fix(event_source): fix decode headers with signed bytes

aws_lambda_powertools/shared/functions.py

@@ -291,3 +291,19 @@ def sanitize_xray_segment_name(name: str) -> str:
 def get_tracer_id() -> str | None:
     xray_trace_id = os.getenv(constants.XRAY_TRACE_ID_ENV)
     return xray_trace_id.split(";")[0].replace("Root=", "") if xray_trace_id else None
+
+
+def decode_header_bytes(byte_list):
+    """
+    Decode a list of byte values that might be signed.
+    If any negative values exist, handle them as signed bytes.
+    Otherwise use the normal bytes construction.
+    """
+    has_negative = any(b < 0 for b in byte_list)
+
+    if not has_negative:
+        # Use normal bytes construction if all values are positive
+        return bytes(byte_list)
+    # Convert signed bytes to unsigned (0-255 range)
+    unsigned_bytes = [(b & 0xFF) for b in byte_list]
+    return bytes(unsigned_bytes)

aws_lambda_powertools/utilities/data_classes/kafka_event.py

@@ -4,6 +4,7 @@
 from functools import cached_property
 from typing import TYPE_CHECKING, Any
 
+from aws_lambda_powertools.shared.functions import decode_header_bytes
 from aws_lambda_powertools.utilities.data_classes.common import CaseInsensitiveDict, DictWrapper
 
 if TYPE_CHECKING:
@@ -110,7 +111,7 @@ def headers(self) -> list[dict[str, list[int]]]:
     @cached_property
     def decoded_headers(self) -> dict[str, bytes]:
         """Decodes the headers as a single dictionary."""
-        return CaseInsensitiveDict((k, bytes(v)) for chunk in self.headers for k, v in chunk.items())
+        return CaseInsensitiveDict((k, decode_header_bytes(v)) for chunk in self.headers for k, v in chunk.items())
 
 
 class KafkaEventBase(DictWrapper):

aws_lambda_powertools/utilities/kafka/consumer_records.py

@@ -4,6 +4,7 @@
 from functools import cached_property
 from typing import TYPE_CHECKING, Any
 
+from aws_lambda_powertools.shared.functions import decode_header_bytes
 from aws_lambda_powertools.utilities.data_classes.common import CaseInsensitiveDict
 from aws_lambda_powertools.utilities.data_classes.kafka_event import KafkaEventBase, KafkaEventRecordBase
 from aws_lambda_powertools.utilities.kafka.deserializer.deserializer import get_deserializer
@@ -115,7 +116,9 @@ def original_headers(self) -> list[dict[str, list[int]]]:
     @cached_property
     def headers(self) -> dict[str, bytes]:
         """Decodes the headers as a single dictionary."""
-        return CaseInsensitiveDict((k, bytes(v)) for chunk in self.original_headers for k, v in chunk.items())
+        return CaseInsensitiveDict(
+            (k, decode_header_bytes(v)) for chunk in self.original_headers for k, v in chunk.items()
+        )
 
 
 class ConsumerRecords(KafkaEventBase):

aws_lambda_powertools/utilities/parser/models/kafka.py

@@ -3,7 +3,7 @@
 
 from pydantic import BaseModel, field_validator
 
-from aws_lambda_powertools.shared.functions import base64_decode, bytes_to_string
+from aws_lambda_powertools.shared.functions import base64_decode, bytes_to_string, decode_header_bytes
 
 SERVERS_DELIMITER = ","
 
@@ -28,9 +28,7 @@ class KafkaRecordModel(BaseModel):
     # key is optional; only decode if not None
     @field_validator("key", mode="before")
     def decode_key(cls, value):
-        if value is not None:
-            return base64_decode(value)
-        return value
+        return base64_decode(value) if value is not None else value
 
