From 24df88bf4638f4ca90dcec6487c44257db007b51 Mon Sep 17 00:00:00 2001
From: Eric Lawson <e.lawson@rocketlabusa.com>
Date: Fri, 22 May 2026 13:34:37 -0600
Subject: [PATCH] fix(core): recognize OAS 3.1 contentMediaType for binary
 classification

Extend ModelUtils.isBinarySchema to recognize
contentMediaType: application/octet-stream alongside the existing
format: binary check. OpenAPI 3.1 / JSON Schema 2020-12 uses
contentMediaType as the binary-content signal, but openapi-generator
only matched format: binary, so 3.1 specs failed to classify file
fields and were routed through plain form params rather than
multipart binary parts.

format: binary remains valid in 3.1 and continues to match.
---
 .../codegen/utils/ModelUtils.java             |  5 ++--
 .../codegen/utils/ModelUtilsTest.java         | 15 ++++++++++
 .../src/test/resources/3_0/binary-schema.yaml | 26 +++++++++++++++++
 .../src/test/resources/3_1/binary-schema.yaml | 29 +++++++++++++++++++
 4 files changed, 73 insertions(+), 2 deletions(-)
 create mode 100644 modules/openapi-generator/src/test/resources/3_0/binary-schema.yaml
 create mode 100644 modules/openapi-generator/src/test/resources/3_1/binary-schema.yaml

diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/utils/ModelUtils.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/utils/ModelUtils.java
index 88346d9046f7..e0f552e5d598 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/utils/ModelUtils.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/utils/ModelUtils.java
@@ -743,9 +743,10 @@ public static boolean isByteArraySchema(Schema schema) {
 
     public static boolean isBinarySchema(Schema schema) {
         return (schema instanceof BinarySchema) ||
-                // format: binary
+                // format: binary, or contentMediaType: application/octet-stream (OAS 3.1)
                 (SchemaTypeUtil.STRING_TYPE.equals(getType(schema))
-                        && SchemaTypeUtil.BINARY_FORMAT.equals(schema.getFormat()));
+                        && (SchemaTypeUtil.BINARY_FORMAT.equals(schema.getFormat())
+                                || "application/octet-stream".equals(schema.getContentMediaType())));
     }
 
     public static boolean isFileSchema(Schema schema) {
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/utils/ModelUtilsTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/utils/ModelUtilsTest.java
index 906ace829bcb..0b46d6545dc7 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/utils/ModelUtilsTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/utils/ModelUtilsTest.java
@@ -750,6 +750,21 @@ public void testModelWithPropertiesOnly() {
         assertFalse(ModelUtils.isModelWithPropertiesOnly(testSchema));
     }
 
+    @Test
+    public void testIsBinarySchemaOAS30FormatBinary() {
+        final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/binary-schema.yaml");
+        Schema fileProp = (Schema) ModelUtils.getSchema(openAPI, "UploadBody").getProperties().get("file");
+        assertTrue(ModelUtils.isBinarySchema(fileProp));
+    }
+
+    @Test
+    public void testIsBinarySchemaOAS31ContentMediaType() {
+        final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_1/binary-schema.yaml");
+        Map<String, Schema> props = ModelUtils.getSchema(openAPI, "UploadBody").getProperties();
+        assertTrue(ModelUtils.isBinarySchema(props.get("file")));
+        assertFalse(ModelUtils.isBinarySchema(props.get("image")));
+    }
+
     @Test
     public void getParentNameMultipleInterfacesTest() {
         OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/oneOf_innerModel.yaml");
diff --git a/modules/openapi-generator/src/test/resources/3_0/binary-schema.yaml b/modules/openapi-generator/src/test/resources/3_0/binary-schema.yaml
new file mode 100644
index 000000000000..de9d8c5ab13f
--- /dev/null
+++ b/modules/openapi-generator/src/test/resources/3_0/binary-schema.yaml
@@ -0,0 +1,26 @@
+openapi: 3.0.3
+info:
+  title: t
+  version: 1.0.0
+paths:
+  /upload:
+    post:
+      operationId: upload
+      requestBody:
+        content:
+          multipart/form-data:
+            schema:
+              $ref: '#/components/schemas/UploadBody'
+      responses:
+        '200':
+          description: ok
+components:
+  schemas:
+    UploadBody:
+      type: object
+      properties:
+        file:
+          type: string
+          format: binary
+      required:
+        - file
diff --git a/modules/openapi-generator/src/test/resources/3_1/binary-schema.yaml b/modules/openapi-generator/src/test/resources/3_1/binary-schema.yaml
new file mode 100644
index 000000000000..4852de8e267d
--- /dev/null
+++ b/modules/openapi-generator/src/test/resources/3_1/binary-schema.yaml
@@ -0,0 +1,29 @@
+openapi: 3.1.0
+info:
+  title: t
+  version: 1.0.0
+paths:
+  /upload:
+    post:
+      operationId: upload
+      requestBody:
+        content:
+          multipart/form-data:
+            schema:
+              $ref: '#/components/schemas/UploadBody'
+      responses:
+        '200':
+          description: ok
+components:
+  schemas:
+    UploadBody:
+      type: object
+      properties:
+        file:
+          type: string
+          contentMediaType: application/octet-stream
+        image:
+          type: string
+          contentMediaType: image/png
+      required:
+        - file