fix(python): serialize JSON header parameter content

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PythonClientCodegen.java

@@ -619,10 +619,21 @@ protected void addAdditionPropertiesToCodeGenModel(CodegenModel codegenModel, Sc
     @Override
     public OperationsMap postProcessOperationsWithModels(
             OperationsMap objs, List<ModelMap> allModels) {
+        List<CodegenOperation> operations = objs.getOperations().getOperation();
+
         if (useIndependentImplicitClients) {
-            renameIndependentClientOperationMembers(
-                    objs.getOperations().getOperation());
+            renameIndependentClientOperationMembers(operations);
+        }
+
+        boolean hasJsonHeader = operations.stream()
+                .flatMap(operation -> operation.headerParams.stream())
+                .anyMatch(parameter ->
+                        parameter.vendorExtensions.containsKey("x-python-json-header"));
+
+        if (hasJsonHeader) {
+            objs.put("x-python-has-json-header", true);
         }
+
         return super.postProcessOperationsWithModels(objs, allModels);
     }
 
@@ -1021,6 +1032,11 @@ public String toVarName(String name) {
     @Override
     public void postProcessParameter(CodegenParameter parameter) {
         super.postProcessParameter(parameter);
+
+        if (parameter.isHeaderParam && isJsonMimeType(parameter.contentType)) {
+            parameter.vendorExtensions.put("x-python-json-header", true);
+        }
+
         // Only operation signatures gain this control argument. Keep model
         // field naming independent of the selected library.
         if (usesLegacyApiCompatibility()

modules/openapi-generator/src/main/resources/python/api.mustache

@@ -1,5 +1,8 @@
 {{>partial_header}}
 
+{{#x-python-has-json-header}}
+import json
+{{/x-python-has-json-header}}
 import warnings
 from pydantic import validate_call, Field, StrictFloat, StrictStr, StrictInt
 from typing import Any, Dict, List, Optional, Tuple, Union
@@ -383,7 +386,14 @@ https://github.com/OpenAPITools/openapi-generator/blob/c84b949df1a9ec04ba75989cb
         # process the header parameters
 {{#headerParams}}
         if {{paramName}} is not None:
+            {{#vendorExtensions.x-python-json-header}}
+            _header_params['{{baseName}}'] = json.dumps(
+                self.api_client.sanitize_for_serialization({{paramName}})
+            )
+            {{/vendorExtensions.x-python-json-header}}
+            {{^vendorExtensions.x-python-json-header}}
             _header_params['{{baseName}}'] = {{paramName}}
+            {{/vendorExtensions.x-python-json-header}}
 {{/headerParams}}
         # process the form parameters
 {{#formParams}}

modules/openapi-generator/src/test/java/org/openapitools/codegen/python/PythonClientCodegenTest.java

@@ -128,6 +128,62 @@ public void testHttpx2Generation(boolean sync, Object poetry1, String backend) t
         Assert.assertFalse(Files.readString(Paths.get(output, "requirements.txt")).contains("httpx >="));
     }
 
+    @Test
+    public void testJsonImportOnlyGeneratedForJsonHeaderContent() throws IOException {
+        File output = Files.createTempDirectory("test").toFile().getCanonicalFile();
+        output.deleteOnExit();
+
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("python")
+                .setInputSpec("src/test/resources/3_0/petstore.yaml")
+                .setOutputDir(output.getAbsolutePath());
+
+        DefaultGenerator generator = new DefaultGenerator();
+        List<File> files = generator.opts(configurator.toClientOptInput()).generate();
+        files.forEach(File::deleteOnExit);
+
+        Path api = Paths.get(
+                output.getAbsolutePath(),
+                "openapi_client",
+                "api",
+                "pet_api.py");
+
+        TestUtils.assertFileNotContains(api, "import json");
+    }
+
+    @Test
+    public void testJsonContentHeaderUsesJsonSerialization() throws IOException {
+        File output = Files.createTempDirectory("test").toFile().getCanonicalFile();
+        output.deleteOnExit();
+
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("python")
+                .setInputSpec("src/test/resources/3_1/python/json-header-content.yaml")
+                .setOutputDir(output.getAbsolutePath());
+
+        DefaultGenerator generator = new DefaultGenerator();
+        List<File> files = generator.opts(configurator.toClientOptInput()).generate();
+        files.forEach(File::deleteOnExit);
+
+        Path api = Paths.get(
+                output.getAbsolutePath(),
+                "openapi_client",
+                "api",
+                "default_api.py");
+
+        TestUtils.assertFileContains(
+                api,
+                "import json",
+                "_header_params['X-Json-Arg'] = json.dumps(",
+                "self.api_client.sanitize_for_serialization(x_json_arg)",
+                "_header_params['X-Plain-Arg'] = x_plain_arg");
+
+        TestUtils.assertFileNotContains(
+                api,
+                "_header_params['X-Json-Arg'] = x_json_arg",
+                "_header_params['X-Plain-Arg'] = json.dumps(");
+    }
+
     @Test
     public void testInitialConfigValues() throws Exception {
         final PythonClientCodegen codegen = new PythonClientCodegen();

modules/openapi-generator/src/test/resources/3_1/python/json-header-content.yaml

@@ -0,0 +1,38 @@
+openapi: 3.1.0
+
+info:
+  title: JSON header content test
+  version: 1.0.0
+
+paths:
+  /test:
+    post:
+      operationId: testJsonHeader
+      parameters:
+        - name: X-Json-Arg
+          in: header
+          required: true
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/HeaderArg'
+
+        - name: X-Plain-Arg
+          in: header
+          required: false
+          schema:
+            type: string
+
+      responses:
+        '204':
+          description: No content
+
+components:
+  schemas:
+    HeaderArg:
+      type: object
+      properties:
+        path:
+          type: string
+        recursive:
+          type: boolean