Add --trace-json option that outputs a JSON trace file

If `--trace-json` option is used, a `trace-TIMESTAMP.json` file will be
created which can be opened by tools like ui.perfetto.dev

Signed-off-by: Marcel Guzik <marcel.guzik@cumulocity.com>

Author: Bravo555

Cargo.lock

@@ -182,6 +182,7 @@ tokio-util = { version = "0.7", features = ["codec"] }
 toml = "0.8"
 tower = "0.4"
 tracing = { version = "0.1", features = ["attributes", "log"] }
+tracing-chrome = "0.7.2"
 tracing-subscriber = { version = "0.3", features = ["time", "env-filter"] }
 try-traits = "0.1"
 tungstenite = "0.20"

Cargo.toml

@@ -35,6 +35,7 @@ tedge_utils = { workspace = true, features = ["timestamp"] }
 thiserror = { workspace = true }
 toml = { workspace = true }
 tracing = { workspace = true }
+tracing-chrome = { workspace = true }
 tracing-subscriber = { workspace = true }
 url = { workspace = true }
 which = { workspace = true }

crates/common/tedge_config/Cargo.toml

@@ -41,6 +41,10 @@ pub struct LogConfigArgs {
     #[clap(long, global = true)]
     #[clap(add(ArgValueCandidates::new(log_level_completions)))]
     pub log_level: Option<tracing::Level>,
+
+    /// Emit a JSON trace file that can be opened by ui.perfetto.dev
+    #[clap(long, global = true)]
+    pub trace_json: bool,
 }
 
 fn log_level_completions() -> Vec<CompletionCandidate> {

crates/common/tedge_config/src/cli.rs

@@ -1,4 +1,5 @@
 use camino::Utf8Path;
+use tracing_chrome::ChromeLayerBuilder;
 use tracing_subscriber::fmt::format::FmtSpan;
 use tracing_subscriber::prelude::*;
 use tracing_subscriber::EnvFilter;
@@ -21,7 +22,7 @@ pub fn log_init(
     sname: &str,
     flags: &LogConfigArgs,
     config_dir: &Utf8Path,
-) -> Result<(), SystemServiceError> {
+) -> Result<Option<tracing_chrome::FlushGuard>, SystemServiceError> {
     let print_file_and_line = std::env::var("RUST_LOG").is_ok();
     let file_level = get_log_level(sname, config_dir)?;
 
@@ -37,9 +38,20 @@ pub fn log_init(
         .with_line_number(print_file_and_line)
         .with_filter(filter_layer);
 
-    tracing_subscriber::registry().with(fmt_layer).init();
+    // chrome layer if `--trace-json`
+    let (chrome_layer, guard) = if flags.trace_json {
+        let (chrome_layer, guard) = ChromeLayerBuilder::new().include_args(true).build();
+        (Some(chrome_layer), Some(guard))
+    } else {
+        (None, None)
+    };
+
+    tracing_subscriber::registry()
+        .with(chrome_layer)
+        .with(fmt_layer)
+        .init();
 
-    Ok(())
+    Ok(guard)
 }
 
 fn filter_layer(flags: &LogConfigArgs, file_level: tracing::Level) -> EnvFilter {

crates/common/tedge_config/src/system_services/log_config.rs

@@ -126,7 +126,7 @@ pub async fn run(mapper_opt: MapperOpt) -> anyhow::Result<()> {
         tedge_config::TEdgeConfigLocation::from_custom_root(&mapper_opt.common.config_dir);
     let config = tedge_config::TEdgeConfig::try_new(tedge_config_location.clone())?;
 
-    log_init(
+    let _guard = log_init(
         "tedge-mapper",
         &mapper_opt.common.log_args,
         &tedge_config_location.tedge_config_root_path,

crates/core/tedge_mapper/src/lib.rs

@@ -410,6 +410,7 @@ mod tests {
                 log_args: LogConfigArgs {
                     debug: false,
                     log_level: None,
+                    trace_json: false,
                 },
                 config_dir: "".into(),
             },