feat(python): eliminate SSE dependency 'httpx_sse' by hard-forking into core_utilities

generators/python/core_utilities/shared/http_sse/__init__.py

@@ -0,0 +1,14 @@
+from ._api import EventSource, aconnect_sse, connect_sse
+from ._exceptions import SSEError
+from ._models import ServerSentEvent
+
+__version__ = "0.4.1"
+
+__all__ = [
+    "__version__",
+    "EventSource",
+    "connect_sse",
+    "aconnect_sse",
+    "ServerSentEvent",
+    "SSEError",
+]

generators/python/core_utilities/shared/http_sse/_api.py

@@ -0,0 +1,110 @@
+import re
+from contextlib import asynccontextmanager, contextmanager
+from typing import Any, AsyncGenerator, AsyncIterator, Iterator, cast
+
+import httpx
+from ._decoders import SSEDecoder
+from ._exceptions import SSEError
+from ._models import ServerSentEvent
+
+
+class EventSource:
+    def __init__(self, response: httpx.Response) -> None:
+        self._response = response
+
+    def _check_content_type(self) -> None:
+        content_type = self._response.headers.get("content-type", "").partition(";")[0]
+        if "text/event-stream" not in content_type:
+            raise SSEError(
+                f"Expected response header Content-Type to contain 'text/event-stream', got {content_type!r}"
+            )
+
+    def _get_charset(self) -> str:
+        """Extract charset from Content-Type header, fallback to UTF-8."""
+        content_type = self._response.headers.get("content-type", "")
+
+        # Parse charset parameter using regex
+        charset_match = re.search(r"charset=([^;\s]+)", content_type, re.IGNORECASE)
+        if charset_match:
+            charset = charset_match.group(1).strip("\"'")
+            # Validate that it's a known encoding
+            try:
+                # Test if the charset is valid by trying to encode/decode
+                "test".encode(charset).decode(charset)
+                return charset
+            except (LookupError, UnicodeError):
+                # If charset is invalid, fall back to UTF-8
+                pass
+
+        # Default to UTF-8 if no charset specified or invalid charset
+        return "utf-8"
+
+    @property
+    def response(self) -> httpx.Response:
+        return self._response
+
+    def iter_sse(self) -> Iterator[ServerSentEvent]:
+        self._check_content_type()
+        decoder = SSEDecoder()
+        charset = self._get_charset()
+
+        buffer = ""
+        for chunk in self._response.iter_bytes():
+            # Decode chunk using detected charset
+            text_chunk = chunk.decode(charset, errors="replace")
+            buffer += text_chunk
+
+            # Process complete lines
+            while "\n" in buffer:
+                line, buffer = buffer.split("\n", 1)
+                line = line.rstrip("\r")
+                sse = decoder.decode(line)
+                # when we reach a "\n\n" => line = ''
+                # => decoder will attempt to return an SSE Event
+                if sse is not None:
+                    yield sse
+
+        # Process any remaining data in buffer
+        if buffer.strip():
+            line = buffer.rstrip("\r")
+            sse = decoder.decode(line)
+            if sse is not None:
+                yield sse
+
+    async def aiter_sse(self) -> AsyncGenerator[ServerSentEvent, None]:
+        self._check_content_type()
+        decoder = SSEDecoder()
+        lines = cast(AsyncGenerator[str, None], self._response.aiter_lines())
+        try:
+            async for line in lines:
+                line = line.rstrip("\n")
+                sse = decoder.decode(line)
+                if sse is not None:
+                    yield sse
+        finally:
+            await lines.aclose()
+
+
+@contextmanager
+def connect_sse(client: httpx.Client, method: str, url: str, **kwargs: Any) -> Iterator[EventSource]:
+    headers = kwargs.pop("headers", {})
+    headers["Accept"] = "text/event-stream"
+    headers["Cache-Control"] = "no-store"
+
+    with client.stream(method, url, headers=headers, **kwargs) as response:
+        yield EventSource(response)
+
+
+@asynccontextmanager
+async def aconnect_sse(
+    client: httpx.AsyncClient,
+    method: str,
+    url: str,
+    **kwargs: Any,
+) -> AsyncIterator[EventSource]:
+    headers = kwargs.pop("headers", {})
+    headers["Accept"] = "text/event-stream"
+    headers["Cache-Control"] = "no-store"
+
+    async with client.stream(method, url, headers=headers, **kwargs) as response:
+        yield EventSource(response)

