[pbs-devel] [PATCH proxmox-backup v3 1/1] proxy/parallel_handler: Improved panic errors with formatted strings

[Laurențiu Leahu-Vlăducu]

* Improved errors when panics occur and the panic message is a
formatted (not static) string. This worked already for &str literals,
but not for Strings.

Downcasting to both &str and String is also done by the Rust Standard
Library in the default panic handler. See:
https://github.com/rust-lang/rust/blob/b605c65b6eb5fa71783f8e26df69975f9f1680ee/library/std/src/panicking.rs#L777

* Switched from eprintln! to tracing::error when logging panics in the
task scheduler.

Signed-off-by: Laurențiu Leahu-Vlăducu <l.leahu-vladucu at proxmox.com>
---
 src/bin/proxmox-backup-proxy.rs | 13 +++++++++----
 src/tools/parallel_handler.rs   | 12 ++++++------
 2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/src/bin/proxmox-backup-proxy.rs b/src/bin/proxmox-backup-proxy.rs
index a6d0a332..e9870532 100644
--- a/src/bin/proxmox-backup-proxy.rs
+++ b/src/bin/proxmox-backup-proxy.rs
@@ -422,11 +422,16 @@ async fn run_task_scheduler() {
         tokio::time::sleep_until(tokio::time::Instant::from_std(delay_target)).await;
 
         match schedule_tasks().catch_unwind().await {
-            Err(panic) => match panic.downcast::<&str>() {
-                Ok(msg) => eprintln!("task scheduler panic: {msg}"),
-                Err(_) => eprintln!("task scheduler panic - unknown type"),
+            Err(panic) => {
+                if let Some(msg) = panic.downcast_ref::<&str>() {
+                    tracing::error!("task scheduler panic: {msg}");
+                } else if let Some(msg) = panic.downcast_ref::<String>() {
+                    tracing::error!("task scheduler panic: {msg}");
+                } else {
+                    tracing::error!("task scheduler panic - cannot show error message due to unknown error type")
+                }
             },
-            Ok(Err(err)) => eprintln!("task scheduler failed - {err:?}"),
+            Ok(Err(err)) => tracing::error!("task scheduler failed - {err:?}"),
             Ok(Ok(_)) => {}
         }
     }
diff --git a/src/tools/parallel_handler.rs b/src/tools/parallel_handler.rs
index 17f70179..d8ee3c72 100644
--- a/src/tools/parallel_handler.rs
+++ b/src/tools/parallel_handler.rs
@@ -135,12 +135,12 @@ impl<I: Send + 'static> ParallelHandler<I> {
         let mut i = 0;
         while let Some(handle) = self.handles.pop() {
             if let Err(panic) = handle.join() {
-                match panic.downcast::<&str>() {
-                    Ok(panic_msg) => msg_list.push(format!(
-                        "thread {} ({}) panicked: {}",
-                        self.name, i, panic_msg
-                    )),
-                    Err(_) => msg_list.push(format!("thread {} ({}) panicked", self.name, i)),
+                if let Some(panic_msg) = panic.downcast_ref::<&str>() {
+                    msg_list.push(format!("thread {} ({i}) panicked: {panic_msg}", self.name));
+                } else if let Some(panic_msg) = panic.downcast_ref::<String>() {
+                    msg_list.push(format!("thread {} ({i}) panicked: {panic_msg}", self.name));
+                } else {
+                    msg_list.push(format!("thread {} ({i}) panicked", self.name));
                 }
             }
             i += 1;
-- 
2.39.5