From 8209a8830c0d2f82c45036f5082c57660abe2061 Mon Sep 17 00:00:00 2001
From: Nikolay Martynov <nikolay.martynov@datadoghq.com>
Date: Thu, 20 Feb 2020 07:20:08 -0500
Subject: [PATCH] Determine agent URL version on first upload call

This should remove http request from critical path during app load
---
 .../common/writer/ddagent/DDAgentApi.java     | 40 ++++++++++---------
 .../trace/api/writer/DDAgentApiTest.groovy    | 18 ++++++---
 2 files changed, 33 insertions(+), 25 deletions(-)

diff --git a/dd-trace-ot/src/main/java/datadog/trace/common/writer/ddagent/DDAgentApi.java b/dd-trace-ot/src/main/java/datadog/trace/common/writer/ddagent/DDAgentApi.java
index a0a0f7ad02..ab1ab439dd 100644
--- a/dd-trace-ot/src/main/java/datadog/trace/common/writer/ddagent/DDAgentApi.java
+++ b/dd-trace-ot/src/main/java/datadog/trace/common/writer/ddagent/DDAgentApi.java
@@ -60,30 +60,18 @@ public class DDAgentApi {
                   Types.newParameterizedType(Map.class, String.class, Double.class)));
   private static final MediaType MSGPACK = MediaType.get("application/msgpack");
 
+  private final String host;
+  private final int port;
+  private final String unixDomainSocketPath;
   private final OkHttpClient httpClient;
-  private final HttpUrl tracesUrl;
+  private HttpUrl tracesUrl;
 
   public DDAgentApi(final String host, final int port, final String unixDomainSocketPath) {
-    this(
-        host,
-        port,
-        endpointAvailable(getUrl(host, port, TRACES_ENDPOINT_V4), unixDomainSocketPath, true),
-        unixDomainSocketPath);
-  }
+    this.host = host;
+    this.port = port;
+    this.unixDomainSocketPath = unixDomainSocketPath;
 
-  DDAgentApi(
-      final String host,
-      final int port,
-      final boolean v4EndpointsAvailable,
-      final String unixDomainSocketPath) {
     httpClient = buildHttpClient(unixDomainSocketPath);
-
-    if (v4EndpointsAvailable) {
-      tracesUrl = getUrl(host, port, TRACES_ENDPOINT_V4);
-    } else {
-      log.debug("API v0.4 endpoints not available. Downgrading to v0.3");
-      tracesUrl = getUrl(host, port, TRACES_ENDPOINT_V3);
-    }
   }
 
   public void addResponseListener(final DDAgentResponseListener listener) {
@@ -128,6 +116,10 @@ public class DDAgentApi {
 
   Response sendSerializedTraces(
       final int representativeCount, final Integer sizeInBytes, final List<byte[]> traces) {
+    if (tracesUrl == null) {
+      detectEndpoint();
+    }
+
     try {
       final RequestBody body =
           new RequestBody() {
@@ -298,6 +290,16 @@ public class DDAgentApi {
     }
   }
 
+  private synchronized void detectEndpoint() {
+    final HttpUrl v4Url = getUrl(host, port, TRACES_ENDPOINT_V4);
+    if (endpointAvailable(v4Url, unixDomainSocketPath, true)) {
+      tracesUrl = v4Url;
+    } else {
+      log.debug("API v0.4 endpoints not available. Downgrading to v0.3");
+      tracesUrl = getUrl(host, port, TRACES_ENDPOINT_V3);
+    }
+  }
+
   @Override
   public String toString() {
     return "DDApi { tracesUrl=" + tracesUrl + " }";
diff --git a/dd-trace-ot/src/test/groovy/datadog/trace/api/writer/DDAgentApiTest.groovy b/dd-trace-ot/src/test/groovy/datadog/trace/api/writer/DDAgentApiTest.groovy
index 6e6a0fb5e6..e5737d0460 100644
--- a/dd-trace-ot/src/test/groovy/datadog/trace/api/writer/DDAgentApiTest.groovy
+++ b/dd-trace-ot/src/test/groovy/datadog/trace/api/writer/DDAgentApiTest.groovy
@@ -34,10 +34,10 @@ class DDAgentApiTest extends DDSpecification {
     def client = new DDAgentApi("localhost", agent.address.port, null)
 
     expect:
-    client.tracesUrl.toString() == "http://localhost:${agent.address.port}/v0.4/traces"
     def response = client.sendTraces([])
     response.success()
     response.status() == 200
+    agent.getLastRequest().path == "/v0.4/traces"
 
     cleanup:
     agent.close()
@@ -50,16 +50,19 @@ class DDAgentApiTest extends DDSpecification {
         put("v0.4/traces") {
           response.status(404).send()
         }
+
+        put("v0.3/traces") {
+          response.status(404).send()
+        }
       }
     }
     def client = new DDAgentApi("localhost", agent.address.port, null)
 
     expect:
-    client.tracesUrl.toString() == "http://localhost:${agent.address.port}/v0.3/traces"
-
     def response = client.sendTraces([])
     !response.success()
     response.status() == 404
+    agent.getLastRequest().path == "/v0.3/traces"
 
     cleanup:
     agent.close()
@@ -77,7 +80,6 @@ class DDAgentApiTest extends DDSpecification {
     def client = new DDAgentApi("localhost", agent.address.port, null)
 
     expect:
-    client.tracesUrl.toString() == "http://localhost:${agent.address.port}/v0.4/traces"
     client.sendTraces(traces).success()
     agent.lastRequest.contentType == "application/msgpack"
     agent.lastRequest.headers.get("Datadog-Meta-Lang") == "java"
@@ -166,8 +168,8 @@ class DDAgentApiTest extends DDSpecification {
     def client = new DDAgentApi("localhost", v3Agent.address.port, null)
 
     expect:
-    client.tracesUrl.toString() == "http://localhost:${v3Agent.address.port}/v0.3/traces"
     client.sendTraces([]).success()
+    v3Agent.getLastRequest().path == "/v0.3/traces"
 
     cleanup:
     v3Agent.close()
@@ -191,9 +193,13 @@ class DDAgentApiTest extends DDSpecification {
     }
     def port = badPort ? 999 : agent.address.port
     def client = new DDAgentApi("localhost", port, null)
+    def result = client.sendTraces([])
 
     expect:
-    client.tracesUrl.toString() == "http://localhost:${port}/$endpointVersion/traces"
+    result.success() == !badPort // Expect success of port is ok
+    if (!badPort) {
+      assert agent.getLastRequest().path == "/$endpointVersion/traces"
+    }
 
     cleanup:
     agent.close()