feat : add a debug option

README.md

@@ -33,7 +33,7 @@ The jar is generated in `build/libs/`.
 Attach the agent using the `-javaagent` option and provide arguments as comma-separated `key=value` pairs:
 
 ```sh
-java -javaagent:path/to/flow-agent.jar=target=<prefix[+prefix...]>,out=<dir>[,format=binary|jsonl][,optimize=<dir>][,ids=<file>] \
+java -javaagent:path/to/flow-agent.jar=target=<prefix[+prefix...]>,out=<dir>[,format=binary|jsonl][,optimize=<dir>][,ids=<file>][,bebug=true] \
      -jar your-application.jar
 ```
 
@@ -60,6 +60,9 @@ java -javaagent:path/to/flow-agent.jar=target=<prefix[+prefix...]>,out=<dir>[,fo
 * **`ids`** (optional)
   Path to an existing ID mapping file to reuse.
 
+* **`debug`** (optional)
+  Activate a listener that show instrumentation events and errors
+
 ### Examples
 
 Record calls using the default (binary) format:

src/main/java/fr/bl/drit/flow/agent/AgentMain.java

@@ -91,6 +91,7 @@ private static void init(String agentArgs, Instrumentation inst) {
     final String outputPath = args.get("out");
     final String format = args.getOrDefault("format", "binary");
     final String optimizePath = args.get("optimize");
+    final Boolean debug = args.getOrDefault("debug", "false").equalsIgnoreCase("true");
     String mappingPath = args.get("ids"); // can be overwritten if optimize is used
 
     if (target.isEmpty()) {
@@ -209,9 +210,14 @@ private static void init(String agentArgs, Instrumentation inst) {
                 (builder, typeDescription, classLoader, module, protectionDomain) ->
                     builder.visit(advice.on(methodMatcher)));
 
-    // agentBuilder =
-    // agentBuilder.with(AgentBuilder.Listener.StreamWriting.toSystemOut());
+    // === debug section ===
 
+    // add a listener to print instrumentation events if debug is enabled
+    if (debug) {
+      agentBuilder = agentBuilder.with(AgentBuilder.Listener.StreamWriting.toSystemOut());
+    }
+
+
     agentBuilder.installOn(inst);
   }