feat(http-client-python): generate structured JSONL/SSE streaming by l0lawrence · Pull Request #11594 · microsoft/typespec

Libba Lawrence (l0lawrence) · 2026-08-07T18:03:45Z

Summary

Generate Azure-flavor client methods that return Stream[T] / AsyncStream[T] for JSONL (application/jsonl) and SSE (text/event-stream) response streams.
Use TCGC streamMetadata / sseMetadata to deserialize JSONL items and dispatch named SSE events to their concrete generated models, including terminal-event handling.
Vendor the JSONL/SSE streaming runtime in generated packages while preserving unbranded raw-byte iterator behavior.
Preserve registered stream item-type references across request overloads.

stream = client.receive()  # Stream[Thing]
for thing in stream:
    ...

Coverage

Emitter structured-streaming tests
Pygen response and serializer coverage
Azure JSONL/SSE regeneration
Sync and async Spector smoke coverage for homogeneous and heterogeneous streams

Notes

This uses the TCGC prerelease containing sseMetadata. The external Azure mock API streaming test still asserts the previous raw-byte contract and is expected to remain failing until that test is aligned with the type-driven behavior.

pkg-pr-new · 2026-08-07T18:05:33Z

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npm i https://pkg.pr.new/@typespec/http-client-python@11594

commit: 1d5dddc

github-actions · 2026-08-07T18:07:39Z

All changed packages have been documented.

✅ @typespec/http-client-python

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`@typespec/http-client-python` - feature ✏️

Generate structured streaming client methods for the Azure flavor: operations whose HTTP response is a JSONL (application/jsonl) or SSE (text/event-stream) stream now return Stream[T] / AsyncStream[T], yielding deserialized model instances instead of raw bytes.,> ,> Stream and AsyncStream are available from the generated package's base namespace. Their runtime (plus the JSONL / SSE decoders) is vendored at _utils/streaming_base.py, so it depends only on the released azure.core.rest.,> ,> python,> from your_sdk import Stream,> ,> stream: Stream[Thing] = client.receive(),> for thing in stream:,> ...,>

github-actions · 2026-08-07T18:19:44Z

Python emitter diff

Baseline gh:006b5cbfca9336a6b9bf127cf716fe645a201fa7 vs this PR.

Diff summary: 129 file(s), +14423 / -76

Rendered diff: inline on the run summary, or the emitter-diff-html artifact.

Informational check (eng/emitter-diff); does not block the PR.

azure-sdk-automation · 2026-08-07T18:23:43Z

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Pull request overview

This PR adds structured streaming support to the TypeSpec Python emitter/generator for the Azure flavor, emitting client methods that return Stream[T] / AsyncStream[T] for JSONL (application/jsonl) and SSE (text/event-stream) responses, using TCGC streaming metadata to drive per-item deserialization and SSE event dispatch. It also vendors a small streaming runtime into generated packages to avoid requiring an unreleased azure.core.streaming dependency.

Changes:

Emit a streaming block in response YAML for structured JSONL/SSE streams (including SSE event/terminal metadata) and preserve it across request overloads.
Generate and write a vendored _utils/streaming_base.py runtime (Stream/AsyncStream + JSONL/SSE decoders) when needed, and update response/operation modeling + response handling to return Stream[T]/AsyncStream[T].
Add emitter-side unit tests for structured-stream detection and update dependency versions to TCGC prereleases that expose sseMetadata.

Reviewed changes

Copilot reviewed 14 out of 15 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
packages/http-client-python/README.md	Documents structured streaming behavior for Azure flavor and the vendored runtime.
packages/http-client-python/package.json	Updates dev dependencies to prereleases and adds an npm `overrides` entry for compiler version alignment.
packages/http-client-python/package-lock.json	Locks new prerelease dependency resolutions used by the emitter/generator tests.
packages/http-client-python/generator/pygen/preprocess/init.py	Preserves `streaming` metadata across generated overload YAML updates.
packages/http-client-python/generator/pygen/codegen/templates/streaming_base.py.jinja2	Adds vendored streaming runtime template (Stream/AsyncStream + JSONL/SSE decoding).
packages/http-client-python/generator/pygen/codegen/serializers/general_serializer.py	Adds serializer for the new streaming runtime template.
packages/http-client-python/generator/pygen/codegen/serializers/builder_serializer.py	Emits response handling that returns Stream/AsyncStream with per-item deserialization callbacks.
packages/http-client-python/generator/pygen/codegen/serializers/init.py	Writes `_utils/streaming_base.py` when structured streaming is present.
packages/http-client-python/generator/pygen/codegen/models/response.py	Models structured stream metadata, stream return annotations, and imports needed for generated operations.
packages/http-client-python/generator/pygen/codegen/models/operation.py	Forces `stream=True` for structured streaming operations and exposes a structured-stream predicate.
packages/http-client-python/generator/pygen/codegen/models/code_model.py	Tracks whether any structured streaming exists to decide if vendored runtime must be emitted.
packages/http-client-python/emitter/test/streaming.test.ts	Adds emitter unit tests for structured-stream detection and kind inference.
packages/http-client-python/emitter/src/http.ts	Emits response `streaming` YAML using TCGC stream/sse metadata; adds structured stream detection helpers.
cspell.yaml	Adds streaming/runtime-related identifiers to the spellchecker dictionary.
.chronus/changes/structured-streaming-2026-0-0.md	Changelog entry describing the new Azure-flavor structured streaming support.

