[Exporter.Geneva] Allow custom string size limit in custom fields (#3360)

Author: xiang17

src/OpenTelemetry.Exporter.Geneva/CHANGELOG.md

@@ -5,6 +5,8 @@
 * Support for specifying resource attributes, including
   `service.name`, `service.instanceId`, and custom attributes.
   ([#3214](https://github.com/open-telemetry/opentelemetry-dotnet-contrib/pull/3214))
+* Allow custom string size limit in custom fields.
+  ([#3360](https://github.com/open-telemetry/opentelemetry-dotnet-contrib/pull/3360))
 
 ## 1.13.0
 

src/OpenTelemetry.Exporter.Geneva/Internal/MsgPack/MsgPackLogExporter.cs

@@ -327,7 +327,7 @@ internal ArraySegment<byte> SerializeLogRecord(LogRecord logRecord)
                     }
 
                     cursor = MessagePackSerializer.SerializeUnicodeString(buffer, cursor, entry.Key, this.stringFieldSizeLimitCharCount);
-                    cursor = MessagePackSerializer.Serialize(buffer, cursor, entry.Value);
+                    cursor = this.SerializeValueWithLimitIfString(buffer, cursor, entry.Value);
                     cntFields += 1;
                 }
             }
@@ -531,6 +531,17 @@ private static void OnProcessScopeForEnvProperties(LogRecordScope scope, MsgPack
         }
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private int SerializeValueWithLimitIfString(byte[] buffer, int cursor, object? value)
+    {
+        if (value is string stringValue)
+        {
+            return MessagePackSerializer.SerializeUnicodeString(buffer, cursor, stringValue, this.stringFieldSizeLimitCharCount);
+        }
+
+        return MessagePackSerializer.Serialize(buffer, cursor, value);
+    }
+
     private sealed class SerializationDataForScopes
     {
         public readonly byte[] Buffer;