Move Reporter logging of non-200 HTTP responses to debug level (#74)

README.md

@@ -13,3 +13,7 @@ Users of these buildpacks don't need to work with this agent directly.
 
 Users that use custom buildpacks or Heroku's [container runtime](https://devcenter.heroku.com/articles/container-registry-and-runtime) can set up this agent manually to get JVM runtime metrics in
 Heroku's dashboard. Add `-javaagent:/path/to/heroku-metrics-agent.jar` to your main `java` process (i.e. in your app's [Procfile](https://devcenter.heroku.com/articles/procfile) or your Dockerfile's [`CMD` instruction](https://docs.docker.com/engine/reference/builder/#cmd)). It will automatically configure itself when run on Heroku and does nothing when run elsewhere.
+
+## Debugging
+
+To enable more detailed logging, set the `HEROKU_METRICS_DEBUG` environment variable to `true`.

src/main/java/com/heroku/agent/metrics/Logger.java

@@ -15,17 +15,23 @@ public static void logException(String at, Throwable t) {
     }
   }
 
-  public static void logResponseError(String at, String message, long status, String response) {
-    System.out.println(
-        "error at=\""
-            + at
-            + "\" component=heroku-java-metrics-agent message=\""
-            + message
-            + "\" status="
-            + status
-            + " response=\""
-            + response
-            + "\"");
+  public static void logReporterResponseError(
+      String at, String message, long status, String response) {
+    // The metrics endpoint returns 401 and 429 from time to time. These errors aren't harmful as
+    // the request will be automatically retried. Customers previously reported log clutter due to these messages. Since
+    // these errors are not actionable for the customer, we now only log at the debug level.
+    if (isDebugEnabled()) {
+      System.out.println(
+          "debug at=\""
+              + at
+              + "\" component=heroku-java-metrics-agent message=\""
+              + message
+              + "\" status="
+              + status
+              + " response=\""
+              + response
+              + "\"");
+    }
   }
 
   private static String formatLogLine(String level, String at, String message) {

src/main/java/com/heroku/agent/metrics/Reporter.java

@@ -42,11 +42,15 @@ private void sendPost(String jsonString, int remainingRetries) {
       // HTTP client error status codes
       if (responseCode >= 400 && responseCode < 500) {
         try {
-          Logger.logResponseError(
-              "send-post",
-              "upstream service error",
-              responseCode,
-              Utils.readAllUtf8(connection.getInputStream()));
+          InputStream errorStream = connection.getErrorStream();
+          String errorStreamAsString = "<response-without-body>";
+
+          if (errorStream != null) {
+            errorStreamAsString = Utils.readAllUtf8(errorStream);
+          }
+
+          Logger.logReporterResponseError(
+              "send-post", "upstream service error", responseCode, errorStreamAsString);
         } catch (IOException e) {
           Logger.logException("send-post", e);
         }