feat: try increasing file descriptor soft limit for service at start

Cargo.toml

@@ -20,6 +20,7 @@ zeroize = { version = "1.7", features = ["derive"] }
 url = "2.5"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
+fdlimit = "0.3"
 
 reqwest = { version = "0.11", default-features = false, features = ["json", "blocking"] }
 jsonrpc-core         = "18.0"

src/cli/serve.rs

@@ -37,6 +37,7 @@ use crate::{
     },
     prelude::*,
     result::{Error, Result},
+    utilities::try_raise_fd_limit,
 };
 
 #[derive(Parser)]
@@ -83,6 +84,8 @@ impl Args {
     pub fn execute(&self) -> Result<()> {
         log::info!("Starting the Bitcoin SPV service");
 
+        try_raise_fd_limit();
+
         let storage = Storage::new(&self.data_dir)?;
         if !storage.is_initialized()? {
             let msg = format!(

src/cli/watch.rs

@@ -8,6 +8,7 @@ use crate::{
     components::{ApiServiceConfig, SpvService, Storage},
     prelude::*,
     result::{Error, Result},
+    utilities::try_raise_fd_limit,
 };
 
 #[derive(Parser)]
@@ -45,6 +46,8 @@ impl Args {
     pub fn execute(&self) -> Result<()> {
         log::info!("Starting the Bitcoin SPV service (readonly)");
 
+        try_raise_fd_limit();
+
         let storage = Storage::new(&self.data_dir)?;
         if !storage.is_initialized()? {
             let msg = format!(

src/components/api_service/mod.rs

@@ -128,7 +128,6 @@ impl SpvRpc for SpvRpcImpl {
         })?;
         log::trace!(">>> tip height in local storage is {stg_tip_height}");
 
-        // TODO Define server errors with enum.
         if stg_tip_height < target_height {
             let desc = format!(
                 "target transaction is in header#{target_height}, \

src/utilities/mod.rs

@@ -1,8 +1,10 @@
 //! Utilities.
 
 mod key;
+mod platform;
 mod type_id;
 pub(crate) mod value_parsers;
 
 pub(crate) use key::Key256Bits;
+pub(crate) use platform::try_raise_fd_limit;
 pub(crate) use type_id::calculate_type_id;

src/utilities/platform.rs

@@ -0,0 +1,17 @@
+//! Enhance the platform environment for continuously running services.
+
+use fdlimit::{raise_fd_limit, Outcome};
+
+pub fn try_raise_fd_limit() {
+    match raise_fd_limit() {
+        Ok(Outcome::LimitRaised { from, to }) => {
+            log::info!("raise file descriptor resource limit from {from} to {to}");
+        }
+        Ok(Outcome::Unsupported) => {
+            log::warn!("raising limit is not supported on this platform");
+        }
+        Err(err) => {
+            log::error!("failed to raise file descriptor resource limit, since {err}");
+        }
+    }
+}