From 9abb543a1b9c36aa1eaf451b002b0a78cbab136f Mon Sep 17 00:00:00 2001
From: Lucas Jia <lucasjia@amazon.com>
Date: Tue, 13 Oct 2026 13:02:17 -0700
Subject: [PATCH] fix(serve): honor request content types

Pass caller-provided content types to request deserializers so JSON and CSV NumPy payloads are decoded correctly. Keep response deserializers pinned to configured Accept types for model servers that return misleading headers.

Fixes #5006
---
 .../sagemaker/serve/builder/schema_builder.py | 20 ++++++++-----
 .../tests/unit/builder/test_schema_builder.py | 30 +++++++++++++++++++
 2 files changed, 42 insertions(+), 8 deletions(-)

diff --git a/sagemaker-serve/src/sagemaker/serve/builder/schema_builder.py b/sagemaker-serve/src/sagemaker/serve/builder/schema_builder.py
index faa8066d52..5505e4b90f 100644
--- a/sagemaker-serve/src/sagemaker/serve/builder/schema_builder.py
+++ b/sagemaker-serve/src/sagemaker/serve/builder/schema_builder.py
@@ -69,18 +69,17 @@ def serialize(self, data) -> bytes:
 class DeserializerWrapper(BaseDeserializer):
     """Wraps the deserializer to comply with the function signature."""
 
-    def __init__(self, deserializer, accept):
+    def __init__(self, deserializer, accept, honor_content_type=False):
         self._deserializer = deserializer
         self._accept = accept
+        self._honor_content_type = honor_content_type
 
     def deserialize(self, stream, content_type: str = None):
         """Deserialize stream into object"""
-        return self._deserializer.deserialize(
-            stream,
-            # We need to overwrite the accept type because model
-            # servers like XGBOOST always returns "text/html"
-            self._accept[0],
+        deserialization_content_type = (
+            content_type if self._honor_content_type and content_type else self._accept[0]
         )
+        return self._deserializer.deserialize(stream, deserialization_content_type)
 
     @property
     def ACCEPT(self):
@@ -133,7 +132,9 @@ def __init__(
             self.input_serializer = self._get_serializer(sample_input)
             self._input_deserializer = self._get_inverse(self.input_serializer)
             self.input_deserializer = DeserializerWrapper(
-                self._input_deserializer, self._input_deserializer.ACCEPT
+                self._input_deserializer,
+                self._input_deserializer.ACCEPT,
+                honor_content_type=True,
             )
 
         if output_translator:
@@ -148,7 +149,10 @@ def __init__(
             self.output_serializer = self._get_inverse(self._output_deserializer)
 
             self.output_deserializer = DeserializerWrapper(
-                self._output_deserializer, self._output_deserializer.ACCEPT
+                self._output_deserializer,
+                self._output_deserializer.ACCEPT,
+                # Some model servers return misleading response types such as text/html.
+                honor_content_type=False,
             )
 
     def _get_serializer(self, obj):
diff --git a/sagemaker-serve/tests/unit/builder/test_schema_builder.py b/sagemaker-serve/tests/unit/builder/test_schema_builder.py
index ce812bb6d4..b2d557acc6 100644
--- a/sagemaker-serve/tests/unit/builder/test_schema_builder.py
+++ b/sagemaker-serve/tests/unit/builder/test_schema_builder.py
@@ -1,4 +1,7 @@
+import json
 import unittest
+from io import BytesIO
+
 import numpy as np
 from sagemaker.serve.builder.schema_builder import SchemaBuilder
 
@@ -54,6 +57,33 @@ def test_generate_marshalling_map(self):
         self.assertIn("input_serializer", mapping)
         self.assertIn("output_deserializer", mapping)
 
+    def test_numpy_input_deserializer_honors_json_content_type(self):
+        schema = SchemaBuilder(np.array([[0]]), np.array([[0]]))
+        stream = BytesIO(json.dumps([[1, 2], [3, 4]]).encode("utf-8"))
+
+        result = schema.input_deserializer.deserialize(stream, content_type="application/json")
+
+        np.testing.assert_array_equal(result, np.array([[1, 2], [3, 4]]))
+
+    def test_numpy_input_deserializer_honors_csv_content_type(self):
+        schema = SchemaBuilder(np.array([[0]]), np.array([[0]]))
+        stream = BytesIO(b"1,2\n3,4\n")
+
+        result = schema.input_deserializer.deserialize(stream, content_type="text/csv")
+
+        np.testing.assert_array_equal(result, np.array([[1, 2], [3, 4]]))
+
+    def test_numpy_output_deserializer_preserves_expected_accept_type(self):
+        expected = np.array([[0.1, 0.9]])
+        schema = SchemaBuilder(np.array([[0]]), expected)
+        stream = BytesIO()
+        np.save(stream, expected)
+        stream.seek(0)
+
+        result = schema.output_deserializer.deserialize(stream, content_type="text/html")
+
+        np.testing.assert_array_equal(result, expected)
+
 
 if __name__ == "__main__":
     unittest.main()