"Hello world!"}</h1>
      </>
    }
}

fn main() {
    yew::Renderer::<App>::new().render();
}

The problem is #[subxt::subxt(runtime_metadata_path = "metadata.scale")] pub mod polkadot {} always throw an error

error: Failed to decode metadata: Could not decode `RuntimeMetadataPrefixed.1`:
           Could not decode `RuntimeMetadata`, variant doesn't exist

I think I followed the steps exactly in the official documentation

1. Build a local blockchain
2. run cargo install subxt-cli
3. run subxt metadata -f bytes > metadata.scale

• What steps I forgot and need to do?

Answer 1

1. Build a local blockchain
2. run cargo install subxt-cli
3. run subxt metadata -f bytes > metadata.scale

How are you building/starting a local blockchain node? The error error: Failed to decode metadata: Could not decode RuntimeMetadataPrefixed.1 implies that there is something wrong with your metadata.scale file.

Perhaps you ran into an error running subxt metadata -f bytes > metadata.scale and the file is empty or doesn't have the expected contents in (how big is it? Can you open it with a text editor?). Perhaps the node you started has some sort of issue. I'd need more information to be able to help with this.