Allow setting host/port without specifying writer type.

dd-trace/src/main/java/com/datadoghq/trace/DDTraceConfig.java

@@ -1,15 +1,19 @@
 package com.datadoghq.trace;
 
+import com.datadoghq.trace.sampling.Sampler;
+import com.datadoghq.trace.writer.DDAgentWriter;
+import com.datadoghq.trace.writer.Writer;
 import java.util.Properties;
 
 /**
- * Config gives priority to system properties and falls back to environment variables.
+ * Config gives priority to system properties and falls back to environment variables. It also
+ * includes default values to ensure a valid config.
  *
  * <p>System properties are {@link DDTraceConfig#PREFIX}'ed. Environment variables are the same as
  * the system property, but uppercased with '.' -> '_'.
  */
 public class DDTraceConfig extends Properties {
-  /** Config keys bel */
+  /** Config keys below */
   private static final String PREFIX = "dd.";
 
   public static final String SERVICE_NAME = "service.name";
@@ -31,9 +35,13 @@ public class DDTraceConfig extends Properties {
 
     final Properties defaults = new Properties();
     defaults.setProperty(SERVICE_NAME, DDTracer.UNASSIGNED_DEFAULT_SERVICE_NAME);
+    defaults.setProperty(WRITER_TYPE, Writer.DD_AGENT_WRITER_TYPE);
+    defaults.setProperty(AGENT_HOST, DDAgentWriter.DEFAULT_HOSTNAME);
+    defaults.setProperty(AGENT_PORT, String.valueOf(DDAgentWriter.DEFAULT_PORT));
+    defaults.setProperty(SAMPLER_TYPE, Sampler.ALL_SAMPLER_TYPE);
+    defaults.setProperty(SAMPLER_RATE, "1.0");
     super.defaults = defaults;
 
-    final Properties baseValues = new Properties(defaults);
     setIfNotNull(SERVICE_NAME, serviceName);
     setIfNotNull(WRITER_TYPE, writerType);
     setIfNotNull(AGENT_HOST, agentHost);
@@ -43,7 +51,7 @@ public class DDTraceConfig extends Properties {
   }
 
   public DDTraceConfig(final String serviceName) {
-    super();
+    this();
     put(SERVICE_NAME, serviceName);
   }
 

dd-trace/src/main/java/com/datadoghq/trace/DDTracer.java

@@ -6,7 +6,6 @@ import com.datadoghq.trace.propagation.HTTPCodec;
 import com.datadoghq.trace.resolver.DDDecoratorsFactory;
 import com.datadoghq.trace.sampling.AllSampler;
 import com.datadoghq.trace.sampling.Sampler;
-import com.datadoghq.trace.writer.DDAgentWriter;
 import com.datadoghq.trace.writer.Writer;
 import com.fasterxml.jackson.annotation.JsonIgnore;
 import io.opentracing.ActiveSpan;
@@ -30,17 +29,14 @@ import lombok.extern.slf4j.Slf4j;
 public class DDTracer extends ThreadLocalActiveSpanSource implements io.opentracing.Tracer {
 
   public static final String UNASSIGNED_DEFAULT_SERVICE_NAME = "unnamed-java-app";
-  public static final Writer UNASSIGNED_WRITER = new DDAgentWriter();
-  public static final Sampler UNASSIGNED_SAMPLER = new AllSampler();
 
+  /** Default service name if none provided on the trace or span */
+  final String serviceName;
   /** Writer is an charge of reporting traces and spans to the desired endpoint */
   final Writer writer;
   /** Sampler defines the sampling policy in order to reduce the number of traces for instance */
   final Sampler sampler;
 
-  /** Default service name if none provided on the trace or span */
-  final String serviceName;
-
   /** Span context decorators */
   private final Map<String, List<AbstractDecorator>> spanContextDecorators = new HashMap<>();
 
@@ -83,11 +79,7 @@ public class DDTracer extends ThreadLocalActiveSpanSource implements io.opentrac
   }
 
   public DDTracer(final Writer writer) {
-    this(writer, new AllSampler());
+    this(UNASSIGNED_DEFAULT_SERVICE_NAME, writer, new AllSampler());
-  }
-
-  public DDTracer(final Writer writer, final Sampler sampler) {
-    this(UNASSIGNED_DEFAULT_SERVICE_NAME, writer, sampler);
   }
 
