feat: add subcommand to provide JSON-RPC APIs without updating any CKB cells

src/cli/init.rs

@@ -89,7 +89,7 @@ pub struct Args {
 
     /// Disable the on-chain difficulty check.
     ///
-    /// Warning
+    /// ### Warning
     ///
     /// For testing purpose only.
     /// Do NOT enable this flag in production environment.

src/cli/mod.rs

@@ -15,6 +15,7 @@ mod deploy;
 mod init;
 mod serve;
 mod sync;
+mod watch;
 
 #[derive(Parser)]
 #[command(author, version, about)]
@@ -33,9 +34,17 @@ pub enum Commands {
     Deploy(deploy::Args),
     /// Initialize a new Bitcoin SPV instance on CKB, and initialize local storage.
     Init(init::Args),
-    /// Run a service to update a Bitcoin SPV instance base on local storage.
+    /// Run a service to update a Bitcoin SPV instance base on local storage,
+    /// and provide JSON-RPC APIs.
+    ///
+    /// If you don't want to update the Bitcoin SPV instance, try the subcommand `watch`.
     Serve(serve::Args),
-    /// Sync data to rebuild local storage base on an existed Bitcoin SPV instance.
+    /// Run a read-only service to provide JSON-RPC APIs,
+    /// without updating for the Bitcoin SPV instance.
+    ///
+    /// If you want to update the Bitcoin SPV instance, try the subcommand `serve`.
+    Watch(watch::Args),
+    /// Sync data to rebuild local storage base on an existed on-chain Bitcoin SPV instance.
     Sync(sync::Args),
 }
 
@@ -121,6 +130,7 @@ impl Cli {
             Commands::Deploy(args) => args.execute()?,
             Commands::Init(args) => args.execute()?,
             Commands::Serve(args) => args.execute()?,
+            Commands::Watch(args) => args.execute()?,
             Commands::Sync(args) => args.execute()?,
         }
         log::info!("Bitcoin SPV on CKB service is stopped.");
@@ -132,6 +142,7 @@ impl Cli {
             Commands::Deploy(ref args) => args.common.configure_logger(),
             Commands::Init(ref args) => args.common.configure_logger(),
             Commands::Serve(ref args) => args.common.configure_logger(),
+            Commands::Watch(ref args) => args.common.configure_logger(),
             Commands::Sync(ref args) => args.common.configure_logger(),
         }
     }

src/cli/watch.rs

@@ -0,0 +1,80 @@
+//! The `watch` sub-command.
+
+use std::{net::SocketAddr, path::PathBuf, thread, time};
+
+use clap::Parser;
+
+use crate::{
+    components::{ApiServiceConfig, SpvService, Storage},
+    prelude::*,
+    result::{Error, Result},
+};
+
+#[derive(Parser)]
+pub struct Args {
+    #[clap(flatten)]
+    pub(crate) common: super::CommonArgs,
+
+    /// The directory, which stores all cached data.
+    #[arg(long)]
+    pub(crate) data_dir: PathBuf,
+
+    #[clap(flatten)]
+    pub(crate) ckb: super::CkbRoArgs,
+
+    #[clap(flatten)]
+    pub(crate) bitcoin: super::BitcoinArgs,
+
+    /// The JSON-RPC server's listen address.
+    #[arg(long)]
+    pub(crate) listen_address: SocketAddr,
+
+    /// A interval in seconds.
+    ///
+    /// - When no better bitcoin blocks, waiting for several seconds.
+    /// - After a CKB transaction is sent, waiting for several seconds.
+    #[arg(long, default_value = "30")]
+    pub(crate) interval: u64,
+
+    /// The batch size that how many Bitcoin headers will be downloaded at once.
+    #[arg(long, default_value = "30")]
+    pub(crate) bitcoin_headers_download_batch_size: u32,
+}
+
+impl Args {
+    pub fn execute(&self) -> Result<()> {
+        log::info!("Starting the Bitcoin SPV service (readonly)");
+
+        let storage = Storage::new(&self.data_dir)?;
+        if !storage.is_initialized()? {
+            let msg = format!(
+                "user-provided data directory \"{}\" is empty, please initialize it",
+                self.data_dir.display()
+            );
+            return Err(Error::other(msg));
+        }
+        let ckb_cli = self.ckb.client();
+        let btc_cli = self.bitcoin.client();
+
+        let spv_service = SpvService {
+            ckb_cli: ckb_cli.clone(),
+            btc_cli: btc_cli.clone(),
+            storage: storage.clone(),
+        };
+
+        let _api_service = ApiServiceConfig::new(self.listen_address).start(spv_service.clone());
+
+        loop {
+            if !spv_service.sync_storage(self.bitcoin_headers_download_batch_size)? {
+                continue;
+            }
+            self.take_a_break();
+        }
+
+        // TODO Handle Ctrl-C and clean resources before exit.
+    }
+
+    fn take_a_break(&self) {
+        thread::sleep(time::Duration::from_secs(self.interval));
+    }
+}