     @field_validator("value", mode="before")
     def data_base64_decode(cls, value):
@@ -41,7 +39,7 @@ def data_base64_decode(cls, value):
     def decode_headers_list(cls, value):
         for header in value:
             for key, values in header.items():
-                header[key] = bytes(values)
+                header[key] = decode_header_bytes(values)
         return value
 
 
@@ -51,7 +49,7 @@ class KafkaBaseEventModel(BaseModel):
 
     @field_validator("bootstrapServers", mode="before")
     def split_servers(cls, value):
-        return None if not value else value.split(SERVERS_DELIMITER)
+        return value.split(SERVERS_DELIMITER) if value else None
 
 
 class KafkaSelfManagedEventModel(KafkaBaseEventModel):

tests/events/kafkaEventMsk.json

@@ -104,6 +104,28 @@
               "dataFormat": "AVRO",
               "schemaId": "1234"
            }
+        },
+        {
+           "topic":"mymessage-with-unsigned",
+           "partition":0,
+           "offset":15,
+           "timestamp":1545084650987,
+           "timestampType":"CREATE_TIME",
+           "key": null,
+           "value":"eyJrZXkiOiJ2YWx1ZSJ9",
+           "headers":[
+              {
+                 "headerKey":[104, 101, 108, 108, 111, 45, 119, 111, 114, 108, 100, 45, -61, -85]
+              }
+           ],
+           "valueSchemaMetadata": {
+              "dataFormat": "AVRO",
+              "schemaId": "1234"
+           },
+           "keySchemaMetadata": {
+              "dataFormat": "AVRO",
+              "schemaId": "1234"
+           }
         }
      ]
   }

tests/unit/data_classes/required_dependencies/test_kafka_event.py

@@ -21,7 +21,7 @@ def test_kafka_msk_event():
     assert parsed_event.decoded_bootstrap_servers == bootstrap_servers_list
 
     records = list(parsed_event.records)
-    assert len(records) == 3
+    assert len(records) == 4
     record = records[0]
     raw_record = raw_event["records"]["mytopic-0"][0]
     assert record.topic == raw_record["topic"]
@@ -40,9 +40,10 @@ def test_kafka_msk_event():
     assert record.value_schema_metadata.schema_id == raw_record["valueSchemaMetadata"]["schemaId"]
 
     assert parsed_event.record == records[0]
-    for i in range(1, 3):
+    for i in range(1, 4):
         record = records[i]
         assert record.key is None
+        assert record.decoded_headers is not None
 
 
 def test_kafka_self_managed_event():
@@ -90,5 +91,5 @@ def test_kafka_record_property_with_stopiteration_error():
     # WHEN calling record property thrice
     # THEN raise StopIteration
     with pytest.raises(StopIteration):
-        for _ in range(4):
+        for _ in range(5):
             assert parsed_event.record.topic is not None

tests/unit/parser/_pydantic/test_kafka.py

@@ -17,7 +17,7 @@ def test_kafka_msk_event_with_envelope():
     )
     for i in range(3):
         assert parsed_event[i].key == "value"
-    assert len(parsed_event) == 3
+    assert len(parsed_event) == 4
 
 
 def test_kafka_self_managed_event_with_envelope():
@@ -70,7 +70,7 @@ def test_kafka_msk_event():
     assert parsed_event.eventSourceArn == raw_event["eventSourceArn"]
 
     records = list(parsed_event.records["mytopic-0"])
-    assert len(records) == 3
+    assert len(records) == 4
     record: KafkaRecordModel = records[0]
     raw_record = raw_event["records"]["mytopic-0"][0]
     assert record.topic == raw_record["topic"]
@@ -88,6 +88,6 @@ def test_kafka_msk_event():
     assert record.keySchemaMetadata.schemaId == "1234"
     assert record.valueSchemaMetadata.dataFormat == "AVRO"
     assert record.valueSchemaMetadata.schemaId == "1234"
-    for i in range(1, 3):
+    for i in range(1, 4):
         record: KafkaRecordModel = records[i]
         assert record.key is None