fix(http-server-csharp): Emit correct ASP.NET Core result methods for non-200/204 status codes

.chronus/changes/fix-csharp-emitter-status-codes-2026-03-04-00-54-22.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http-server-csharp"
+---
+
+Fix controller generation to use correct ASP.NET Core result methods for non-200/204 status codes. Previously all operations returned `Ok(...)` or `NoContent()` regardless of the declared status code. Now operations returning 202 use `Accepted(...)`, and other status codes use `StatusCode(code, ...)`.

packages/http-server-csharp/src/lib/service.ts

@@ -103,6 +103,7 @@ import {
   getCSharpType,
   getCSharpTypeForIntrinsic,
   getCSharpTypeForScalar,
+  getControllerReturnStatement,
   getFreePort,
   getHttpDeclParameters,
   getImports,
@@ -873,7 +874,7 @@ export async function $onEmit(context: EmitContext<CSharpServiceEmitterOptions>)
         });
 
       const hasResponseValue = response.name !== "void";
-      const resultString = `${status === 204 ? "NoContent" : "Ok"}`;
+      const returnStatement = getControllerReturnStatement(status, hasResponseValue);
       if (!this.#isMultipartRequest(httpOperation)) {
         return this.emitter.result.declaration(
           operation.name,
@@ -887,9 +888,9 @@ export async function $onEmit(context: EmitContext<CSharpServiceEmitterOptions>)
           ${
             hasResponseValue
               ? `var result = await ${this.emitter.getContext().resourceName}Impl.${operationName}Async(${getBusinessLogicCallParameters(parameters)});
-          return ${resultString}(result);`
+          ${returnStatement}`
               : `await ${this.emitter.getContext().resourceName}Impl.${operationName}Async(${getBusinessLogicCallParameters(parameters)});
-          return ${resultString}();`
+          ${returnStatement}`
           }
         }`,
         );
@@ -915,9 +916,9 @@ export async function $onEmit(context: EmitContext<CSharpServiceEmitterOptions>)
           ${
             hasResponseValue
               ? `var result = await ${this.emitter.getContext().resourceName}Impl.${operationName}Async(${getBusinessLogicCallParameters(parameters)});
-          return ${resultString}(result);`
+          ${returnStatement}`
               : `await ${this.emitter.getContext().resourceName}Impl.${operationName}Async(${getBusinessLogicCallParameters(parameters)});
-          return ${resultString}();`
+          ${returnStatement}`
           }
         }`,
         );
@@ -956,7 +957,7 @@ export async function $onEmit(context: EmitContext<CSharpServiceEmitterOptions>)
         });
 
       const hasResponseValue = response.name !== "void";
-      const resultString = `${status === 204 ? "NoContent" : "Ok"}`;
+      const returnStatement = getControllerReturnStatement(status, hasResponseValue);
       return this.emitter.result.declaration(
         operation.name,
         code`
@@ -969,9 +970,9 @@ export async function $onEmit(context: EmitContext<CSharpServiceEmitterOptions>)
           ${
             hasResponseValue
               ? `var result = await ${this.emitter.getContext().resourceName}Impl.${operationName}Async(${getBusinessLogicCallParameters(parameters)});
-          return ${resultString}(result);`
+          ${returnStatement}`
               : `await ${this.emitter.getContext().resourceName}Impl.${operationName}Async(${getBusinessLogicCallParameters(parameters)});
-          return ${resultString}();`
+          ${returnStatement}`
           }
         }`,
       );

packages/http-server-csharp/src/lib/utils.ts

@@ -1032,6 +1032,31 @@ export function getCSharpStatusCode(entry: HttpStatusCodesEntry): string | undef
   }
 }
 
+/**
+ * Returns the full return statement for a controller action based on the HTTP status code.
+ * Maps well-known status codes to their idiomatic ASP.NET Core ControllerBase methods,
+ * and falls back to `StatusCode(code, ...)` for all other numeric codes.
+ */
+export function getControllerReturnStatement(
+  status: HttpStatusCodesEntry,
+  hasValue: boolean,
+): string {
+  if (typeof status === "number") {
+    switch (status) {
+      case 200:
+        return hasValue ? "return Ok(result);" : "return Ok();";
+      case 202:
+        return hasValue ? "return Accepted(result);" : "return Accepted();";
+      case 204:
+        return "return NoContent();";
+      default:
+        return hasValue ? `return StatusCode(${status}, result);` : `return StatusCode(${status});`;
+    }
+  }
+  // Fallback for ranges and "*"
+  return hasValue ? "return Ok(result);" : "return Ok();";
+}
+
 export function isEmptyResponseModel(program: Program, model: Type): boolean {
   if (model.kind !== "Model") return false;
   if (model.properties.size === 0) return true;

packages/http-server-csharp/test/generation.test.ts

@@ -2023,6 +2023,53 @@ model FileAttachmentMultipartRequest {
   );
 });
 
+it("Produces Accepted result for 202 response with body", async () => {
+  await compileAndValidateMultiple(
+    tester,
+    `
+    model AcceptedResponse {
+      @statusCode statusCode: 202;
+      jobId: string;
+    }
+
+    @post
+    op startJob(): AcceptedResponse;
+    `,
+    [["ContosoOperationsController.cs", ["return Accepted(result)"]]],
+  );
+});
+
+it("Produces Accepted result for 202 response without body", async () => {
+  await compileAndValidateMultiple(
+    tester,
+    `
+    model AcceptedNoBodyResponse {
+      @statusCode statusCode: 202;
+    }
+
+    @post
+    op startJob(): AcceptedNoBodyResponse;
+    `,
+    [["ContosoOperationsController.cs", ["return Accepted()"]]],
+  );
+});
+
+it("Produces StatusCode result for 201 response with body", async () => {
+  await compileAndValidateMultiple(
+    tester,
+    `
+    model CreatedResponse {
+      @statusCode statusCode: 201;
+      id: string;
+    }
+
+    @post
+    op createResource(): CreatedResponse;
+    `,
+    [["ContosoOperationsController.cs", ["return StatusCode(201, result)"]]],
+  );
+});
+
 const multipartSpec = `
 @error
 model NotFoundErrorResponse {