Files not reviewed (1)

packages/http-client-python/package-lock.json: Generated file

+    def iter_events(self, iter_bytes: Iterator[bytes]) -> Iterator[T_co]:
+        """Iterate over events from a byte iterator.
+
+        :param iter_bytes: An iterator of byte chunks.
+        :type iter_bytes: Iterator[bytes]
+        :return: An iterator of decoded data.
+        :rtype: Iterator[DecodedType_co]
+        """
+        ...
+
+
+@runtime_checkable
+class AsyncStreamDecoder(Protocol[T_co]):
+    """Protocol for async stream decoders."""
+
+    # Why this isn't async def: https://mypy.readthedocs.io/en/stable/more_types.html#asynchronous-iterators
+    def aiter_events(self, iter_bytes: AsyncIterator[bytes]) -> AsyncIterator[T_co]:
+        """Asynchronously iterate over events from a byte iterator.
+
+        :param iter_bytes: An asynchronous iterator of byte chunks.
+        :type iter_bytes: AsyncIterator[bytes]
+        :return: An asynchronous iterator of decoded data.
+        :rtype: AsyncIterator[DecodedType_co]
+        """
+        ...


+async def aiter_lines(iter_bytes: AsyncIterator[bytes]) -> AsyncIterator[str]:
+    """Iterate over lines from a byte iterator.
+
+    :param iter_bytes: An iterator of byte chunks.
+    :type iter_bytes: Iterator[bytes]
+    :rtype: Iterator[str]
+    :return: An iterator of lines.
+    """


Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: e57edafe-9764-4b99-a1ae-0efd56e8729e

Libba Lawrence (l0lawrence) · 2026-08-10T17:46:00Z


    def serialize_init_file(self, clients: list[Client]) -> str:
        template = self.env.get_template("init.py.jinja2")
+        expose_streaming_types = (


Instead of doing this and exposing Stream directly since we are going to eventually use azure-core, should we not expose this and instead type the outputs as Iterators that will eventually become an iterator created by azure-core vs gen code vendor?

microsoft-github-policy-service Bot added the emitter:client:python Issue for the Python client emitter: @typespec/http-client-python label Aug 7, 2026

Libba Lawrence (l0lawrence) changed the title ~~feat(http-client-python): generate structured JSONL/SSE streaming (Azure flavor)~~ feat(http-client-python): generate structured JSONL/SSE streaming Aug 7, 2026

Libba Lawrence (l0lawrence) requested a lite review from Copilot August 7, 2026 19:01

Copilot started reviewing on behalf of Libba Lawrence (l0lawrence) August 7, 2026 19:01 View session

Libba Lawrence (l0lawrence) force-pushed the l0lawrence-jsonl-sse-streaming-codegen branch from 4a36e0a to d93a175 Compare August 7, 2026 19:02

Copilot AI reviewed Aug 7, 2026

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Libba Lawrence (l0lawrence) force-pushed the l0lawrence-jsonl-sse-streaming-codegen branch from d93a175 to c3924da Compare August 7, 2026 19:14

feat(http-client-python): generate structured JSONL and SSE streams

294b0c5

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com> Copilot-Session: e57edafe-9764-4b99-a1ae-0efd56e8729e

Libba Lawrence (l0lawrence) force-pushed the l0lawrence-jsonl-sse-streaming-codegen branch from c3924da to 294b0c5 Compare August 7, 2026 19:22

Merge branch 'main' into l0lawrence-jsonl-sse-streaming-codegen

1d5dddc

Libba Lawrence (l0lawrence) commented Aug 10, 2026

View reviewed changes

Comment thread packages/http-client-python/generator/pygen/codegen/models/operation.py

Libba Lawrence (l0lawrence) commented Aug 10, 2026

View reviewed changes

This was referenced Aug 10, 2026

feat(typespec-ts): generate structured JSONL and SSE streaming by default l0lawrence/typespec-azure#1

Closed

feat(typespec-ts): streaming Azure/typespec-azure#5196

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feat(http-client-python): generate structured JSONL/SSE streaming - #11594

feat(http-client-python): generate structured JSONL/SSE streaming#11594
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Libba Lawrence (l0lawrence) commented Aug 7, 2026

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