generators/python/core_utilities/shared/http_sse/_decoders.py

@@ -0,0 +1,59 @@
+from typing import List, Optional
+
+from ._models import ServerSentEvent
+
+
+class SSEDecoder:
+    def __init__(self) -> None:
+        self._event = ""
+        self._data: List[str] = []
+        self._last_event_id = ""
+        self._retry: Optional[int] = None
+
+    def decode(self, line: str) -> Optional[ServerSentEvent]:
+        # See: https://html.spec.whatwg.org/multipage/server-sent-events.html#event-stream-interpretation  # noqa: E501
+
+        if not line:
+            if not self._event and not self._data and not self._last_event_id and self._retry is None:
+                return None
+
+            sse = ServerSentEvent(
+                event=self._event,
+                data="\n".join(self._data),
+                id=self._last_event_id,
+                retry=self._retry,
+            )
+
+            # NOTE: as per the SSE spec, do not reset last_event_id.
+            self._event = ""
+            self._data = []
+            self._retry = None
+
+            return sse
+
+        if line.startswith(":"):
+            return None
+
+        fieldname, _, value = line.partition(":")
+
+        if value.startswith(" "):
+            value = value[1:]
+
+        if fieldname == "event":
+            self._event = value
+        elif fieldname == "data":
+            self._data.append(value)
+        elif fieldname == "id":
+            if "\0" in value:
+                pass
+            else:
+                self._last_event_id = value
+        elif fieldname == "retry":
+            try:
+                self._retry = int(value)
+            except (TypeError, ValueError):
+                pass
+        else:
+            pass  # Field is ignored.
+
+        return None

generators/python/core_utilities/shared/http_sse/_exceptions.py

@@ -0,0 +1,5 @@
+import httpx
+
+
+class SSEError(httpx.TransportError):
+    pass

generators/python/core_utilities/shared/http_sse/_models.py

@@ -0,0 +1,15 @@
+import json
+from dataclasses import dataclass
+from typing import Any, Optional
+
+
+@dataclass(frozen=True)
+class ServerSentEvent:
+    event: str = "message"
+    data: str = ""
+    id: str = ""
+    retry: Optional[int] = None
+
+    def json(self) -> Any:
+        """Parse the data field as JSON."""
+        return json.loads(self.data)

generators/python/sdk/versions.yml

@@ -1,5 +1,14 @@
 # yaml-language-server: $schema=../../../fern-versions-yml.schema.json
 # For unreleased changes, use unreleased.yml
+- version: 4.31.0
+  changelogEntry:
+    - summary: |
+        - Removed external dependency on httpx-sse by bringing SSE handling in-house. 
+        - Fixed SSE handling of events longer than or containing escaped newlines.
+      type: feat
+  createdAt: "2025-10-06"
+  irVersion: 60
+
 - version: 4.30.4-rc1
   changelogEntry:
     - summary: |

generators/python/src/fern_python/generators/sdk/client_generator/endpoint_response_code_writer.py

