Merge pull request #961 from aws-powertools/fix/logger-duplicate-header-key-exception

fix: handle duplicate keys in logger state to prevent ArgumentException

Author: hjgraca

libraries/src/AWS.Lambda.Powertools.Logging/Internal/PowertoolsLogger.cs

@@ -396,14 +396,26 @@ private static bool CustomFormatter<TState>(TState state, Exception exception, o
             return false;
 
 #if NET8_0_OR_GREATER
-        var stateKeys = (state as IEnumerable<KeyValuePair<string, object>>)?
-            .ToDictionary(i => i.Key, i => PowertoolsLoggerHelpers.ObjectToDictionary(i.Value));
+        var stateKeys = new Dictionary<string, object>();
+        if (state is IEnumerable<KeyValuePair<string, object>> keyValuePairs)
+        {
+            foreach (var kvp in keyValuePairs)
+            {
+                stateKeys[kvp.Key] = PowertoolsLoggerHelpers.ObjectToDictionary(kvp.Value);
+            }
+        }
 #else
-        var stateKeys = (state as IEnumerable<KeyValuePair<string, object>>)?
-            .ToDictionary(i => i.Key, i => i.Value);
+var stateKeys = new Dictionary<string, object>();
+if (state is IEnumerable<KeyValuePair<string, object>> keyValuePairs)
+{
+    foreach (var kvp in keyValuePairs)
+    {
+        stateKeys[kvp.Key] = kvp.Value;
+    }
+}
 #endif
 
-        if (stateKeys is null || stateKeys.Count != 2)
+        if (stateKeys.Count != 2)
             return false;
 
         if (!stateKeys.TryGetValue(_originalformat, out var originalFormat))

libraries/tests/AWS.Lambda.Powertools.Logging.Tests/PowertoolsLoggerTest.cs

@@ -1750,6 +1750,48 @@ public void Log_Cold_Start(bool willLog, string awsInitType)
             // Assert
             Assert.Contains($"\"coldStart\":{willLog.ToString().ToLower()}", outPut);
         }
+        
+        [Fact]
+        public void Log_WhenDuplicateKeysInState_LastValueWins()
+        {
+            // Arrange
+            var loggerName = Guid.NewGuid().ToString();
+            var service = Guid.NewGuid().ToString();
+            var logLevel = LogLevel.Information;
+
+            var configurations = Substitute.For<IPowertoolsConfigurations>();
+            configurations.Service.Returns(service);
+            configurations.LogLevel.Returns(logLevel.ToString());
+            configurations.LoggerOutputCase.Returns(LoggerOutputCase.PascalCase.ToString());
+
+            var systemWrapper = Substitute.For<IConsoleWrapper>();
+
+            var loggerConfiguration = new PowertoolsLoggerConfiguration
+            {
+                Service = service,
+                MinimumLogLevel = logLevel,
+                LoggerOutputCase = LoggerOutputCase.PascalCase,
+                LogOutput = systemWrapper
+            };
+
+            var provider = new PowertoolsLoggerProvider(loggerConfiguration, configurations);
+            var logger = provider.CreateLogger(loggerName);
+
+            // Create state with duplicate keys (simulating duplicate HTTP headers)
+            var stateWithDuplicates = new List<KeyValuePair<string, object>>
+            {
+                new("Content-Type", "application/json"),
+                new("Content-Type", "application/x-www-form-urlencoded"), // This should win
+                new("Accept", "text/html"),
+                new("Accept", "*/*") // This should win
+            };
+
+            // Act - This should not throw an exception
+            logger.Log(logLevel, new EventId(), stateWithDuplicates, null, (state, ex) => "Test message");
+
+            // Assert
+            systemWrapper.Received(1).WriteLine(Arg.Any<string>());
+        }
 
         public void Dispose()
         {