   /**

dd-trace/src/main/java/com/datadoghq/trace/sampling/AllSampler.java

@@ -6,7 +6,12 @@ import com.datadoghq.trace.DDBaseSpan;
 public class AllSampler extends AbstractSampler {
 
   @Override
-  public boolean doSample(DDBaseSpan<?> span) {
+  public boolean doSample(final DDBaseSpan<?> span) {
     return true;
   }
+
+  @Override
+  public String toString() {
+    return "AllSampler { sample=true }";
+  }
 }

dd-trace/src/main/java/com/datadoghq/trace/sampling/Sampler.java

@@ -2,8 +2,8 @@ package com.datadoghq.trace.sampling;
 
 import com.datadoghq.trace.DDBaseSpan;
 import com.datadoghq.trace.DDTraceConfig;
-import com.datadoghq.trace.DDTracer;
 import java.util.Properties;
+import lombok.extern.slf4j.Slf4j;
 
 /** Main interface to sample a collection of traces. */
 public interface Sampler {
@@ -18,6 +18,7 @@ public interface Sampler {
    */
   boolean sample(DDBaseSpan<?> span);
 
+  @Slf4j
   final class Builder {
     public static Sampler forConfig(final Properties config) {
       final Sampler sampler;
@@ -29,10 +30,15 @@ public interface Sampler {
         } else if (ALL_SAMPLER_TYPE.equals(configuredType)) {
           sampler = new AllSampler();
         } else {
-          sampler = DDTracer.UNASSIGNED_SAMPLER;
+          log.warn(
+              "Sampler type not configured correctly: Type {} not recognized. Defaulting to AllSampler.",
+              configuredType);
+          sampler = new AllSampler();
         }
       } else {
-        sampler = DDTracer.UNASSIGNED_SAMPLER;
+        log.warn(
+            "Sampler type not configured correctly: No config provided! Defaulting to AllSampler.");
+        sampler = new AllSampler();
       }
       return sampler;
     }

dd-trace/src/main/java/com/datadoghq/trace/writer/DDApi.java

@@ -103,9 +103,10 @@ public class DDApi {
         log.debug("Error while sending " + size + " " + type + " to the DD agent.", e);
       } else if (loggingRateLimiter.tryAcquire()) {
         log.warn(
-            "Error while sending {} {} to the DD agent. Message: {} (going silent for {} seconds)",
+            "Error while sending {} {} to the DD agent. {}: {} (going silent for {} seconds)",
             size,
             type,
+            e.getClass().getName(),
             e.getMessage(),
             SECONDS_BETWEEN_ERROR_LOG);
       }

dd-trace/src/main/java/com/datadoghq/trace/writer/ListWriter.java

@@ -63,4 +63,9 @@ public class ListWriter extends CopyOnWriteArrayList<List<DDBaseSpan<?>>> implem
       latches.clear();
     }
   }
+
+  @Override
+  public String toString() {
+    return "ListWriter { size=" + this.size() + " }";
+  }
 }

dd-trace/src/main/java/com/datadoghq/trace/writer/LoggingWriter.java

@@ -30,4 +30,9 @@ public class LoggingWriter implements Writer {
   public void start() {
     log.info("start()");
   }
+
+  @Override
+  public String toString() {
+    return "LoggingWriter { }";
+  }
 }

dd-trace/src/main/java/com/datadoghq/trace/writer/Writer.java

@@ -2,11 +2,11 @@ package com.datadoghq.trace.writer;
 
 import com.datadoghq.trace.DDBaseSpan;
 import com.datadoghq.trace.DDTraceConfig;
-import com.datadoghq.trace.DDTracer;
 import com.datadoghq.trace.Service;
 import java.util.List;
 import java.util.Map;
 import java.util.Properties;
+import lombok.extern.slf4j.Slf4j;
 
 /** A writer is responsible to send collected spans to some place */
 public interface Writer {
@@ -36,6 +36,7 @@ public interface Writer {
    */
   void close();
 
