feat(typespec-ts): streaming

.chronus/changes/structured-jsonl-sse-streaming-2026-7-30-0-0-0.md

@@ -0,0 +1,7 @@
+---
+changeKind: feature
+packages:
+  - "@azure-tools/typespec-ts"
+---
+
+Generate structured JSONL and SSE streaming operations by default. A JSONL or SSE stream response now returns `Promise<AsyncIterable<T>>` of deserialized items/events instead of the previous raw binary `Uint8Array` body. An operation returning `JsonlStream<T>` lazily decodes JSON Lines into `AsyncIterable<T>`, and an operation returning `SSEStream<T>` returns an `AsyncIterable` of the event payload types, dispatching each Server-Sent Event by its `event:` name (using `@azure/core-sse`), deserializing each payload, and stopping at the terminal event. This is the default behavior — there is no opt-in option.

packages/typespec-ts/package.json

@@ -57,12 +57,16 @@
     "@azure/core-lro": "catalog:",
     "@azure/core-paging": "catalog:",
     "@azure/core-rest-pipeline": "catalog:",
+    "@azure/core-sse": "catalog:",
     "@azure/core-util": "catalog:",
     "@azure/logger": "catalog:",
     "@typespec/compiler": "workspace:^",
     "@typespec/http": "workspace:^",
     "@typespec/openapi": "workspace:^",
     "@typespec/rest": "workspace:^",
+    "@typespec/streams": "workspace:^",
+    "@typespec/sse": "workspace:^",
+    "@typespec/events": "workspace:^",
     "@typespec/versioning": "workspace:^",
     "@typespec/xml": "workspace:^",
     "@typespec/ts-http-runtime": "catalog:",

packages/typespec-ts/spector.config.yaml

@@ -115,6 +115,7 @@ specs:
   azure/client-generator-core/client-doc: true
   azure/client-generator-core/response-as-bool: true
   documentation: true
+  streaming/sse: true
 
   # Disabled: needs tcgc upgrade https://github.com/Azure/typespec-azure/pull/3997
   client/structure/renamed-operation: false

packages/typespec-ts/src/index.ts

@@ -26,7 +26,9 @@ import {
   PollingHelpers,
   SerializationHelpers,
   SimplePollerHelpers,
+  SseStreamingHelpers,
   StorageCompatHelpers,
+  StreamingHelpers,
   UrlTemplateHelpers,
   XmlHelpers,
 } from "./modular/static-helpers-metadata.js";
@@ -87,6 +89,10 @@ import { emitNonModelResponseTypes, emitTypes } from "./modular/emit-models.js";
 import { emitSamples } from "./modular/emit-samples.js";
 import { emitTests } from "./modular/emit-tests.js";
 import { getClassicalClientName } from "./modular/helpers/naming-helpers.js";
+import {
+  packageHasSseStreaming,
+  packageHasStructuredStreaming,
+} from "./modular/helpers/operation-helpers.js";
 import type { ModularEmitterOptions } from "./modular/interfaces.js";
 import { packageUsesXmlSerialization } from "./modular/serialization/build-xml-serializer-function.js";
 import { transformClientOptions } from "./transform/transform-client-options.js";
@@ -140,6 +146,8 @@ export async function $onEmit(context: EmitContext) {
       ...MultipartHelpers,
       ...CloudSettingHelpers,
       ...XmlHelpers,
+      ...(packageHasStructuredStreaming(dpgContext) ? StreamingHelpers : {}),
+      ...(packageHasSseStreaming(dpgContext) ? SseStreamingHelpers : {}),
       ...(resolvedEmitterOptions.generateTest ? CreateRecorderHelpers : {}),
       ...(resolvedEmitterOptions.enableStorageCompat ? StorageCompatHelpers : {}),
     },
@@ -449,6 +457,10 @@ export async function $onEmit(context: EmitContext) {
         if (packageUsesXmlSerialization(dpgContext.sdkPackage)) {
           dependencies["fast-xml-parser"] = "^4.5.0";
         }
+        // Add @azure/core-sse if structured SSE streaming is used
+        if (packageHasSseStreaming(dpgContext)) {
+          dependencies["@azure/core-sse"] = "^2.1.3";
+        }
         modularPackageInfo = {
           ...modularPackageInfo,
           dependencies,
@@ -502,6 +514,9 @@ export async function $onEmit(context: EmitContext) {
       if (packageUsesXmlSerialization(dpgContext.sdkPackage)) {
         additionalDependencies["fast-xml-parser"] = "^4.5.0";
       }
+      if (packageHasSseStreaming(dpgContext)) {
+        additionalDependencies["@azure/core-sse"] = "^2.1.3";
+      }
       const modularPackageInfo = {
         exports: getModuleExports(context, modularEmitterOptions),
         ...(Object.keys(additionalDependencies).length > 0 && {

packages/typespec-ts/src/modular/external-dependencies.ts

@@ -217,6 +217,11 @@ export const AzureCoreDependencies: CoreDependencies = {
     module: "@azure/core-rest-pipeline",
     name: "NodeReadableStream",
   },
+  createSseStream: {
+    kind: "externalDependency",
+    module: "@azure/core-sse",
+    name: "createSseStream",
+  },
 };
 
 export const AzureIdentityDependencies = {