tomd: support sample rates for counters, for issue #10

src/main/java/com/timgroup/statsd/ConvenienceMethodProvidingStatsDClient.java

@@ -6,6 +6,11 @@ public ConvenienceMethodProvidingStatsDClient() {
         super();
     }
 
+    @Override
+    public final void count(String aspect, long delta) {
+        count(aspect, delta, 1.0);
+    }
+
     /**
      * Convenience method equivalent to {@link #count(String, long)} with a value of 1.
      */

src/main/java/com/timgroup/statsd/NoOpStatsDClient.java

@@ -9,7 +9,7 @@
  */
 public final class NoOpStatsDClient extends ConvenienceMethodProvidingStatsDClient {
     @Override public void stop() { }
-    @Override public void count(String aspect, long delta) { }
+    @Override public void count(String aspect, long delta, double sampleRate) { }
     @Override public void recordGaugeValue(String aspect, long value) { }
     @Override public void recordGaugeDelta(String aspect, long delta) { }
     @Override public void recordSetEvent(String aspect, String value) { }

src/main/java/com/timgroup/statsd/NonBlockingStatsDClient.java

@@ -140,10 +140,13 @@ public void stop() {
      *     the name of the counter to adjust
      * @param delta
      *     the amount to adjust the counter by
+     * @param sampleRate
+     *     the sampling rate being employed. For example, a rate of 0.1 would tell StatsD that this counter is being sent
+     *     sampled every 1/10th of the time.
      */
     @Override
-    public void count(String aspect, long delta) {
-        send(messageFor(aspect, delta, "c"));
+    public void count(String aspect, long delta, double sampleRate) {
+        send(messageFor(aspect, delta, "c", sampleRate));
     }
 
     /**
@@ -201,7 +204,12 @@ public void recordExecutionTime(String aspect, long timeInMs) {
     }
 
     private String messageFor(String aspect, Object value, String type) {
-        return String.format("%s%s:%s|%s", prefix, aspect, value, type);
+        return messageFor(aspect, value, type, 1.0);
+    }
+
+    private String messageFor(String aspect, Object value, String type, double sampleRate) {
+        final String messageFormat = (sampleRate == 1.0) ? "%s%s:%s|%s" : "%s%s:%s|%s@%f";
+        return String.format(messageFormat, prefix, aspect, value, type, sampleRate);
     }
 
     private void send(final String message) {

src/main/java/com/timgroup/statsd/StatsDClient.java

@@ -36,6 +36,21 @@ public interface StatsDClient {
      */
     void count(String aspect, long delta);
 
+    /**
+     * Adjusts the specified counter by a given delta.
+     *
+     * <p>This method is non-blocking and is guaranteed not to throw an exception.</p>
+     *
+     * @param aspect
+     *     the name of the counter to adjust
+     * @param delta
+     *     the amount to adjust the counter by
+     * @param sampleRate
+     *     the sampling rate being employed. For example, a rate of 0.1 would tell StatsD that this counter is being sent
+     *     sampled every 1/10th of the time.
+     */
+    void count(String aspect, long delta, double sampleRate);
+
     /**
      * Increments the specified counter by one.
      * 

src/test/java/com/timgroup/statsd/NonBlockingStatsDClientTest.java

@@ -39,6 +39,14 @@ public void stop() throws Exception {
         assertThat(server.messagesReceived(), contains("my.prefix.mycount:9223372036854775807|c"));
     }
 
+    @Test(timeout=5000L) public void
+    sends_counter_value_with_rate_to_statsd() throws Exception {
+        client.count("mycount", Long.MAX_VALUE, 0.00024);
+        server.waitForMessage();
+
+        assertThat(server.messagesReceived(), contains("my.prefix.mycount:9223372036854775807|[email protected]"));
+    }
+
     @Test(timeout=5000L) public void
     sends_counter_increment_to_statsd() throws Exception {
         client.incrementCounter("myinc");