+  @Slf4j
   final class Builder {
     public static Writer forConfig(final Properties config) {
       final Writer writer;
@@ -51,10 +52,19 @@ public interface Writer {
         } else if (LOGGING_WRITER_TYPE.equals(configuredType)) {
           writer = new LoggingWriter();
         } else {
-          writer = DDTracer.UNASSIGNED_WRITER;
+          log.warn(
+              "Writer type not configured correctly: Type {} not recognized. Defaulting to DDAgentWriter.",
+              configuredType);
+          writer =
+              new DDAgentWriter(
+                  new DDApi(
+                      config.getProperty(DDTraceConfig.AGENT_HOST),
+                      Integer.parseInt(config.getProperty(DDTraceConfig.AGENT_PORT))));
         }
       } else {
-        writer = DDTracer.UNASSIGNED_WRITER;
+        log.warn(
+            "Writer type not configured correctly: No config provided! Defaulting to DDAgentWriter.");
+        writer = new DDAgentWriter();
       }
 
       return writer;

dd-trace/src/test/groovy/com/datadoghq/trace/DDTraceConfigTest.groovy

@@ -6,6 +6,7 @@ import com.datadoghq.trace.writer.DDAgentWriter
 import com.datadoghq.trace.writer.ListWriter
 import com.datadoghq.trace.writer.LoggingWriter
 import spock.lang.Specification
+import spock.lang.Unroll
 
 import java.lang.reflect.Field
 import java.lang.reflect.Modifier
@@ -67,22 +68,22 @@ class DDTraceConfigTest extends Specification {
 
     then:
     config.getProperty(SERVICE_NAME) == "unnamed-java-app"
-    config.getProperty(WRITER_TYPE) == null
+    config.getProperty(WRITER_TYPE) == "DDAgentWriter"
-    config.getProperty(AGENT_HOST) == null
+    config.getProperty(AGENT_HOST) == "localhost"
-    config.getProperty(AGENT_PORT) == null
+    config.getProperty(AGENT_PORT) == "8126"
-    config.getProperty(SAMPLER_TYPE) == null
+    config.getProperty(SAMPLER_TYPE) == "AllSampler"
-    config.getProperty(SAMPLER_RATE) == null
+    config.getProperty(SAMPLER_RATE) == "1.0"
 
     when:
     config = new DDTraceConfig("A different service name")
 
     then:
     config.getProperty(SERVICE_NAME) == "A different service name"
-    config.getProperty(WRITER_TYPE) == null
+    config.getProperty(WRITER_TYPE) == "DDAgentWriter"
-    config.getProperty(AGENT_HOST) == null
+    config.getProperty(AGENT_HOST) == "localhost"
-    config.getProperty(AGENT_PORT) == null
+    config.getProperty(AGENT_PORT) == "8126"
-    config.getProperty(SAMPLER_TYPE) == null
+    config.getProperty(SAMPLER_TYPE) == "AllSampler"
-    config.getProperty(SAMPLER_RATE) == null
+    config.getProperty(SAMPLER_RATE) == "1.0"
   }
 
   def "specify overrides via system properties"() {
@@ -144,4 +145,25 @@ class DDTraceConfigTest extends Specification {
 
     tracer.spanContextDecorators.size() == 2
   }
+
+  @Unroll
+  def "verify single override on #source for #key"() {
+    when:
+    System.setProperty(PREFIX + key, value)
+    def tracer = new DDTracer()
+
+    then:
+    tracer."$source".toString() == expected
+
+    where:
+
+    source    | key            | value           | expected
+    "writer"  | "default"      | "default"       | "DDAgentWriter { api=DDApi { tracesEndpoint=http://localhost:8126/v0.3/traces } }"
+    "writer"  | "writer.type"  | "LoggingWriter" | "LoggingWriter { }"
+    "writer"  | "agent.host"   | "somethingelse" | "DDAgentWriter { api=DDApi { tracesEndpoint=http://somethingelse:8126/v0.3/traces } }"
+    "writer"  | "agent.port"   | "9999"          | "DDAgentWriter { api=DDApi { tracesEndpoint=http://localhost:9999/v0.3/traces } }"
+    "sampler" | "default"      | "default"       | "AllSampler { sample=true }"
+    "sampler" | "sampler.type" | "RateSampler"   | "RateSampler { sampleRate=1.0 }"
+    "sampler" | "sampler.rate" | "100"           | "AllSampler { sample=true }"
+  }
 }