@@ -2,7 +2,6 @@
 
 from ..context.sdk_generator_context import SdkGeneratorContext
 from fern_python.codegen import AST
-from fern_python.external_dependencies.httpx_sse import HttpxSSE
 from fern_python.external_dependencies.json import Json
 from fern_python.generators.sdk.client_generator.constants import CHUNK_VARIABLE, RESPONSE_VARIABLE
 from fern_python.generators.sdk.client_generator.pagination.abstract_paginator import (
@@ -99,7 +98,18 @@ def _handle_success_stream(self, *, writer: AST.NodeWriter, stream_response: ir_
                     AST.VariableDeclaration(
                         name=EndpointResponseCodeWriter.EVENT_SOURCE_VARIABLE,
                         initializer=AST.Expression(
-                            AST.ClassInstantiation(HttpxSSE.EVENT_SOURCE, [AST.Expression(RESPONSE_VARIABLE)])
+                            AST.ClassInstantiation(
+                                class_=AST.ClassReference(
+                                    qualified_name_excluding_import=(),
+                                    import_=AST.ReferenceImport(
+                                        module=AST.Module.local(
+                                            *self._context.core_utilities._module_path, "http_sse", "_api"
+                                        ),
+                                        named_import="EventSource",
+                                    ),
+                                ),
+                                args=[AST.Expression(RESPONSE_VARIABLE)],
+                            )
                         ),
                     ),
                     AST.ForStatement(
@@ -119,7 +129,7 @@ def _handle_success_stream(self, *, writer: AST.NodeWriter, stream_response: ir_
                                 conditions=[
                                     AST.IfConditionLeaf(
                                         condition=AST.Expression(
-                                            f"{EndpointResponseCodeWriter.SSE_VARIABLE}.data == {stream_response_union.terminator}"
+                                            f"{EndpointResponseCodeWriter.SSE_VARIABLE}.data == {repr(stream_response_union.terminator)}"
                                         ),
                                         code=[AST.ReturnStatement()],
                                     ),
@@ -131,16 +141,77 @@ def _handle_success_stream(self, *, writer: AST.NodeWriter, stream_response: ir_
                                     AST.YieldStatement(
                                         self._context.core_utilities.get_construct(
                                             self._get_streaming_response_data_type(stream_response),
-                                            AST.Expression(
-                                                Json.loads(
-                                                    AST.Expression(f"{EndpointResponseCodeWriter.SSE_VARIABLE}.data")
-                                                )
-                                            ),
+                                            AST.Expression(f"{EndpointResponseCodeWriter.SSE_VARIABLE}.json()"),
                                         ),
                                     ),
                                 ],
                                 handlers=[
-                                    noop_except_handler,
+                                    AST.ExceptHandler(
+                                        body=[
+                                            AST.Expression(
+                                                AST.FunctionInvocation(
+                                                    function_definition=AST.Reference(
+                                                        qualified_name_excluding_import=(),
+                                                        import_=AST.ReferenceImport(
+                                                            module=AST.Module.built_in(("logging",)),
+                                                            named_import="warning",
+                                                        ),
+                                                    ),
+                                                    args=[
+                                                        AST.Expression(
+                                                            f'f"Skipping SSE event with invalid JSON: {{e}}, sse: {{{EndpointResponseCodeWriter.SSE_VARIABLE}!r}}"'
+                                                        )
+                                                    ],
+                                                )
+                                            ),
+                                        ],
+                                        exception_type="JSONDecodeError",
+                                        name="e",
+                                    ),
+                                    AST.ExceptHandler(
+                                        body=[
+                                            AST.Expression(
+                                                AST.FunctionInvocation(
+                                                    function_definition=AST.Reference(
+                                                        qualified_name_excluding_import=(),
+                                                        import_=AST.ReferenceImport(
+                                                            module=AST.Module.built_in(("logging",)),
+                                                            named_import="warning",
+                                                        ),
+                                                    ),
+                                                    args=[
+                                                        AST.Expression(
+                                                            f'f"Skipping SSE event due to model construction error: {{type(e).__name__}}: {{e}}, sse: {{{EndpointResponseCodeWriter.SSE_VARIABLE}!r}}"'
+                                                        )
+                                                    ],
+                                                )
+                                            ),
+                                        ],
+                                        exception_type="(TypeError, ValueError, KeyError, AttributeError)",
+                                        name="e",
+                                    ),
+                                    AST.ExceptHandler(
+                                        body=[
+                                            AST.Expression(
+                                                AST.FunctionInvocation(
+                                                    function_definition=AST.Reference(
+                                                        qualified_name_excluding_import=(),
+                                                        import_=AST.ReferenceImport(
+                                                            module=AST.Module.built_in(("logging",)),
+                                                            named_import="error",
+                                                        ),
+                                                    ),
+                                                    args=[
+                                                        AST.Expression(
+                                                            f'f"Unexpected error processing SSE event: {{type(e).__name__}}: {{e}}, sse: {{{EndpointResponseCodeWriter.SSE_VARIABLE}!r}}"'
+                                                        )
+                                                    ],
+                                                )
+                                            ),
+                                        ],
+                                        exception_type="Exception",
+                                        name="e",
+                                    ),
                                 ],
                             ),
                         ],
@@ -156,7 +227,7 @@ def _handle_success_stream(self, *, writer: AST.NodeWriter, stream_response: ir_
                         conditions=[
                             AST.IfConditionLeaf(
                                 condition=AST.Expression(
-                                    f"{EndpointResponseCodeWriter.STREAM_TEXT_VARIABLE} == {stream_response_union.terminator}"
+                                    f"{EndpointResponseCodeWriter.STREAM_TEXT_VARIABLE} == {repr(stream_response_union.terminator)}"
                                 ),
                                 code=[AST.ReturnStatement()],
                             ),