Properly fall-back on UDS profiling URL (#9401)

Author: jbachorik

internal-api/src/main/java/datadog/trace/api/Config.java

@@ -4741,8 +4741,18 @@ public String getFinalProfilingUrl() {
       // when agentless profiling is turned on we send directly to our intake
       return "https://intake.profile." + site + "/api/v2/profile";
     } else {
-      // when profilingUrl and agentless are not set we send to the dd trace agent running locally
-      return getAgentUrl() + "/profiling/v1/input";
+      // When profilingUrl and agentless are not set we send to the dd trace agent running locally
+      // However, there are two gotchas:
+      // - the agentHost, agentPort split will trip on IPv6 addresses because of the colon -> we
+      // need to use the agentUrl
+      // - but the agentUrl can be unix socket and OKHttp doesn't support that so we fall back to
+      // http
+      //
+      // There is some magic behind the scenes where the http url will be converted to UDS if the
+      // target is a unix socket only
+      String baseUrl =
+          agentUrl.startsWith("unix:") ? "http://" + agentHost + ":" + agentPort : agentUrl;
+      return baseUrl + "/profiling/v1/input";
     }
   }
 

internal-api/src/test/groovy/datadog/trace/api/ConfigTest.groovy

@@ -1665,6 +1665,19 @@ class ConfigTest extends DDSpecification {
     config.getFinalProfilingUrl() == configuredUrl + "/profiling/v1/input"
   }
 
+  def "uds profiling url"() {
+    setup:
+    def configuredUrl = "unix:///path/to/socket"
+    def props = new Properties()
+    props.setProperty(TRACE_AGENT_URL, configuredUrl)
+
+    when:
+    Config config = Config.get(props)
+
+    then:
+    config.getFinalProfilingUrl() == "http://" + config.getAgentHost() + ":" + config.getAgentPort() + "/profiling/v1/input"
+  }
+
   def "fallback to DD_TAGS"() {
     setup:
     environmentVariables.set(DD_TAGS_ENV, "a:1,b:2,c:3")