refactor(audience): extract named constants for HTTP header, URL helper, and field length

Replaces the x-immutable-publishable-key literal, the inline
BaseUrl(...) + MessagesPath URL construction, and the repeated 256
MaxFieldLength literal in MessageBuilder with named Constants
helpers. Pure refactor of code already on main - no behaviour
change.

Author: ImmutableJeffrey

src/Packages/Audience/Runtime/Core/Constants.cs

@@ -14,11 +14,16 @@ internal static class Constants
         internal const int DefaultFlushSize = 20;
         internal const int MaxBatchSize = 100;
         internal const int StaleEventDays = 30;
+        internal const int MaxFieldLength = 256; // Backend schema limit.
 
         internal const string LibraryName = "com.immutable.audience";
         internal const string Surface = "unity";
         internal const string ConsentSource = "UnitySDK";
 
+        internal const string PublishableKeyHeader = "x-immutable-publishable-key";
+
+        internal static string MessagesUrl(string publishableKey) => BaseUrl(publishableKey) + MessagesPath;
+
         internal static string BaseUrl(string publishableKey) =>
             publishableKey != null && publishableKey.StartsWith(TestKeyPrefix)
                 ? SandboxBaseUrl

src/Packages/Audience/Runtime/Events/MessageBuilder.cs

@@ -13,13 +13,13 @@ internal static Dictionary<string, object> Track(
             Dictionary<string, object> properties = null)
         {
             var msg = BuildBase("track", packageVersion);
-            msg["eventName"] = Truncate(eventName, 256);
+            msg["eventName"] = Truncate(eventName, Constants.MaxFieldLength);
 
             if (!string.IsNullOrEmpty(anonymousId))
-                msg["anonymousId"] = Truncate(anonymousId, 256);
+                msg["anonymousId"] = Truncate(anonymousId, Constants.MaxFieldLength);
 
             if (!string.IsNullOrEmpty(userId))
-                msg["userId"] = Truncate(userId, 256);
+                msg["userId"] = Truncate(userId, Constants.MaxFieldLength);
 
             if (properties != null && properties.Count > 0)
                 msg["properties"] = properties;
@@ -37,13 +37,13 @@ internal static Dictionary<string, object> Identify(
             var msg = BuildBase("identify", packageVersion);
 
             if (!string.IsNullOrEmpty(anonymousId))
-                msg["anonymousId"] = Truncate(anonymousId, 256);
+                msg["anonymousId"] = Truncate(anonymousId, Constants.MaxFieldLength);
 
             if (!string.IsNullOrEmpty(userId))
-                msg["userId"] = Truncate(userId, 256);
+                msg["userId"] = Truncate(userId, Constants.MaxFieldLength);
 
             if (!string.IsNullOrEmpty(identityType))
-                msg["identityType"] = Truncate(identityType, 256);
+                msg["identityType"] = Truncate(identityType, Constants.MaxFieldLength);
 
             if (traits != null && traits.Count > 0)
                 msg["traits"] = traits;
@@ -59,10 +59,10 @@ internal static Dictionary<string, object> Alias(
             string packageVersion)
         {
             var msg = BuildBase("alias", packageVersion);
-            msg["fromId"] = Truncate(fromId, 256);
-            msg["fromType"] = Truncate(fromType, 256);
-            msg["toId"] = Truncate(toId, 256);
-            msg["toType"] = Truncate(toType, 256);
+            msg["fromId"] = Truncate(fromId, Constants.MaxFieldLength);
+            msg["fromType"] = Truncate(fromType, Constants.MaxFieldLength);
+            msg["toId"] = Truncate(toId, Constants.MaxFieldLength);
+            msg["toType"] = Truncate(toType, Constants.MaxFieldLength);
             return msg;
         }
 
@@ -76,7 +76,7 @@ private static Dictionary<string, object> BuildBase(string type, string packageV
                 ["context"] = new Dictionary<string, object>
                 {
                     ["library"] = Constants.LibraryName,
-                    ["libraryVersion"] = Truncate(packageVersion, 256)
+                    ["libraryVersion"] = Truncate(packageVersion, Constants.MaxFieldLength)
                 },
                 ["surface"] = Constants.Surface
             };

src/Packages/Audience/Runtime/Transport/HttpTransport.cs

@@ -38,7 +38,7 @@ internal HttpTransport(
         {
             _store = store ?? throw new ArgumentNullException(nameof(store));
             _publishableKey = publishableKey ?? throw new ArgumentNullException(nameof(publishableKey));
-            _url = Constants.BaseUrl(publishableKey) + Constants.MessagesPath;
+            _url = Constants.MessagesUrl(publishableKey);
             _onError = onError;
             _client = handler != null ? new HttpClient(handler) : new HttpClient();
             _client.Timeout = TimeSpan.FromSeconds(30);
@@ -78,7 +78,7 @@ internal async Task<bool> SendBatchAsync(CancellationToken ct = default)
             try
             {
                 using var request = new HttpRequestMessage(HttpMethod.Post, _url);
-                request.Headers.Add("x-immutable-publishable-key", _publishableKey);
+                request.Headers.Add(Constants.PublishableKeyHeader, _publishableKey);
 #if IMMUTABLE_AUDIENCE_GZIP
                 var compressed = Gzip.Compress(payload);
                 request.Content = new ByteArrayContent(compressed);