feat: introduce explicit error handling

Ref n0-computer/iroh#2741

Author: dignifiedquire

Cargo.lock

@@ -27,7 +27,6 @@ unexpected_cfgs = { level = "warn", check-cfg = ["cfg(iroh_docsrs)"] }
 unused-async = "warn"
 
 [dependencies]
-anyhow = { version = "1" }
 erased_set = "0.8"
 http-body-util = "0.1.0"
 hyper = { version = "1", features = ["server", "http1"] }
@@ -37,6 +36,7 @@ prometheus-client = { version = "0.22", optional = true }
 reqwest = { version = "0.12", default-features = false, features = ["json", "rustls-tls"] }
 serde = { version = "1", features = ["derive"] }
 struct_iterable = "0.1"
+thiserror = "2.0.6"
 time = { version = "0.3.21", features = ["serde-well-known"] }
 tokio = { version = "1", features = ["rt", "net", "fs"]}
 tracing = "0.1"

Cargo.toml

@@ -177,10 +177,10 @@ impl Core {
     /// Encodes the current metrics registry to a string in
     /// the prometheus text exposition format.
     #[cfg(feature = "metrics")]
-    pub fn encode(&self) -> Result<String, std::fmt::Error> {
+    pub fn encode(&self) -> String {
         let mut buf = String::new();
-        encode(&mut buf, &self.registry)?;
-        Ok(buf)
+        encode(&mut buf, &self.registry).expect("writing to string always works");
+        buf
     }
 }
 

src/core.rs

@@ -15,6 +15,17 @@ use std::collections::HashMap;
 /// Reexport to make matching versions easier.
 pub use struct_iterable;
 
+/// Potential errors from this library.
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    /// Indicates that the metrics have not been enabled.
+    #[error("Metrics not enabled")]
+    NoMetrics,
+    /// Any IO related error.
+    #[error("IO: {0}")]
+    Io(#[from] std::io::Error),
+}
+
 /// Increment the given counter by 1.
 #[macro_export]
 macro_rules! inc {
@@ -40,7 +51,7 @@ macro_rules! set {
 }
 
 /// Parse Prometheus metrics from a string.
-pub fn parse_prometheus_metrics(data: &str) -> anyhow::Result<HashMap<String, f64>> {
+pub fn parse_prometheus_metrics(data: &str) -> HashMap<String, f64> {
     let mut metrics = HashMap::new();
     for line in data.lines() {
         if line.starts_with('#') {
@@ -57,7 +68,7 @@ pub fn parse_prometheus_metrics(data: &str) -> anyhow::Result<HashMap<String, f6
         }
         metrics.insert(metric.to_string(), value.unwrap());
     }
-    Ok(metrics)
+    metrics
 }
 
 /// Configuration for pushing metrics to a remote endpoint.

src/lib.rs

@@ -54,7 +54,7 @@ use std::net::SocketAddr;
 
 /// Start a server to serve the OpenMetrics endpoint.
 #[cfg(feature = "metrics")]
-pub async fn start_metrics_server(addr: SocketAddr) -> anyhow::Result<()> {
+pub async fn start_metrics_server(addr: SocketAddr) -> std::io::Result<()> {
     crate::service::run(addr).await
 }
 
@@ -63,7 +63,7 @@ pub async fn start_metrics_server(addr: SocketAddr) -> anyhow::Result<()> {
 pub async fn start_metrics_dumper(
     path: std::path::PathBuf,
     interval: std::time::Duration,
-) -> anyhow::Result<()> {
+) -> Result<(), crate::Error> {
     crate::service::dumper(&path, interval).await
 }