fix(perf): suppress table output in JSON mode

Suppress table output meant to provide human-friendly visualization
when using the `--json` CLI option and its argument is `-`, that is,
when the JSON output targets stdout.

Fixes #2544.

perf/src/client.rs

@@ -2,6 +2,7 @@
 use std::path::PathBuf;
 use std::{
     net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr},
+    path::Path,
     sync::Arc,
     time::{Duration, Instant},
 };
@@ -166,15 +167,22 @@ pub async fn run(opt: Opt) -> Result<()> {
     let stats_fut = async {
         let interval_duration = Duration::from_secs(opt.interval);
 
+        #[cfg(feature = "json-output")]
+        let allow_table_output = opt.json.clone().is_none_or(|path| path != Path::new("-"));
+        #[cfg(not(feature = "json-output"))]
+        let allow_table_output = true;
+
         loop {
             let start = Instant::now();
             tokio::time::sleep(interval_duration).await;
             {
                 stats.on_interval(start, &stream_stats);
 
-                stats.print();
-                if opt.common.conn_stats {
-                    println!("{:?}\n", connection.stats());
+                if allow_table_output {
+                    stats.print();
+                    if opt.common.conn_stats {
+                        println!("{:?}\n", connection.stats());
+                    }
                 }
             }
         }

perf/src/stats.rs

@@ -120,12 +120,11 @@ impl Stats {
 
     #[cfg(feature = "json-output")]
     pub fn print_json(&self, path: &Path) -> io::Result<()> {
-        match path {
-            path if path == Path::new("-") => json::print(self, std::io::stdout()),
-            _ => {
-                let file = File::create(path)?;
-                json::print(self, file)
-            }
+        if path == Path::new("-") {
+            json::print(self, std::io::stdout());
+        } else {
+            let file = File::create(path)?;
+            json::print(self, file)
         }
         Ok(())
     }