Add --trace-tmp

Author: sourcefrog

NEWS.md

@@ -8,6 +8,8 @@
 
 - New: Support for reading and writing archives over SFTP. Credentials currently must come from an sftp-agent.
 
+- New: Added `--trace-tmp`, which writes a detailed trace to a temporary file, whose name is printed to stderr.
+
 ## 24.8.0
 
 - Fixed: `restore --only` specifying a subdirectory no longer fails due to parent directories missing from the destination.

src/bin/conserve.rs

@@ -53,6 +53,10 @@ struct Args {
     #[arg(long, short = 'D', global = true)]
     debug: bool,
 
+    /// Write a detailed trace to a temporary file.
+    #[arg(long, global = true)]
+    trace_tmp: bool,
+
     /// Control timestamps prefixes on stderr.
     #[arg(long, value_enum, global = true, default_value_t = TraceTimeStyle::None)]
     trace_time: TraceTimeStyle,
@@ -714,7 +718,13 @@ fn main() -> Result<ExitCode> {
         Level::INFO
     };
     let monitor = Arc::new(TermUiMonitor::new(!args.no_progress));
-    let _flush_tracing = enable_tracing(&monitor, &args.trace_time, console_level, &args.log_json);
+    let _flush_tracing = enable_tracing(
+        &monitor,
+        &args.trace_time,
+        console_level,
+        &args.log_json,
+        args.trace_tmp,
+    );
     let result = args.command.run(monitor.clone());
     debug!(elapsed = ?start_time.elapsed());
     if let Some(metrics_path) = args.metrics_json {

src/misc.rs

@@ -15,7 +15,6 @@
 
 use std::time::Duration;
 
-
 use crate::stats::Sizes;
 
 pub fn bytes_to_human_mb(s: u64) -> String {

src/termui/trace.rs

@@ -7,7 +7,7 @@ use std::fmt::Debug;
 use std::fs::OpenOptions;
 use std::path::PathBuf;
 
-use tracing::{Level, trace};
+use tracing::{Level, info, trace};
 use tracing_appender::non_blocking::WorkerGuard;
 use tracing_subscriber::{
     Registry, filter,
@@ -35,6 +35,7 @@ pub fn enable_tracing(
     time_style: &TraceTimeStyle,
     console_level: Level,
     json_path: &Option<PathBuf>,
+    trace_tmp: bool,
 ) -> Option<WorkerGuard> {
     let time_style = time_style.clone();
     let console_layer = tracing_subscriber::fmt::Layer::default()
@@ -43,6 +44,23 @@ pub fn enable_tracing(
         .with_timer(time_style)
         .with_filter(filter::Targets::new().with_target("conserve", console_level));
     let json_layer;
+    let (trace_tmp_layer, tmp_path) = if trace_tmp {
+        let (tmp_file, tmp_path) = tempfile::Builder::new()
+            .prefix(&format!("conserve-trace-{}-", std::process::id()))
+            .suffix(".log")
+            .tempfile()
+            .expect("create trace temp file")
+            .keep()
+            .expect("keep trace temp file");
+        let layer = tracing_subscriber::fmt::Layer::default()
+            .with_writer(tmp_file)
+            .with_ansi(false)
+            .with_timer(time::uptime())
+            .with_filter(filter::Targets::new().with_target("conserve", Level::TRACE));
+        (Some(layer), Some(tmp_path))
+    } else {
+        (None, None)
+    };
     let flush_guard;
     if let Some(json_path) = json_path {
         let file_writer = OpenOptions::new()
@@ -65,9 +83,13 @@ pub fn enable_tracing(
     Registry::default()
         .with(console_layer)
         .with(json_layer)
+        .with(trace_tmp_layer)
         .init();
 
     trace!("Tracing enabled");
+    if let Some(tmp_path) = tmp_path {
+        info!("Trace temp file: {}", tmp_path.display());
+    }
     flush_guard
 }
 

tests/cli.rs

@@ -1,5 +1,5 @@
 // Conserve backup system.
-// Copyright 2016-2024 Martin Pool.
+// Copyright 2016-2026 Martin Pool.
 
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of the GNU General Public License as published by

tests/cli_tests/trace.rs

@@ -1,7 +1,10 @@
-// Copyright 2023 Martin Pool
+// Copyright 2023-2026 Martin Pool
 
 //! Tests for trace-related options and behaviors of the Conserve CLI.
 
+use std::fs::read_to_string;
+use std::path::Path;
+
 use assert_cmd::prelude::*;
 use assert_fs::TempDir;
 use assert_fs::prelude::*;
@@ -21,3 +24,28 @@ fn no_trace_timestamps_by_default() {
             "TRACE conserve::termui::trace: Tracing enabled",
         ));
 }
+
+#[test]
+fn trace_to_tmp_file() {
+    let temp_dir = TempDir::new().unwrap();
+    let assert = run_conserve()
+        .args(["init", "--trace-tmp"])
+        .arg(temp_dir.child("archive").path())
+        .assert()
+        .success();
+    let stderr = String::from_utf8(assert.get_output().stderr.clone())
+        .expect("stderr should be valid UTF-8");
+    println!("Stderr output:\n{stderr}");
+    let tmp_file = stderr
+        .lines()
+        .find_map(|line| line.strip_prefix("  INFO conserve::termui::trace: Trace temp file: "))
+        .expect("couldn't extract trace file path from stderr");
+    let tmp_path = Path::new(tmp_file);
+    assert!(tmp_path.exists(), "trace file {tmp_path:?} should exist");
+    let trace_content = read_to_string(tmp_path).expect("read trace file");
+    println!("Trace file content:\n{trace_content}");
+    assert!(
+        trace_content.contains("TRACE conserve::termui::trace: Tracing enabled"),
+        "trace file should contain trace lines"
+    );
+}