dd-trace/src/test/groovy/com/datadoghq/trace/ServiceTest.groovy

@@ -54,7 +54,7 @@ class ServiceTest extends Specification {
 
     setup:
     def writer = spy(new DDAgentWriter())
-    def tracer = new DDTracer(writer, new AllSampler())
+    def tracer = new DDTracer(DDTracer.UNASSIGNED_DEFAULT_SERVICE_NAME, writer, new AllSampler())
 
 
     when:

dd-trace/src/test/java/ExampleWithLoggingWriter.java

@@ -1,37 +0,0 @@
-import com.datadoghq.trace.DDTracer;
-import com.datadoghq.trace.Service;
-import com.datadoghq.trace.sampling.AllSampler;
-import com.datadoghq.trace.writer.LoggingWriter;
-import io.opentracing.Span;
-
-public class ExampleWithLoggingWriter {
-
-  public static void main(final String[] args) throws Exception {
-
-    final DDTracer tracer = new DDTracer(new LoggingWriter(), new AllSampler());
-    tracer.addServiceInfo(new Service("api-intake", "spark", Service.AppType.CACHE));
-
-    final Span parent =
-        tracer.buildSpan("fetch.backend").withServiceName("api-intake").startManual();
-
-    parent.setBaggageItem("scope-id", "a-1337");
-
-    Thread.sleep(100);
-
-    final Span child =
-        tracer
-            .buildSpan("delete.resource")
-            .asChildOf(parent)
-            .withResourceName("delete")
-            .startManual();
-
-    Thread.sleep(100);
-
-    child.finish();
-
-    Thread.sleep(100);
-
-    parent.finish();
-    tracer.close();
-  }
-}

dd-trace/src/test/java/com/datadoghq/trace/DDTracerTest.java

@@ -30,7 +30,7 @@ public class DDTracerTest {
     spans.add(span);
     spans.add(span);
 
-    final DDTracer tracer = new DDTracer(writer, sampler);
+    final DDTracer tracer = new DDTracer(DDTracer.UNASSIGNED_DEFAULT_SERVICE_NAME, writer, sampler);
 
     tracer.write(spans);
     tracer.write(spans);

dd-trace/src/test/java/com/datadoghq/trace/sampling/ExampleWithDDAgentWriter.java

@@ -1,52 +0,0 @@
-package com.datadoghq.trace.sampling;
-
-import com.datadoghq.trace.DDTracer;
-import com.datadoghq.trace.writer.DDAgentWriter;
-import com.datadoghq.trace.writer.Writer;
-import io.opentracing.Span;
-
-public class ExampleWithDDAgentWriter {
-
-  public static void main(final String[] args) throws Exception {
-
-    // Instantiate the DDWriter
-    // By default, traces are written to localhost:8126 (the ddagent)
-    final Writer writer = new DDAgentWriter();
-
-    // Instantiate the proper Sampler
-    // - RateSampler if you want to keep `ratio` traces
-    // - AllSampler to keep all traces
-    final Sampler sampler = new AllSampler();
-
-    // Create the tracer
-    final DDTracer tracer = new DDTracer(writer, sampler);
-
-    final Span parent =
-        tracer
-            .buildSpan("hello-world")
-            .withServiceName("my-service-name")
-            .withSpanType("web")
-            .startManual();
-
-    Thread.sleep(100);
-
-    parent.setBaggageItem("a-baggage", "value");
-
-    final Span child =
-        tracer
-            .buildSpan("hello-world")
-            .asChildOf(parent)
-            .withResourceName("my-resource-name")
-            .startManual();
-
-    Thread.sleep(100);
-
-    child.finish();
-
-    Thread.sleep(100);
-
-    parent.finish();
-
-    writer.close();
-  }
-}