Dirty memory check may fail connecting to RavenDB when using external mode (#4917)

* Favor connection string over server URL when trying to connect to RavenDB to retrieve dirty memory details

* Update comment to reflect reality

* Update audit comment

---------

Co-authored-by: Brandon Ording <[email protected]>

Author: mauroservienti

src/ServiceControl.Audit.Persistence.RavenDB/MemoryInformationRetriever.cs

@@ -8,12 +8,12 @@ namespace ServiceControl.Audit.Persistence.RavenDB;
 
 class MemoryInformationRetriever(DatabaseConfiguration databaseConfiguration)
 {
-    // What does a connection string look like? Is it only a URI or could it contain other stuff?
-    // The ?? operator is needed because ServerUrl is populated when running embedded and connection
-    // string when running in external mode. However, the tricky part is that when tests are run they
-    // behave like if it was external mode. If the connection string contain always only the server
-    // URL, this code is safe, otherwise it need to be adjusted to extract the server URL.
-    readonly HttpClient client = new() { BaseAddress = new Uri(databaseConfiguration.ServerConfiguration.ServerUrl ?? databaseConfiguration.ServerConfiguration.ConnectionString) };
+    // Connection string is composed of the server URL. The ?? operator is needed because ServerUrl
+    // is populated when running embedded and connection string when running in external mode.
+    // However, the tricky part is that when tests are run they behave like if it was external mode.
+    // Only one of ConnectionString and ServerUrl will be non-null, so we'll check ConnectionString first
+    // to be consistent with the error instance implementation, where ServerUrl always has a value.
+    readonly HttpClient client = new() { BaseAddress = new Uri(databaseConfiguration.ServerConfiguration.ConnectionString ?? databaseConfiguration.ServerConfiguration.ServerUrl) };
 
     record ResponseDto
     {

src/ServiceControl.Persistence.RavenDB/MemoryInformationRetriever.cs

@@ -8,11 +8,12 @@ namespace ServiceControl.Persistence.RavenDB;
 
 class MemoryInformationRetriever(RavenPersisterSettings persisterSettings)
 {
-    // What does a connection string look like? Is it only a URI or could it contain other stuff?
-    // The primary instance has only the concept of a connection string (vs the Audit instance having
-    // both a ServiceUrl and a ConnectionString). If the connection string contain always only the
-    // server URL, this code is safe, otherwise it need to be adjusted to extract the server URL.
-    readonly HttpClient client = new() { BaseAddress = new Uri(persisterSettings.ServerUrl ?? persisterSettings.ConnectionString) };
+    // Connection string is composed of the server URL. The ?? operator is needed because ServerUrl
+    // is populated when running embedded and connection string when running in external mode.
+    // However, the tricky part is that when tests are run they behave like if it was external mode.
+    // ServerUrl is always populated by the persister settings, hence the code first checks for the
+    // presence of a connection string, and if null, falls back to ServerUrl
+    readonly HttpClient client = new() { BaseAddress = new Uri(persisterSettings.ConnectionString ?? persisterSettings.ServerUrl) };
 
     record ResponseDto
     {