http: emit indented JSON in the metrics stream endpoint

To remove the need to decode and re-encode in the CLI

agent/agent_endpoint.go

@@ -181,7 +181,7 @@ func (s *HTTPHandlers) AgentMetricsStream(resp http.ResponseWriter, req *http.Re
 
 	flusher, ok := resp.(http.Flusher)
 	if !ok {
-		return nil, fmt.Errorf("Streaming not supported")
+		return nil, fmt.Errorf("streaming not supported")
 	}
 
 	resp.WriteHeader(http.StatusOK)
@@ -196,6 +196,7 @@ func (s *HTTPHandlers) AgentMetricsStream(resp http.ResponseWriter, req *http.Re
 		encoder: json.NewEncoder(resp),
 		flusher: flusher,
 	}
+	enc.encoder.SetIndent("", "    ")
 	s.agent.baseDeps.MetricsHandler.Stream(req.Context(), enc)
 	return nil, nil
 }

command/debug/debug.go

@@ -2,6 +2,7 @@ package debug
 
 import (
 	"archive/tar"
+	"bufio"
 	"compress/gzip"
 	"context"
 	"encoding/json"
@@ -529,17 +530,10 @@ func (c *cmd) captureMetrics(ctx context.Context, timestampDir string) error {
 	}
 	defer fh.Close()
 
-	decoder := json.NewDecoder(stream)
-	encoder := json.NewEncoder(fh)
-	// TODO: is More() correct here?
-	for decoder.More() {
-		var raw interface{}
-		if err := decoder.Decode(&raw); err != nil {
-			return fmt.Errorf("failed to decode metrics: %w", err)
-		}
-		if err := encoder.Encode(raw); err != nil {
-			return fmt.Errorf("failed to write metrics to file: %w", err)
-		}
+	b := bufio.NewReader(stream)
+	_, err = b.WriteTo(fh)
+	if err != nil && !errors.Is(err, context.DeadlineExceeded) {
+		return fmt.Errorf("failed to copy metrics to file: %w", err)
 	}
 	return nil
 }