From 9583f23b1ce4f4cbb11c3ed2b72339e4c2ab4a11 Mon Sep 17 00:00:00 2001
From: Heiko Seeberger <hseeberger@users.noreply.github.com>
Date: Thu, 16 Nov 2023 20:32:17 +0100
Subject: [PATCH] refactor: better main function (#37)

---
 hello-tracing-backend/src/main.rs   | 23 +++++++++--------------
 hello-tracing-common/src/lib.rs     |  2 +-
 hello-tracing-common/src/tracing.rs |  1 +
 hello-tracing-gateway/src/main.rs   | 23 +++++++++--------------
 4 files changed, 20 insertions(+), 29 deletions(-)

diff --git a/hello-tracing-backend/src/main.rs b/hello-tracing-backend/src/main.rs
index 89249bb..9259e2d 100644
--- a/hello-tracing-backend/src/main.rs
+++ b/hello-tracing-backend/src/main.rs
@@ -1,3 +1,5 @@
+#![feature(result_option_inspect)]
+
 mod api;
 
 use anyhow::{Context, Result};
@@ -11,33 +13,26 @@ use std::panic;
 use tracing::{error, info};
 
 #[tokio::main]
-async fn main() {
+async fn main() -> Result<()> {
     // Load configuration first, because needed for tracing initialization.
-    let config = match Config::load().context("load configuration") {
-        Ok(config) => config,
-        Err(error) => {
-            log_error(error);
-            return;
-        }
-    };
+    let config = Config::load()
+        .context("load configuration")
+        .inspect_err(log_error)?;
 
     // If tracing initialization fails, nevertheless emit a structured log event.
-    if let Err(error) = init_tracing(config.tracing.clone()) {
-        log_error(error);
-        return;
-    }
+    init_tracing(config.tracing.clone()).inspect_err(log_error)?;
 
     // Replace the default panic hook with one that uses structured logging at ERROR level.
     panic::set_hook(Box::new(|panic| error!(%panic, "process panicked")));
 
     // Run and log any error.
-    if let Err(error) = run(config).await {
+    run(config).await.inspect_err(|error| {
         error!(
             error = format!("{error:#}"),
             backtrace = %error.backtrace(),
             "process exited with ERROR"
         );
-    };
+    })
 }
 
 #[derive(Debug, Deserialize)]
diff --git a/hello-tracing-common/src/lib.rs b/hello-tracing-common/src/lib.rs
index f539048..c3d691d 100644
--- a/hello-tracing-common/src/lib.rs
+++ b/hello-tracing-common/src/lib.rs
@@ -5,7 +5,7 @@ use time::{format_description::well_known::Rfc3339, OffsetDateTime};
 pub mod otel;
 pub mod tracing;
 
-pub fn log_error(error: impl Display) {
+pub fn log_error(error: &impl Display) {
     let now = OffsetDateTime::now_utc().format(&Rfc3339).unwrap();
     let error = serde_json::to_string(&json!({
         "timestamp": now,
diff --git a/hello-tracing-common/src/tracing.rs b/hello-tracing-common/src/tracing.rs
index cb0d0a3..8a9958c 100644
--- a/hello-tracing-common/src/tracing.rs
+++ b/hello-tracing-common/src/tracing.rs
@@ -6,6 +6,7 @@ use opentelemetry::{
 };
 use opentelemetry_otlp::WithExportConfig;
 use serde::Deserialize;
+
 use tracing::{error, Subscriber};
 use tracing_subscriber::{
     fmt, layer::SubscriberExt, registry::LookupSpan, util::SubscriberInitExt, EnvFilter, Layer,
diff --git a/hello-tracing-gateway/src/main.rs b/hello-tracing-gateway/src/main.rs
index d729550..9bd5b36 100644
--- a/hello-tracing-gateway/src/main.rs
+++ b/hello-tracing-gateway/src/main.rs
@@ -1,3 +1,5 @@
+#![feature(result_option_inspect)]
+
 mod api;
 mod backend;
 
@@ -13,33 +15,26 @@ use std::panic;
 use tracing::{error, info};
 
 #[tokio::main]
-async fn main() {
+async fn main() -> Result<()> {
     // Load configuration first, because needed for tracing initialization.
-    let config = match Config::load().context("load configuration") {
-        Ok(config) => config,
-        Err(error) => {
-            log_error(error);
-            return;
-        }
-    };
+    let config = Config::load()
+        .context("load configuration")
+        .inspect_err(log_error)?;
 
     // If tracing initialization fails, nevertheless emit a structured log event.
-    if let Err(error) = init_tracing(config.tracing.clone()) {
-        log_error(error);
-        return;
-    }
+    init_tracing(config.tracing.clone()).inspect_err(log_error)?;
 
     // Replace the default panic hook with one that uses structured logging at ERROR level.
     panic::set_hook(Box::new(|panic| error!(%panic, "process panicked")));
 
     // Run and log any error.
-    if let Err(error) = run(config).await {
+    run(config).await.inspect_err(|error| {
         error!(
             error = format!("{error:#}"),
             backtrace = %error.backtrace(),
             "process exited with ERROR"
         );
-    };
+    })
 }
 
 #[derive(Debug, Deserialize)]