Add process tags to remote config (#7840)

## Summary of changes

adding process tags next to the service name in remote config requests

equivalent Java PR: DataDog/dd-trace-java#8705
related change on the agent side:
DataDog/datadog-agent#36049

## Reason for change

AIDM-195

## Implementation details

## Test coverage

I didn't see any existing tests on the content of the requests, didn't
really feel like adding some.

## Other details
<!-- Fixes #{issue} -->


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---------

Co-authored-by: Andrew Lock <[email protected]>

Author: vandonr

tracer/src/Datadog.Trace/ProcessTags.cs

@@ -20,52 +20,56 @@ internal static class ProcessTags
     public const string EntrypointBasedir = "entrypoint.basedir";
     public const string EntrypointWorkdir = "entrypoint.workdir";
 
-    public static readonly string SerializedTags = GetSerializedTags();
+    // two views on the same data
+    public static readonly List<string> TagsList = GetTagsList();
+    public static readonly string SerializedTags = GetSerializedTagsFromList(TagsList);
 
-    /// <summary>
-    /// From the full path of a directory, get the name of the leaf directory.
-    /// </summary>
-    private static string GetLastPathSegment(string directoryPath)
+    private static List<string> GetTagsList()
     {
-        // Path.GetFileName returns an empty string if the path ends with a '/'.
-        // We could use Path.TrimEndingDirectorySeparator instead of the trim here, but it's not available on .NET Framework
-        return Path.GetFileName(directoryPath.TrimEnd('\\').TrimEnd('/'));
+        // ⚠️ make sure entries are added in alphabetical order of keys
+        var tags = new List<string>(3); // Update if you add more entries below
+        tags.AddNormalizedTag(EntrypointBasedir, GetLastPathSegment(AppContext.BaseDirectory));
+        tags.AddNormalizedTag(EntrypointName, GetEntryPointName());
+        // workdir can be changed by the code, but we consider that capturing the value when this is called is good enough
+        tags.AddNormalizedTag(EntrypointWorkdir, GetLastPathSegment(Environment.CurrentDirectory));
+
+        return tags;
     }
 
-    private static string GetSerializedTags()
+    /// <summary>
+    /// normalizes the tag value (keys are hardcoded so they don't need that)
+    /// and adds it to the list iff not null or empty
+    /// </summary>
+    private static void AddNormalizedTag(this List<string> tags, string key, string? value)
     {
-        // ⚠️ make sure entries are added in alphabetical order of keys
-        List<KeyValuePair<string, string?>> tags =
-        [
-            new(EntrypointBasedir, GetLastPathSegment(AppContext.BaseDirectory)),
-            new(EntrypointName, GetEntryPointName()),
-            // workdir can be changed by the code, but we consider that capturing the value when this is called is good enough
-            new(EntrypointWorkdir, GetLastPathSegment(Environment.CurrentDirectory))
-        ];
-
-        // then normalize values and put all tags in a string
-        var serializedTags = StringBuilderCache.Acquire();
-        foreach (var kvp in tags)
+        if (string.IsNullOrEmpty(value))
         {
-            if (!string.IsNullOrEmpty(kvp.Value))
-            {
-                serializedTags.Append($"{kvp.Key}:{NormalizeTagValue(kvp.Value!)},");
-            }
+            return;
         }
 
-        serializedTags.Remove(serializedTags.Length - 1, length: 1); // remove last comma
-        return StringBuilderCache.GetStringAndRelease(serializedTags);
+        // TraceUtil.NormalizeTag does almost exactly what we want, except it allows ':',
+        // which we don't want because we use it as a key/value separator.
+        var normalizedValue = TraceUtil.NormalizeTag(value).Replace(oldChar: ':', newChar: '_');
+        tags.Add($"{key}:{normalizedValue}");
     }
 
-    private static string? GetEntryPointName()
+    private static string GetSerializedTagsFromList(List<string> tags)
     {
-        return EntryAssemblyLocator.GetEntryAssembly()?.EntryPoint?.DeclaringType?.FullName;
+        return string.Join(",", tags);
     }
 
-    private static string NormalizeTagValue(string tagValue)
+    /// <summary>
+    /// From the full path of a directory, get the name of the leaf directory.
+    /// </summary>
+    private static string GetLastPathSegment(string directoryPath)
     {
-        // TraceUtil.NormalizeTag does almost exactly what we want, except it allows ':',
-        // which we don't want because we use it as a key/value separator.
-        return TraceUtil.NormalizeTag(tagValue).Replace(oldChar: ':', newChar: '_');
+        // Path.GetFileName returns an empty string if the path ends with a '/'.
+        // We could use Path.TrimEndingDirectorySeparator instead of the trim here, but it's not available on .NET Framework
+        return Path.GetFileName(directoryPath.TrimEnd('\\').TrimEnd('/'));
+    }
+
+    private static string? GetEntryPointName()
+    {
+        return EntryAssemblyLocator.GetEntryAssembly()?.EntryPoint?.DeclaringType?.FullName;
     }
 }

tracer/src/Datadog.Trace/RemoteConfigurationManagement/Protocol/RcmClientTracer.cs

@@ -12,12 +12,13 @@ namespace Datadog.Trace.RemoteConfigurationManagement.Protocol
 {
     internal class RcmClientTracer
     {
-        public RcmClientTracer(string runtimeId, string tracerVersion, string service, string env, string? appVersion, List<string> tags)
+        public RcmClientTracer(string runtimeId, string tracerVersion, string service, string env, string? appVersion, List<string> tags, List<string>? processTags)
         {
             RuntimeId = runtimeId;
             Language = TracerConstants.Language;
             TracerVersion = tracerVersion;
             Service = service;
+            ProcessTags = processTags;
             Env = env;
             AppVersion = appVersion;
             Tags = tags;
@@ -35,6 +36,9 @@ public RcmClientTracer(string runtimeId, string tracerVersion, string service, s
         [JsonProperty("service")]
         public string Service { get; }
 
+        [JsonProperty("process_tags")]
+        public List<string>? ProcessTags { get; }
+
         [JsonProperty("extra_services")]
         public string[]? ExtraServices { get; set; }
 

tracer/src/Datadog.Trace/RemoteConfigurationManagement/RemoteConfigurationManager.cs

@@ -69,7 +69,7 @@ public static RemoteConfigurationManager Create(
             return new RemoteConfigurationManager(
                     discoveryService,
                     remoteConfigurationApi,
-                    rcmTracer: new RcmClientTracer(settings.RuntimeId, settings.TracerVersion, serviceName, TraceUtil.NormalizeTag(tracerSettings.Environment), tracerSettings.ServiceVersion, tags),
+                    new RcmClientTracer(settings.RuntimeId, settings.TracerVersion, serviceName, TraceUtil.NormalizeTag(tracerSettings.Environment), tracerSettings.ServiceVersion, tags, tracerSettings.PropagateProcessTags ? ProcessTags.TagsList : null),
                     pollInterval: settings.PollInterval,
                     gitMetadataTagsProvider,
                     subscriptionManager);

tracer/test/Datadog.Trace.Tests/RemoteConfigurationManagement/RemoteConfigurationApiTests.cs

@@ -243,7 +243,8 @@ private static GetRcmRequest GetRequest(string backendClientStage = null)
             service: nameof(RemoteConfigurationApiTests),
             env: "RCM Test",
             appVersion: "1.0.0",
-            tags: []);
+            tags: [],
+            processTags: ["a.b:c", "x.y:z"]);
 
         var state = new RcmClientState(
             rootVersion: 1,