node/cli: export genesis metadata

This commit adds a new subcommand to the CLI that exports metadata from
the compiled-in runtime, similar to the existing subcommands like
`export-genesis-state` and `export-genesis-wasm`.

A typical usage would be

```bash
sugondat-node export-genesis-metadata --raw binary_metadata.scale
subxt codegen --file binary_metadata.scale | \
	rustfmt --edition=2021 --emit=stdout > src/metadata.rs
```

Ideally, it would be solved by [paritytech/polkadot-sdk#2745] and thus we could
just take the wasm blob (either exported by `export-genesis-wasm`) and just get
it from there via simple of the shelf tools. Until then, we will have this command.

[paritytech/polkadot-sdk#2745]: paritytech/polkadot-sdk#2745

sugondat-chain/node/src/cli.rs

@@ -1,3 +1,4 @@
+use crate::command::export_genesis_metadata;
 use std::path::PathBuf;
 
 /// Sub-commands supported by the collator.
@@ -28,6 +29,10 @@ pub enum Subcommand {
     /// Remove the whole chain.
     PurgeChain(cumulus_client_cli::PurgeChainCmd),
 
+    // intentianally left out: the docs will be generated from the subcommand rustdoc.
+    #[allow(missing_docs)]
+    ExportGenesisMetadata(export_genesis_metadata::ExportGenesisMetadataCmd),
+
     /// Export the genesis state of the parachain.
     ExportGenesisState(cumulus_client_cli::ExportGenesisStateCommand),
 

sugondat-chain/node/src/command.rs

@@ -17,6 +17,8 @@ use crate::{
     service::new_partial,
 };
 
+pub(crate) mod export_genesis_metadata;
+
 fn load_spec(id: &str) -> std::result::Result<Box<dyn ChainSpec>, String> {
     Ok(match id {
         "dev" => Box::new(chain_spec::development_config()),
@@ -168,6 +170,13 @@ pub fn run() -> Result<()> {
 				cmd.run(config, polkadot_config)
 			})
 		},
+        Some(Subcommand::ExportGenesisMetadata(cmd)) => {
+            let runner = cli.create_runner(cmd)?;
+            runner.sync_run(|config| {
+                cmd.run(&config)?;
+                Ok(())
+            })
+        },
 		Some(Subcommand::ExportGenesisState(cmd)) => {
 			let runner = cli.create_runner(cmd)?;
 			runner.sync_run(|config| {

sugondat-chain/node/src/command/export_genesis_metadata.rs

@@ -0,0 +1,70 @@
+use crate::command::new_partial;
+use sc_client_api::HeaderBackend;
+use sc_service::Configuration;
+use sp_api::{Metadata, ProvideRuntimeApi};
+use sp_core::hexdisplay::HexDisplay;
+use std::fs;
+use std::io::{self, Write};
+use std::path::PathBuf;
+
+/// Export the genesis metadata of the parachain.
+///
+/// This will print the metadata into the specified file or stdout if no file is specified. By
+/// default, the metadata is printed in hex format. Use the `--raw` flag to print the metadata in
+/// binary format.
+///
+/// To use it with subxt, you can use the following commands:
+///
+///     $ sugondat-node export-genesis-metadata --raw > metadata.bin
+///     $ subxt codegen --file metadata.bin | rustfmt --edition=2021 --emit=stdout > src/metadata.rs
+///
+#[derive(Debug, clap::Parser)]
+#[clap(verbatim_doc_comment)]
+pub struct ExportGenesisMetadataCmd {
+    #[allow(missing_docs)]
+    #[command(flatten)]
+    pub shared_params: sc_cli::SharedParams,
+
+    /// Output file name or stdout if unspecified.
+    #[arg()]
+    pub output: Option<PathBuf>,
+
+    /// Write output in binary. Default is to write in hex.
+    #[arg(short, long)]
+    pub raw: bool,
+}
+
+impl ExportGenesisMetadataCmd {
+    /// Exports the metadata for the genesis block.
+    ///
+    /// Basically, this returns the metadata returned from the compiled-in runtime.
+    pub fn run(&self, config: &Configuration) -> sc_cli::Result<()> {
+        let partials = new_partial(&config)?;
+        let client = partials.client.clone();
+        let hash = client.info().genesis_hash;
+        let metadata: sp_core::OpaqueMetadata = client
+            .runtime_api()
+            .metadata(hash)
+            .map_err(|e| format!("Failed to fetch metadata from client: {:?}", e))?;
+
+        let output_buf: Vec<u8> = if self.raw {
+            metadata.to_vec()
+        } else {
+            format!("0x{:?}", HexDisplay::from(&*metadata)).into_bytes()
+        };
+
+        if let Some(output) = &self.output {
+            fs::write(output, output_buf)?;
+        } else {
+            io::stdout().write_all(&output_buf)?;
+        }
+
+        Ok(())
+    }
+}
+
+impl sc_cli::CliConfiguration for ExportGenesisMetadataCmd {
+    fn shared_params(&self) -> &sc_cli::SharedParams {
+        &self.shared_params
+    }
+}